Dissertations / Theses on the topic 'Astrometric'

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1985.<br>MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.<br>Bibliography: leaves 381-389.<br>by Michael Mark Colavita.<br>Ph.D.

The Astrometric Telescope Facility (ATF) is designed to be a space-based facility searching for planets and extra solar planetary systems. In order to be able to positively identify other planetary systems such as Uranus/Neptune-class planets, the ATF is required to be capable of surveying approximately 100 stars within about 10 parsecs of the earth, of measuring a change in the relative position of stars to an accuracy of 10 microarcseconds, and of being stable for about 10 to 20 years. The ATF approach to astrometry is to modulate the intensity on the focal plane of the telescope by a moving Ronchi ruling or grating and then to determine the relative star positions from the phases of the modulated signals. This approach reduces boise from background stray light and reduces random noise by averaging over many measurements. The optical performance of the ATF system has been modeled mathematically using the concept of the system transfer function. Each subsystem has been studied analytically. The relationship between the measured parameter and aberrations of the system has been established analytically. Error sources from the system have been identified and calibration for the system is provided. Design and optimization for the astrometric telescope and gratings have been investigated. The key issues to reach the 10 microarcseconds are addressed.

Measuring stellar parallax, position and proper motion is the task of astrometry. With the development of new and much more accurate equipment, different noise sources are likely to affect the very precise measurements made with future instruments. Some of these sources are: stellar surface structures, circumstellar discs, multiplicity and weak microlensing. Also exoplanets may act as a source of perturbation. In this thesis I present an investigation of stellar surface structures as a practical limitation to ultra-high-precision astrometry. The expected effects in different regions of the HR-diagram are quantified. I also investigate the astrometric effect of exoplanets, since their astrometric detection will be possible with future projects such as Gaia and SIM PlanetQuest. Stellar surface structures like spots, plages and granulation produce small surface areas of different temperatures, i.e. of different brightness, which will influence integrated properties such as the total flux (zeroth moment of the brightness distribution), radial velocity and photocenter position (first moments of the brightness distribution). Also the third central moment of the brightness distribution, interferometrically observable as closure phase, will vary due to irregularities in the brightness distribution. All these properties have been modelled, using both numerical simulations and analytical methods, and statistical relations between the variations of the different properties have been derived. Bright and/or dark surface areas, randomly spread over the stellar surface, will lead to a binomial distribution of the number of visible spots and the dispersion of such a model will be proportional topN, where N is the number of spots or surface structures. The dispersion will also be proportional to the size of each spot, A. The dispersions of the integrated properties are therefore expected to be/ ApN. It is noted that the commonly used spot filling factor, f / AN, is notthe most relevant characteristic of spottiness for these effects. Both the simulations and the analytic model lead to a set of statistical relations for the dispersions or variations of the integrated properties. With ,e.g. knowledge of the photometric variation, m, it is possible to statistically estimate the dispersions for the other integrated properties. Especially interesting is the variation of the observed photocenter, i.e. the astrometric jitter. A literature review was therefore made of the observed photometric and radial-velocity variations for various types of stars. This allowed to map the expected levels of astrometric jitter across the HR diagram. From the models it is clear that for most stellar types the astrometric jitter due to stellar surface structures is expected to be of order 10 μAU or greater. This is more than the astrometric displacement typically caused by an Earth-sized exoplanet in the habitable zone of a long-lived main-sequence star, which is about 1–4 μAU. Only for stars with extremely low photometric variability (&lt; 0.5 mmag) and low magnetic activity, comparable to that of the Sun, will the astrometric jitter be of order 1 μAU, sufficient to allow astrometric detection of an Earth-sized planet in the habitable zone. While stellar surface structure may thus seriously impair the astrometric detection of small exoplanets, it has in general negligible impact on the detection of large (Jupiter-size) planets.

In November 2012, the European Space Agency (ESA) is planning to launch Gaia, a mission designed to measure with microarcsecond accuracy the astrometric properties of over a billion stars. Microarcsecond astrometry requires extremely accurate positional measurements of individual stellar transits on the focal plane, which can be disrupted by radiation-induced Charge Transfer Inefficiency (CTI). Gaia will suffer radiation damage, impacting on the science performance, which has led to a series of Radiation Campaigns (RCs) being carried out by industry to investigate these issues. The goal of this thesis is to rigorously assess these campaigns and facilitate how to deal with CTI in the data processing. We begin in Chapter 1 by giving an overview of astrometry and photometry, introducing the concept of stellar parallax, and establishing why observing from space is paramount for performing global, absolute astrometry. As demonstrated by Hipparcos, the concept is sound. After reviewing the Gaia payload and discussing how astrometric and photometric parameters are determined in practice, we introduce the issue of radiation-induced CTI and how it may be dealt with. The on board mitigating strategies are investigated in detail in Chapter 2. Here we analyse the effects of radiation damage as a function of magnitude with and without a diffuse optical background, charge injection and the use of gates, and also discover a number of calibration issues. Some of these issues are expected to be removed during flight testing, others will have to be dealt with as part of the data processing, e.g. CCD stitches and the charge injection tail. In Chapter 3 we turn to look at the physical properties of a Gaia CCD. Using data from RC2 we probe the density of traps (i.e. damaged sites) in each pixel and, for the first time, measure the Full Well Capacity of the Supplementary Buried Channel, a part of every Gaia pixel that constrains the passage of faint signals away from the bulk of traps throughout the rest of the pixel. The Data Processing and Analysis Consortium (DPAC) is currently adopting a 'forward modelling' approach to calibrate radiation damage in the data processing. This incorporates a Charge Distortion Model (CDM), which is investigated in Chapter 4. We find that although the CDM performs well there are a number of degeneracies in the model parameters, which may be probed further by better experimental data and a more realistic model. Another way of assessing the performance of a CDM is explored in Chapter 5. Using a Monte Carlo approach we test how well the CDM can extract accurate image parameters. It is found that the CDM must be highly robust to achieve a moderate degree of accuracyand that the fitting is limited by assigning finite window sizes to the image shapes. Finally, in Chapter 6 we summarise our findings on the campaign analyses, the on-board mitigating strategies and on how well we are currently able to handle radiation damage in the data processing.

A real-time discrete-event simulation model is built to emulate the functional operations of the Thaw telescope of the Allegheny Observatory and its attached scientific instrument. The OASIS software system is used to communicate with the simulation model. This simulation model, written in Ada, consists of three major parts. The Command Receiver and the Data Transmitter are software written to service the incoming telecommands and outgoing telemetry, the Command Processor is the actual simulator itself consisting of a Command Retriever, a Scanner, a Parser, a Command Interpreter, and the actual Thaw telescope simulation. The motivation for our simulation model and discussion of design issues are presented in chapters 1 and 2. The details of the model are documented in chapters 3, 4, and 5. The final two chapters include examples, questions, thoughts for future work, and conclusions.

