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van, Saders Jennifer Lynn. "Using Modern Stellar Observables to Constrain Stellar Parameters and the Physics of the Stellar Interior." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1404130939.
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Badenes, Carles, Christine Mazzola, Todd A. Thompson, Kevin Covey, Peter E. Freeman, Matthew G. Walker, Maxwell Moe, et al. "Stellar Multiplicity Meets Stellar Evolution and Metallicity: The APOGEE View." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/627094.
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We use the multi-epoch radial velocities acquired by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to perform a large-scale statistical study of stellar multiplicity for field stars in the Milky Way, spanning the evolutionary phases between the main sequence (MS) and the red clump. We show that the distribution of maximum radial velocity shifts (Delta RVmax) for APOGEE targets is a strong function of log g, with MS stars showing Delta RVmax as high as similar to 300 km s(-1), and steadily dropping down to similar to 30 km s(-1) for log g similar to 0, as stars climb up the red giant branch (RGB). Red clump stars show a distribution of Delta RVmax values comparable to that of stars at the tip of the RGB, implying they have similar multiplicity characteristics. The observed attrition of high Delta RVmax systems in the RGB is consistent with a lognormal period distribution in the MS and a multiplicity fraction of 0.35, which is truncated at an increasing period as stars become physically larger and undergo mass transfer after Roche Lobe overflow during H-shell burning. The Delta RVmax distributions also show that the multiplicity characteristics of field stars are metallicity-dependent, with metal-poor ([Fe/H] less than or similar to -0.5) stars having a multiplicity fraction a factor of 2-3 higher than metal-rich ([Fe/H] less than or similar to 0.0) stars. This has profound implications for the formation rates of interacting binaries observed by astronomical transient surveys and gravitational wave detectors, as well as the habitability of circumbinary planets.
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Burke, Christopher J. "Survey for transiting extrasolar planets in stellar systems stellar and planetary content of the Open Cluster NGC 1245 /." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1132168623.
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Ireland, Lewis George. "Stellar models with magnetism and rotation : mixing length theories and convection simulations." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34350.
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Some low-mass stars appear to have larger radii than predicted by standard 1D structure models; prior work has suggested that inefficient convective heat transport, due to rotation and/or magnetism, may ultimately be responsible. In this thesis, we explore this possibility using a combination of 1D stellar models, 2D and 3D simulations, and analytical theory. First, we examine this issue using 1D stellar models constructed using the Modules for Experiments in Stellar Astrophysics (MESA) code. We begin by considering standard models that do not explicitly include rotational/magnetic effects, with convective inhibition modelled by decreasing a depth-independent mixing length theory (MLT) parameter αMLT. We provide formulae linking changes in αMLT to changes in the interior specific entropy, and hence to the stellar radius. Next, we modify the MLT formulation in MESA to mimic explicitly the influence of rotation and magnetism, using formulations suggested by Stevenson (1979) and MacDonald and Mullan (2014) respectively. We find rapid rotation in these models has a negligible impact on stellar structure, primarily because a star’s adiabat, and hence its radius, is predominantly affected by layers near the surface; convection is rapid and largely uninfluenced by rotation there. Magnetic fields, if they influenced convective transport in the manner described by MacDonald and Mullan (2014), could lead to more noticeable radius inflation. Finally, we show that these non-standard effects on stellar structure can be fabricated using a depth-dependent αMLT: a non-magnetic, non-rotating model can be produced that is virtually indistinguishable from one that explicitly parameterises rotation and/or magnetism using the two formulations above. We provide formulae linking the radially-variable αMLT to these putative MLT reformulations. We make further comparisons between MLT and simulations of convection, to establish how heat transport and stellar structure are influenced by rotation and magnetism, by looking at the entropy content of 2D local and 3D global convective calculations. Using 2D “box in a star” simulations, created using the convection code Dedalus, we investigate changes in bulk properties of the specific entropy for increasingly stratified domains. We observe regions stable against convection near the bottom boundary, resulting in the specific entropy in the bulk of the domain exceeding the bottom boundary value: this could be a result of physical effects, such as increased amounts of viscous dissipation for more supercritical, highly stratified cases, but may also be influenced by the artificial boundary conditions imposed by these local simulations. We then turn to 3D global simulations, created using the convection code Rayleigh, and investigate these same properties as a function of rotation rate. We find the average of the shell-averaged specific entropy gradient in the middle third of the domain to scale with rotation rate in a similar fashion to the scaling law derived via MLT arguments in Barker et al. (2014), i.e., |⟨ds/dr⟩| ∝ Ω^4/5.
