Dissertationen zum Thema „Photometry, astronomical“

The goal of this study was to obtain photometry of three poorly studied close binary star systems. These observations were obtained at Lowell Observatory in Flagstaff, Arizona and the Ball State University Observatory. In both cases charged coupled device detectors were used. Light variations were detected in all three stars. For one of the binaries the temperatures of the component stars were found by fitting multi-color light curves with black body models. In addition, the temperature difference between the two hemispheres of the secondary star was found. This difference is believed to be the product of heating by the stellar companion.
Department of Physics and Astronomy

Starspots are not well understood for contact binary star systems. The following properties of spots were systematically investigated: temperature, radius, colatitude, and longitude. Spots were modeled on an AE Phe like contact binary system. The spots were changed in a systematic manner. The light curve phases of primary minimum and primary maximum were affected by these parameter changes in a systematic manner, as well as the secondary minimum and maximum. It will be shown that it is possible to use the shift in these phases to study starspots over time. This information can also be used to identify the presence of spots in binary star systems.Starspots on contact binary systems are not commonly found at a longitude near 180°. The results of this study show that starspots near 180° should be the easiest to detect using photometric techniques. This is the most significant result from this study. Either there is an unknown physical reason why contact binary stars do not have starspots near a longitude of 180°, or the starspots are there and the photometric data has been misinterpreted.
Department of Physics and Astronomy

We have conducted three surveys to try and locate distant star forming galaxies. The most general survey used deep 2μ images with optical CCD photometry to locate objects with peculiar SEDs. Using the IR data we should be able to locate rapidly star forming galaxies to z = 25. With a 3σ detection limit of 18.5 at K we have found no objects with z > 5 but we have found several blue objects at z < 4 in 16min² of sky. This suggests tha there is no extremely luminous early phase of galaxy formation. We have found several blue objects at z < 4 in 10min² of sky. Of particular interest is an object which has a flat SED from V to K but shows a strong spectral break between B and V and a weaker break at 5800Å. We suggest these may be Lyman limit and Lyman α forest absorption at z-3.8 in a galaxy forming ≈400M(⊙) year⁻¹ of stars. A large sample of galaxies (100 objects) selected to have similar properties (R – I < .5, B – R > 1) has also been found. From this sample it appears this possible high redshift star forming phase only contributes 1/10 of the metal present in disks or spheroids. We have also found 30 Lyman α emission line companions to 12 z = 3 quasars. These objects have Lyman α equivalent widths (50Å) and luminosities (V = 24) consistent with galaxies forming ≈100M(⊙) year⁻¹ of stars. Also, 2 of the quasars have 8 companions and may be in cluster environments. A final survey analyzed optical to IR SEDs of luminous blue radio galaxies at z > 1. In these objects we find SEDs indicative of star formation rates between 10 and 100M(⊙) year⁻¹ but interpretation is difficult due to the AGN component of the sources. While these data seem to suggest a significant star forming phase taking place in galaxies at z ≈ 3-4, interpreting this result is difficult since we cannot determine if we are observing disk or spheroidal populations. In the case of the quasar companions and the radio galaxies, consideration of their dense environments and current epoch morphology suggest that these may be spheroids but these galaxies may not be typical of galaxies in general.

Red dwarf stars are one proposed solution to the dark matter problem in the Milky Way Galaxy These cool, low luminosity stars are difficult to detect and segregate in surveys. This study utilizes photometric data obtained on the Kron-Cousins photometric system to develop criteria that classifies stars as red. Two of the color indices are then used to create a two-color diagram to allow separation of giant and dwarf stars. An algorithm based on calculated equations is provided to separate the giant and dwarf stars after detection. A third class of stars, subdwarfs, is addressed as a potential problem in future surveys. Some suggestions for detecting and removing these contaminating stars from the data are offered. Finally, a colormagnitude diagram is developed for red dwarf stars with KronCousins photometry. This curve allows for fairly accurate determination of photometric parallaxes for the red dwarf stars.An attempt was made to segregate the red dwarfs into velocity classes prior to calibrating the color-magnitude diagram. It was found that this approach offered no additional useful information.
Department of Physics and Astronomy

The aim of this work has been to increase our understanding of the surface brightness distributions of late-type stars through Doppler imaging and eclipse mapping techniques. Combining spectroscopic and photometric observations with the technique of Doppler Imaging, I have reconstructed surface images of the G2V star He 699 (for 08 October 2000), which show high latitude and polar structures. In the case of the KOV star AB Dor, the Doppler images for January 1992 and November 1993 show a large polar cap with small dark features also present at intermediate to high latitudes. As the phase sampling of the observations was insufficient to apply the sheared-image method it was not possible to detect any differential rotation. In the second part of my thesis I determine the surface brightness distribution of the primary component of the RS CVn eclipsing binary SV Cam. I have used extrapolated size distributions of sunspots to an active star to synthesize images of stellar photospheres with high spot filling factors. The resulting surface images, reconstructed with the Maximum Entropy eclipse mapping technique, show large spurious spot features at the quadrature points. It is concluded that two-spot modelling or chi-squared minimisation techniques are more susceptible to spurious structures being generated by systematic errors, arising from incorrect assumptions about photospheric surface brightness, than simple Fourier analysis of the light-curves. Spectrophotometric data from 9 HST orbits, observed in November 2001, have been used to eclipse-map the primary component of SV Cam. In combination with its HIPPAR- COS parallax it is found that the surface flux in the eclipsed low-latitude region is about 30% lower than computed from the best fitting PHOENIX model atmosphere. This flux deficit can only be accounted for if about a third of the primary's surface is covered with unresolved spots. However, when the spottedness from the eclipsed region is applied to the entire surface of the primary star, there still remains an unaccounted flux deficit. The remaining flux deficit is explained by the presence of a large polar spot extending down to latitude 48+/-6 deg. When the Maximum Entropy eclipse mapping technique is used to fit SV Cam's lightcurve, the observed minus computed residuals show strong spurious peaks at the quadrature points. It is only possible to reduce these peaks with the addition of a polar cap and the reduction of the primary star's temperature, to account for the star being peppered with unresolvable spots. Motivated by this result we investigate the limb darkening of the primary component of SV Cam. The wavelength dependence of the limb darkening is analysed by sub-dividing the HST lightcurve into 10 bands of equal emission flux. Flux variations between the first and fourth contact of the primary eclipse indicate that the limb darkening decreases towards longer wavelengths, in accordance with published limb darkening laws. Comparing fits of ATLAS and PHOENIX model atmospheres we find a wavelength dependence of the best fitting model. Due to its smooth cutoff at the stellar limb, the spherical geometry of the PHOENIX model atmosphere gives the best fit during partial eclipse. Between the second and third contact the difference between spherical and plane-parallel geometry is less important.

The European Space Agency's Herschel Space Observatory is comprised of three cryogenically cooled instruments commissioned to explore the far infrared/submillimetre universe. The Spectral and Photometric Imaging REceiver (SPIRE) is one of Herschel's instruments and consists of a three band imaging photometer and a two band imaging spectrometer. Canada is involved in the SPIRE project through provision of instrument development hardware and software, mission flight software, and support personnel. This thesis discusses Fourier transform spectroscopy (FTS) and FTS data processing. A detailed discussion is included on FTS phase correction, with results presented from the optimization of an enhanced Forman phase correction routine developed for this work. This thesis discusses the design, verification, and use of the hardware and software provided by Dr. Naylor's group as it relates to SPIRE verification testing. Results of the photometer characterization are presented. The current status of SPIRE and its future schedule is also discussed.
xvii, 239 leaves : ill. (some col.) ; 28 cm.

For 20 years now, gravitational microlensing observations towards the Galactic bulge have provided us with a wealth of information about the stellar and planetary content of our Galaxy, which is inaccessible via other current methods. This thesis summarises work on two research topics that arose in the context of exoplanetary microlensing, but we take a step back and consider ways of increasing our understanding of more fundamental phenomena: firstly, stellar microlenses in our Galaxy that were stereoscopically observed and, secondly, the morphological variety of binary-lens light curves. In autumn 2008, the ESA Rosetta spacecraft surveyed the Galactic bulge for microlensing events. With a baseline of ∼1.6 AU between the spacecraft and ground observations, significant parallax effects can be expected. We develop a photometry pipeline to deal with a severely undersampled point spread function in the crowded fields of the Galactic bulge, making use of complementary ground observations. Comparison of Rosetta and OGLE light curves provides the microlens parallax π[subscript{E}] , which constrains the mass and distance of the observed lenses. The lens mass could be fully determined if future proper motion measurements were obtained, whereas the lens distance additionally requires the determination of the source distance. In the second project, we present a detailed study of microlensing light curve morphologies. We provide a complete morphological classification for the case of the equal-mass binary lens, which makes use of the realisation that any microlensing peak can be categorised as one of only four types: cusp-grazing, cusp-crossing, fold-crossing or fold-grazing. As a means for this classification, we develop a caustic feature notation, which can be universally applied to binary lens caustics. Ultimately, this study aims to refine light curve modelling approaches by providing an optimal choice of initial parameter sets, while ensuring complete coverage of the relevant parameter space.

Volume-limited samples indicate that red dwarfs are the most abundant stars in the Milky Way and account for most of its mass, despite their low individual masses. However, because of their low luminosity, they are extremely underdetected in magnitude-limited surveys. Complicating the task of identification is the fact that they have the same temperature as red giants and thus are in the same spectral class. We must therefore look for certain spectral features to differentiate between dwarfs and giants. Intermediate-to-broad-band photometry is one method that allows us to perform this task quantitatively. The 2MASS point source catalog contains data for -0.5 billion objects, including photometry in three broadband infrared filters. This paper discusses the manner in which these data can be analyzed to find red dwarfs and the success rate of such analysis.
Department of Physics and Astronomy

Over recent years there has been an increase of the number of secure supermassive black hole (SMBH) detections. These SMBH measurements have lead astronomers to establish well defined empirical relationships between the SMBH mass and some of the properties of the host galaxy. The number of galaxies with SMBH mass measurements is currently limited to about 100. One approach of expanding the study of the SMBH is to use the empirical relations for estimating M[subscript(bh)] for larger samples of galaxies. The investigation of the SMBH population (or SMBH mass function) for large sample of galaxies in the nearby universe has helped to constrain the SMBH and the galaxy evolution. Previous estimates of the SMBH mass function at low redshift were produced mainly by combining the measurements of the galaxy luminosity or velocity function with one of the SMBH scaling relations. In the first part of the thesis I will present an independent construction of the nearby supermassive black hole mass function by applying the optical M[subscript(bh)]–L relation onto the Millennium Galaxy Catalogue (MGC). Additionally, in the second part I will provide photometric analysis of all UKIDSS galaxies for which SMBH masses have been measured. I will derive composite profiles of brightness, ellipticity and position angles of each galaxy. I will show that the Sérsic function fits the brightness profile of the majority of the elliptical galaxies and the bulge of disk galaxies and I will provide alternative multi-component fits when necessary. Then these photometric parameters will be used for constructing the M[subscript(bh)]–L relation in the near-IR and to investigate the M[subscript(bh)]–n relation. In the third part I will construct the near-IR SMBH mass function for the Galaxy and Mass Assembly (GAMA) survey. For this purpose I will apply the newly derived M[subscript(bh)]–L relation onto an elliptical subsample of K-band images. The advantage of this SMBH mass function is that during the M[subscript(bh)]–L construction I used the same quality images and techniques used on the GAMA survey. Apart from the M[subscript(bh)]–L relation, the M[subscript(bh)]–sigma relation was used as an alternative approach for a subsample of galaxies for which the velocity dispersions were available. Furthermore, I employed both local SMBH mass functions (MGC & GAMA) for estimating the SMBH mass density at redshift zero and accounted for the dependence of the total SMBH density on the look-back time by comparing with semi-analytic SMBH mass functions. Finally, from the SMBH mass density I estimated the baryon fraction that is locked into SMBHs.

The first confirmed detection of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found by radial velocity measurements in a four-day orbit around the nearby star 51 Pegasi by Mayor and Queloz in 1995. This finding encouraged the development of the method known as transit method that detects distant planets by measuring the small darkening of a star light curve as an orbiting planet passes between it and the Earth. The first detection of a transiting exoplanet, HD 209458 b, in 1999 by D. Charbonneau and collaborators and G. W. Henry and collaborators, and the discoveries obtained for this planet during follow- up observations (first planet with a detectable atmosphere containing oxygen and carbon, first detection of an evaporating hydrogen atmosphere and being one of the first two exoplanets to be directly observed spectroscopically) demonstrated the high scientific potential of planets discovered with this method. Transit photometry is currently the most effective and sensitive method for detecting extrasolar planets. Several surveys have taken this approach, such as the ground-based MEarth, SuperWASP, KELT, HAT-South, TFRM-PSES, NGTS or the Evryscope, as well as the space-based CoRoT, Kepler, the recently commissioned, TESS and the future PLATO missions. The photometric precision and accuracy achieved by an astronomical survey is a key factor in detecting a transiting signal or any other kind of variability. Many of the systematic variations in a given light curve are shared by light curves of other stars in the same data set. In order to remove those systematics, one can identify the objects in the field that suffer from the same kind of variations as the target (correlated noise) and then build and apply a filter based on the light curves of these comparison stars. Wavelets have unique properties that make them an ideal tool for analyzing signals of non- stationary nature. In comparison to the sine wave used in the Fourier transform, which is smooth and of infinite length, the wavelet is irregular in shape and compactly supported. Their irregular shape allows to analyze signals with discontinuities, transients, singularities and sharp changes, while their compactly supported nature allows temporal localization of the signal's features. Along this work we lay out the framework from which the main goal of this thesis, the Wavelet-based Trend Filtering Algorithm (TFAW) will be built from. TFAW is a wavelet-based modification of the Trend Filtering Algorithm developed by Kovács, Bakos and Noyes (2005). TFAW is a totally generic, Python-based, parallelized algorithm useful to improve the performance of signal detection, reconstruction and characterization, provided that a set of comparison light curves sharing the same systematics and trends as the target time series is available. differs from other wavelet-based noise-filtering algorithms in that it does not require any parametric model fitting or any extra computational method. TFAW estimates the noise contribution of the signal from its Stationary Wavelet Transform (SWT) at each iteration step and the de-noising is done through the subtraction of this contribution from the signal. TFAW de-noises the signal without modifying any of its intrinsic properties contrary to wavelet coefficient thresholding that can lead to distortions of the signal and introduce artificial oscillations or ripples around discontinuities. Tests conducted on simulated and real (coming from the TFRM-PSES, Evryscope, CoRoT and Kepler surveys) TFAW-filtered light curves show an improvement of 40% (although it can be higher) in their standard deviations with respect to the ones detrended with TFA, leading to a better characterization of the signal, without modifying its features. It improves the transit detection rate a factor 2-5 for low SNR signals with respect TFA. We demonstrate that the TFAW-filtered light curve yields better MCMC posterior distributions, diminishes the bias in the fitted transit parameters and their uncertainties and narrows the credibility intervals up to a factor 10 for simulated transits. Finally, TFAW is able to isolate the different underlying signals within a light curve with multiple periodic signals, such as multi-transit signals, transients, modulations or other kinds of stellar variabilities.
El descubrimiento del exoplaneta gigante 51 Pegasi b (detectado por Mayor y Queloz en 1995), mediante el método de las velocidades radiales, promovió el desarrollo de una nueva técnica de detección. Esta técnica, conocida como el método del tránsito, detecta exoplanetas midiendo el pequeño oscurecimiento del flujo estelar cuando el planeta pasa entre la estrella y el observador. El método del tránsito es, actualmente, el modo más eficiente y sensible para detectar planetas extrasolares. Muchas misiones han seguido este modo de observación, aquellas basadas en tierra, como MEarth, SuperWASP, KELT, HAT-South, TFRM-PSES, NGTS o el Evryscope; así como aquellas misiones espaciales como COnvection ROtation and planetary Transits (CoRoT), Kepler, TESS y la futura misión PLATO. La precisión fotométrica y la exactitud conseguida por una misión es un factor clave en la detección y caracterización de una señal correspondiente a un tránsito o a cualquier otro tipo de variabilidad. Las wavelets tienen unas propiedades que las hacen ideales para analizar señales de naturaleza no estacionaria. La forma irregular de las wavelets permite analizar señales con discontinuidades, singularidades o cambios bruscos mientras que su naturaleza compacta permite la localización temporal de las características de la señal. En este trabajo presentamos el Wavelet-based Trend Filtering Algorithm (TFAW). TFAW es un algoritmo totalmente genérico, desarrollado y paralelizado en Python basado en el Trend Filtering Algorithm (TFA) desarrollado por Kovács, Bakos y Noyes (2005). El algoritmo es útil para mejorar el rendimiento en la detección, reconstrucción y caracterización de señales astrofísicas. TFAW difiere de otros métodos de filtrado de ruido basados en wavelets en que no requiere ningún modelo de ajuste paramétrico o cualquier otro método computacional. TFAW estima la contribución de ruido de la señal a partir de su Stationary Wavelet Transform (SWT) y el filtrado se realiza eliminando esta contribución de la señal. Además, TFAW es capaz de hacer el filtrado de la señal sin modificar ninguna de sus características intrínsecas a diferencia de otros métodos como los umbrales calibrados de los coeficientes wavelet que pueden dar lugar a distorsiones de la señal o introducir oscilaciones o perturbaciones artificiales alrededor de discontinuidades. En curvas de luz simuladas, TFAW mejora la detección de tránsitos en un factor 2.5 para señales con bajo SNR. TFAW proporciona una mejor representación y caracterización de señales simuladas y reales (provenientes de las misiones TFRM-PSES, Evryscope, CoRoT y Kepler) afectadas por ruido. Así mismo, proporciona mejores probabilidades a posteriori y una disminución del bias y las incertidumbres de los parámetros ajustados mediante MCMC.