The project PRISMA is the first network for systematic surveillance of meteor and atmosphere. More specifically this thesis is about the astrometric and photometric characterization of PRISMA cameras and also the computation of meteoric trajectories. In the first and second chapter there is a general overview of meteor phenomena and a theoric description of meteoroid interaction with the atmosphere. At the beginning of the third chapter there is a description of the project, what it deals with and who partecipates. Then there is the general specification of the Basler camera and the tests that have been conducted on a single camera. These tests have been useful to understand how temperature variations could affect the response of the camera and which magnitude the camera works better. In the fourth chapter it can be find the procedure to clean and subsequently to obtain the catalogs from the images taken with the Basler camera. Then it is explained what is the procedure to arrived at an astrometric solution with the software Scamp. Afterwards the obtained results are illustrated. In the last chapter, the dynamic calculation is explained to get the meteoric trajectory from the astrometric images taken from two stations of PRISMA network, Lignan and Torino.

We present new astrometric measurements from our ongoing monitoring campaign of the HR 8799 directly imaged planetary system. These new data points were obtained with NIRC2 on the W.M. Keck II 10 m telescope between 2009 and 2014. In addition, we present updated astrometry from previously published observations in 2007 and 2008. All data were reduced using the SOSIE algorithm, which accounts for systematic biases present in previously published observations. This allows us to construct a self-consistent data set derived entirely from NIRC2 data alone. From this data set, we detect acceleration for two of the planets (HR 8799b and e) at >3 sigma. We also assess possible orbital parameters for each of the four planets independently. We find no statistically significant difference in the allowed inclinations of the planets. Fitting the astrometry while forcing coplanarity also returns chi(2) consistent to within 1 sigma of the best fit values, suggesting that if inclination offsets of less than or similar to 20 degrees are present, they are not detectable with current data. Our orbital fits also favor low eccentricities, consistent with predictions from dynamical modeling. We also find period distributions consistent to within 1 sigma with a 1:2:4:8 resonance between all planets. This analysis demonstrates the importance of minimizing astrometric systematics when fitting for solutions to highly undersampled orbits.

The effect of Intra-pixel sensitivity variation (IPSV) in charge-coupled devices (CCDs) can be important in astronomical applications. This thesis studies the IPSV in a front-illuminated three-phase EEV05-20 CCD used in the Automated Patrol Telescope (APT), from multiple points of view. To explore the detailed sensitivity variation within pixels, the CCD was scanned using a 4 \mu meter diameter light beam in four colour bands: B, V, R and I. The resulting images clearly show the IPSVs due to the CCD electrode structure, and its dependence on wavelength. Unexpected ghost images appear in the scan images that are most likely due to the charge transfer inefficiency (CTI) of the CCD. A correction procedure for the CTI effect is presented. Using the pixel response function (PRF) which was derived from the CCD scans, instrumental point spread functions (iPSFs) were calculated from dithered images observed by the APT. The accurate iPSFs allowed us to generate a variety of simulated images of APT observations, enabling us to analyse in detail the effect of IPSV on astronomical observations. One of the astronomical impacts of IPSV is on photometry. The IPSV effect on the precision for estimating star fluxes was studied using both observed and simulated images. The IPSV effect can be expressed as magnitude estimation error maps plotted against the fractional part of a star's coordinates. The IPSV effect introduces \pm 4% errors in star fluxes for observed images with the APT in V band. Another astronomical impact of IPSV is on astrometry. IPSV influences the precision for estimating star coordinates, and this was studied using a number of simulated images. The IPSV effect can be expressed as coordinate estimation error maps plotted against the fractional part of a star's coordinates. The IPSV effect introduces \sim 0.02 pixel errors in RMS for images observed with the APT in V band. The appearance of the unexpected ghost images in the CCD scans suggested that CTI might also affect observed images. We examined the effects on PSFs and photometry. The CTI effect does affect the shapes of PSFs, but only to a small fraction. Its effect on photometry is negligible.

Thesis (Ph. D.) -- University of Maryland, College Park, 2007.<br>Thesis research directed by: Physics. Title from t.p. of PDF. On t. p. "eta" is a Greek symbol. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The identification of known asteroids on existing CCD pictures would allow us to obtain accurate astrometric and photometric asteroid properties. Some asteroids might have ambiguous orbital elements, thus their identification along with their exact positions on multiple picture frames could significantly improve their orbital elements. Furthermore, the possibility of identifying known asteroids on older pictures, sometimes preceding their discovery date, might allow the study of non-gravitational effects like the Yarkovsky effect. Identifying a potential Yarkovsky effect on asteroids is challenging because it is extremely weak. However, this effect cumulates with time, therefore, it is necessary to find astronomical pictures that are as old as possible. In addition, we need to collect high quality CCD pictures and use a methodology that would allow obtaining a statistically significant sample of asteroids. To accomplish this, we decided to use the online archive of the Subaru telescope at Mauna Kea Hawaii because it has a prime-focus camera with a very high resolution of 80 millions pixels very well suited to capture serendipitous asteroids. In addition, the Subaru online archive has pictures from the last 10 years. The methodology used in this thesis is to build a database that contains the orbital elements of all the known asteroids, allowing us to write a program that calculates the approximate position of all the asteroids at the date and time of each CCD picture we collect. To obtain a more precise position, the program also interfaces the JPL NASA Horizons on-line computation service. Every time an asteroid is found on a picture, Horizons sends its theoretical location back to the program. A later visual identification of this asteroid at this theoretical location on the picture triggers its input into our sample for further study. This method allowed us to visually confirm 508 distinct asteroids on 692 frames with an average diameter of 3.6 km. Finally, we use the theory (given in appendix A) to calculate the theoretical drift of these asteroids that we compare with the one we measured on the CCD pictures.<br>ID: 031001319; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Title from PDF title page (viewed March 27, 2013).; Thesis (M.S.)--University of Central Florida, 2012.; Includes bibliographical references (p. 192-195).<br>M.S.<br>Masters<br>Physics<br>Sciences<br>Physics

Ingeniero Civil Eléctrico<br>La tecnología de terahercios se encuentra en un estado de desarrollo atrasado con respecto a las tecnologías usadas en las bandas adyacentes, como la óptica infrarroja o la electróni- ca de microondas. En particular, no se poseen fuentes compactas de radiación que operen dentro esta banda logrando buenos niveles de potencia y amplios rangos de frecuencia. Las útiles propiedades de la radiación de terahercios como su capacidad de detectar moléculas complejas, buena resolución espacial y ser radiación no ionizante, hacen que el desarrollo de tecnología para esta banda sea un área con creciente interés. En el contexto del desarrollo de una nueva línea de investigación sobre espectroscopía molecular, en el Laboratorio de Terahertz y Astrofotónica de la Universidad de Chile, se realiza este trabajo que consiste en el desarrollo experimental de un sistema láser para la ali- mentación de fotomezcladores. Este sistema tiene como objetivo la generación de dos señales ópticas de alta estabilidad y coherencia, cuya diferencia de frecuencias puede ser ajustada de forma continua dentro del rango de 10 GHz a 300 GHz. Para esto, se utiliza un esquema basado en un peine de frecuencias óptico sobre el cual se enclava por inyección un láser de diodos de frecuencia sintonizable. Esto consigue tener una fuente infrarroja de alta precisión dentro de un gran rango. Además, se genera una segunda señal por medio de modulación en amplitud (AM), la cual es sintonizable dentro de un rango igual al espaciado producido por el peine óptico. En conjunto, estas señales logran abarcar un amplio espectro de frecuencias de forma continua sin perder estabilidad ni calidad de las señales. En este trabajo se logra implementar los subsistemas para la generación de cada una de las señales requeridas y se estudia la capacidad de estos para trabajar dentro del rango deseado. Para la señal generada por enclavamiento por inyección, se logra probar el concepto dentro de un rango reducido, principalmente por falta de un buen sistema de medición de altas frecuencias. Para la señal generada por modulación AM, se logran resultados positivos en todo el rango de diseño. Finalmente, se proponen modificaciones al sistema para mejorar su desempeño.<br>Este trabajo ha sido parcialmente financiado por Conicyt, a través de su fondo ALMA para el desarrollo de la astronomía, Proyecto 31140025, QUIMAL, Proyecto 1500010, CATA-Basal PFB06 y Fondecyt 1151213

The two-century period prior to the publication of Newton's Principia (first edition 1687; third edition 1726) was most important in terms of the radical changes that occurred in the observation, perception, and understanding of celestial objects that in turn spurred Newton to deduce his laws of gravitation and motion. Surprisingly, much of the available observational data embedded in contemporary texts from that two-century period has remained unused by modern astronomers, and this thesis (a) describes large amounts of data that were found and reanalyzed during the course of this Ph.D. research project, (b) places these data and their resulting analyses in context with the astronomy of the early-modern era, and (c) shows how modern astronomers and historians benefit from such information. The emphasis is placed here on west-European observations, as observations made elsewhere (eastern Europe, Asia) were isolated (not communicated for convenient rapid use by contemporary astronomers elsewhere) and did not develop or employ the level of precision that was utilized by western European astronomers through the extensive discussions that developed from correspondence and publication in Europe.

This thesis work presents the formulation for a tool developed in MATLAB to determine the mass of a space object from the fusion of astrometric and photometric data. The application for such a tool is to better model the mass estimation method used for high area-to-mass ratio objects found in high altitude orbit regimes. Typically, the effect of solar radiation pressure is examined with angles observations to deduce area-to-mass ratio calculations for space objects since the area-to-mass ratio can greatly affect its orbital dynamics. On the other hand, photometric data is not sensitive to mass but is a function of the albedo-area and the rotational dynamics of the space object. Thus from these two data types it is possible to disentangle intrinsic properties using albedo-area and area-to-mass and ultimately determine the mass of a space object. Three case studies were performed for the different orbit regimes: geosynchronous, highly elliptic, and medium earth orbit. The position states were either initialized with a two line element set or with initial orbit determination methods to simulate data which was run through an unscented Kalman filter to estimate the translational and rotational states of the space object as well as the mass an albedo area. In the geosynchronous and highly elliptic cases the tool was able to accurately predict the mass value to within 5kg of the true value based on a 95% confidence interval which will allow applications to understanding high area-to-mass objects with high certainty.

Les éphémérides issues d'intégrations numériques qui peuvent être facilement téléchargées des sites de l'IMCCE ou du JPL, ont une très bonne précision pour les observations récentes. En même temps, un autre type d'éphémérides, celles analytiques comme TASS, décrivent en détail le système dynamique par une représentation en combinaison de fréquences propres. Notre but est d'associer ces deux types d'éphémérides pour l'utiliser dans les études de la rotation des satellites naturelles. Cela signifie qu'il faut reconstruire des éphémérides à long terme et de haute précision montrant les caractéristiques du système comme les fréquences propres à partir des intégrations numériques. La principale difficulté est d'éviter l'intervalle de temps limité des éphémérides numériques. Dans notre travail, nous partons de la représentation des éléments d'orbite de Titan sur 10 000 ans issues de TASS comme exemple et comme standard. Nous expérimentons comment obtenir les fréquences propres sur 1000 ans d'éphémérides de TASS, et comment obtenir la représentation analytique de la longitude moyenne de Titan sur cet intervalle limité. A cause de cette durée de 1000 ans, au lieu de l'analyse en fréquence, nous utilisons la méthode des moindres carrées, en particulier pour les termes à longue période. L'efficacité et l’exactitude de l'ensemble de la méthode sont vérifiées en comparant les représentations de la longitude moyenne de Titan issue de TASS par la méthode des moindres carrées et par la représentation standard de TASS sur 10 000 ans. Finalement et c'est ce qui importe, nous obtenons une représentation du mouvement de Titan pour les 1000 ans d'éphémérides du JPL. Il existe une différence de 60 km dans l'amplitude du terme principal entre les représentations du JPL et de TASS. Cette différence est considérée comme issue du système. L'intervalle de temps limité des éphémérides influence les fréquences propres et induit des erreurs dans les termes à longues périodes comme contenant la longitude du nœud de Titan. Pour toutes les autres composantes ou presque, leurs amplitudes et phases sont similaires à celles de TASS. L'erreur de représentation est inférieure à 100 km sur 1000 ans et la déviation standard est de 26 km environ<br>The numerical integration ephemeris, which are convenient to download from online service of IMCCE, or Horizons of JPL have very good precision based on recent observations. Meanwhile, another kind, the analytical ephemeris like TASS, describes in detail the dynamical system by combination representation of proper frequencies. We plan to make a connection between those two different type ephemeris, that it ’s benefited us to study the rotation of natural satellites with its high precision ephemeris, those instantaneous positions, velocity, and those system characteristics like proper frequencies. The main difficulty is to avoid the shortcoming of the limited interval of observation ephemeris.In our work, we take the combination representation of Titan with 10,000 years TASS ephemeris as an example and standard. Then, we experiment to obtain both the analytical representation of the mean longitude of Titan and the proper frequencies involved in it with 1,000 years TASS ephemeris by analysis frequency. Due to limited timespan, we extend the method with a least square method, especially for the long period terms. We verify the effectiveness and exactness of the whole method in rebuilt the combination representation.Finally and most important, we get the combination representation of Titan with 1000 years JPL ephemeris. Between the solution of JPL and the representation of TASS, there exists a 60 km difference in the amplitude of the major component, that is considered as a system difference. The limited interval ephemeris makes the influence of the proper frequency, which brings the error into the long period term like the one from the node of Titan. For nearly all other components, those amplitudes and phases are similar with the relative terms of TASS. The error of our representation is less than 100 kilometres over 1,000 years and the standard deviation is about 26 kilometres