R Coronae Borealis (RCB) stars belong to a rare class of variable stars characterized by sudden and unpredictable declines, which are believed to be caused by dust cloud obscuration. In spite of the fact that these stars are so rare (only about 40 are known in our Galaxy), there are many reasons for investigating them. The unusual variability and peculiar chemical composition make them unique among all known types of variable stars. Their evolution and the nature of their unpredictable minima are still not entirely understood. Very few observations of RCB stars during the decline phase exist. Only three RCB stars (R CrB, RY Sgr and V854 Cen) have been studied in detail and only a few declines have been completely covered by observations. This thesis investigates the spectroscopic and photometric characteristics of RCB variables during their decline phases. A programme of photometric and spectroscopic observations of nine RCB and three HdC stars has been undertaken at Mt John University Observatory (MJUO) over a period of two and a half years. The programme includes some typical examples of RCB stars (Teff ~ 7000 K), as well as some cool ones (Teff ~ 5000 K). One of the most unusual of all RCB stars, V854 Cen, is also included. The photometric observations, as part of the long-term monitoring of RCB stars at MJUO, have provided the UBVRIphotometry and have served as a decline indicator. Complex colour changes during the declines were monitored and compared with the spectroscopy. The photometry during the recovery phases of the nine RCB stars in the last 12 years was used for studying the extinction properties of the gas obscuring the photosphere. An analysis of 26 different declines shows that the material causing the declines has extinction properties similar to those of the interstellar medium. The medium and high-resolution spectroscopy has been obtained for six declines of different programme stars using the 1-m telescope at MJUO. Although the duration and depth of the declines are very different, they all show similar photometric and spectroscopic characteristics. The results have been compared with other observations and used to examine a simple line-region model (E1/E2/BL), which attempts to describe the evolution and origin of emission lines during a decline. In general, the evolution of various emission lines observed in this work is consistent with their classification into these three groups. However, some characteristics of the emission lines indicate a different origin from that suggested by the model. A very rich emission line spectrum was monitored during the 1998 decline of V854 Cen, while only the most prominent lines were observed in the other stars. Short-lived high-excitation lines from the initial decline phase, such as CI and 01, were classified as Ei. They show a characteristic, shock-induced red shift indicating the photospheric origin. Lines classified as E2 are mainly from the low-excitation ions and neutral atoms. All lines from this group appear at the very beginning of the decline and are visible through to the late recovery phase, slightly blue-shifted relative to the stellar velocity. The lines of the low-excitation ions exhibit a complex structure with a strong central and two weaker components, one on each side. Their absolute flux evolution has been compared with the changes in the stellar continuum flux. The behaviour of these lines indicates that they are not affected by the dust cloud in the same way as the photospheric continuum. Assuming that the dust cloud is formed at about 2R* and taking into account the acceleration obtained from the analysis of the high-velocity Nal D absorption lines, the position of the E2 line emitting region was estimated to be about 3R* - 5R*. The third group (BL) consists of broad emission lines, which are a typical feature of all observed declines. The most prominent broad lines present in all RCB stars belong to the Nal D doublet. The observations demonstrate that these lines are the strongest in V854 Cen, due to the significant amount of material produced by its frequent declines. In contrast to the E2 lines, whose fluxes have been found to decrease during the decline, the absolute flux of the broad lines stays constant throughout the whole decline phase. This is consistent with the idea that the broad emission is a permanent feature, whose visibility depends only on the photospheric brightness. Various Nal D components (sharp and broad emission and high-velocity absorption) have been analysed in a number of RCB declines and presented in this thesis. The high-velocity blue-shifted Nal D absorption demonstrates similar velocities (between -230 kms-1 and -400 kms-1), structure and behaviour in the different declines. The observations from the 1998 decline of V854 Cen clearly show that the high-velocity absorption lines can also appear during the initial decline phase. This suggests that they can be associated with the clouds formed in some previous declines, as well as with the current one. The spectroscopic observations of the 1998 decline of V854 Cen obtained in this thesis represent the first almost complete coverage of a decline of this star.

El trabajo que presentamos en esta tesis tiene como finalidad la operación, calibración y análisis de datos ópticos del instrumento OMC (Optical Monitoring Camera) a bordo del satélite INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory). La cámara OMC ofrece, por primera vez, la oportunidad de realizar observaciones fotométricas de larga duración en el rango óptico, simultáneamente con las de rayos X y rayos gamma. En la primera parte de la tesis describimos el proyecto INTEGRAL/OMC y sus operaciones científicas, detallando el proceso que hemos seguido para la construcción del catálogo de entrada de la OMC. Definimos la estrategia y requisitos que debe satisfacer el software de apuntado encargado de generar los telecomandos que controlan el funcionamiento de la cámara. La combinación del catálogo y el software de apuntado, junto con el buen funcionamiento del algoritmo de centrado de a bordo, han permitido la determinación del apuntado de la OMC, a bordo y en tiempo real, con una precisión mejor que 1 píxel desde el inicio mismo de las operaciones. La segunda parte se centra en el procedimiento que hemos elaborado para el análisis de los datos. Describimos el flujo de datos desde que llegan a tierra, pasando por los distintos sistemas de procesamiento, hasta que, finalmente, se convierten en datos científicos listos para ser utilizados por la comunidad astrofísica. Detallamos todos los aspectos relacionados con la calibración del instrumento. Explicamos los distintos algoritmos desarrollados para el análisis científico de los datos OMC, haciendo especial énfasis en las soluciones adoptadas para mejorar los resultados fotométricos y astrométricos del instrumento. En la última parte presentamos los archivos y catálogos resultantes de las observaciones realizadas con la cámara OMC. Describimos los archivos de datos procesados en tiempo real y de datos consolidados, así como el portal Web de acceso a los datos OMC. Avanzamos lo que será el catálogo final de la OMC, que contendrá todas las fuentes observadas y detectadas por este instrumento, una vez finalizada la misión INTEGRAL. Presentamos también dos de los subcatálogos preliminares obtenidos tras analizar determinados grupos de fuentes: "Contrapartidas ópticas de fuentes de altas energías del 4º Catálogo IBIS/ISGRI" y "Primer catálogo de fuentes variables observadas con la OMC".
The work presented in this thesis describes the system that allows the operation, calibration and data analysis of the OMC instrument (Optical Monitoring Camera) on board the ESA's INTEGRAL spacecraft (INTErnational Gamma-Ray Astrophysics Laboratory). The OMC camera offers, for the first time, the opportunity to perform long photometric observations in the optical range simultaneously to those in the X-ray and gamma-ray bands. In the first part of the thesis we describe the INTEGRAL/OMC project and its scientific operations, giving some details about the building process of the OMC Input Catalogue. We define the strategy and requirements of the OMC Pointing Software which generates the telecommands to control the camera operations. The combination of both the Input Catalogue and the Pointing Software, as well as the excellent behaviour of the on-board centring algorithm, allow us the on-board determination in real time of the OMC pointing direction with an accuracy better than 1 pixel from the beginning of the mission operations. The second part is focused on the development involved in the data analysis procedures. We describe the data flow starting when the telemetry data are received at Earth, followed by the different data processing stages present in the systems, until they are finally converted into scientific data which can be used by the astrophysics community. We explain all aspects related to the instrument calibration and the algorithms developed for the OMC scientific analysis, making special emphasis in the adopted solutions that allowed us to improve the photometric and astrometric results. In the last part we present the archives and catalogues compiled with the OMC data obtained during INTEGRAL observations. We describe the consolidated and near real time data archives as well as the OMC Archive Web Portal. We summarize the contents of the final OMC Catalogue which will be published at the end of the INTEGRAL mission including all sources observed and detected by OMC. In addition we present two preliminary sub-catalogues obtained by analysing some specific objects groups: "OMC optical monitoring of sources in the 4th IBIS/ISGRI catalogue" and "The first INTEGRAL/OMC Catalogue of optically variable sources".

The main purpose of this thesis is to map the radial variation of the stellar density for the young stellar population in the Galactic anticenter direction in order to understand the structure and location of the Perseus spiral arm. A uvbyHbeta Stroemgren photometric survey covering 16 square degrees in the anticenter direction was carried out using the Wide Field Camera at the Isaac Newton Telescope. This is the natural photometric system for identifying young stars and obtaining accurate estimates of individual distances and ages. As a result, a main catalog of 35974 stars with all Stroemgren indexes has been obtained, together with a extended one with 96980 stars with partial data. The central 8 square degrees have a limiting magnitude of V~17mag, while the outer region reaches V~15.5mag. These large samples permit us to analyze the stellar surface density variation associated to the Perseus arm and to study the properties of the stellar component and the interstellar extinction in the anticenter direction. To compute the physical parameters for these stars two different approaches have been used, 1) the available pre-Hipparcos empirical calibrations based on cluster data and trigonometric parallaxes, and 2) a new model based method using atmospheric models and evolutionary tracks, optimized for stars up to Teff>7000K. Results for both of them have been compared with Hipparcos data looking for possible biases and trends. The obtained physical parameters allow us to select the intermediate young stars useful for our studies (B5-A3). These stars are young enough to still have a small intrinsic velocity dispersion (making them respond stronger to a perturbation), but they are also old enough to have approached a dynamic equilibrium with the spiral perturbation. Through their stellar distances, and after defining distance complete samples between 1.2 and 3kpc, we can trace the density distribution in the anticenter direction, finding a clear overdensity around 1.7kpc with an amplitude of 10% that can be associated to the Perseus arm. Those distance complete samples, having a statistical significant number of stars, built using the new model based method for distance estimation, show a significance of the Perseus arm peak overdensity larger than 3sigma. Exponential fittings also allowed us to constrain the radial scale length of the young population of the Galaxy between 2.0 and 2.6kpc, as well as to estimate the stellar density at the solar vicinity for stars between B4 and A1 type stars in 0.022star/pc2, well in agreement with the results obtained in the new version of the Besancon Galaxy Model. In addition, all these data allow the creation of a 3D extinction map, that carefully analyzed shows the presence of a dust layer clearly in front of the location of the stellar overdensity of the arm, suggesting that the corotation radius of the spiral pattern is further away of the position of the Perseus arm. The detection of this dust lane supports the existence of a density wave. Definitive confirmation will come from the ongoing spectroscopic survey using WYFFOS at the William Herschel Telescope in order to obtain radial velocities for a large subsample of the stars in our photometric catalog, that will allow us to trace the possible kinematic perturbation due to the presence of the Perseus arm.
Avui en dia, i després de molts anys d’investigació, encara no disposem d’una teoria completa sobre la forma i l’origen dels patrons espirals de la Via Làctia. I tot i ser conscients que són un factor important per explicar l’evolució dels discos galàctics, la manca d’evidències observacionals sobre els braços espirals de la nostra Galàxia és evident. Moltes preguntes clau encara no tenen resposta, com ara: quin és el mecanisme de formació i evolució de l’estructura espiral en discs estel•lars? Es tracta d’estructures transitòries o són estructures de llarga durada? Quins són els seus components bàsics; estrelles o gas? El treball realitzat durant aquesta tesi pretén ajudar a resoldre algun d’aquests interrogants. El principal objectiu és traçar el braç espiral de Perseu en la direcció de l’anticentre Galàctic. La feina desenvolupada es pot separar en tres apartats. En primer lloc, un mostreig amb fotometria Strömgren en la direcció de l’anticentre Galàctic, mitjançant el qual hem obtingut un catàleg de 96.980 estrelles, 35.974 d’elles amb informació completa en els sis filtres uvbyHβ, i totes elles en una regió de 16 graus quadrats del cel. En segon lloc, per tal d’obtenir els paràmetres físics per a aquestes estrelles, hem creat un nou mètode a partir de models atmosfèrics i evolutius. Finalment, s’ha utilitzat tota aquesta informació per estudiar la distribució de la densitat estel•lar en la direcció de l’anticentre. Aquestes dades també ens han permès crear un mapa d’extinció tridimensional, a partir del quan hem analitzat la distribució de pols així com la seva relació amb el braç espiral de Perseu.

The topics treated in this thesis are the design, the integration and the use of the ultra-fast single photon photometer IQuEYE (Italian Quantum Eye). The implementation of this instrument represents an important step in a project, initiated in 2005, for the realization of a Quantum Photometer (QuantEYE) for the telescope EELT (European Extremely Large Telescope) of 42 meters in diameter, now under construction, which is scheduled for completion in 2018. Such an instrument would represent a breakthrough in observational Astronomy and it would allow extending the knowledge gained from theoretical and experimental Quantum Optics to the Astrophysics. QuantEYE is designed to extract from the light collected the information enclosed in the statistical distribution of photons through spatial and temporal analysis of the correlation functions of order higher than first, beyond the capability of "classics" instrumentation. The instrument described in this thesis, IQuEYE, is a prototype for NTT (ESO New Technology Telescope). It is essentially a fixed aperture photometer that collects light within a field of view of few arcseconds, dividing the telescope light beam into four equal parts, and focuses each sub-beam on an independent single photon-counting diode SPAD. The innovative photon time-tagging system is based on a rubidium atomic clock, corrected on long time scale the by means of a GPS signal. This system allows the identification of each photon with a relative precision better than 100ps and an absolute UTC precision of 500ps for an hour of observation. The instrument can identify in this way up to eight million photons per second, that means IQuEYE is able to sustain flows of photons up to a maximum rate of 8MHz. All arrival times, digitized at 25ps, are stored, in this way post-processing analysis and data reprocessing in time are allowed. The first part of the thesis is devoted to the detailed description of the instrument, starting from design phase, with particular attention for opto-mecanics, to its integration. IQuEYE is now fully operative and has already been used in three ob-servation campaigns at La Silla (Chile) during the months of January and December 2009 and July-August 2010. The thesis then collects the results of some observations performed and presents them in its second part, with the aim of demonstrating the potential of the instrument. So a brief description of a first experiment for the feasibility of intensity interferometry is given. Moreover the observation of an exoplanetary transit which allows us to double the accuracy in determining the period of mid-transit, is described. Finally the results for the observation of rapidly varying objects (three optical pulsars) are exposed, together with some analysis tools developed specifically for our data. The acquired data have an excellent quality. Through their analysis the best determination of the Crab pulsar (PSR B0531 +21) period was achieved. Furthermore the optical light curves for PSR B0833-45 (weak pulsar in the Vela constellation, at the limits of visibility for NTT) and B0540-69. In this way the validity of IQuEYE in HTRA High Time Resolution Astronomy has been demonstrated.
Gli argomenti trattati in questa tesi sono la progettazione, l’integrazione e l’utilizzo del fotometro ultrarapido a conteggio di singolo fotone IQuEYE (Italian Quantum Eye). L’implementazione di questo strumento rappresenta un passo fondamentale in un progetto avviato nel 2005 che mira alla realizzazione di un fotometro quantistico, QuantEYE, per il telescopio EELT (European Extremely Large Telescope) di 42 metri di diametro, oggi in fase di costruzione, la cui ultimazione è prevista per il 2018. Un tale strumento rappresenterebbe una svolta nell’astronomia osservativa, permettendo di estendere le conoscenze sviluppate nell’ambito dell’ottica quantistica teorica e sperimentale all’ambito astrofisico. QuantEYE è progettato per estrarre dalla luce raccolta le informazioni contenute nella statistica di distribuzione spaziale e temporale dei fotoni mediante l’analisi delle funzioni di correlazione di ordine superiore al primo, limite al quale si fermano gli strumenti astronomici “classici”. Lo strumento descritto nella presente tesi, IQuEYE, è un prototipo destinato all’uso su NTT (ESO New Technology Telescope). Si tratta essenzialmente di un contatore di singoli fotoni progettato per raccogliere la luce suddividendo la pupilla del telescopio attraverso quattro canali indipendenti che utilizzano dei rivelatori di tipo SPAD. L’innovativo sistema di etichettatura temporale dei fotoni rilevati si basa su un orologio atomico al rubidio, per corregere la deriva del quale viene usato un segnale GPS interpolato su lunga scala temporale. Tale sistema permette di identificare ogni fotone con una precisione relativa migliore di 100ps ed una precisione assoluta riferita ad UTC di 500ps per un’ora di osservazione. Lo strumento è in grado identificare in questo modo fino ad otto milioni di fotoni al secondo, cioè di sostenere flussi di fotoni fino ad un limite massimo di 8MHz. Tutti i tempi di arrivo, digitalizzati a 25ps, vengono salvati e permettono l’analisi differita e la rielaborazione nel tempo. La prima parte della tesi è dedicata alla descrizione dettagliata dello strumento, a partire dalla fase di progettazione, il disegno optomeccanico, fino alla sua integrazione. IQuEYE è oggi perfettamente funzionante ed è stato già utilizzato in tre campagne osservative a La Silla (Cile) durante i mesi di gennaio e dicembre 2009 e luglio-agosto 2010. La tesi raccoglie quindi i risultati di alcune delle osservazioni effettuate e li presenta nella seconda parte, con l’intento di dimostrare le potenzialità dello strumento. Vengono descritti sommariamente un primo esperimento di fattibilità per l’interferometria di intensità e l’osservazione di un transito esoplanetario che permette di raddoppiare la precisione nella determinazione del periodo di metà transito rispetto agli strumenti utilizzati da altri autori. Per finire sono esposti i risultati ottenuti nell’osservazione di oggetti rapidamente variabili, tre pulsar ottiche, e alcuni strumenti di analisi dati sviluppati specificatamente. I dati acquisiti hanno una qualità eccellente e hanno permesso di ottenere la miglior determinazione mai conseguita del periodo di pulsazione per PSR B0531+21 (la pulsar della nebulosa del Granchio). Sono inoltre state ricavate le prime curve di luce ottiche da decenni a questa parte per PSR B0833-45 (debole pulsar nella costellazione della Vela, ai limiti di visibilità per NTT) e per B0540-69. In questo modo la validità di IQuEYE nell’ambito dell’astronomia ad alta risoluzione temporale è stata ampiamente dimostrata.

The significant increase of astronomical data necessitates new strategies and developments to analyse a large amount of information, which no longer is efficient if done by hand. Supervised machine learning is an example of one such modern strategy. In this work, we apply the classification technique on Gaia+2MASS+WISE data to explore the usage of supervised machine learning on large astronomical archives. The idea is to create an algorithm that recognises entries with unusual infrared properties which could be interesting for follow-up observations. The programming is executed in MATLAB and the training of the algorithms in the classification learner application of MATLAB. Each catalogue; Gaia+2MASS+WISE contains ~109, 5×108 and 7×108 (The European Space Agency 2019, Skrutskie et al. 2006, R. M. Cutri IPAC/Caltech) entries respectively. The algorithms searches through a sample from these archives consisting of 765266 entries, corresponding to objects within a <500 pc range. The project resulted in a list of 57 entries with unusual infrared properties, out of which 8 targets showed none of the four common features that provide a natural physical explanation to the unconventional energy distribution. After more comprehensive studies of the aforementioned targets, we deem it necessary for further studies and observations on 2 out of the 8 targets (Nr.1 and Nr.8 in table 3) to establish their true nature. The results demonstrate the applicability of machine learning in astronomy as well as suggesting a sample of intriguing targets for further studies.
Inom astronomi samlas stora mängder data in kontinuerligt och dess tillväxt ökar snabbt för varje år. Detta medför att manuella analyser av datan blir mindre och mindre lönsama och kräver istället nya strategier och metoder där stora datamängder snabbare kan analyseras. Ett exempel på en sådan strategi är vägledd maskininlärning. I detta arbete utnyttjar vi en vägled maskininlärnings teknik kallad klassificering. Vi använder klassificerings tekniken på data från de tre stora astronomiska katalogerna Gaia+2MASS+WISE för att undersöka användningen av denna teknik på just stora astronomiska arkiv. Idén är att skapa en algorithm som identifierar objekt med okontroversiella infraröda egenskaper som kan vara intressanta för vidare observationer och analyser. Dessa ovanliga objekt är förväntade att ha en lägre emission i det optiska våglängdsområdet och en högre emission i det infraröda än vad vanligtvis är observerad för en stjärna. Programmeringen sker i MATLAB och träningsprocessen av algoritmerna i MATLABs applikation classification learner. Algoritmerna söker igenom en samling data bestående av 765266 objekt, från katalogerna Gaia+2MASS+WISE. Dessa kataloger innehåller totalt ~109, 5×108 och 7×108 (The European Space Agency 2019, Skrutskie et al. 2006, R. M. Cutri IPAC/Caltech) objekt vardera. Det begränsade dataset som algoritmerna söker igenom motsvarar objekt inom en radie av <500 pc. Många av de objekt som algoritmerna identifierade som ”ovanliga” tycks i själva verket vara nebulösa objekt. Den naturliga förklaringen för dess infraröda överskott är det omslutande stoft som ger upphov till värmestrålning i det infraröda. För att eliminera denna typ av objekt och fokusera sökningen på mer okonventionella objekt gjordes modifieringar av programmen. En av de huvudsakliga ändringarna var att introducera en tredje klass bestående av stjärnor inneslutna av stoft som vi kallar "YSO"-klassen. Ytterligare en ändring som medförde förbättrade resultat var att introducera koordninaterna i träningen samt vid den slutgiltiga klassificeringen och på så vis, identifiering av intressanta kandidater. Dessa justeringar resulterade i en minskad andelen nebulösa objekt i klassen av ”ovanliga” objekt som algoritmerna identifierade. Projektet resulterade i en lista av 57 objekt med ovanliga infraröda egenskaper. 8 av dessa objekt påvisade ingen av det fyra vanligt förekommande egenskaperna som kan ge en naturlig förklaring på dess överflöd av infraröd strålning. Dessa egenskaper är; nebulös omgivning eller påvisad stoft, variabilitet, Hα emission eller maser strålning. Efter vidare undersökning av de 8 tidigare nämnda objekt anser vi att 2 av dessa behöver vidare observationer och analys för att kunna fastslå dess sanna natur (Nr.1 och Nr.8 i tabell 3). Den infraröda strålningen är alltså inte enkelt förklarad för dessa 2 objekt. Resultaten av intressanta objekt samt övriga resultat från maskininlärningen, visar på att klassificeringstekniken inom maskininlärning är användbart på stora astronomiska datamängder.