AIMS: We develop a new theoretical framework to generate Besançon Galaxy Model Fast Approximate Simulations (BGM FASt) to address fundamental questions of the Galactic structure and evolution performing multi-parameter inference. The flexibility of BGM FASt allows the inference of fundamental parameters related to the stellar initial mass function (IMF), the star formation history (SFH), the density distribution, the kinematics and the chemo-dynamics, among others. BGM FASt allows the study of different Milky Way (MW) components. In this thesis we are focused in a first application of our strategy to simultaneously infer the IMF and the SFH of the MW disc. METHOD: BGM FASt is based on a reweighing scheme, that uses a specific pre-sampled simulation. We use BGM FASt together with an approximate Bayesian computation algorithm to obtain the posterior probability distribution function of the inferred parameters, by automatically comparing synthetic versus observed data. Our full strategy is codified to run on Apache Spark and Hadoop, suited to deal with large surveys. BGM FASt is implemented in the big data infrastructure known as Gaia Data Analytics Framework (GDAF) at the University of Barcelona. To evaluate the performance of BGM FASt we execute a set of validation tests comparing density, colour, mass and age distributions of BGM FASt versus BGM standard simulations. We present two scientific cases that compare synthetic versus Tycho-2 colour-magnitude diagrams. We obtain for the first time using BGM an IMF and SFH of the thin disc by exploring a 6-Dimensional parameter space. We use Gaia data-release 2 magnitudes, colours, and parallaxes for stars with G<12 to explore a parameter space with 15 dimensions. This includes simultaneously the IMF and, for the first time, a non-parametric SFH for the Galactic disc. RESULTS: The set of tests applied show a very good agreement between equivalent simulations performed with BGM FASt and standard BGM. It has resulted to be 10000 times faster. We demonstrate it is a very valuable tool to perform multi-parameter inference using large catalogues. The two scientific demonstration cases of our strategy applied to Tyhco-2 data gives us, for the first time using BGM, a full 6D posterior probability distribution function of the parameters involved in the IMF and the SFH of the thin disc component. Using Gaia DR2 we find an imprint of a star formation burst 2-3 Gyr ago in the Galactic thin disc domain. Our results show a decreasing trend followed by a Star Formation Rate (SFR) enhancement starting at about 5 Gyr ago and continuing until about 1 Gyr ago. This enhancement is detected with high statistical significance by discarding the null hypothesis of an exponential SFH. The timescale and the amount of stellar mass generated during this SFR enhancement event lead us to hypothesise that its origin, currently under investigation, is not intrinsic to the disc. When we adopt a non-parametric SFH the resulting IMF for the thin disc has an alpha3 of approximately 2 for masses M larger than 1.53 Msun and alpha2 approximately 1.3 for the mass range between 0.5 and 1.53Msun. CONCLUSIONS: BGM FASt has allowed us to increase our knowledge about the IMF and the SFH of the MW disc. Our results have shown that the evolution of the SFR with time is much more complex than a simple mathematical exponential decreasing shape. We have seen how the imposition of a mathematical shape for the SFH has a clear impact into the derivation of the IMF at high masses. The good performance of our whole strategy opens very promising perspectives, among them, the possibility to study whether the IMF variates with the time or not.

Velmi přesná následná astrometrie je nezbytným předpokladem sledování blízkozemních objektů, které mohou představovat riziko srážky se Zemí. Tato práce přináší ucelený přehled přesné astrometrie, obsahuje potřebnou matematickou teorii, postup předzpracování snímků v astronomii, a nastiňuje použití filtrů. Navrhuje nové metody pro vyrovnání pozadí snímků před provedením astrometrického měření pro případ, kdy nejsou dostupné kalibrační snímky. Tyto metody jsou založeny na vytvoření syntetického flatfieldu pomocí aplikování filtru na snímek a následné užití tohoto flatfieldu pro odstranění pozadí snímku. Metody byly otestovány na vzorových snímcích a vzápětí použity k získání astrometrických pozic prvního mezihvězdného objektu 1I/2017 U1 ('Oumuamua).

Nowadays, CCD observations are widely used to determine astrometric positions of minor planets differentially. Especially, follow-up observational programs require to produce and analyse a large number of CCD frames. This dissertation discusses the methods which are used to process such astrometrical CCD frames and extract scientific information from them. These methods are then combined into a complete astrometric software package. Among all corrections which have to be taken into consideration, special attention is given to the effects of differential chromatic refraction (DCR). It is demonstrated how the influence of DCR can be reduced using the photometric data of reference stars taken from the UCAC2 catalogue. In this way, for several test frames a gain in positional accuracy of about 15 percent has been achieved at a zenith distance of 65 degrees. Furthermore, different measurement algorithms of the image positions as well as the properties of several transformation models for the conversion between measured and tangential coordinates are analysed. In addition, the algorithm for automatic identification of reference stars is improved. With respect to the analysis of frames taken through follow-up observations of minor planets, software requirements are formulated. Considering these aspects the automatic universal computer program MpCCD has been developed and is presented and tested here. Particularly, it is compared to other astrometric applications, which are advised to be employed for the determination of minor planet positions by the IAU's Minor Planet Center. The developed software is able to measure positions of minor planets with high accuracy. For a series of test frames an average uncertainty of 62mas in the positions was achieved. This uncertainty is similar to the accuracy level of the UCAC2 catalogue used for the analysis<br>Für Zwecke der differentiellen astrometrischen Positionsbestimmung von Kleinplaneten werden heutzutage verbreitet CCD-Beobachtungen eingesetzt. Insbesondere im Rahmen von Follow-up-Beobachtungsprogrammen sind eine Vielzahl von Aufnahmen herzustellen und auszuwerten. In dieser Arbeit werden Verfahren zur Auswertung solcher astrometrischer CCD-Aufnahmen diskutiert und später zu einem kompletten Messsystem für Kleinplaneten zusammengefügt. Unter den zu berücksichtigenden Korrekturen erhalten die Effekte der differentiellen chromatischen Refraktion (DCR) besondere Aufmerksamkeit. Es wird demonstriert, wie sich der Einfluss der DCR verringern lässt, indem die fotometrischen Angaben des Referenzsternkataloges UCAC2 hinzugezogen werden. Für Testaufnahmen ergaben sich so Verbesserungen der Lagegenauigkeit von 15 Prozent bei einer Zenitdistanz von 65 Grad. Des Weiteren werden verschiedene Messalgorithmen für Bildpositionen sowie die Eigenschaften diverser Transformationsmodelle für die Überführung von gemessenen in Tangentialkoordinaten untersucht. Außerdem erfolgt eine Weiterentwicklung des Algorithmus zur automatischen Identifikation von Referenzsternen. In Hinblick auf die Auswertung von Follow-up-Beobachtungen von Kleinplaneten werden Anforderungen an Software formuliert. Das nach diesen Gesichtspunkten entwickelte automatische universelle Computerprogramm MpCCD wird vorgestellt und getestet. Insbesondere findet ein Vergleich mit anderen astrometrischen Programmen statt, die vom Minor Planet Center der IAU zur Positionsbestimmung von Kleinplaneten empfohlen werden. Die entwickelte Software ist in der Lage, Positionen von Kleinplaneten mit hoher Genauigkeit zu ermitteln. Die für eine Reihe von Testaufnahmen verbliebenen Positionsunsicherheiten der Neupunkte von durchschnittlich 62mas liegen im Bereich der Koordinaten-Unsicherheiten des zur Auswertung verwendeten Referenzsternkataloges UCAC2

Open clusters are groups of stars, gravitationally bound together, that were born from the same molecular cloud and, thus, share similar positions, kinematics, ages and metallicities. Traditional methods to detect open clusters rely in the visual inspection of regions of the sky to look for positional overdensities of stars, which then are checked to follow an isochrone pattern in a colour-magnitude diagram. The publication of the second Gaia data release, with more than 1.3 billion stars with parallax and proper motion measurements together with mean photometry in three broadbands, boosted the development of novel machine learning-based techniques to automatise the search for open clusters, using both the astrometric and photometric information. The characterised open clusters in the Galaxy are popular tracers of properties of the Galactic disc such as the structure and evolution of the spiral arms, or testbed for stellar evolution studies for instance, because their astrophysical parameters are estimated with greater precision than for field stars. Therefore, a good understanding of the open cluster population in the Milky Way is key for Galactic archaeology studies. Our aim for this thesis is to transform classical methodologies to detect different kinds of patterns from astronomical data, that mostly relies on visual inspection, to an automatic data mining procedure to extract meaningful information from stellar catalogues. We also aim to use the result of the application of machine learning techniques to Gaia data, in a broader Galactic context. We have developed a data mining methodology to blindly search for open clusters in the Galactic disc. First, we use a density-based clustering algorithm, DBSCAN, to search for overdensities in the five-dimensional astrometric parameter space in Gaia data. The deployment of the clustering step in a Big Data environment, at the MareNostrum supercomputer located in the Barcelona Supercomputing Center, prevents the search to be limited by computational limitations. Second, the detected overdensities are classified into mere statistical or physical overdensities using an artificial neural network trained to recognise the isochrone pattern that open cluster member stars follow in a colour-magnitude diagram. We estimate astrophysical parameters such as ages, distances and line-of-sight extinctions for the whole open cluster population using an artificial neural network trained on well-known open clusters. We use this additional information, together with radial velocities gathered from different space-based and ground-based surveys, to trace the Galactic spiral present-day structure using GaussianMixtureModels to associate the young (< 30 Myr) open clusters to their mother spiral arms. We also describe the spiral arms evolution during the last 80 Myr to provide new insights into the nature of the Milky Way spiral structure. The automatization of the open cluster detection procedure, together with its deployment in a Big Data environment, has resulted in more than 650 new open clusters detected with this methodology. The new UBC clusters (named after the University of Barcelona) represent one-third of the actual open clusters census (2017 objects with Gaia DR2 parameters), and it is the largest single contribution to the open cluster catalogue. We are able to add 264 young open clusters (< 30 Myr) to the 84 high-mass star- forming regions traditionally used to trace spiral arms, to increase the Galactocentric azimuth range where the Milky Way spiral arms are defined, and better estimate their present-day parameters. By analysing the age distribution of the open clusters across the Galactic spiral arms, and computing the spiral arms pattern speeds following the open clusters orbits from their birthplaces, we are able to disfavour classical density waves as the main mechanism for the formation of the Milky Way spiral arms, favouring a transient behaviour. This thesis has shown that the use of machine learning, with proper treatment of the computational resources, has a long journey ahead in a data-dominated future for Astronomy.<br>Els cúmuls estel·lars oberts són conjunts d'estels, lligats gravitatòriament, nascuts al mateix núvol molecular que tenen propietats similars. Aquests cúmuls són traçadors populars de la estructura del disc Galàctic, com ara els braços espirals. El segon llançament de dades de Gaia, amb més de 1300 milions d'estels, impossibilita la detecció de cúmuls a partir de mètodes tradicionals degut al gran volum del catàleg. Per això, el desenvolupament de tècniques automàtiques per aquest fi ha crescut juntament amb el volums dels catàlegs a analitzar. Hem desenvolupat una metodologia per a la cerca a cegues de cúmuls oberts al disc Galàctic. Hem utilitzat un algoritme de clustering, DBSCAN, per trobar sobredensitats en l'espai astromètric de cinc dimensions de Gaia. La implementació del mètode de clustering a un entorn de Big Data, al superordinador MareNostrum, ens permet cercar cúmuls oberts basant-nos en les seves propietats físiques. Les sobredensitats detectades s'identifiquen com a cúmuls oberts reals per mitjà d'una xarxa neuronal artificial que reconeix isòcrones en un diagrama de color-magnitud. L'automatització del procediment de detecció amb l'ús de tècniques de Big Data, ha resultat en més de 650 nous cúmuls. Aquests nous cúmul representen un terç de la població actual, i és la contribució individual més gran al catàleg. Hem pogut estimar les propietats físiques dels cúmuls com distància, edat i extinció, fent servir una xarxa neuronal artificial entrenada sobre cúmuls coneguts. Fem servir aquesta informació, juntament amb mesures de velocitat radial, per traçar l'estructura espiral actual de la nostra Galàxia associant els cúmuls oberts més joves (< 30 milions d'anys) al braç espiral on s'han format. Amb això, hem augmentat el nombre de traçadors de braços espirals, afegint 264 cúmuls joves als traçadors utilitzats tradicionalment. Això ens ha permès estimar millor els paràmetres actuals d'aquests braços. Analitzant la distribució en edat dels cúmuls dins dels braços espirals, i calculant la velocitat en la que aquests braços es mouen a partir de l'orbita dels cúmuls, hem pogut desfavorir la teoria clàssica d'ona de densitat com a mecanisme principal de formació de l'estructura espiral, trobant un comportament més transitori dels braços.