More than 80% of the stars in the Universe are expected to have initial masses below eight to ten times the mass of our sun. These low mass stars, including our sun, become cool red giants during one of the final evolutionary stages of their life: the Asymptotic Giant Branch (or AGB) phase. AGB stars are among the main producers of carbon and heavy (s-process) elements in the Universe. These elements are synthesized inside the star and mixed to the stellar atmosphere where stellar winds are responsible for the loss of more than 50% of the stellar mass, hence, AGB stars are strong polluters of the interstellar medium. The ejected material can clump together into dusty particles which may serve as ingredients for the birth of new stars and planets. When most of the AGB stellar envelope is lost, the AGB star stops releasing nuclear energy from interior processes and swaps its giant face for a planetary nebulae look, whereafter it fades away as a white dwarf.

The dredge-up of carbon and s-process elements into the AGB atmosphere causes an important chemical anomaly among them: initial oxygen-rich stars (M stars) are transformed into carbon-rich stars (C stars). As a consequence, a group of oxygen-rich AGB stars exists which makes the transition between M and C stars. These transition stars are classified as S.

Although AGB stars are identified as producers of heavy elements, their nucleosynthesis and mixing processes are weakly constrained due to large uncertainties on their estimated temperature, gravity and chemical composition. Stronger constraints on the atmospheric parameter space, hence interior processes, of AGB stars can be obtained by investigating the atmosphere of S stars. Since they are transition objects on the AGB, they trace the rise of the s-process. S stars are less numerous than C stars, but their optical spectra are brighter making it easier to identify atomic and molecular lines. Therefore, S stars belong to the most interesting objects along the AGB to perform this task.

From a practical point of view, the spectra of S stars are extremely difficult to study since they are dominated by different, overlapping molecular bands, and the spectral shape may vary strongly from star to star due to their transition status. Therefore, tailored model atmospheres for S stars are of utmost importance to understand the spectroscopic, and even photometric, changes in terms of variations in the atmospheric parameters. A comparison between the models and observations aims not only at constraining the atmospheric parameter space of S stars, it will also test the reliability of 1D state-of-the-art model atmospheres for such complex stars.

From an evolutionary point of view, the S-star family is contaminated with stars who gained their atmospheric enrichment in heavy elements from a companion star. Evidences were found that these binary S stars are not at all located on the AGB, hence, they are labelled as extrinsic S stars while S stars on the AGB are labelled as intrinsic. The difference in evolutionary stages between intrinsic and extrinsic S stars was already found 20 years ago, however, a separation in terms of surface temperature, gravity and chemical composition is not well-established due to the lack of S-star model atmospheres. Such a distinction in atmospheric parameters will facilitate the discovery of these intruders and even help to calibrate stellar evolutionary models of single and binary stars.

To achieve these goals, the first step consists in the construction of a grid of model atmospheres for S stars. The grid will be used to quantify the influence of atmospheric parameters on the model structure and emergent flux. These results will be analyzed to derive precise atmospheric parameters of observed S stars, using a set of well-defined photometric and spectroscopic indices. Once the best model atmosphere has been selected for all observed S stars, their atmospheric parameters will be discussed in view of their evolutionary stage. The best-fitting model atmosphere will also be used to derive abundances from spectral syntheses. The abundance profiles are compared with stellar evolution model prediction to constrain nucleosynthesis and mixing processes inside S stars. Derived abundances of unstable elements will be used to estimate, for the first time, the age of AGB stars. Finally, their abundance profile will be discussed as a function of their time spent on the AGB.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

The development and commissioning of an 8-channel astronomical photometer is described. The design is based on a low dispersion grating spectrograph in which the spectrum produced is focussed onto a mosaic of mirrors which redirect the radiation in the spectral bands into the appropriate detector channels. Filters are used to further define the spectral passbands. The detectors used are photomultipliers, whose response features have been matched to the individual channels. The instrument is under the control of a dedicated microprocessor with a further microprocessor used for data acquisition. The photometer has been employed in an observing programme on the 0.9m James Gregory telescope at St Andrews. Observations of standard uvby stars have allowed transformations equations to be derived for the Strӧmgren system. The eclipsing binary SV Cam has been observed and a revised ephemeris found.

Il lavoro presentato in questa tesi è parte di un progetto a lungo termine, il cui scopo è quello di produrre un'accurata fotometria nel vicino infrarosso delle variabili di tipo RR Lyrae per un insieme di ammassi globulari Galattici che coprono un ampio intervallo in metallicità e che contengono una numero sufficiente di RR Lyrae. In questa tesi sono presentati i risultati ottenuti per gli ammassi globulari Galattici M68 e NGC3201, e per l'ammasso della Grande Nube di Magellano Reticulum. Tali risultati sono tutti basati su osservazioni effettuate con SOFI/NTT. I dati raccolti ci hanno permesso di fornire stime accurate delle magnitudini J e K per una gran parte delle RR Lyrae degli ammassi, e in definitiva ci hanno permesso di derivare in un contesto omogeneo la pendenza della relazione Periodo-Luminosità nella banda K (PLK). La pendenza trovata è in buon accordo con le predizioni teoriche. Sulla base di tale accordo, abbiamo utilizzato le PLK teoriche per stimare la distanza degli ammassi studiati. Le distanze ottenute per M68 e NGC3201 mostrano un accordo piuttosto buono con le stime indipendenti più recenti ed accurate (claibrazioni Baade-Wesselink, metodo del FOBE, relazione periodoluminosità delle d Scuti). La distanza ottenuta per Reticulum è in buon accordo con le stime più accurate per la Grande Nube di Magellano e, insieme a dati già raccolti per le RR Lyrae di campo della Grande Nube di Magellano, può fornire vincoli robusti sulla struttura tridimensionale di questa galassia. Infine, quando tutti i dati per l'intero campione di ammassi sarà stato raccolto ed analizzato, sarà possibile conseguire i seguenti obiettivi, su un ampio intervallo di metallicità: - derivare, sulla base della una nuova calibrazione della PLK, nuove distanze assolute per le RR Lyrae di campo per le quali è disponibile la fotometria nella banda K, e di confrontare tali distanze con quelle basate sul metodo di Baade-Wesselink; · fornire, sulla base delle relazioni periodo-colore PL(J-K) predette ed osservate, stime indipendenti dell'arrossamento interstellare nella direzione degli ammassi studiati; - produrre un ulteriore test, su un ampio intervallo di metallicità, dell'accuratezza delle predizioni, sia evolutive che pulsazionali, adottate per costruire le relazioni PLK e PL(J-K); - ottenere accurati diagrammi Colore-Magnitudine (CMD) ottici/infrarossi per gli ammassi studiati sulla base dei dati infrarossi raccolti e dei dati ottici disponbili in letteratura. Tali CMD ci consentiranno di effettuare un solido confronto fra teoria e osservazione sulla base dei colori (V-J) e (V-K), che sono solo marginalmente affetti da incertezze sistematiche; - utilizzare i colori (V-K) per derivare stime accurate delle temparature efficaci delle RR Lyrae degli ammassi studiati, che a loro volta possono essere usate per fornire una stima della abbondanza di elio. Questo risultato è particolarmente interessante, poiché gli ammassi globulari sono fra gli oggetti più antichi che possono essere trovati nella Galassia, e quindi l'abbondanza di elio stimata può fornire indizi sull'abbondanza di elio primordiale.
The work carried out in this thesis is part of a long-term project aimed at measuring accurate near-infrared magnitudes of RR Lyrae stars in a sample of Galactic globular clusters that cover a wide metallicity range ( 2.3 [ / ] 1.3 Fe H − £ £ − ) and host a sizable population of RR Lyrae stars ( 10 RR N ³ ). In this thesis we will present the result obtained for the Galactic globular clusters M68 and NGC3201, and for the Large Magellanic Cloud cluster Reticulum. The results for these clusters are all based on the observations carried out with SOFI/NTT. The data collected allowed us to provide accurate estimates of J, K mean magnitudes for a large portion of the cluster RR Lyrae variables, and in turn to derive in a homogeneous context the slope of the K-band Period-Luminosity relation (PLK). The slope of the observed PLK relation agrees quite well with theoretical pulsational predictions. On the basis of this agreement between our empirical PLK relations and the theoretical ones, we adopted the latter for estimating the absolute distances to the target clusters. The distances obtained for M68, NGC 3201, and Reticulum disclose a fairly good agreement with the most recent and accurate independent estimates (Baade-Wesselink calibration, FOBE method, d Scuti Period-Luminosity relation). Current data, together with near-infrared data already collected, will allow us to accomplish the following goals: • to derive, on the basis of the new empirical calibration of the PLK , absolute distances for field RR Lyrae stars for which are available mean K magnitudes and to compare them with distances based on Baade-Wesselink method; • to provide, on the basis of predicted and observed PL(J-K)relations, independent estimates of the reddening toward the target clusters; • to supply an independent test on a wide metallicity range of the accuracy of both evolutionary and pulsational predictions adopted to construct the PLK and the PL(J-K) relations; • to obtain accurate optical/near-infrared Color-Magnitude diagrams (CMDs) for the target clusters by adopting the new data and the optical data available in the literature. 6 These CMDs will allow us to compare theory and observations by using color indexes (V-J), (V-K), which are only marginally affected by systematic uncertainties; • to use (V-K) colors to derive accurate estimates of the effective temperatures of the globular clusters RR Lyrae stars, which in turn can be used to provide an estimate of the helium abundance. This result is particularly interesting, because globular clusters are among the oldest objects that can be found in the Galaxy, and therefore the estimated helium estimates can give a hint on the primordial helium abundance.

Most of the efforts on the search and characterization of Earth-like exoplanets are currently focused on low mass stars. Some important properties related to the structure and processes in this type of stars are still unknown, so a careful characterization is essential as one of the next steps in exoplanet sciences. The characterization of stellar activity in low mass stars was carried out through several techniques that allowed us both to model and to simulate the relationships between the observational data and the stellar properties. Several empyrical relations for low mass stars allow to find correlations between certain activity indicators and the rotation period. These have permitted us to generate synthetic samples of stars with stochastic distributions of stellar and geometric properties allowing to estimate the inclination of the rotation axis from the distribution in the activity-vsini diagram. The methodology was applied to a sample of 1200 observed low mass stars and the best candidates for a targeted transit search were selected. Spot modelling techniques allow to obtain physical information about the stellar surface from time series photometric and spectroscopic data. In this work we analyse Kepler photometry of LHS 6343 A, an M-dwarf being eclipsed by a brown dwarf companion every 12.718 days, and showing photometric oscillations with the same periodicity and a phase lag of 100º from the eclipses. The accurate modeling of the Kepler data allowed to explain these oscillations with the presence of active regions appearing at a fixed longitude, thus suggesting a possible magnetic connection between both components. On the other hand, we also studied an alternative explanation for the photometric oscillations in LHS 6343 A in terms of the Doppler beaming effect, showing that this could be the main cause of the observed oscillations. Stellar activity effects are responsible for the noise observed at different amplitude and timescales on time series data. Such noise represents one of the main limitations for exoplanetary sciences. In order to characterize it, we designed a methodology to simulate the photosphere of an active rotating star through the integration of small surface elements from Phoenix atmosphere models. This allows to characterize the signal produced by activity and further study its relationship with the stellar properties, as well as the possible effects produced on exoplanet measurements. The methodology allowed us to present several strategies in order to correct or reduce the effects of spots on the photometry of exoplanet transits, as these may induce significant variations on the measurement of the planetary radius. We focused on a comprehensive analysis of HD 189733, a K5 star hosting a giant planet, which has simultaneous photometric (MOST) and spectroscopic (SOPHIE) data available. An accurate surface map was obtained using the methodology above, accurately reproducing the light curve and radial velocity observations. Such map was used in order to study the effects of activity on the exoplanet transits. We showed that the effects of spot-crossing events are significant even for mid-infrared wavelengths. Moreover, the chromatic effects of spots not occulted by the planet show a signal with a wavelength dependence and amplitude that are very similar to the signature of the atmosphere of a planet dom- inated by dust. The radial velocity theoretical curve is in agreement with the observations up to the typical instrumental systematics of SOPHIE. The results from this work conclude that it is essential to correctly model the stellar activity signals for exoplanetary sciences, and we provide some tools and strategies to characterize and reduce such effects and extract astrophysical information.
Actualment, la major part dels esforços per la cerca i caracterització d’exoplanetes de tipus terrestre es centren en aquells que orbiten estrelles de baixa massa. Algunes de les característiques importants de l’estructura i els processos d’aquest tipus d’estrelles són encara poc coneguts, i per tant és important fer-ne un estudi acurat com un dels següents passos en el camp de l’exoplanetologia. En concret, el senyal produïit pels fenòmens d’activitat estel•lar, degut a la presència de taques i fàcules, introdueix variacions en les mesures fotomètriques i espectroscòpiques amb una periodicitat modulada per la rotació de l’estrella. En aquesta tesi s’ha realitzat un estudi dels fenòmens d’activitat a la fotosfera d’estrelles de baixa massa a través de diverses tècniques que ens han permès modelitzar o bé simular les relacions entre les propietats estel•lars i les dades observables. La simulació de mostres estadístiques d’estrelles basada en les relacions conegudes entre l’activitat estel•lar i la rotació ha permés implementar una tècnica per estimar la inclinació de l’eix de les estrelles a partir de mesures espectroscòpiques, resultant en un catàleg amb les millors candidates per una cerca de planetes amb trànsits. Per a la caracterització dels fenòmens relacionats amb l’activitat i un estudi acurat dels seus efectes sobre les mesures i cerques d’exoplanetes, s’ha aprofitat la disponibilitat de dades fotomètriques de Kepler juntament amb tècniques de modelització de taques, centrant-nos particularment en l’estudi de LHS 6343 A per obtenir informació d’activitat en la seva superfície. A més, s’ha dissenyat un simulador dels efectes d’activitat a la fotosfera basat en tècniques d’integració de superfície i models d’atmosfera Phoenix, que permet obtenir sèries temporals de dades sintètiques i estudiar els efectes de les regions actives sobre les mesures de trànsits de planetes. En particular, s’ha modelat el cas de HD189733. Els resultats d’aquest treball conclouen que és essencial una correcta modelització del senyal de l’activitat estel•lar en el camp de l’exoplanetologia, i es proporcionen algunes eines i estratègies per tal de caracteritzar i corregir aquests efectes i obtenir-ne informació astrofísica.

PLAnetary Transits and Oscillations of stars (PLATO) est une mission scientifique spatiale européenne dédiée à la sismologie stellaire et à la recherche d’exoplanètes, et dont le développement est coordonné par l’Agence Spatiale Européenne. Avec un intérêt majeur sur des planètes du type terrestre située dans la zone habitable des étoiles du type solaire de la séquence principale, cette mission repose sur de la photométrie de très haute précision et exige une très grande stabilité des mesures. Elle s’appuie sur des techniques bien éprouvées : la méthode de transits pour la détection des planètes, suivie de mesures de vitesses radiales réalisées au sol, et l'analyse des oscillations stellaires pour la caractérisation des leurs étoiles hôtes. Grace à son très large champ de vue couvrant plus de deux mille dégrées carrés du ciel, l’instrument PLATO sera capable d’observer plusieurs centaines de milliers d’étoiles de magnitude apparente inférieure à treize dans le visible, et de détecter des milliers de systèmes planétaires. Par ailleurs, en raison des contraintes télémétriques du satellite, l’extraction photométrique de la majorité des étoiles devra être effectuée à bord en s’appuyant sur des méthodes optimisées. Pour autant, la méthode d’extraction photométriques par masques a été adoptée pour sa faisabilité compte-tenu des contraintes à bord. Dans ce contexte, la problématique de développement des masques photométriques optimaux représente le cœur du travail de recherche présenté dans cette thèse. Dans les missions précédentes de la même catégorie de PLATO, à savoir CoRoT, Kepler et TESS, des masques photométriques ont été conçus selon une approche reposant uniquement sur la minimisation du rapport bruit sur signal, car la sensibilité à laquelle un transit planétaire peut être identifié, dans une courbe de lumière, est fortement corrélée à son niveau de bruit. En revanche, plus il est facile d'identifier une planète, en raison d'un niveau de bruit suffisamment faible, plus élevée est la probabilité que des objets en arrière-plan entrant dans la scène (par exemple des systèmes binaires reproduisant des vrais transits planétaires) soient détectés. Étant donné que la plupart des étoiles-cible de PLATO n’auront pas des images au sol pour l’identification des faux positifs, une conception de masques photométriques reposant uniquement sur la sensibilité de détection des vrais transits planétaires, sans faire suffisamment attention aux potentiels faux positifs, n’est donc pas forcément la meilleure stratégie. Pour vérifier cette hypothèse, deux métriques scientifiques ont été introduites nous permettant de quantifier directement la sensibilité d'un masque à la détection des vrais, d’une part, et de faux transits planétaires, d’autre part. Ainsi, le masque optimal a été défini comme étant celui qui donne le meilleur compromis entre ces deux métriques. Cette approche, originale à cette thèse, s’est avérée décisive pour la détermination d’un modèle de masque statistiquement capable de détecter des planètes de façon quasi-optimale, tout en étant substantiellement moins sensible aux faux positifs. Globalement, ces travaux constituent une étape importante dans la conception des chaînes de traitement des données bord et sol de la mission PLATO, ainsi que pour ses algorithmes de détection et de caractérisation des transits planétaires
PLAnetary Transits and Oscillations of stars (PLATO) is a European spatial scientific mission dedicated to asteroseismology and searching for exoplanets, and whose development is being carried out by the European Space Agency. With focus on Earth-like planets orbiting the habitable zone of main-sequence Sun-like stars, the mission relies on very high precision photometry and requires great stability of measurements. The mission is founded upon well-proven techniques: the transit method for detecting exoplanets, along with radial velocity follow-up from the ground, and the analysis of stellar oscillations for characterizing their host stars. Thanks to its very large field of view encompassing more than two thousand square degrees of the sky, the PLATO instrument will be able to observe several hundreds of thousands of stars with apparent magnitude lower than thirteen in the visible band, and thousands of planetary systems. In contrast, because of satellite telemetry constraints, photometry will have to be extracted in flight for most of the PLATO targets. For that, mask-based (aperture) photometry was adopted because of its sufficiently high performance and relatively low complexity for implementing on board. In this context, the development of optimal photometric apertures represents the core of the research work presented in this thesis. In the previous missions of the same category of PLATO (i.e. CoRoT, Kepler and TESS), photometric apertures were designed following an approach based uniquely on the minimization of the noise-to-signal ratio, because the sensitivity at which a planet transit can be found in a light curve is strongly correlated to its noise level. On the other hand, the higher the ease in identifying a transit-like signal because of a sufficiently low noise level, the higher the probability that background objects in the scene (e.g. binary systems reproducing legitimate planet transits) are detected. Since most of the PLATO targets will not have images available on ground for the identification of false positives, conceiving photometric masks based solely on how well a transit-like signal can be detected, paying no attention to potential false positives may not be the best strategy. To verify the consistence of this hypothesis, two science metrics were introduced allowing one to directly quantify the sensitivity of an aperture in detecting true and false planet transits. Then, the optimal aperture was defined as that which gives the best compromise between these two metrics. Such an approach, novel to this thesis, has been proven to be decisive for the determination of a mask model capable to provide near maximum planet yield and substantially reduced occurrence of false positives. Overall, this work constitutes an important step in the design of both on-board and on-ground science data processing pipelines of the PLATO mission