We report on recent advancement in the theory of light propagation in the Solar System aiming at sub-micro-arcsecond level of accuracy: (1) A solution for the light ray in 1.5PN approximation has been obtained in the field of N arbitrarily moving bodies of arbitrary shape, inner structure, oscillations, and rotational motion. (2) A solution for the light ray in 2PN approximation has been obtained in the field of one arbitrarily moving pointlike body.

In the study of Very High-Energy (VHE) astrophysical phenomena the next generation of Imaging Atmospheric Cherenkov Telescopes (IACT) will play a key role thanks to specific ground-based astronomical observations. In this context, the ASTRI project developed a novel instrument endowed with a Schwarzschild-Couder dual-mirror optical configuration (that has never been adopted before in gamma-ray astronomy) and a dedicated Cherenkov camera entirely designed by the Istituto Nazionale di Astrofisica (INAF) based on SiPM sensors. The prototype telescope ASTRI– Horn is located in Italy and carried out successfully in 2019 the techno- logy validation phase, paving the way for the realization of the MiniAr- ray: 9 identical telescopes working in stereoscopic mode to be installed in Tenerife (Canary Islands) within the next three years. However, several issues related to the pointing performances emerged during operations with ASTRI–Horn. Actually, the pointing calibration is generally a critical aspect for Cherenkov telescopes, as their cameras are designed for the detection of nanosecond atmospheric flashes rather than for imaging the starfield and, consequently, it is impossible to use the standard astrometry of the focal plane. Furthermore, in the case of ASTRI, the compactness of the mechanical structure prevents from installing an auxiliary monitoring camera sharing the same optical system of the telescope. Despite these difficulties, the optimization of the pointing performances is crucial for ensuring the scientific accuracy of the whole system. The present PhD thesis aims at the development and validation of new astrometric techniques for the pointing calibration of the ASTRI telescope exploiting the so-called Variance method, a statistical algorithm implemented in the Cherenkov camera electronic board. Thanks to the Variance, the AS- TRI telescope is endowed with an ancillary output owning the potentiality to image the stellar component of the night sky background in the Field of View (FoV), with a quite coarse angular resolution (~11°, corresponding to the pixel size of the Cherenkov camera), but a relatively good sensitivity for an IACT (visual magnitude limit ~7). As we discuss in this document the Variance constitutes a unique opportunity for enhancing the pointing performances of the telescope, and we demonstrate that our procedures offer a chance to reach the critical accuracy level required for achieving the scientific objectives of the ASTRI project. Unfortunately, in this period the COVID-19 pandemic and other accidental events, heavily delayed the maintenance operations on the ASTRI– Horn telescope, and up to now it is still impossible to make new observations dedicated to the validation of our procedures, hence only data taken in previous months were used. As in any other experimental activity, new data taken on purpose would have considerably facilitated our work, but due to the present situation, we focused our attention on Variance data available in the ASTRI archive that has never been explored before. The resulting work represents the first complete and detailed analysis of the Variance method together with its numerous unexplored applications. Our custom astrometry techniques allowed us to reveal that ASTRI–Horn was affected by two kinds of systematic errors, that we characterized and measured for the first time. The experience gained with archive data allowed us to understand how to apply our routines for calibrating the incoming ASTRI MiniArray, indicating an effective strategy to match the crucial requirement for the pointing accuracy. The resulting procedure has already been inserted into the calibration plan of the MiniArray and its Online Observation Quality System (OOQS). The structure of the present document is articulated in eight chapters and three appendices, whose content can be summarized as follows. Chapter 1 presents the status of the art in VHE astrophysics, focusing on the observational features of cosmic rays and gamma rays, together with a description of the main open questions in this research field. Chapter 2 is dedicated to IACTs, presenting their history and operating principles, and introducing the major examples of instruments currently in activity worldwide. Chapter 3 focuses on the ASTRI project, presenting both the prototype telescope ASTRI–Horn and the incoming observatory of the MiniArray. In particular, it is reported a detailed description of the most relevant sub-systems for this thesis: the camera, the optical scheme, and the pointing strategy. Chapter 4 goes into the details of the Variance method. A technical description of its functioning at the electronic level is provided at first, while the core of the chapter is dedicated to our routines for the production of sky images and their calibration. Chapter 5 reports specific tools and procedures that we developed for the analysis of Variance images: the astrometric calibration, the de-convolution of the star signal, and the transformation function to correct the artifacts introduced by the geometric arrangement of the pixels. Chapter 6 describes the algorithm to assess the alignment of the Cherenkov camera to the optical axis of the telescope exploiting the apparent rotation of the FoV during long observing runs in tracking mode. Chapter 7 shows a custom procedure for the star identification developed on purpose for Variance images (as it is impossible to adopt the standard astrometry software for their analysis) allowing to monitor in real-time the actual pointing direction of the telescope. Chapter 8 contains the concluding remarks. It summarizes the main results achieved in this thesis, highlighting their importance but also some limitations and suggesting further improvements. Future perspectives of this work are briefly presented at last, with particular attention to its implementation on the incoming ASTRI MiniArray. At the end of this document, three appendices report additional/complementary material concerning respectively metrological techniques for the inspection of shape and reflectivity of primary mirror segments (A), more details about the software developed for this thesis and the access to it (B), and the massive activity of outreach and education carried out during the doctoral period in the field of Cherenkov astronomy (C).

L'etude presentee ici concerne la prediction et l'observation des occultations d'etoiles par les asteroides. Le sujet traite comprend la modelisation et le developpement d'algorithmes de predictions des occultations stellaires completes par l'amelioration de leur precision a travers des considerations theoriques et observationnelles. Pour cela je developpe dans un premier temps toutes les definitions relatives aux ephemerides en m'attachant plus particulierement aux notions de reperes et systemes de references celestes et terrestres. Je presente ensuite les differentes echelles de temps s'y rattachant pour finalement proposer des algorithmes de calculs d'ephemerides des planetes, des asteroides et des etoiles avec une precision interne de l'ordre de 1 mas. Je developpe alors un modele de prediction des occultations stellaires en presentant une methode de recherche systematique de ces phenomenes et un algorithme de calcul des lieux sur terre d'ou ils sont observables. Je decris quelles en sont les approximations et montre que dans l'etat actuel de la connaissance des orbites des asteroides, le taux de reussite observationnel des predictions d'occultations ne depasse guere 40% quelque soit le degre de precision du modele utilise. Je propose alors des solutions pour ameliorer la prediction de ces phenomenes en completant le modele de calcul presente ici, et en recherchant a travers l'observation astronomique des solutions pour ameliorer la connaissance astrometrique et photometrique des asteroides. Enfin, je montre qu'il est possible d'atteindre un taux de reussite compris entre 70% et 80%, et presente quelles sont les conditions pour parvenir a un taux de reussite superieur a 90%.