Our view of Globular Clusters has deeply changed in the last decade. Modern spectroscopic and photometric data have conclusively established that globulars are neither coeval nor monometallic, reopening the issue of the formation of such systems. Their formation is now schematized as a two-step process, during which the polluted matter from the more massive stars of a first generation gives birth, in the cluster innermost regions, to a second generation of stars with the characteristic signature of fully CNO-processed matter. To date, star-to-star variations in abundances of the light elements (C, N, O, Na) have been observed in stars of all evolutionary phases in all properly studied Galactic globular clusters. Multiple or broad evolutionary sequences have also been observed in nearly all the clusters that have been observed with good signal-to-noise in the appropriate photometric bands. The body of evidence suggests that spreads in light-element abundances can be fairly well traced by photometric indices including near ultraviolet passbands, as CNO abundance variations affect mainly wavelengths shorter than ~400 nm owing to the rise of some NH and CN molecular absorption bands. Here, we exploit this property of near ultraviolet photometry to trace internal chemical variations and combined it with low resolution spectroscopy aimed to derive carbon and nitrogen abundances in order to maximize the information on the multiple populations. This approach has been proven to be very effective in (i) detecting multiple population, (ii) characterizing their global properties (i.e., relative fraction of stars, location in the color-magnitude diagram, spatial distribution, and trends with cluster parameters) and (iii) precisely tagging their chemical properties (i.e., extension of the C-N anticorrelation, bimodalities in the N content).

Our view of Globular Clusters has deeply changed in the last decade. Modern spectroscopic and photometric data have conclusively established that globulars are neither coeval nor monometallic, reopening the issue of the formation of such systems. Their formation is now schematized as a two-step process, during which the polluted matter from the more massive stars of a first generation gives birth, in the cluster innermost regions, to a second generation of stars with the characteristic signature of fully CNO-processed matter. To date, star-to-star variations in abundances of the light elements (C, N, O, Na) have been observed in stars of all evolutionary phases in all properly studied Galactic globular clusters. Multiple or broad evolutionary sequences have also been observed in nearly all the clusters that have been observed with good signal-to-noise in the appropriate photometric bands. The body of evidence suggests that spreads in light-element abundances can be fairly well traced by photometric indices including near ultraviolet passbands, as CNO abundance variations affect mainly wavelengths shorter than ~400 nm owing to the rise of some NH and CN molecular absorption bands. Here, we exploit this property of near ultraviolet photometry to trace internal chemical variations and combined it with low resolution spectroscopy aimed to derive carbon and nitrogen abundances in order to maximize the information on the multiple populations. This approach has been proven to be very effective in (i) detecting multiple population, (ii) characterizing their global properties (i.e., relative fraction of stars, location in the color-magnitude diagram, spatial distribution, and trends with cluster parameters) and (iii) precisely tagging their chemical properties (i.e., extension of the C-N anticorrelation, bimodalities in the N content).

Several projects in astronomy require detectors with a high number of resolution elements on the sky. For this reason, many observatories equipped their telescopes with a particular kind of detectors, the so-called wide-field imagers, that fulfil this requirement. In this thesis we show that, with a careful data analysis based on an accurate point-spread-function (PSF) modelling and geometric-distortion correction, it is possible to obtain high astrometric and photometric accuracy over wide field of views (FoVs). The prescriptions discussed in the thesis can be extended to the most of the detectors that are or will be placed at ground and space observatories. In the first part of the thesis, we mainly focus on detectors working in the near-infrared (NIR) regime. We want to concentrate on NIR imaging because of the increasing interest of the astronomical community for this wavelength range, which will be the baseline for JWST. In the second part of the thesis we also present a couple of applications to optical wide-field imagers (LBC@LBT and the CCD mounted at the Asiago Schmidt telescope). We start by investigating the astrometric and photometric performance of the NIR wide-field imager HAWK-I@VLT. We adapt to HAWK-I the techniques originally developed for the Hubble Space Telescope (HST) imagers to obtain high-precision astrometry and photometry, and then adapted to the ground-based, wide-field imager mounted at the 2.2-m MPI/ESO telescope. We accurately model HAWK-I PSFs and solve for the geometric distortion of the detector. With this careful data reduction, we are able to reach an astrometric accuracy of a few milliarcsec (mas) over the entire FoV of the instrument. Together with the distortion-correction package, we also create astro-photometric catalogues of seven fields (four stellar clusters, two extragalactic fields and one region toward the Galactic centre). Furthermore, to test the reached astrometric accuracy, we compute relative proper motions for stars in two globular clusters (M 22 and M 4) and successfully separate cluster members from background/foreground objects. Proper-motion-selected colour-magnitude diagrams of the globular cluster M 22 allow us to study its multiple stellar populations, finding that the two stellar populations hosted in the sub-giant branches of M 22 have the same radial distribution from the cluster centre out to 9 arcmin, within our uncertainty. We then move to the wide-field imager VIRCAM@VISTA. Again, we export the tools made for HAWK-I to this imager and solve for the distortion of the detector. The geometric-distortion correction of VIRCAM is quite challenging because the tangential-plane projection effects are not negligible over a FoV larger than 1 sq. deg on the sky. We start by using the 2MASS catalogue as reference frame, and then we auto-calibrate the geometric distortion as done for the HAWK-I detector. This way, we are able to correct the geometric distortion of VIRCAM to an astrometric accuracy of about 8 mas. Finally, we use the `VISTA Variables in the Vía Láctea' (VVV) data to compute M 22 globular-cluster relative proper motions. VVV observations are not designed to such high-astrometric-accuracy purposes, but, with our tools, we are able to reach a proper-motion precision of ~1.4 mas/yr and separate cluster and field stars, as well as to measure the motion difference between Galactic bulge and disc stars toward the direction of M 22. In the last part of the thesis we describe our new project, focused to exploit the data coming from the planet-hunting K2 mission, the re-designed Kepler mission after the problems that occurred to its spacecraft. The analysis of crowded environments using K2 data can be very complex with classical (aperture-based) photometric approaches. Our method is instead specifically developed to deal with these particular regions (stellar clusters and toward the Galactic centre) and its key ingredients are PSF astrometry and photometry, high-angular-resolution input catalogues and PSF-based neighbour subtraction. We first address the problem of the K2 undersampled PSFs which fine structures, if not properly modelled, can introduce systematic errors that worsen both astrometry and photometry. To this aim, we follow the iterative method made to model HST undersampled PSFs. We then use a high-angular-resolution, ground-based catalogue to identify all detectable objects in the field and, for each of them, we measure their flux after we subtract all close-by neighbours. This way, we increase the number of measurable sources in the field and obtain a more reliable estimate of their flux. Most importantly, for variable stars, eclipsing binaries and exoplanet candidates, this method leads to a more reliable value of the true amplitude or eclipse/transit depth of their light curves because we reduce light-dilution effects. This is particularly interesting for exoplanets, as the true radius of the transiting objects would be otherwise under-estimated. We apply this method to the first K2 Campaign that covered two open clusters (M 35 and NGC 2158) and extract about 50000 light curves from only one channel of K2. This number is more than two times the total number of sources usually analysed over the entire FoV (76 channels) in a typical K2 Campaign. For bright stars, we reach a photometric precision of ~30 parts per million, comparable with other works in the literature focused on isolated stars. At the faint end, we measure objects down to 5 magnitudes fainter than in any published work with K2 data so far, and show that the PSF photometry performs better than aperture photometry in this magnitude regime. The improvement here described is more significant in crowded regions. Within the field of these two clusters we also find more than 2000 variable stars. All the projects developed during this thesis have also interesting long-term perspectives, since they can be seen as complementary or in preparation to future space-based missions like TESS and PLATO. Candidate exoplanets from Kepler/K2 (but also from the forthcoming TESS) observations can potentially be interesting targets for JWST, and then E-ELT
Diversi progetti in astronomia richiedono rivelatori con un elevato numero di elementi risolutivi in cielo. Per questo motivo, molti osservatori hanno equipaggiato i loro telescopi con un particolare tipo di rivelatori, i cosiddetti rivelatori a grande campo, che soddisfano tale requisito. In questa tesi mostriamo come sia possibile ottenere astrometria e fotometria di elevata accuratezza su grandi campi con un'attenta analisi dei dati basata sul modellare accuratamente le funzioni di sorgenti puntiformi (dall'inglese point-spread functions, o PSFs) e sulla correzione della distorsione geometrica. Le metodologie di lavoro discusse in questa tesi possono essere estese alla maggior parte dei rivelatori che sono o verranno collocati in osservatori da terra e da spazio. Nella prima parte della tesi ci focalizziamo principalmente sui rivelatori che lavorano nel regime del vicino infrarosso. Vogliamo concentrarci su tali camere infrarosse a causa del crescente interesse della comunità astronomica a queste lunghezze d'onda, che saranno alla base di JWST. Tuttavia nella seconda parte della tesi presentiamo anche alcuni esempi di applicazioni con rivelatori a grande campo che lavorano nella parte ottica dello spettro elettromagnetico (la camera LBC montata al telescopio LBT e il rivelatore montato al telescopio Schmidt di Asiago). Inizialmente esaminiamo le prestazioni astrometriche e fotometriche del rivelatore infrarosso a grande campo HAWK-I montato al VLT. Adattiamo per i dati HAWK-I le tecniche originariamente sviluppate per ottenere astrometria e fotometria di alta precisione con le camere di Hubble Space Telescope (HST), e successivamente estese alla camera a grande campo posta al telescopio da terra di 2.2 m dell'ESO/MPI. Modelliamo accuratamente le PSFs e correggiamo la distorsione geometrica di HAWK-I. Con questa attenta analisi dei dati, riusciamo a raggiungere un'accuratezza astrometrica di qualche millesimo di arcosecondo (mas) su tutto il campo di vista dello strumento. Oltre alla correzione della distorsione, costruiamo anche cataloghi astro-fotometrici di sette campi (quattro ammassi stellari, due campi extragalattici e un campo in direzione del centro Galattico). Inoltre, per testare l'accuratezza astrometrica raggiunta, calcoliamo i moti propri relativi delle stelle in due ammassi globulari (M 22 e M 4) e separiamo con successo i membri di ammasso da quelli di campo. Diagrammi colore-magnitudine decontaminati dalle stelle di campo grazie ai moti propri ci permettono di studiare le popolazioni stellari multiple dell'ammasso M 22, e di trovare che le due popolazioni visibili nei rami delle sub-giganti di M 22 hanno, entro gli errori delle nostre misure, la stessa distribuzione radiale dal centro dell'ammasso fino a 9 arcominuti. Successivamente ci spostiamo sul rivelatore VIRCAM montato al telescopio VISTA. Adattiamo nuovamente per questa camera i programmi sviluppati per HAWK-I e correggiamo la distorsione geometrica. La correzione della distorsione si è rivelata ardua perché su campi di vista estesi più di un 1 grado quadrato in cielo gli effetti dovuti alla proiezione della sfera celeste sul piano tangente di un'immagine non sono trascurabili. Per questo motivo, usiamo inizialmente come riferimento il catalogo 2MASS e poi auto-calibriamo la distorsione come fatto per HAWK-I. In questo modo siamo in grado di correggere la distorsione di VIRCAM e di raggiungere un'accuratezza astrometrica di circa 8 mas. Infine usiamo i dati provenienti dalle osservazioni di `VISTA Variables in the Vía Láctea' (VVV) per calcolare i moti propri delle stelle dell'ammasso globulare M 22. Le osservazioni di VVV non sono concepite per conseguire progetti basati su un'elevata accuratezza astrometrica, ma con i nostri strumenti raggiungiamo una precisione nei moti propri dell'ordine di 1.4 mas/yr, separiamo le stelle di campo da quelle di ammasso, ed inoltre misuriamo la differenza tra il moto proprio delle stelle del Bulge e del Disco della nostra Galassia nella direzione di M 22. Nell'ultima parte della tesi descriviamo il progetto focalizzato nello sfruttare i dati dal cacciatore di pianeti K2, il successore della missione Kepler, ridisegnata dopo i vari problemi in cui è incorsa. L'analisi di ambienti ad alta densità stellare usando i dati K2 può risultare molto complessa con le classiche tecniche fotometriche (basate sulla fotometria di apertura). Il nostro metodo invece è stato specificatamente elaborato per analizzare queste regioni (ammassi stellari e nella direzione del centro Galattico) e i suoi elementi chiave sono astrometria e fotometria di PSF, cataloghi ad alta risoluzione angolare e sottrazione delle stelle vicine tramite l'utilizzo della PSF. Inizialmente affrontiamo il problema delle PSFs sottocampionate di K2 le cui strutture su piccola scala, se non correttamente modellate, possono introdurre errori sistematici che peggiorano l'astrometria e la fotometria. Per questo scopo, seguiamo il metodo iterativo progettato per modellare le PSFs sottocampionate di HST. Successivamente utilizziamo un catalogo ad alta risoluzione angolare, ottenuto con telescopi da terra, per identificare tutte le sorgenti rilevabili nel campo e, per ciascuna di esse, misuriamo il flusso dopo aver sottratto tutte le stelle vicine. In questo modo aumentiamo il numero di sorgenti analizzabili nel campo e otteniamo una stima più veritiera del loro flusso. In particolare per stelle variabili, binarie ad eclissi ed esopianeti questo metodo permette di ottenere un valore più realistico della vera ampiezza o profondità dell'eclissi/transito della loro curva di luce poiché diminuiamo gli effetti di diluizione della luce. Questo risvolto è particolarmente importante per gli esopianeti perché altrimenti il vero raggio del pianeta verrebbe sottostimato. Applichiamo questo metodo alla prima campagna osservativa della missione K2 in cui sono stati osservati due ammassi aperti (M 35 e NGC 2158) ed estraiamo le curve di luce di più di 50000 oggetti da un solo canale di lettura di una delle camere K2. Questo numero è più del doppio del numero di oggetti normalmente analizzati in tutto il campo di vista di K2 (76 canali) in una data campagna osservativa. Per le stelle brillanti raggiungiamo una precisione fotometrica di circa 30 parti per milione, un valore confrontabile con quanto si può trovare in altri lavori in letteratura su stelle isolate. Inoltre riusciamo ad estendere la nostra analisi a stelle fino a 5 magnitudini più deboli di quanto studiato in lavori già pubblicati, e mostriamo che per questi oggetti deboli la fotometria di PSF è migliore di quella di apertura. Tale miglioramento è maggiori nei campi a più alta densità stellare. Infine troviamo più di 2000 stelle variabili in questi due ammassi. Tutti i progetti sviluppati in questa tesi hanno anche interessanti prospettive a lungo termine in quanto possono essere visti come complementari o in preparazione a missioni da spazio future come TESS e PLATO. I candidati pianeti trovati con le osservazioni di Kepler/K2 (ma anche dell'imminente TESS) possono potenzialmente essere target interessanti per JWST, e successivamente per E-ELT

Cette thèse s'inscrit dans le cadre de la mission spatiale Rosetta et porte sur les propriétés spectrophotométriques de la comète 67P/Churyumov-Gerasimenko à l’aide de l’instrument OSIRIS. Cet instrument est composé de deux caméras pour les observations du noyau et de la coma de la comète. Elles permettent d’acquérir des images avec des filtres qui opèrent dans la gamme du proche UV au proche IR. Dans un premier temps, j'ai analysé les courbes spectrophotométriques des taches claires qui sont apparues sur le noyau de la comète. Une étude comparative de celles-ci grâce aux données du spectro-imageur VIRTIS a ainsi permis de constater que les taches claires sont liées à la glace de H2O. Dans un second temps, j’ai entrepris une étude spectrophotométrique de la région Khonsu, qui a mis en évidence les variations saisonnières de la pente spectrale de différents terrains. Par la suite, j’ai élargi mon analyse des taches à tout le noyau de la comète. J’ai détecté plus de 50 taches claires dues à la présence de glace de H2O et j’ai produit une carte pour repérer leurs emplacements sur le noyau, afin d’étudier plus en détail leur répartition et leur évolution au cours de temps. Ceci m’a permis d’identifier quatre types de taches regroupés en fonction de leur morphologie et de constater qu'elles sont dues à différentes sources d'activité cométaire
This thesis is based on the spectrophotometric properties of the comet 67P/Churyumov-Gerasimenko, using the OSIRIS instrument of Rosetta space mission. Composed of two scientific cameras to observe the nucleus and the coma of the comet, OSIRIS images are acquired with multiple filters, that span the near-UV to near-IR wavelength range. They were used to study the spectrophotometric curves of the exposed bright features that appeared on the surface of the cometary nucleus, leading to a comparative study, that was carried out in collaboration with the VIRTIS spectro-imager aboard Rosetta, that demonstrated, that these exposures are related to H2O ice, using its absorption band located at 2 microns. The thesis further details a spectrophotometric study of the Khonsu region in the southern latitudes of the comet, where the seasonal variation of the spectral slope of different types of terrains is explored. Finally, the results of an extended survey of exposed bright features are presented. More than 50 individual features are presented under four morphologies along with an albedo calculation, suggesting that different activity sources are responsible for their appearance on the nucleus

This thesis concerns the detection of transient phenomena on very short timescales exploiting the Cherenkov Telescope Array facility. A timely analysis of transients is crucial in current multi-messenger astrophysics and the Real-Time Analysis system takes care to analyze the data during the observation time and to generate scientific alerts when the detections are confirmed. In this work the gamma-ray analysis maximum likelihood and aperture photometry methods are detailed and two different tools (ctools and RTA aperture photometry tool) are compared. The RTA aperture photometry tool, implemented in this work, will provide a reliable and quick method to evaluate the detection significance and estimate the flux of the target in short time observations. It is described in detail. The test results for a Crab-like source and a short GRB afterglow are shown and the detection time thresholds are highlighted.