Ingeniero Civil Eléctrico<br>En la Astronomía ha habido un salto cuantitativo gigantesco desde el nacimiento de la tecnología CCD y las imágenes digitales. A pesar de ello, todavía existe un espacio de mejora en lo que respecta a las técnicas para estimación de parámetros importantes que caracterizan a las estrellas. Es por eso que esta Memoria de Título se presenta como objetivo el estudiar y cuantificar el uso de nuevos enfoques de estimación modernas no aplicados aún en esta disciplina para la estimación de la posición de objetos luminosos (Astrometría). Para poder entender el problema se presenta qué es una cámara digital y su uso en la astronomía, especificamente en la astrometría, además de presentar importantes conceptos astronómicos que se usan a lo largo de la memoria, como lo son el Point Spread Function y el Full Width at Half Maximum. Por otro lado, se da un repaso a los elementos de estimación necesarios para resolver el problema, como Cramér-Rao, Cramér-Rao Bayesiano y los estimadores Esperanza Condicional, Maximum Likelihood y Least Squares. La implementación del estimador se realizará a partir de una formalización completa del problema de estimación en astrometría, donde se incluirá también el trabajo de los algoritmos necesarios para encontrar el valor numérico tanto del estimador como de su error cuadrático medio. Se mostrará también la resolución de la cota de Cramér-Rao, tanto para la versión paramétrica como la bayesiana. Se hace un análisis de las herramientras presentadas usando como figura de mérito el MSE (Error Cuadrático Medio). A partir de ello, se muestra cómo varía este valor como función del tamaño del pixel, la relación de señal-ruido y sus ganancias relativas, para posteriormente estudiar las diferencias entre la Cota Bayesiana de Cramér-Rao y el MSE de la Esperanza Condicional, el estimador propuesto para el problema. Finalmente se concluye, viendo que existen ganancias significativas del enfoque Bayesiano en regímenes de baja relación señal-ruido y gran tamaño de pixel. Además se verifica que la cota Bayesiana de Cramér-Rao es un buen predictor del MSE de la Esperanza Condicional, lo cual trae nuevas preguntas que se pueden plantear como trabajo futuro a partir de esta Memoria de Título.

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<br>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

En 1992, l'agence spatiale europeenne chargeait un comite d'experts d'etablir les priorites scientifiques des ses futures grandes missions spatiales. En reponse, ce comite recommandait a l'esa l'initiation d'un programme en interferometrie avec deux objectifs. Le premier est la realisation d'observations astrometriques avec des precisions de l'ordre de 10 micro-secondes d'arc et le second, la detection de planetes extra-solaires en interferometrie infrarouge. Dans ce memoire, apres un rappel des grands principes de l'interferometrie, je presente les etudes de concepts d'interferometres adaptes a chacun des types de mission identifies precedemment. Dans une premiere partie, plusieurs configurations d'interferometres sont presentees, compatibles avec la mission d'astrometrie globale gaia et permettant la detection directe des franges dans un plan image. Ces configurations font l'objet d'une analyse comparative, suivi d'une proposition d'architecture pour la configuration retenue. Dans une deuxieme partie, je presente l'etude, dans la cadre de la mission darwin de l'esa, d'un concept d'interferometre dedie a la detection de planetes extra-solaires dans le domaine spectral de l'infrarouge thermique. Les principes de l'interferometrie a frange noire sont rappelees, et les performances en terme de temps d'integration du concept retenu, compose de 6 telescopes collecteurs de 1. 5 m de diametre en orbite a 1 u. A. Du soleil, sont estimees. La derniere partie de ce memoire est consacree a l'etude de l'implantation d'un mode imagerie sur le concept d'instrument identifie pour le mode detection de planetes de la mission darwin. L'utilisation d'un seul banc de recombinaison des faisceaux pour realiser les deux missions est propose, en ayant rajoute les fonctionnalites propres a l'imagerie par synthese d'ouverture. Cette partie est completee par une estimation des performances de la mission imagerie.

Thesis (Ph.D.)--George Mason University, 2009.<br>Vita: p. 234. Thesis director: John F. Wallin. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Computational Sciences and Informatics. Title from PDF t.p. (viewed Oct. 11, 2009). Includes bibliographical references (p. 224-233). Also issued in print.

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.<br>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.

Building upon its success with the Hipparcos space astrometry mission launched in 1989, the European Space Agency has agreed to fund the construction of its successor, Gaia, and its launch in 2011. Despite the similarities between the two missions, Gaia will be orders of magnitude more powerful, more sensitive, but also more complex in terms of data processing. Growing from 120,000 stars with Hipparcos to about 120,000E4 stars with Gaia does not simply mean pushing the computing resources to their limits (1 second of processing per star yields 38 years for the whole Gaia-sky). It also means facing situations that did not occur with Hipparcos either by luck or because those cases were carefully removed from the Hipparcos Input Catalogue.<p><p>This manuscript illustrates how some chunks of the foreseen Gaia data reduction pipeline can be trained and assessed using the Hipparcos observations. This is especially true for unresolved binaries because they pop up so far down in the Gaia pipeline that, by the time they get there, there is essentially no difference between Hipparcos and Gaia data. Only the number of such binaries is different, going from two thousand to ten million.<p><p>Although the computing time clearly becomes an issue, one cannot sacrifice the robustness and correctness of the reduction pipeline for the sake of speed. However, owing to the requirement that everything must be Gaia-based (no help from ground-based results), the very robustness of the reduction has to be assessed as well. For instance, the underlying assumptions of some statistical tests used to assess the quality of the fits used in the Hipparcos pipeline might no longer hold with Gaia. That may not affect the fit itself but rather the quality indicators usually accompanying those fits. For the final catalogue to be a success, these issues must be addressed as soon as possible.<p><br>Agrégation de l'enseignement supérieur, Orientation sciences<br>info:eu-repo/semantics/nonPublished

Thesis (PhD) - Faculty of Information and Communication Technology, Faculty of Life and Social Sciences, Swinburne University of Technology, 2009.<br>Submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy, Faculty of Information and Communication Technology, Swinburne University of Technology, 2009. Typescript. Bibliography: p. 165-186.