In the last decades spectroscopic and photometric evidence has proven that globular clusters host multiple stellar populations characterized by different chemical abundances. The aim of my thesis is to give a contribution in the analysis of multiple stellar populations in Galactic globular clusters, using observations collected both with ground-based telescopes and with the Hubble Space Telescope. The first part of the thesis presents an overview regarding the topic of multiple stellar populations in Galactic globular clusters, from the first photometric and spectroscopic discoveries to the various theories developed to describe the formation and evolution of different stellar generations in a cluster. Then a description of my work regarding multiple stellar populations in the globular clusters NGC 6121, NGC 6397, and NGC 6752 is given. Using ground-based FORS2@VLT observations of external regions of these three globular clusters, we identified multiple stellar populations in the main sequence of NGC 6121 and NGC 6752. This work has been possible thanks to high-precision photometry and appropriate combinations of colors and magnitudes. We presented the radial distribution of the two stellar populations hosted by each globular cluster, combining our result for the external regions with the fraction of first and second stellar generation measured in the central regions using Hubble Space Telescope data. Both for NGC 6121 and for NGC 6752, we found that the radial distribution of the number ratio of the blue main sequence to the red main sequence is almost flat inside ~17 arcmin from the center of each cluster. Hydrodynamical and N-body simulations for the formation and evolution of multiple stellar populations predict that second generation stars form in the inner regions of the cluster and are initially more concentrated than first generation stars. The subsequent long-term dynamical evolution, driven by two-body relaxation, gradually erases the initial differences in the first and second generation spatial distributions; this is the reason why, for long relaxation-time systems (e.g. omega Cen), second generation stars are concentrated in the globular cluster inner regions and retain some memory of the initial predicted spatial segregation. The relaxation-times of the globular clusters NGC 6121 and NGC 6752 are quite short (less then 1 Gyr), and therefore the two populations hosted by each cluster are today well-mixed, as demonstrated by their flat distribution. In this work, we have also given an estimate of how much the second generation is enriched in helium with respect to the first generation, finding a mild (Delta Y ~ 0.02) difference between the two sequences for both the clusters. I am a Co-I of the Hubble Space Telescope Treasury programme ``UV Legacy Survey of Galactic Globular Clusters: Shedding Light on Their Populations and Formation'' (GO-13297, PI: G. Piotto). The second part of the thesis is based on this project. The aim of the Hubble Space Telescope treasury programme GO-13297 is the characterization and analysis of multiple stellar populations in a sample containing 56 globular clusters, using UV/blue and optical filters. Using the Hubble Space Telescope treasury programme data, we analyzed the multiple stellar populations of the metal-rich globular cluster NGC 6352. The combination of UV/blue and optical observations has made possible to split and follow the two stellar populations across all the evolutionary sequences of all color-magnitude diagrams. We estimated the enrichment in helium of the second stellar generation, finding Delta Y~0.03. Moreover, we developed an innovative technique to put an upper limit on the relative age between the two stellar generations, with a careful discussion of the impact on relative age of all possible sources of uncertainty in the cluster parameters, such as the error on \Delta Y or variations of metallicity and alpha-enhancement. Considering all these uncertainties together, we found that the two stellar populations of NGC 6352 are coeval within ~300 Myr. This result will be useful to constraint theoretical models of formation and evolution of multiple stellar populations in globular clusters. Finally, in the last part of the thesis, I summarize the results presented in this work and present a list of works that I would like to realize in future.
Negli ultimi decenni, prove spettroscopiche e fotometriche hanno dimostrato che gli ammassi globulari ospitano popolazioni stellari multiple caratterizzate da abbondanze chimiche differenti. Lo scopo della mia tesi e` dare un contributo nell'analisi delle popolazioni stellari multiple negli ammassi globulari della nostra Galassia, usando osservazioni acquisite sia con telescopi da terra che con l'Hubble Space Telescope. La prima parte della tesi e` una panoramica sul tema delle popolazioni stellari multiple negli ammassi globulari galattici, dalle prime scoperte fotometriche e spettroscopiche alle varie teorie sviluppate per descrivere la formazione ed l'evoluzione delle differenti generazioni stellari in un ammasso. In seguito, viene data una descrizione del mio lavoro sulle popolazioni stellari multiple negli ammassi globulari NGC 6121, NGC 6397 e NGC 6752. Usando le osservazioni da terra effettuate con FORS2@VLT delle regioni esterne di questi tre ammassi globulari, abbiamo identificato popolazioni stellari multiple nella sequenza principale di NGC 6121 e NGC 6752. Questo lavoro e` stato possible grazie a fotometria di alta precisione e combinazioni appropriate di colori e magnitudini. Abbiamo mostrato la distribuzione radiale delle due popolazioni stellari ospitate da ciascuno ammasso globulare, combinando il nostro risultato per le regioni esterne con la frazione di stelle di prima e seconda generazione misurate nelle regioni centrali con i dati dell'Hubble Space Telescope. Per entrambi gli ammassi NGC 6121 e NGC 6752, abbiamo trovato che la distribuzione radiale dei rapporti fra il numero di stelle nella sequenza principale blu e in quella rossa e` abbastanza piatta entro ~17 arcmin dal centro di ogni ammasso. Simulazioni idrodinamiche e a N-corpi riguardanti la formazione ed evoluzione delle popolazioni stellari multiple, predicono che le stelle di seconda generazione si formano nelle regioni interne dell'ammasso e sono inizialmente piu` concentrate rispetto alla prima generazione. La successiva evoluzione dinamica a lungo termine, guidata dal rilassamento a due corpi, cancella gradualmente le differenze iniziali tra le distribuzioni spaziali della prima e seconda generazione; questa e` la ragione per cui, in sistemi caratterizzati da tempi di rilassamento lunghi (per esempio omega Cen), le stelle di seconda generazione sono concentrate nelle regioni interne e conservano la memoria della segregazione spaziale iniziale predetta. I tempi di rilassamento degli ammassi globulari NGC 6121 e NGC 6752 sono abbastanza corti (meno di 1 Gyr), e percio` le due popolazioni ospitate da ogni ammasso sono oggi ben mescolate, come dimostrato dalla loro distribuzione spaziale piatta. In questo lavoro, diamo anche una stima di quanto la seconda generazione e` arricchita in elio rispetto alla prima generazione, trovando una leggera differenza (Delta Y ~0.02) tra le due sequenze per entrambi gli ammassi. Io sono uno dei Co-I del programma Treasury dell'Hubble Space Telescope "UV Legacy Survey of Galactic Globular Clusters: Shedding Light on Their Populations and Formation'' (GO-13297, PI: G. Piotto). La seconda parte della tesi e` basata su questo progetto. Lo scopo del programma Treasury GO-13297 dell'Hubble Space Telescope e` la caratterizzazione e analisi di popolazioni stellari multiple in un campione contenente 56 ammassi globulari, usando filtri UV/blu e ottici. Sfruttando i dati del programma Treasury dell'Hubble Space Telescope, abbiamo analizzato le popolazioni stellari multiple dell'ammasso globulare, caratterizzato da alta metallicita`, NGC 6352. La combinazione di osservazioni UV/blu e ottiche ha reso possibile individuare e seguire le due popolazioni stellari lungo tutte le sequenze evolutive dei diagrammi colore-magnitudine. Abbiamo stimato l'arricchimento in elio della seconda generazione, trovando Delta Y~0.03. Inoltre, abbiamo sviluppato una tecnica innovativa per porre un limite superiore sull'eta` relativa tra le due generazioni stellari, considerando attentamente l'impatto sull'eta` relativa di tutte le possibili sorgenti di incertezza nei parametri dell'ammasso, come l'errore su Delta Y o le variazioni di metallicita` e alpha-enhancement. Considerando tutte queste incertezze insieme, abbiamo trovato che le popolazioni stellari si NGC 6352 sono coeve entro ~300 Myr. Questo risultato sara` utile per vincolare i modelli teorici di formazione ed evoluzione di popolazioni stellari multiple negli ammassi globulari. Infine, nell'ultima parte della tesi, riassumo i risultati presentati in questo lavoro e presento una lista di lavori che vorrei realizzare in futuro.

Cette thèse présente plusieurs contributions au software developé pour le traitement d’images dans le cadre du LSST. Notre objectif est d'utiliser le code et les algorithmes LSST existants, afin de créer un pipeline dédié à la détection des supernovae de type Ia. Pour la détection des supernovae nous utilisons une technique appelée soustraction optimale d'images qui implique la construction de coadditions. Nous étudions aussi le comportement des différents objets dans le temps et construisons des courbes de lumière qui représentent leur cycle de vie en fonction de l'intensité lumineuse de chaque détection sur plusieurs nuits. Enfin, pour analyser un nombre excessif de candidats, nous utilisons des algorithmes d'apprentissage machine.Notre première contribution concerne le développement des taches de coaddition automatisée adaptées pour construire des images de référence et de science avec un haut rapport signal-sur-bruit. La contribution suivante est lié à l’addition de mesures et l’étude de résidus des images d’analyse de différence, y-compris la sélection des seuils adaptés et l'étiquetage basée sur les valeurs quantitativess des résidus pour identifier les mauvaises détections, les artéfacts et les flux réellement significatifs. Notre suivante contribution est un algorithme pour sélectionner et générer les courbes de lumière candidates. Finalement, on applique une classification machine learning pour trouver des type Ia supernovae en utilisant la méthode random forest. Ces résultats ont permis l’identification des supernovae de type Ia simulées et réelles parmis les candidats avec une haute précision
This thesis will present several contributions to the software developed for the LSST telescope with the purpose of contributing to the detection of type Ia supernovae. Our objective is to use the existing LSST code and algorithms, in order to create a type Ia supernovae detection dedicated pipeline.Since detecting supernovae requires a special type of processing, we use a technique known as the Optimal Image Subtraction which implies the construction of coadditions. Afterwards, we study the behavior of the different objects through time and build light curves that represent their life cycle in terms of the light intensity of each detection on several nights. Lastly, in order to analyze an excessive number of candidates, we employ machine learning algorithms to identify what curves are more probable to be type Ia supernovae. Our first contribution concerns the development of adapted and automatized coaddition tasks for building high signal-to-noise reference and science images. The next contribution is related to the addition of measurements and study of the residuals on difference image analysis, including the selection with adapted thresholding and the assignation of labels. We also propose, as contributions, an algorithm to select and generate the different candidate light curves through the selection of objects with recurrent detections through time and in the different bandpasses. Finally, we apply the machine learning classification approach to find type Ia supernovae by means of using a random forest classifier and based strictly on geometrical features that are present in the light curves

This Thesis is devoted to the study of the optical companions of Millisecond Pulsars in Galactic Globular Clusters (GCs) as a part of a large project started at the Department of Astronomy of the Bologna University, in collaboration with other institutions (Astronomical Observatory of Cagliari and Bologna, University of Virginia), specifically dedicated to the study of the environmental effects on passive stellar evolution in galactic GCs. Globular Clusters are very efficient “Kilns” for generating exotic object, such as Millisecond Pulsars (MSP), low mass X-ray binaries(LMXB) or Blue Straggler Stars (BSS). In particular MSPs are formed in binary systems containing a Neutron Star which is spun up through mass accretion from the evolving companion (e.g. Bhattacharia & van den Heuvel 1991). The final stage of this recycling process is either the core of a peeled star (generally an Helium white dwarf) or a very light almos exhausted star, orbiting a very fast rotating Neutron Star (a MSP). Despite the large difference in total mass between the disk of the Galaxy and the Galactic GC system (up a factor 103), the percentage of fast rotating pulsar in binary systems found in the latter is very higher. MSPs in GCs show spin periods in the range 1.3 ÷ 30ms, slowdown rates ˙P 1019 s/s and a lower magnetic field, respect to ”normal” radio pulsars, B 108 gauss . The high probability of disruption of a binary systems after a supernova explosion, explain why we expect only a low percentage of recycled millisecond pulsars respect to the whole pulsar population. In fact only the 10% of the known 1800 radio pulsars are radio MSPs. Is not surprising, that MSP are overabundant in GCs respect to Galactic field, since in the Galactic Disk, MSPs can only form through the evolution of primordial binaries, and only if the binary survives to the supernova explosion which lead to the neutron star formation. On the other hand, the extremely high stellar density in the core of GCs, relative to most of the rest of the Galaxy, favors the formation of several different binary systems, suitable for the recycling of NSs (Davies at al. 1998). In this thesis we will present the properties two millisecond pulsars companions discovered in two globular clusters, the Helium white dwarf orbiting the MSP PSR 1911-5958A in NGC 6752 and the second case of a tidally deformed star orbiting an eclipsing millisecond pulsar, PSR J1701-3006B in NGC6266

This Thesis is devoted to the study of the optical companions of Millisecond Pulsars in Galactic Globular Clusters (GCs) as a part of a large project started at the Department of Astronomy of the Bologna University, in collaboration with other institutions (Astronomical Observatory of Cagliari and Bologna, University of Virginia), specifically dedicated to the study of the environmental effects on passive stellar evolution in galactic GCs. Globular Clusters are very efficient “Kilns” for generating exotic object, such as Millisecond Pulsars (MSP), low mass X-ray binaries(LMXB) or Blue Straggler Stars (BSS). In particular MSPs are formed in binary systems containing a Neutron Star which is spun up through mass accretion from the evolving companion (e.g. Bhattacharia & van den Heuvel 1991). The final stage of this recycling process is either the core of a peeled star (generally an Helium white dwarf) or a very light almos exhausted star, orbiting a very fast rotating Neutron Star (a MSP). Despite the large difference in total mass between the disk of the Galaxy and the Galactic GC system (up a factor 103), the percentage of fast rotating pulsar in binary systems found in the latter is very higher. MSPs in GCs show spin periods in the range 1.3 ÷ 30ms, slowdown rates ˙P 1019 s/s and a lower magnetic field, respect to ”normal” radio pulsars, B 108 gauss . The high probability of disruption of a binary systems after a supernova explosion, explain why we expect only a low percentage of recycled millisecond pulsars respect to the whole pulsar population. In fact only the 10% of the known 1800 radio pulsars are radio MSPs. Is not surprising, that MSP are overabundant in GCs respect to Galactic field, since in the Galactic Disk, MSPs can only form through the evolution of primordial binaries, and only if the binary survives to the supernova explosion which lead to the neutron star formation. On the other hand, the extremely high stellar density in the core of GCs, relative to most of the rest of the Galaxy, favors the formation of several different binary systems, suitable for the recycling of NSs (Davies at al. 1998). In this thesis we will present the properties two millisecond pulsars companions discovered in two globular clusters, the Helium white dwarf orbiting the MSP PSR 1911-5958A in NGC 6752 and the second case of a tidally deformed star orbiting an eclipsing millisecond pulsar, PSR J1701-3006B in NGC6266

One of the major challenges in modern astrophysiscs is to understand the origin and the evolution of galaxies, the bright Early-Type Galaxies (ETGs) in particular, in the context of a Universe dominated by Cold Dark Matter (CDM), with some kind of Dark Energy in form of the Cosmological Constant ?. These spheroidal systems are of interest in their own right as they contain more than half of the total stellar mass in the local Universe (Fukugita et al 1998). Giant elliptical galaxies are the most massive stellar systems and they appear to define a homogeneous class of objects which predominantly consist of uniformly old and red populations, which implies that they must have formed at high redshift, have negligible amounts of gas and very little star formation (Bressan et al. 1993). There is strong observational evidence that ellipticals are already in place at z ~ 2-3 and that formed most of their stars well before a redshift z=1 (Searle et al. 1973; Brinchmann & Ellis 2000; Treu et al. 2005; van der Wel et al. 2005). These galaxies are therefore likely to be good probes of galaxy evolution, star formation and metal enrichment in the early Universe. The main goal of this PhD thesis is the derivation of a tool that combines the results derived from the cosmo-chemo-dynamical models of elliptical galaxies obtained from N-body simulations, together with the spectro-photometric models computed from the stellar Evolutionary Population Synthesis (EPS) technique. The aim is to reproduce the observational integrated properties of early-type galaxies in any photometric bandpass, and in particular in the systems used by the modern imaging surveys of observational cosmology, that cover any spectral range. The EPS technique is based on Simple Stellar Populations (SSPs) due to their characteristics, these are suitable for purposes of population synthesis of more complex systems of stellar populations, such as simulated ETGs derived from numerical simulations, and so are suitable for the modelling of the integrated properties (light), and allow easy testing for different input prescriptions in the description of a galaxy (different masses, star formation, initial mass functions, physical processes, etc.) and reproduction of basic observational constraints. In the present work, the approach allows the computation of spectroscopic and photometric quantities by combining the EPS technique to three-dimensional self-consistent cosmo-chemo-dynamical Tree-SPH numerical simulations, carried on in the last years by the Padova group (Merlin & Chiosi 2006, 2007), that follow the evolution of ETGs from the epoch of their complex formation to the present. The method has been tested so far on three simulated galaxies: these models have different cosmological metrics, both cold dark matter (CDM) scenarios, one in the SCDM and two in the ?CDM cosmologies. In the first part of the thesis we consider the template galaxies, which have been dynamically simulated with a detailed chemical evolution, and recover their spectro-photometric evolution in the rest-frame and the integrated properties, such as magnitudes and colors, at the different epochs through the entire history of the Universe up to the formation of present-day ellipticals. This is done in particluar for two inportant photometric systems, the Bessell-Brett passbands and the Sloan Digital Sky Survey (SDSS). The advent of the modern giant telescope facilities has opened a new era in observational cosmology and galaxy evolution can be traced back to its early stages. In this sense, deep multicolor imaging surveys are established as a powerful tool to access the population of faint galaxies with relatively high efficiency. These surveys sample the whole spectral range from the UV to the near-IR bands, enabling galaxy evolution to be followed on a wider range of redshifts. Starting from the evolutionary synthesis results we compute the evolutionary and cosmological corrections, along with magnitudes and colors and their evolution at different redshifts for the simulated galaxies at our disposal. We consider the COSMOS (Giavalisco et al. 2004) and the GOODS (Scoville et al 2007) databases, which allow us to select a sample of galaxies that are catalogued as early-type and to make a qualitative and quantitative comparison between the theoretical results obtained from our model galaxies and the observational data. For the COSMOS database we find that the models follow the general trend for all data at high redshift and, in particular, are in good agreement with those galaxies selected as ellipticals. For the galaxies selected from the GOODS database, theoretical colors seem to match better with data than what found for the COSMOS data. Having a better morphological classificator, the selection is done by eye and by correlating a catalog of photometric and spectroscopic redshifts with a morphological one for GOODS in contrast to the selection derived from the automated pipelines used for COSMOS, is certainly discriminating in favour of the GOODS database. For both datasets our findings show that simulated colors for the different cosmological scenarios follow the general trend at lower redshifts and are in good agreement with the data up to z ~ 1, where the number of early-type galaxies observed falls abruptly. In conclusion, within the redshift range considered, all the simulated colors reproduce quite well the observational data. The dynamical and geometrical informations, derived from the numerical simulations, and the spectro-photometric properties, recovered from our tool, combined together, allow to tackle in some detail important physical issues that deal with the scaling relations governing the photometric and structural parameters of ETGs, and in particluar with the Kormendy relation that allows a comparison with observables in the luminosity-radius plane. The method we introduced for the derivation of the parameters that enter the scaling laws deals with the construction of artificial images in a bi-dimensional plane, starting from the three-dimensional structure of the simulated galaxies. By matching the population synthesis models with the three-dimensional geometric information of the galaxy's structure along with the chemical details, both provided by the N-body simulations, we create synthetic images of a galaxy in a given photometric system, from which we derive the structural and morphological parameters, such as the galaxy's effective radius and the luminosity within this, the shape indices through Fourier and Sersic analysis, color profiles, and radial profiles of most of the parameters that define the structure of galaxies. The most interesting aspect of these results is that the investigation of the simulated galaxies, via the photometric analysis of the artificial images, led us to recover properties that resemble those of observed galaxies. The results obtained in this way are studied and compared within the scaling laws, the Kormendy relation in particular, as it is the only one we can construct so far, due to the limited resolution of our simulations. The observational data with which we compare our simulated results have been selected form the SDSS database. We separate a subsample of elliptical galaxies, and our findings show that the values of luminosities and effective radii, the two parameters that compare in the Kormendy relation, measured for our model galaxies are consistent with the archivial data from the SDSS.

The aim of this thesis is to study the stellar populations of Galactic open and globular clusters through high-precision, high-accuracy wide-field astrometry (∼ 1 mas) and photometry (∼ 0.01 mag). This thesis is organized into three parts. - The first part introduces the benefits and advantages of the wide field in astrometry, and describes in detail the method we have developed to obtain high-precision photometric and astrometric mea- surements. - The second part discusses the achieved scientific results. The method is applied mainly on three telescope/camera systems (LBC@LBT, WFI@2.2m, WFC3/UVIS@HST), with which two stellar systems were observed: the open cluster M 67 and the globular cluster ω Cen. Thanks to proper- motion measurements, it was possible to disentangle, in both cases, cluster members from field objects in the foreground and in the background. This allowed us to undertake several projects, among which is the study of the end of the white dwarf cooling sequence in M 67 and the mea- surement of its absolute proper motion using as reference background galaxies, the analysis of the ω Cen multiple stellar populations and their relative radial distribution. - The last part presents the projects for the forthcoming future: absolute proper motions of globular clusters, tidal tails analysis and application of our methods to other wide-field imagers, such as HAWK-I@VLT and VISTA, in which our group is deeply involved in the VVV survey (2000 hours of observation already allocated).
Lo scopo di questa tesi è lo studio delle popolazioni stellari di ammassi aperti e globulari mediante astrometria e fotometria, entrambe di alta precisione e accuratezza (∼ 0.01 mag, ∼ 1 mas), con strumenti a grande campo. La tesi è strutturata in tre parti principali. - Nella prima parte si sottolineano i benefici e i vantaggi del grande campo, e viene descritto nei dettagli il metodo per ottenere fotometria e astrometria di alta precisione. - La seconda parte riguarda i risultati scientifici ottenuti. Il metodo viene applicato principalmente a 3 camere (LBC@LBT, WFI@2.2m, WFC3/UVIS@HST) con le quali sono stati osservati l’ammasso aperto M 67 e l’ammasso globulare ω Centauri. Grazie alla misura dei moti propri è stato possibile, in entrambi i casi, separare stelle membre dagli oggetti di campo. Ciò ha permesso di intraprendere diversi progetti, tra cui lo studio della fine della sequenza di raffreddamento delle nane bianche in M 67 e la misura del suo moto proprio assoluto usando come riferimento le galassie sullo sfondo; l’analisi delle diverse popolazioni stellari di ω Cen, e la loro distribuzione spaziale. - Nella parte finale sono presentati i nostri progetti per l’immediato futuro: moti propri assoluti degli ammassi globulari, studio delle code mareali, e applicazione del metodo astrofotometrico ad altre camere a grande campo, come HAWK-I@VLT e VISTA. In particolare il nostro gruppo è pesantemente coinvolto nella survey VVV (2000 ore di osservazione gia` allocate e quelle del primo anno già acquisite).

The European space mission Rosetta, during its still ongoing journey to the comet 67P/Churyumov-Gerasimenko, on 10 July 2010 made an intermediate stop flying close to the asteroid 21 Lutetia at a distance of less than 3200 km and observed it from a varying observing point, otherwise inaccessible from Earth. Less than four months later, on 4 November 2010, the EPOXI mission, extension of the NASA Deep Impact mission, offered another unexpected opportunity approaching the small hyperactive Jupiter family comet 103P/Hartley 2 a few days after its perihelion passage at a distance of less than 700 km from its nucleus. Those encounters provided an extremely important possibility for the advance in understanding our Solar System formation and history. Asteroids and comets are indeed the unique left samples of the primordial planetesimals that accreted in the original solar nebula. They are therefore key bodies for understanding the conditions and the processes occurred during the Solar System initial formation phases. The principal aim of this thesis is therefore to provide an advance in the small bodies science, particularly comets, through the photometric analysis of high-resolution observations obtained by the two mentioned space missions. Investigations of asteroid 21 Lutetia, observed on 10 July 2010 through the OSIRIS imaging system (Optical Spectroscopic and Infrared Remote Imaging System) onboard the Rosetta spacecraft, have been focused mainly on its surface physical properties. The integral phase curve analysis and Hapke's modeling showed that the regolith particles constituting Lutetia's surface are highly re ecting, very small, compact and opaque, and form a low-porosity and overall smooth layer over the high-density nucleus of Lutetia. The quite at and featureless spectra observed suggest, together with the high density, that Lutetia is an X-type asteroid for the spectral taxonomy and that it has possibly an enstatite chondrite composition. Moreover the spectral slope is found to vary signicantly with phase angle showing a pronounced reddening. This evidence, still to be completely explained, may be one possible explanation of the continuously changing spectral slope of Lutetia spectrum observed from Earth. We found strong evidences of color variegation over the surface of Lutetia, and in particular on a geologically interesting surface area, called Baetica Region. The variegation of this region, found to be about 10%, suggests the presence of bluer particles on the crater walls, indicative of bigger grains, possibly revealing fresh material, and of redder particles at the bottom of the slant, where debris deposits are potentially present. In view of a future extension of the work to the resolved photometric analysis, a series of complementary processing tools which make use of the high resolution shape model have been implemented. The photometric analysis of comet 103P/Hartley 2, visited by EPOXI spacecraft on 4 November 2010, and pictured through MRI (Medium Resolution Imager) multi-band imaging system, has been focused instead on the cometary atmosphere and its dust and gas features and emission processes. The study of the colors and reddening of the dust, through narrowband continuum observations, shows that dust in Hartley 2 coma is slightly redder in the tailward direction than in the sunward direction. This is tentatively explained considering that ices and refractories are both emitted in the sunward direction, but, while ices sublimate, refractories are pushed away by the Sun's radiation pressure and form a slightly redder tail. A detailed study of OH emission structures in the period spanning from the day of perihelion up to 10 days afterward, has been performed. It shows an overall radial antisunward OH distribution in all observations apart the closest approach (CA) images, where a radial sunward jet coming from the central waist of the nucleus is evident in the very innermost regions of the coma, within 35 km from the nucleus. This OH feature, very close to the nucleus, provided an indication of a possible secondary emission mechanisms. The prompt emission (PE) of excited OH molecules coming from photodissociation of water has been proposed. CN structure analysis in the near-nucleus region shows instead a rounded structure, within 35 km from the nucleus, which is interpreted as an indication that CN is emitted in the coma by grains or particles that are aected by the nucleus rotation. OH observations have been further investigated in order to derive the water production rate in the coma of Hartley 2. A coma model has been adopted, correspondent to vectorial model but extending inside the coma down to the nucleus. A water production rate of 1.17e28 mol/s (logQ = 28.07) has been evaluated, consistent with other authors measurements (see Knight et al., 2013). However the water production rate is found to be varying as function of time with a periodicity that suggests a correlation with the nucleus rotation, which has a period of about 18 hours. However a strong peak in the production rate is observed, correspondent to CA nucleus-resolved observations. The prompt emission mechanism for OH brightness has been invoked as possible responsible and an evaluation of the theoretical observable OH PE flux through MRI-OH narrowband filter has been performed, yielding an intensity of about 26% of the fluorescence emission at about 50 km from the nucleus. However, this is probably an overestimate of the prompt emission, considering indeed a value of about 10%, observations are well reproduced by the cometary model used, even in the innermost coma. All the studies performed in this thesis will have a direct application to the upcoming encounter of Rosetta with the comet 67P/Churyumov-Gerasimenko occurring on August 2014, and lasting more than a year, until December 2015. Rosetta will approach the comet, deliver a lander on its surface and escort the comet along its orbit up to its next perihelion passage. This encounter is expected to revolutionize the cometary science, giving answer to most of the up-to-date still unexplained comets mysteries. The investigations performed on asteroid Lutetia and comet Hartley 2 will be therefore combined together for data reduction, analysis, procedures implementation and results interpretation, with the final aim to obtain a better understanding of comets in all their aspects.
La missione Rosetta dell'Agenzia Spaziale Europea, durante il suo viaggio verso la cometa 67P/Churyumov-Gerasimenko, attualmente in corso, ha effettuato una tappa intermedia il 10 luglio 2010, passando a meno di 3 200 km dall'asteroide 21 Lutetia osservando questo corpo minore da vari punti di vista inaccessibili da Terra. Meno di quattro mesi dopo, il 4 novembre 2010, la missione EPOXI, estensione della precedente Deep Impact della NASA, ci ha offerto un'altra straordinaria occasione, avvicinandosi a meno di 700 km dal nucleo della piccola cometa super-attiva 103P/Hartley 2 alcuni giorni dopo il suo passaggio al perielio. Questi passaggi ravvicinati hanno costituito un'enorme opportunita per l'avanzamento delle conoscenze sulla formazione e sulla storia del nostro Sistema Solare. Gli asteroidi e le comete sono infatti gli unici resti ancora esistenti dei planetesimi primordiali che si svilupparono nella nebulosa solare originaria. Essi sono quindi fondamentali per lo studio delle condizioni iniziali e dei processi che si vericarono durante le fasi iniziali di formazione del Sistema Solare. Lo scopo principale di questa tesi e pertanto quello di apportare un avanzamento nella scienza dei piccoli corpi del Sistema Solare, in particolare le comete, attraverso l'analisi fotometrica di immagini ad alta risoluzione ottenute mediante le due missioni spaziali Rosetta ed EPOXI. L'analisi delle immagini di Lutetia, ottenute mediante OSIRIS (Optical Spectroscopic and Infrared Remote Imaging System), il telescopio ottico a bordo della sonda Rosetta, e stata focalizzata principalmente sullo studio delle proprietà fisiche della supercie asteroidale. Attraverso l'indagine sulla curva di fase integrale e la sua modellazione mediante il modello fotometrico di Hapke, e stato possibile stimare che le particelle di regolite che costituiscono la supercie di Lutetia sono altamente riflettenti, molto piccole, compatte ed opache, e formano uno strato sostanzialmente liscio, a bassa porosità, che ricopre il nucleo molto denso di Lutetia (3.4e3 kg/m^3, Patzold et al., 2011). Gli spettri osservati, sostanzialmente piatti e privi di caratteristici assorbimenti, combinati con l'elevata densita di Lutetia, suggeriscono una classi- cazione spettrale tassonomica che lo identica come un asteroide di tipo X con una composizione dominata da enstatite condrite. La pendenza spettrale presenta una signicativa variazione all'aumentare dell'angolo di fase evidenziando un pronunciato arrossamento. Questo fenomeno, che necessita ancora oggi una spiegazione esaustiva, potrebbe essere responsabile dell'ampia variazione nella pendenza spettrale di Lutetia osservata da Terra. Tramite l'analisi dei colori sulla supercie di Lutetia, sono state osservate evidenze di variegazione superciale, in particolare nella regione denominata Baetica Region, considerata geologicamente interessante. In questa regione, si misura una variegazione di circa il 10%, che probabilmente indica la presenza di grani di dimensioni maggiori, vista la colorazione piu blu sulle pareti del cratere, il che potrebbe essere riconducibile alla presenza di materiale piu fresco. Mentre le regioni ai piedi del cratere sembrano essere arrossate, ad indicare materiale piu no, trattandosi probabilmente di depositi di detriti causati da frane. In vista di una futura estensione del presente lavoro alla fotometria risolta, sono stati implementati una serie di strumenti di analisi complementari che fanno uso del modello di forma di Lutetia per poter eettuare studi locali dettagliati oltre che globali sulla supercie. L'analisi delle immagini della cometa 103P/Hartley 2, osservata mediante la camera multi-banda MRI (Medium Resolution Imager) a bordo della sonda EPOXI, e stata incentrata invece sulla fotometria dell'atmosfera cometaria, in particolare sullo studio delle strutture di gas e polvere presenti nella chioma, e sui meccanismi di emissione del gas. Lo studio dei colori, effettuato mediante osservazioni nel continuo a banda stretta, hanno permesso di notare che la polvere nella chioma della Hartley 2 e leggermente arrossata in direzione della coda. Questo fenomeno potrebbe essere spiegato considerando che i ghiacci e le particelle di polvere sono emessi generalmente in direzione solare e che, mentre i ghiacchi sublimano sotto l'influsso del calore del sole, i materiali refrattari vengono invece spinti dalla pressione di radiazione e formano una coda di sola polvere che quindi e leggermente piu rossa. E' stato poi affrontato lo studio delle strutture visibili nell'emissione del gas OH, nel periodo che si estende dal giorno del perielio ai 10 giorni successivi. L'OH ha una distribuzione prevalentemente antisolare in quasi tutte le osservazioni, a parte quelle acquisite durante il massimo avvicinamento (Closest Approach, CA) alla cometa. In queste ultime infatti, e evidente un getto di gas in direzione solare proveniente dalla zona centrale del nucleo cometario, che si estende entro un raggio di 35 km dal nucleo. Questa struttura, molto vicina al nucleo, costituisce un'indicazione della presenza di un meccanismo di emissione secondario. E stato suggerito possa trattarsi di emissione diretta (prompt emission, PE) di molecole di OH eccitate, proveniente direttamente dalla fotodissociazione dell'acqua. L'analisi delle strutture di CN nelle regioni vicine al nucleo hanno rivelato invece una struttura curva, anch'essa entro 35 km dal nucleo, che e stata interpretata come indicazione del fatto che il gas CN viene emesso nella chioma non direttamente dal nucleo, ma piuttosto da grani e particelle che sono influenzate dalla rotazione del nucleo, la quale sarebbe pertanto responsabile della forma incurvata, piuttosto che radiale, delle strutture. Le osservazioni in OH sono state ulteriormente utilizzare per lo studio del tasso di produzione di acqua nella chioma della cometa Hartley 2. L'OH e infatti un diretto prodotto della dissociazione dell'acqua. E stato utilizzato un modello di chioma corrispondente a quello vettoriale oltre la zona di collisione, ma esteso all'interno della sfera di collisione, no alle regioni prossime al nucleo. E stato trovato un tasso di produzione d'acqua di 1:17 1028 mols1 (logQ = 28:07), compatibile con le misure effettuate da altri autori (vedi Knight et al., 2013). Il tasso di produzione d'acqua risulta comunque variabile in funzione del tempo, mostrando una periodicità compatibile con la rotazione del nucleo, che ha un periodo di circa 18 ore. Nelle immagini ad alta risoluzione, acquisite durante il CA sembra esserci un picco di produzione superiore alla media osservata. Il meccanismo di emissione di OH dovuto alla PE e stato pertanto proposto come possibile responsabile e ne e stata effettuata una valutazione della quantità teorica osservabile attraverso il filtro a banda stretta dell'OH della camera MRI. Risulta che, ad una distanza di 50 km dal nucleo, la PE avrebbe un'intensità pari al 26% dell'emissione dovuta a fluorescenza. Probabilmente tale valore teorico sovrastima la percentuale di emissione diretta. Considerando invece che la PE abbia un'efficienza pari al 10% della fluorescenza, le osservazioni vengono ben riprodotte dal modello cometario utilizzato, anche nelle vicinanze del nucleo. Tutte le analisi svolte in questa tesi avranno una diretta applicazione nell'imminente incontro di Rosetta con la cometa 67P/Churyumov-Gerasimenko che avverrà ad agosto 2014 e durerà fino a dicembre 2015. Rosetta si avvicinerà infatti alla cometa, rilascerà un modulo di atterraggio sulla sua supercie e seguira la cometa lungo la sua orbita no al suo prossimo passaggio al perielio. Ci si aspetta che questo incontro rivoluzioni la scienza cometaria, portando risposte alla maggior parte dei misteri ancora irrisolti. Le analisi compiute sull'asteroide 21 Lutetia e sulla cometa 103P/Harltey 2 saranno pertanto combinate insieme per la riduzione e l'analisi dei dati, l'implementazione di procedure e l'interpretazione dei risultati, in occasione dell'arrivo di Rosetta sulla cometa, con lo scopo ultimo di ottenere una migliore comprensione delle comete in tutti i loro aspetti.