This thesis describes the development of an astrometric facility at the Sydney University Stellar Interferometer (SUSI) with an aim to measure at high precision the relative astrometry of bright close binary stars and ultimately to detect the presence of exoplanets within those binary star systems through observations of the systems’ perturbed motion. At the core of the facility is a new beam combiner that is phase-referenced to an existing primary beam combiner in the visible wave- length regime. The latter provides post-processed fringe-tracking information to the former for fringe stabilization and coherent integration of pre-recorded stellar fringes using newly developed data reduction software. Interference fringe packets of a binary star are recorded alternately; first the fringe packet of the primary, then the secondary, finally back to the primary again. The measurement of the fringe packet separation is facilitated by an air-filled differential delay line and a network of interferometer-based metrology systems. Characterizations and initial astronomical observations carried out with the dual beam combiner setup demonstrated for the first time the success of the dual-star phase-referencing technique in visible (~1μm) wavelengths. The current astrometric precision is larger than 100μas while the long term astrometric accuracy is yet to be characterized. In a parallel development, a complementary observing method using only the primary beam combiner is also demonstrated in this thesis. Relative astrometry of binary stars up to ~0.8” separation with this technique has been demonstrated to have precision of better than 100μas. A simple detection limit analysis based on a list of target binary stars estimates up to two exoplanet detections can be achieved with SUSI if the new astrometric facility attains precision of 10μas while the primary beam combiner operates at its designed peak performance. Finally, one new stellar companion was resolved and a preliminary astrometry for another suspected companion was estimated from the astronomical observation data collected throughout the course of this thesis.

Les supernovas de type Ia (SNIa) sont des objets transitoires, observables pour une durée de quelques mois et dont la luminosité à son maximum équivaut à celle d'une galaxie entière. Une fois standardisées (c'est à dire corrigées de leurs principales variabilités), elles représentent, un excellent indicateur de distance et ont permis de mettre en évidence, en 1998, ce que l'on peut représenter comme une accélération de l’expansion de l'Univers. Cette thèse s’intéresse à trois points qui concerne l’étude de la cosmologie par les SNIa :En premier lieu on s'intéresse à la chaîne de production des données et à la qualité des images pour le Large Synoptic Survey Telescope (LSST), qui couvrira un large éventail de domaines scientifique, y compris l'observation des SNIa. Actuellement en préparation pour LSST (dont les observations commenceront en 2020), cette chaîne de production a été testée en effectuant le traitement d’images provenant d’un relevé antérieur (champ profond du CFHT). Les paramètres de qualité astrométriques et photométriques présentent une dispersion légèrement supérieure à celle requise par le cahier de charges du LSST. En ce qui concerne la photométrie, les sources de cette dispersion restent à être comprises. Pour ce qui est de l'astrométrie, la qualité obtenue sera vraisemblablement suffisante lorsque l'ajustement par astrométrie simultanée sera implémenté.Ensuite, on propose une méthode permettant de corriger l'effet induit par les vitesses propres des SNIa se trouvant dans des amas de galaxies. En effet, ces vitesses propres sont particulièrement importantes du fait des interactions gravitationnelles, et perturbent la mesure du décalage spectral cosmologique lié à l'expansion de l'Univers. On a pris en compte un échantillon de 145 SNIa à faible décalage spectral (0,005 &lt; z &lt; 0,123), observées par la collaboration Nearby SuperNova Factory. Parmi ces SNIa, 11 SNIa ont été associées à des amas de galaxies. Ces corrections de vitesses propres ont ainsi permis de diminuer la dispersion sur le diagramme de Hubble de 0,137+/-0,36 mag à 0,130 +/- 0,38 mag, pour les SNIa appartenant à des amas. Bien que le poids de ces corrections soit relativement modeste, on a montré qu'elles sont statistiquement significatives. Ce type de corrections pourraient être prises en considération dans de futures analyses cosmologiques. Enfin on s'intéresse à la question de la détectabilité de possibles anisotropies de l’expansion de l'Univers avec les données de SNIa. Étant donné que la distribution spatiale des données actuelles est connue pour limiter la détection d’une anisotropie dans les distances mesurées des SNIa, on a établi des simulations permettant de déterminer si un effet dipolaire d'amplitude comparable à la borne supérieure des observations actuelles (AD=10-3) pourrait être détecté avec les observations futures du LSST. Plusieurs scénarios ont été considérés, chacun considérant un nombre de SNIa différent. Chacun de ces scénarios est étudié suivant deux variantes correspondant à deux directions, l'une (polaire) pour laquelle la distribution de données de LSST serait la plus symétrique possible, l'autre suivant une direction perpendiculaire à celle-ci (équatoriale). On montre que pour les simulations comportant 5000 SNIa, un dipôle d’amplitude AD=10-3 serait détecté indépendamment de sa direction. On constate que la distance statistique entre les distributions obtenues pour un dipôle simulé et les simulations sans dipôle augmente à mesure que le nombre de SNIa simulées est grand. On constate aussi que cette distance statistique est plus grande pour les dipôles alignés sur la direction équatoriale que pour ceux suivant la direction polaire. (...)<br>Type Ia supernovae (SNIa) are transient objects, which remains observable in the optical for a period of a few months, and whose luminosity at its maximum is comparable to that of a whole galaxy. They represent, once standardized (i.e. corrected for their main variabilities), an excellent distance indicator and, in 1998, provided the first evidence for the acceleration of the expansion of the Universe. This thesis investigates three points in the cosmological SNIa pipeline:First, we focused on the data processing and the quality of the images for the Large Synoptic Survey Telescope (LSST), that will provide data for a number of cosmological observables, including the observation of SNIa. In preparation for LSST (which will start operations in 2020), we carried out a similar data processing strategy on images from a previous survey (deep field of CFHT) and compared to the required parameters of LSST. A dispersion slightly higher than that required was obtained. For photometry, although this excess is small, the sources of this dispersion remain to be understood. For astrometry, the obtained quality is likely to be sufficient when simultaneous astrometry fitting will be implemented.In a second moment, we propose a method to correct the effect of peculiar velocities of SNIa inside galaxy clusters. Indeed, these velocities ​​are more important in the clusters of galaxies, because of the gravitational interactions, and the measurement of the cosmological redshift related to the expansion of the Universe. These peculiar velocities were corrected using a sample of 145 SNIa with a low spectral shift (0.005

Studying the motion of black hole systems in our Galaxy allows us to constrain the distances and velocities of these systems. We used radio telescopes around the globe to measure these motions and report the first observationally determined birth velocity distribution for black holes, helping us understand how these objects are born. We used the motion of unclassified radio sources to identify a new subpopulation of possible Galactic black hole candidates.