This thesis is focused on the photometric analysis of stellar light curves (LCs), to search for variable stars and transiting extrasolar planets. In particular, this study is carried out on crowded fields which include open clusters (OCs). The context of my work is the photometric preparatory survey “The Asiago Pathfinder for HARPS-N” (APHN; PI: Bedin) aimed at characterising OCs (i.e. M44, NGC752, M35, NGC2158 and M67) to be observed with the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N), mounted at the Telescopio Nazionale Galileo (TNG). The APHN survey was also recently extended to an additional sample of OCs which were chosen as targets for the Kepler extended mission K2 (Howell et al. 2014), in view of creating astrophotometric master input catalogues for high-precision photometry of Kepler and K2 data, following the method developed by (Libralato et al. 2015a). We also analysed data coming from other ground-based facilities, such as the SuperWASP or the STELLA1 Telescope. Searches for transiting exoplanets within OCs, while challenging (van Saders & Gaudi 2011), are particularly useful to constrain the properties of both the host star and planet, and to unveil the planetary formation and evolution mechanisms (Janes 1996; Fischer & Valenti 2005). The first part of the thesis reviews the different photometric techniques so far developed and present in the literature to search for exoplanets and, in general, for stellar variability studies (chapter 1). A short review of the principal ground and space-based projects is also given at the end of this chapter. Chapter 2 describes the origin of systematics errors (“red noise”) and gives a description of the methods developed to correct the LCs before the search for variability. A description of the different type of stellar variability and of the algorithms used to search for periodical signals is given in chapter 3. My original analysis of the OCs data is described in the last four chapters, starting from M44 in chapter 4. There, after a description of the observational setup, I discuss the detrending algorithms, the procedure to detect periodic signal, and my results in terms of newly discovered variables, including a study of the gyrochronological period versus colour relation. The following chapters are organised in a similar way, but covering NGC752 (chapter 5), M35 & NGC2158 (chapter 6) and M67 (chapter 7), respectively.
Questa tesi è incentrata sull’analisi fotometrica delle curve di luce stellari (LCs), per ricercare stelle variabili e pianeti extrasolari in transito. In particolare, questo studio viene condotto su campi affollati che includono ammassi aperti. Il contesto del mio lavoro è la mappatura fotometrica preparatoria “The Asiago Pathfinder for HARPS-N” (APHN; PI: Bedin), finalizzata alla caratterizzazione degli ammassi aperti (ad esempio M44, NGC752, M35, NGC2158 and M67), al fine di essere impiegata allo spettrografo HARPS-N (acronimo per High Accuracy Radial velocity Planet Searcher for the Northern hemisphere) installato al Telescopio Nazionale Galileo (TNG). Recentemente, la mappatura APHN è stata estesa ad un campionamento addizionale di ammassi aperti che sono stati scelti quali obiettivi per la missione K2, prolungamento della missione Kepler (Howell et al. 2014), allo scopo di creare un catalogo astro-fotometrico di base delle componenti che verranno analizzate con i set di dati delle missioni Kepler e K2 (Libralato et al. 2015a). Altre strumentazioni sono state coinvolte, come ad esempio quelle del progetto SuperWASP oppure quelle del telescopio STELLA1, i cui dati sono stati analizzati in questa tesi. Le ricerche di esopianeti in transito all’interno di ammassi aperti, benchè ardue (van Saders & Gaudi 2011), sono particolarmente utili per limitare le proprietà sia della stella ospitante, sia del pianeta e di svelare il meccanismo di formazione ed evoluzione planetaria (Janes 1996; Fischer & Valenti 2005). La prima parte della tesi è una recensione delle differenti tecniche fotometriche adottate dalla comunità scientifica nella ricerca di esopianeti e, più in generale, della variabilità stellare (capitolo 1), focalizzandosi sulle mappature fotometriche degli ammassi aperti. Una breve recensione sui principali progetti da terra e da spazio viene data alla fine di questo capitolo. Il capitolo 2 analizza le cause degli errori sistematici (“red noise”) e descrive i metodi sviluppati per correggere le curve di luce prima della ricerca di variabilità. Una descrizione delle differenti tipologie di variabilità stellare e degli algoritmi usati per la ricerca di segnali periodici viene data nel capitolo 3. La mia analisi degli ammassi aperti sopra citati è descritta negli ultimi quattro capitoli, partendo da M44 nel capitolo 4. Qui, dopo una descrizione delle attrezzature per le osservazioni, tratto degli algoritmi per la correzione da errori sistematici, della procedura per individuare segnali periodici e dei miei risultati in termini di variabili appena scoperte, includendo uno studio della relazione girocronologica fra la periodicità e il colore della stella. I capitoli seguenti sono organizzati in maniera simile, ma trattano, rispettivamente, di NGC752 (capitolo 5), di M35 & NGC2158 (capitolo 6) e di M67 (capitolo 7).

This Ph.D. Thesis has been carried out in the framework of a long-term and large project devoted to describe the main photometric, chemical, evolutionary and integrated properties of a representative sample of Large and Small Magellanic Cloud (LMC and SMC respectively) clusters. The globular clusters system of these two Irregular galaxies provides a rich resource for investigating stellar and chemical evolution and to obtain a detailed view of the star formation history and chemical enrichment of the Clouds. The results discussed here are based on the analysis of high-resolution photometric and spectroscopic datasets obtained by using the last generation of imagers and spectrographs. The principal aims of this project are summarized as follows: • The study of the AGB and RGB sequences in a sample of MC clusters, through the analysis of a wide near-infrared photometric database, including 33 Magellanic globulars obtained in three observing runs with the near-infrared camera SOFI@NTT (ESO, La Silla). • The study of the chemical properties of a sample of MCs clusters, by using optical and near-infrared high-resolution spectra. 3 observing runs have been secured to our group to observe 9 LMC clusters (with ages between 100 Myr and 13 Gyr) with the optical high-resolution spectrograph FLAMES@VLT (ESO, Paranal) and 4 very young (<30 Myr) clusters (3 in the LMC and 1 in the SMC) with the near-infrared high-resolution spectrograph CRIRES@VLT. • The study of the photometric properties of the main evolutive sequences in optical Color- Magnitude Diagrams (CMD) obtained by using HST archive data, with the final aim of dating several clusters via the comparison between the observed CMDs and theoretical isochrones. The determination of the age of a stellar population requires an accurate measure of the Main Sequence (MS) Turn-Off (TO) luminosity and the knowledge of the distance modulus, reddening and overall metallicity. For this purpose, we limited the study of the age just to the clusters already observed with high-resolution spectroscopy, in order to date only clusters with accurate estimates of the overall metallicity.

This Ph.D. Thesis has been carried out in the framework of a long-term and large project devoted to describe the main photometric, chemical, evolutionary and integrated properties of a representative sample of Large and Small Magellanic Cloud (LMC and SMC respectively) clusters. The globular clusters system of these two Irregular galaxies provides a rich resource for investigating stellar and chemical evolution and to obtain a detailed view of the star formation history and chemical enrichment of the Clouds. The results discussed here are based on the analysis of high-resolution photometric and spectroscopic datasets obtained by using the last generation of imagers and spectrographs. The principal aims of this project are summarized as follows: • The study of the AGB and RGB sequences in a sample of MC clusters, through the analysis of a wide near-infrared photometric database, including 33 Magellanic globulars obtained in three observing runs with the near-infrared camera SOFI@NTT (ESO, La Silla). • The study of the chemical properties of a sample of MCs clusters, by using optical and near-infrared high-resolution spectra. 3 observing runs have been secured to our group to observe 9 LMC clusters (with ages between 100 Myr and 13 Gyr) with the optical high-resolution spectrograph FLAMES@VLT (ESO, Paranal) and 4 very young (<30 Myr) clusters (3 in the LMC and 1 in the SMC) with the near-infrared high-resolution spectrograph CRIRES@VLT. • The study of the photometric properties of the main evolutive sequences in optical Color- Magnitude Diagrams (CMD) obtained by using HST archive data, with the final aim of dating several clusters via the comparison between the observed CMDs and theoretical isochrones. The determination of the age of a stellar population requires an accurate measure of the Main Sequence (MS) Turn-Off (TO) luminosity and the knowledge of the distance modulus, reddening and overall metallicity. For this purpose, we limited the study of the age just to the clusters already observed with high-resolution spectroscopy, in order to date only clusters with accurate estimates of the overall metallicity.

The aim of this research project was twofold: on one hand, we have developed an automatic photometric pipeline with a real time images reduction, which directly provide lightcurves of objects observed in the field. The lightcurves themselves are analyzed in order to catch light diming due to a transit. On the other hand, we contribute to investigate the dynamical and physical structure of the planetary systems hosted in multiple stellar systems and to compare the results with the current knowledge both of the planetary and stellar formation in order to gain a new insight on the evolution of extrasolar systems. Even if this PhD Thesis is made up of these two different but complementary aspects, however the final aim of both converges: it contributes to the comprehension of the planetary formation mechanism in order to identify both the environment conditions where these objects could form and some clues on their physical properties. Moreover, the results may be applied to the future space missions: the reduction pipeline could be exploited in whatever surveys of transit search thanks to its automatic nature while the theoretical results could be the starting point for the future investigations from space. Part I: Photometric reduction and analysis software. An exoplanetary transit occurs when it crosses the line of sight between the observer and the star around which it is orbiting. The flux decrease that it provokes allows us to find out certain orbital parameters and some physical characteristics of the planet that are inaccessible through other techniques. The diversity of the performed studies and the acquired knowledge after the detection of HD 209458b 's transits motivated the use of this technique as a tool for exoplanet discoveries. In this thesis, we describe the reduction algorithm developed in the RATS (RAdial velocities and Transit Search) project context in order to automatically achieve the lightcurves of photometric stars devoted to the search for exoplanets using the transit method. The main aim of the RATS project is twofold. The detection of extra solar planets that transit the disk of their parent star is the main scientific drive of the whole project. We have planned to observe simultaneously thousands of stars (magnitude range between 9th to 14th) in selected star fields for five years since the beginning of 2005. In this manner we are confident to find new transiting planets. The second aim of the project is to use its observing strategy and the scientific data management as a bench work for future planetary transits search mission in order to value it effectiveness. In particular, RATS projects seeks high precision photometric results performed with stellar images which have been purposely defocused in order to avoid saturation of brighter stars because of the size of Schmidt FoV. Moreover, to maximize the transit probability, each RATS field has been partitioned in seven adjacent sub-fields sequentially pointed. Up to now, two missions already plan to exploit this untypical strategy: the French CoRoT mission devoted to extrasolar planets search and asteroseismology is planning to collect CCD images which are slightly de-focused; the same observational approach has also been proposed for the Kepler extrasolar space mission as well. Originally, this research project foresaw many observations from the Cima Ekar Schmidt telescope equipped with a frame transfer CCD lended from INAF-OACT (Istituto Nazionale di AstroFisica-Osservatorio Astronomico di Catania) in concomitance to the very beginning of RATS project. For reasons out of my hands, some months ago INAF-OACT unexpectedly demand it back and the observations were stopped for a considerable amount of time. This aspect, added to the bad weather conditions of the most of 2006, has lessened images acquisition relative to initial expectations. However, in order to automatically reduce the images obtained so far, we have developed an automatic reduction algorithm RATS{ARP (Automatic Reduction Pipeline) which directly provides light curves of objects in the pre-selected RATS fields. The light curves themselves are analyzed in order to catch light diming due to a planetary transit. This software is based on different modules all called from a main program shell script, each being deputy to an individual step for photometric reduction of images. The described procedure has been applied both to the images in focus and to defocused ones, in particular two stellar fields have been analyzed among those chosen for the project. RATS{ARP has shown its robustness in managing both kind of images, performing all its tasks till lightcurve files creation with satisfactory time consuming: it has taken 90 seconds for each image in focus and 180 seconds for each defocused frame, depending on the crowding of the field. Therefore, the pipeline can manage different kind of images and it fulfills all its task. Thereby, we can say that RATS-ARP can be exported to projects different from RATS thanks to its pliability. In particular, thanks to its automatic development approach, it could be easily applicable to future space missions which intend to search exoplanets with the transit method with small adjustments. A detailed analysis for the future implementation of RATS database has been, finally, performed. Requirements and structure of this archive have been identified in order to help in developing a database that can be offered both to scientific community and to non-specialists. Part II: Dynamical simulations The present dynamical configuration of planets in binary star systems may not reflect their formation process since the binary orbit may have changed in the past after the planet formation process was completed. An observed binary system may have been part of a former hierarchical triple that became unstable after the planets completed their growth around the primary star. Alternatively, in a dense stellar environment even a single stellar encounter between the star pair and a singleton may significantly alter the binary orbit. In both cases the planets we observe at present would have formed when the dynamical environment was different from the presently observed one. We have numerically integrated the trajectories of the stars (binary plus singleton) and of test planets, hosted around the primary star of the inner binary, to investigate the above mentioned mechanisms. Different values of mutual inclination, binary separation and singleton initial semimajor axis are explored in a statistical way. Our simulations show that the circumstellar environment during planetary formation around the primary was gravitationally less perturbed when the binary was part of a hierarchical triple because the binary was necessarily wider and, possibly, less eccentric. We find that a significant mutual inclination between the singleton and the binary is a key factor for instability of the planetary system in terms of orbital spacing, eccentricity, and mass of the individual planets. Infact, from our integration we have found that when the mutual inclination is larger than 40, the fraction of planets in the binary surviving the chaotic phase of the triple declines dramatically. and for an inclination around 90, the percentage of surviving planets is lower than 20% for all binaries with a semimajor axis smaller than 200 AU. The combination of eccentricity and inclination oscillations of the binary companion induced by the secular perturbations of the singleton and the sequence of close encounters preceding the ejection of one star fully destabilize a planetary system extending beyond 1 AU from the star. Even in the case of a single stellar encounter the present appearance of a planetary system in a binary may significantly differ from what it had while planet formation was ongoing. However, while in the case of instability of a triple the trend is always towards a tighter and more eccentric binary system, when a single stellar encounter affects the system the orbit of the binary can become wider and be circularized. We can conclude that the frequency of planets in binaries with low separation may be strongly reduced by the residence of the pair in the past in a temporary inclined hierarchical triple.

Gaia is an extremely ambitious astrometric space mission adopted within the scientific programme of the European Space Agency (ESA) in October 2000. It aims to measure with very high accuracy the positions, motions and parallaxes of a large number of stars and galactic objects, including also for almost all the objects information about their brightness, colour, radial velocity, orbits and astrophysical parameters. Gaia requires a demanding data processing system on both data volume and processing power. The treatment of the Gaia data has been designed as an iterative process between several systems each one solving different aspects of the data reduction system. In this thesis we have addressed the design and implementation of the Intermediate Data Updating (IDU) system. IDU is the instrument calibration and astrometric data processing system more demanding in data volume and processing power of the data processing system of the Gaia satellite data. Without this system, Gaia would not be able to provide the envisaged accuracies and its presence is fundamental to get the optimum convergence of the iterative process on which all the data processing of the spacecraft is based. The design and implementation of an efficient IDU system is not a simple task and a good knowledge of the Gaia mission is fundamental. The design and implementation of IDU is not only referring to the actual design and coding of the system but also to the management and scheduling of all the related development tasks, system tests and in addition the coordination of the teams contributing to this system. The developed system is very flexible and modular so it can be easily adapted and extended to cope with the changes on the operational processing requirements. In addition, the design and implementation of IDU presents a variety of interesting challenges; covering not only the purely scientific problems that appear in any data reduction but also the technical issues for the processing of the huge amount of data that Gaia is providing. The design has also been driven by the characteristics and restrictions of the execution environment and resources -- Marenostrum supercomputer hosted by the Barcelona Supercomputing Center (BSC) (Spain). Furthermore, we have developed several tools to make the handling of the data easier; including tailored data access routines, efficient data formats and an autonomous application in charge of handling and checking the correctness of all the input data entering and produced by IDU. Finally, we have been able to test and demonstrate how all the work done in the design and implementation of IDU is more than capable of dealing with the real Gaia data processing. We have basically executed two of the IDU tasks over the first ten months of routine operational Gaia data. This execution has been the very first cyclic data processing level run over real data so far. Executing IDU at Marenostrum over that amount of data for the first time has been a challenging task and from the results obtained we are confident that the system, we have designed and that constitutes the bulk of this thesis, is ready to cope with the Gaia data according to the requirements sets. Furthermore, the presented design provides a solid IDU system foundation for the challenging task of processing the Gaia data during the forthcoming years.
Gaia es la misión espacial astrométrica más ambiciosa de la Agencia Espacial Europea (ESA). El satélite fue lanzado el 19 de Diciembre de 2013 y su objetivo principal es la determinación, con una resolución y precisión sin precedentes, de las posiciones, distancias y velocidades de más de mil millones de estrellas de nuestra galaxia. Esta Tesis se centra en el desarrollo del sistema de procesado IDU, "Intermediate Data Updating". IDU es una de las etapas de calibración instrumental y reducción de datos astrométricos más exigente del sistema de procesado del satélite Gaia. Sin este sistema, Gaia no podría alcanzar el nivel de precisión que se quiere obtener y su presencia es fundamental para lograr la convergencia óptima del sistema iterativo de procesado de datos en el que se basa la reducción de datos de Gaia. El procesado de los datos de Gaia es un gran reto tecnológico. En particular, el gran volumen de datos a procesar y el elevado número de procesos involucrados ha implicado el diseño de un sistema de distribución y procesado de datos muy complejo. Este procesado se basa en un sistema iterativo entre varios procesos en el que se añaden de manera continuada los nuevos datos recibidos del satélite. De entre estos procesos, esta tesis se centra en el diseño e implementación de IDU, donde se vuelven a procesar todos los datos brutos usando las calibraciones más recientes obtenidas del resto de procesos. El diseño e implementación de IDU ha supuesto una gran variedad de retos; incluyendo los problemas puramente científicos pero también las dificultades técnicas que aparecen en el procesado del gran volumen de datos de Gaia y la gestión de todas las tareas de desarrollo, test y coordinación de los equipos que contribuyen a este sistema. IDU se ejecuta en el supercomputador Marenostrum, gestionado por el "Barcelona Supercomputing Center" (BSC). Finalmente, esta tesis incluye los resultados de la primera ejecución operacional de IDU la cual ha servido para demostrar que el sistema desarrollado esta listo para afrontar el exigente reto de procesar los datos reales de Gaia durante los próximos años de misión.

In questi tre anni ho lavorato sulla riduzione di dati fotometrici e spettroscopici della galassia sferoidale nana Sagittario. L'analisi è stata effettuata utilizzando dati nei filtri V e I presi con strumento VIMOS@VLT in modalità Imaging (per la fotometria) e MOS (per la spettroscopia multi oggetto). I dati fotometrici consistono in 8 campi distribuiti lungo l'asse maggiore e minore della galassia più 6 campi centrati su 6 ammassi globulari probabilmente appartenenti alla galassia nana Sagittario (NGC 4147, Pal5, Pal12, Arp2, Ter7, Ter8 ). L'indagine fotometrica mi ha permesso di ottenere un catalogo che conta più di 400000 oggetti. Questo grande campione è stato utilizzato per selezionare target per la spettroscopia a bassa risoluzione con MOS@VIMOS, uno strumento in grado di osservare contemporaneamente circa 150 oggetti nei 4 rilevatori di cui è dotato, ciascuno dei quali osserva in cielo un'area di 7x8 arcmin. Lo scopo ultimo di questa analisi spettroscopica è di realizzare una mappa delle velocità radiali delle stelle con l'intento di separare gli oggetti della Via Lattea dagli oggetti di Sagittario. In tal modo si sono ottenuti spettri per circa 1200 stelle. Lo studio degli spettri mi ha dunque permesso di selezionare tramite un triplo filtro (colore,magnitudine e velocità radiale) una lista "pulita" di stelle di Sagittario che conta 230 oggetti. Infine, questo campione di 230 oggetti è stato osservato con lo spettroscopio ad alta risoluzione FLAMES@ESO. Data la capacità di questo strumento di osservare un grande numero di oggetti, alle 230 stelle di Sagittario sono state aggiunte circa 1400 stelle vicine alle prime in colore e magnitudine; confido in tal modo di ottenere un catalogo di stelle di Sagittario molto più numeroso delle iniziali 230 stelle. Con questi spettri potrò anzitutto confermare le velocità radiali precedentemente calcolate, aumentando notevolmente la precisione delle misure (da una incertezza di circa 15-20 km/s conto di passare a una incertezza inferiore a 1 km/s), e al contempo misurando abbondanze chimiche con grande precisione.
I undertook a photometric and spectroscopic survey of Sgr dSph with VIMOS@VLT, to derive colour - magnitude diagrams (CMD) and radial velocities across the extension of the galaxy. I observed 8 fields along the major and minor axis of the galaxy (along 7 and 2 degrees respectively), plus 6 globular cluster likely associated with the galaxy ( NGC 4147, Pal5, Pal12, Arp2, Ter7, Ter8 ). All of them were observed with V and I filters. The photometric catalogue was then used to select target for VIMOS-MOS high resolution mode. I obtained spectra for about 1200 stars: 250 stars in the Sgr main body fields were established as Sgr dSph members, and will now be the subject of high resolution spectroscopy studies for the purpose of chemical analysis using FLAMES@VLT This constitutes one of the richest photometric and spectroscopic homogeneous catalog of Sgr dSph stars ever obtained.

Aquesta tesi engloba el treball fet durant els ultims quatre anys com a estudiant de doctorat a l’Institut de Física d’Altes Energies (IFAE), emmarcat dins de la col·labaració Sloan Digital Sky Survey II Supernova (SDSS-II/SNe) Survey. Al primer capítol (§1) s’introdueixen els principals conceptes del Model Estàndar de Cosmologia, presentant els seus orígens, les propietats dels seus continguts, i les mesures de distància i brillantor. També es reconstrueix l’història de l’univers des del Big Bang i es resumeixen alguns dels descobriments més excitants que han confirmat les prediccions del Model Estàndar. Seguidament (§2), es dona una explicació detallada de les supernoves (SNe), incloenthi el mecanisme físic que dóna lloc a les explosions, les diferències entre els diferents tipus, i la seva classificació espectral. També es descriuen les propietats fotomètriques i espectroscòpiques de les supernoves de tipus Ia. Tot seguit, es resumeixen les mesures del ritme d’explosions, les propietats de les gal·làxies on resideixen les supernoves, i el seu ús en Cosmologia a través del diagrama de Hubble. Al següent capítol, (§3) es descriu la col·laboració SDSS-II/SNe Survey, una extensió de tres anys (2005-2007) del projecte Sloan (SDSS) que ha detectat i mesurat corbes de llum de centenars de supernoves tot escanejant el cel en repetides ocasions. Vam contribuir al seguiment espectroscòpic de les supernoves de SDSS-II/SNe, obtenint 23 espectres de supernoves durant 4 nits d’Octubre i Novembre (5-6 Oct. i 4-5 Nov.) del 2007, utilitzant el Telescopio Nazionale Galileo (TNG) situat a l’Observatorio del Roque de Los Muchachos (ORM) a l’illa de La Palma. Al capítol §4 es descriu tot el procés de reducció de les dades, des de l’adquisició de les imatges fins als espectres calibrats en flux i longitud d’ona. A continuació de la reducció dels espectres, al capítol §5, s’analitza una de les supernoves de tipus Ia menys lluminoses mai conegudes, la peculiar 2007qd, per la qual vam mesurar el primer espectre. Les propietats observades de la 2007qd la situen a la subclasse anomenada 2002cx, com a membre intermig entre la 2002cx i la 2008ha, enllaçant aquetes. Es presenten les observacions espectroscòpiques i fotomètriques de la supernova 2007qd i es comparen les seves propietats peculiars amb un ventall d’altres supernoves. Aquest anàlisi va ser publicat a McClelland et al. (2010). Al capítol §6, s’utilitzen les supernoves Ia descobertes pel SDSS-II/SNe Survey durant els tres anys d’activitat, per buscar dependències entre les propietats fotomètriques de les supernoves Ia i la projecció de la distància fins al centre de la gal·làxia on resideixen, utilitzant la distància com a aproximació a les propietats locals de les gal·làxies (ritme de creació d’estrelles, metalicitat local, etc.). Trobem que l’excés de color de les supernoves, parametritzat per AV a MLCS2k2 i per c a SALT2 decreix amb la distància projectada, en particular per les gal·làxies espirals. A més, amb menys significància, també es troba que l’amplada de la corba de llum, obtinguda amb MLCS2k2, està correlacionada amb la separació entre la supernova i el centre de la gal·làxia per les el·líptiques, així les supernoves amb corbes de llum més estretes, per tant menys lluminoses, s’observen més aviat a més distància del centre gal·làctic. Aquest anàlisi va ser presentat a la conferència Supernovae and their Host Galaxies que es va fer al Juny del 2011 a Sydney, i serà publicat a Galbany et al. (2011). Finalment, al capítol §7, es resumeix i es donen les conclusions d’aquesta tesi.
Esta tesis engloba el trabajo realizado durante los últimos cuatro años como estudiante de doctorado en el Institut de Física d’Altes Energies (IFAE), enmarcardo en la colabaración Sloan Digital Sky Survey II Supernova (SDSS-II/SNe) Survey. En el primer capítulo (§1) se introducen los principales conceptos del Modelo Estándar de Cosmología, presentando sus orígenes, las propiedades de sus contenidos, y las medidas de distancia y brillo. También se reconstruyen la historia del universo desde el Big Bang y se resumen algunos de los descubrimientos más excitantes que han confirmado las predicciones del Modelo Estándar. Seguidamente (§2), se da una explicación detallada de las supernovas (SNe), incluyendo el mecanismo físico que da lugar a las explosiones, las diferencias entre los diferentes tipos, y su clasificación espectral. También se describen las propiedades fotomètricas y espectroscópicas de las supernovas de tipo Ia. A continuación, se resumen las medidas del ritmo de explosión, las propiedades de las galaxias donde residen las supernovas, y su uso en Cosmología a través del diagrama de Hubble. En el siguiente capítulo, (§3) se describe SDSS-II/SNe Survey, una extensión de tres años (2005-2007) del proyecto Sloan (SDSS) que ha detectado y medido curvas de luz para centenares de supernovas a través de escanear el cielo en repetidas ocasiones. Como parte del seguimiento espectroscópico de las supernova de SDSS-II/SNe, contribuímos obteniendo 23 espectros de supernovas durante 4 noches de Octubre y Noviembre (5-6 Oct. y 4-5 Nov.) del 2007, utilizando el Telescopio Nazionale Galileo (TNG) situado en el Observatorio del Roque de Los Muchachos (ORM) en La Palma. En el capítulo §4 se describe toda la reducción de datos, desde la adquisición de las imágenes hasta los espectros calibrados en flujo y longitud de onda. Siguiendo la reducción de los espectros, en el capítulo §5, se describe una de las supernovas de tipo Ia menos luminosa jamàs conocida, la peculiar 2007qd, para la cual medimos el primer espectro. Las propiedades observadas de la 2007qd la sitúan en la subclase llamada 2002cx, como miembro intermedio entre las supernovas 2002cx y 2008ha, enlazándolas. Se presentan las observaciones espectroscópicas y fotométricas de la supernova 2007qd y se comparan su propiedades con un conjunto de otras supernovas. Éste análisis fue publicado en McClelland et al. (2010). En el capítulo §6, se utilizan las supernovas Ia descubiertas por SDSS-II/SNe Survey durante los tres años de actividad, para buscar dependencias entre las propiedades fotométricas de las supernovas Ia y la proyección de la distancia hasta el centro de la galaxia donde residen, utilizando la distancia como aproximación a las propiedades locales de las galaxias (ritmo de creación de estrellas, metalicidad local, etc.). Encontramos que el exceso de color de las supernovas, parametrizado por AV en MLCS2k2 y por c en SALT2 decrece con la distancia, en particular para las galaxias espirales. Además, y con menos significancia, también se encuentra que la amplitud de la curva de luz, obtenida con MLCS2k2, está correlacionada con la separación entre la supernova y el centro de la galaxia para las galaxias elípticas, así las supernovas con curvas de luz más estrechas, y menos luminosas, se observan a más distancia del centro galactico. Este análisis fue presentado en la conferencia Supernovae and their Host Galaxies que tuvo lugar en Junio del 2011 en Sydney, y serà publicado en Galbany et al. (2011). Finalmente, en §7, se resume y se presentan las conclusiones de esta tesis.
This thesis comprises the work I have been doing during the last four years at Institut de Física d’Altes Energies (IFAE) as a PhD student, and has to be understood within the context of the Sloan Digital Sky Survey II Supernova (SDSS-II/SNe) survey. The content of this thesis is ordered as follows. In the next Chapter (§1) I introduce the main concepts of the Standard Model of Cosmology, presenting the origins, the properties of its contents, and the distance and the brightness measurements. I also reconstruct the history of universe since the Big Bang and summarize some of the most exciting discoveries that have confirmed the Standard Model predictions. In §2, a detailed explanation of supernovae (SNe) is given, including the physical mechanism that accounts for their explosions, the differences among the several types of SNe, and their spectral classification. We also describe the spectroscopic and photometric properties of Type-Ia SNe. After that, we review the SNe rate of the explosion measurements, the properties of their host galaxies, and their use in Cosmology through the Hubble diagram. After that, in §3, I describe the SDSS-II/SNe survey, a three-year (2005-2007) extension of SDSS of which I am an external collaborator, which has detected and measured light-curves for several hundred supernovae through repeat scans of the sky. As a part of the spectroscopic follow-up of the SDSS-II/SNe candidates, we contributed to the project taking spectra of 23 SNe during four nights in October and November (5-6 Oct. and 4-5 Nov.) of 2007 using the Telescopio Nazionale Galileo (TNG) located at the Observatorio del Roque de Los Muchachos (ORM) in La Palma. In §4, the whole reduction procedure, from the acquisition of the raw data by the telescope camera to the final flux-calibrated spectra, is described. Following the spectra reduction, in §5, I describe one of the most subluminous type-Ia events known, the peculiar 2007qd supernova, for which we took the first spectrum. The observed properties of 2007qd place it in the 2002cx subclass of supernovae, specifically as a member intermediate to 2002cx and 2008ha, linking these objects. We present the photometric and spectroscopic observations of 2007qd and compare its unique properties with a range of other SNe. This work was compiled and published in McClelland et al. (2010). Then, in §6, the three-year sample of Type Ia supernovae (SNe Ia) discovered by the SDSS-II/SNe Survey is used to look for dependencies between photometric SN Ia properties and the projected distance to the host galaxy center, using the distance as a proxy for local galaxy properties (local star-formation rate, local metallicity, etc.). We find that the excess color of the SN, parametrized by AV in MLCS2k2 and by c in SALT2 decreases with the projected distance, in particular for spiral galaxies. At a lower significance we find that the light-curve width, as obtained from MLCS2k2 , is correlated with the SN-galaxy separation for elliptical hosts, so that SNe Ia with narrower light-curves, hence dimmer, are more commonly observed at large distances from the host galaxy core. This analysis was presented in the Supernovae and their Host Galaxies conference which was held at Sydney, Australia in June 2011, and will be published in Galbany et al. (2011). Finally, in §7 we give a summary and the conclusions of this thesis.

One of the main themes in extragalactic astronomy for the next decade will be the evolution of galaxies over cosmic time. It has, however, become clear that the properties and the evolution of galaxies are intimately linked to the growth of their Supermassive Black Holes (SMBH). Understanding the formation of galaxies, and their subsequent evolution, will therefore be incomplete without clearifing the connection between the SMBHs and their host galaxies. The formation, assembly history, and environmental impact of the SMBHs that are ubiquitous in the nuclei of luminous galaxy remain today some of the main unsolved problems in cosmic structure formation studies. To understand galaxy evolution we need to study this subject from a different point of view. We need tools that can help us to trace the behavior of SMBHs and their host galaxies at high redshift and in active galaxies, and we need to understand how AGN feedback acts. In the first part of this thesis work we seek to find a tracer for the stellar velocity dispersion sigma* in order to give a tool in the study of the M_bh-sigma* relation even in active or high redshift galaxies, were sigma* cannot be measured directly. We perform an extensive study on the kinematics of the gas as described by the three gas emission lines [OIII], [NII] and Halpha using the SDSS database, in order to find the best tracer for sigma* and to get some clues concerning the effect of AGN on the gas kinematic. We will study three subsamples of AGN, Star Forming (SF) and Transition (TR) galaxies. A new analysis of the SDSS spectra was required due to the need of a robust stellar continuum subtraction, in order to take into account the stellar absorption features on the gas emission lines. A particular attention has been devoted in establishing the quality of the line fitting program, and the statistical analysis of the suitability of the gas emission lines was rigorous. The main results of this first part can be summarized as follows: --We show that [OIII] line do have a correlation with sigma*; this correlation is poor, with a Pearson correlation coefficient ranging from 0.42 to 0.55 in the different subsamples. The slope of the relation is statistically less than unity, and the AGN sample shows the lowest value. --Halpha and [NII] show a tighter relation, with a Pearson correlation coefficient of 0.60 and 0.62, respectively, in the AGN subsample. All results from our measures of the intrinsic scatter and of the correlation coefficient show that [NII] and Halpha lines are more tightly tied to sigma* than [OIII]. --In any case the slope of the relation between the gas and the stars is lower than unity, even if Halpha and [NII] lines show slopes that are usually steeper than the slope of the sigma*-sigma_[OIII] relation. --The slope, scatter, correlation coefficient are similar using the three emission lines in the SF sample, while they differ in the TR and AGN samples. Particularly, we observe the slope in the AGN sample to be shallower in the sigma*-sigma_[OIII] relation with respect to the slope in the TR and SF, with b_TR showing an intermediate value between b_SF and b_AGN. On the other side, the slope of the sigma*-sigma_[NII] relation for the three AGN, TR and SF samples agree within uncertainties. Halpha emission line shows b_SF~ b_TR, while b_AGN results to be shallower as in the case of [OIII]. --We propose an equation for the sigma_gas/sigma* for each of the three line, in the different subsamples, using different regression methods. In our opinion these findings indicate that in SF or SB galaxies the ionized gas is less perturbed by non-gravitational effects from the central engine than in AGNs, so the measured sigma_gas is subvirial as observed in quiescent galaxies. The reason for the slope in the sigma*-sigma_[OIII] relation to be lower than in the cases of [NII] or Halpha lines could reside in the fact that [OIII] is nearer to the central engine in AGN, and consequently is more subject to its non gravitational acceleration; sigma_[OIII] is then more broadened respect to sigma_[NII] or sigma_Halpha and its position in a sigma*-sigma_gas plot migrate toward higher values of sigma_gas, therefore decreasing the slope of the relation. A conclusive test of [NII] being a better tracer for the stellar velocity dispersion respect to the [OIII] line is represented by the fact that in a M_bh-sigma_gas plot theM_bh-sigma_[NII] presents the lowest scatter. In the second part of this thesis work we will look at the effects of AGN feedback in galaxy clusters. About one third of clusters present a central drop in the core gas temperature, with central cooling time shorter than the cluster age; it should be observed in these cases a massive flow of cooling gas. This is not, and some heating mechanism is required. AGN feedback is so invoked to solve the so called ``cooling flow problem''; anyway, while theoretical models still presents AGN feedback that produces red and dead ellipticals recent observations suggest that AGN feedback cannot be as efficient as to completely suppress star formation. The goal of this Section of the Thesis is to establish whether the Cool Core Clusters (CCC) and Non Cool Core Clusters (NCCC) are characterized by a different star formation rate, and if this difference can be assessed with the use of broad band optical, NIR and UV colors. The work was carried out using the extended Highest X-ray Flux Galaxy Cluster Sample (HIFLUGCS) of both CCC and NCCC clusters, matched with the SDSS, 2MASS and GALEX surveys. We first performed a careful photometrical re-analysis of SDSS data, since SDSS data are affected by a wrong sky subtraction and because several targets are partially blended and needed a careful ad-hoc analysis. The main results of this first part can be summarized as follows: --We fitted the color-magnitude relation for all the data points to retrieve the slopes b for each color-magnitude relations, and then derived the zero points using the zp=mean(color)-mean(mag)*b separately for the two CCC and NCCC sample, under the hypothesis that galaxies both in CCC and NCCC follow the same color-magnitude relation, and that the two samples differ just for the mean colors. --We observe that the mean color differences are systematically positive, so indicating that they are probably physically different in our samples. --In a pure cooling flow model, we should observe a correlation between the mass deposit rate calculated from X-ray observations and the colors of galaxies, since the star formation due to the cooling gas falling on the central galaxies should give bluer colors in galaxies undergoing stronger star formation. In our case, we don't see any correlation. --The differences we found are compatible in our opinion with CCC central galaxies to have recent or ongoing SF. Still, a pure cooling flow model is excluded by our findings. Our preliminary calculation to find the mean difference in SFR between CCC and NCCC galaxies from g-r color indicates SFR of no more than 2-5 M_sun/yr.
Uno dei più promettenti temi nell'astronomia extragalattica per i prossimi decenni sarà l'evoluzione delle galassie. E' divenuto sempre più chiaro come le loro proprietà e la loro evoluzione siano intimamente collegate alla crescita dei buchi neri supermassicci (SMBH) nei loro nuclei. Per capire la formazione delle galassie, e la loro successiva evoluzione, bisognerà chiarire la connessione tra i SMBH e le loro galassie ospiti. I SMBH sono presenti in quasi tutti i nuclei delle galassie; la loro formazione, il loro accrescimento, e il loro impatto sulla materia circostante rappresentano alcuni dei problemi ancora irrisolti nella storia della formazione delle strutture cosmiche. Per capire l'evoluzione delle galassie, è necessario studiare questo soggetto da più punti di vista. Abbiamo bisogno sia di strumenti che permettano di tracciare il comportamento dei SMBH e delle loro galassie ospiti anche ad alto redshift o in galassie attive, sia di comprendere come agisca il cosiddetto AGN "feedback" all'interno delle singole galassie. Nella prima parte di questo lavoro il nostro obiettivo è determinare un tracciante per la dispersione di velocità stellare sigma*, allo scopo di offrire uno strumento nello studio della relazione tra la massa dei SMBH M_bh e sigma* anche in galassie attive o ad alto redshift, dove sigma* non può essere misurata direttamente. Proponiamo uno studio estensivo della cinematica del gas descritta dalle tre righe d'emissione di [OIII], [NII] e Halpha utilizzando l'archivio della Sloan Digital Sky Survey (SDSS), in modo da stabilire quale sia il miglior tracciante per sigma* e in modo da capire come l'AGN influenzi la cinematica del gas. Sono stati presi in considerazione tre sottocampioni di galassie, rispettivamente AGN, Star Forming (SF) e Transition (TR). Abbiamo effettuato una nuova analisi degli spettri SDSS; poichè gli assorbimenti stellari possono influenzare o addirittura sopraffare le emissioni del gas ionizzato, è stato necessario sottrarre il continuo stellare. Una attenzione particolare è stata dedicata a stabilire la qualità dei programmi usati nel fit, e all'analisi statistica dell'idoneità delle tre righe d'emissione prese in considerazione come possibili traccianti della dispersione di velocità stellare. I risultati principali di questa prima parte possono essere riassunti nei seguenti punti: --Abbiamo dimostrato che sigma_[OIII], correla con sigma*; tuttavia la correlazione è debole, con un coefficiente di correlazione di Pearson che varia tra 0.42 a 0.55 nei tre sottocampioni di galassie AGN, SF e TR. La pendenza della relazione è statisticamente più bassa dell'unità, e nel campione degli AGN si registra la pendenza più bassa.} -- Le relazioni sigma*-sigma_[NII] e sigma*-sigma_Halpha sono più strette della sigma*-sigma_[OIII], e il coefficiente di correlazione di Pearson diventa di 0.60 e 0.62, rispettivamente per [NII] e Halpha, nel campione delle galassie AGN. Tutti i risultati delle nostre misure di scatter intrinseco e di correlazione mostrano che le righe d'emissione di [NII] and Halpha sono meglio correlate alla dispersione di velocità stellare rispetto all'[OIII]. --In tutti i casi troviamo una pendenza b<1, anche se le righe d'emissione di [NII] and Halpha mostrano pendenze generalmente maggiori di quelle trovate con la relazione sigma*-. -- Le pendenze e i coefficienti di correlazione sono simili usando qualunque delle tre righe di emissione nel sottocampione delle galassie SF; osserviamo invece che la pendenza nel campione degli AGN risulta piu' bassa nella relazione sigma*-sigma_[OIII] rispetto a quella trovata nei campioni SF e TR, con b_{AGN}