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Gazzano, Jean-christophe. "Populations stellaires et systèmes planétaires observés par CoRoT." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10031/document.
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Dans le cadre de ma thèse, j'ai effectué l'analyse spectrale d'un échantillon massif de spectres stellaires dans le contexte du programme exoplanète de la mission CoRoT. J'ai tiré avantage des instruments Flames/GIRAFFE pour observer près de 2000 étoiles dans le but de comprendre les populations stellaires dans les champs CoRoT. Dans ce but, j'ai implémenté, calibré, testé, et appliqué une chaîne de traitement et de réduction fiable et efficace afin de réduire et d'analyser automatiquement (en utilisant l'algorithme de paramétrisation MATISSE, Gazzano et al. 2010) un large échantillon de spectres stellaires. J'ai déterminé la vitesse barycentrique radiale, une estimation de la vitesse de rotation projetée sur la ligne de visée, la température effective, la gravité de surface, de la métallicité global et l'enrichissement des éléments par rapport au fer pour 1 227 étoiles dans trois des champs CoRoT. Ainsi, j'ai construit un des premiers échantillons affranchis de biais de sélection pour toute étude concernant la relation planète métallicité dans les champs CoRoT et démontré que le nombre des étoiles naines a été généralement sous-estimé par la classification photométrique (Exo-Dat, Deleuil et al. 2009). J'ai appliqué la relation reliant le nombre de planètes détectées à la métallicité de l'étoile hôte (Udry & Santos 2007), parfaitement en accord avec le nombre actuel de détection planétaire dans les champs CoRoT correspondant (Gazzano et al. 2010). En utilisant les paramètres atmosphériques MATISSE, nous avons déterminé les distances et nous les avons combinées avec des informations cinématiques (les mouvements propres du catalogue PPMXL - Roeser et al. (2010), et l'astrométrie). Nous avons dérivé les composantes de cinématique Galactique : position et vitesse. Cela m'a permis d'étudier les populations stellaires dans les champs CoRoT /exoplanète et de quantifier le gradient de métallicité dans la Galaxie (Gazzano et al. En préparation). J'ai par ailleurs montré que les étoiles à planètes détectées dans les champs considérés pour ma thèse sont exclusivement des étoiles de disque mince. J'ai également participé au suivi des candidats planète CoRoT à l'aide de spectroscopie à haute résolution. J'ai effectué l'analyse spectrale, avec le logiciel VWA (Bruntt et al. 2010b,a), des étoiles hôtes pour la mission spatiale CoRoT. Ces études ont conduit à la détermination des paramètres fondamentaux de l'étoile, qui est une étape indispensable pour la caractérisation complète de la planèteDuring my Ph.D., I performed the spectral analysis of a massive sample of stellar spectra in the context of the CoRoT /Exoplanet mission. We took advantage of the Flames/GIRAFFE multi-fibre instrument to observe almost 2 000 stars with the aim of understanding the stellar populations in the CoRoT fields. To these purposes, I implemented, calibrated, tested and applied an automatic pipeline to reduce and analyse automatically (using the parameterization algorithm MATISSE, Gazzano et al. 2010) a large sample of stellar spectra. I derived the barycentric radial velocity, an estimate of the rotational velocity projected on the line of sight, the effective temperature, the surface gravity, the overall metallicity and the -enhancement for 1227 stars in three of the CoRoT fields. Hence, I built one of the first unbiased samples for any study regarding planet metallicity relationship in the CoRoT fields and demonstrated that the amount of dwarf stars was generally underestimated by the photometric classification (in Exo-Dat, Deleuil et al. 2009). I applied the relationship linking the number of planets as a function of the metallicity of the host star (Udry & Santos 2007), totally in agreement with the current number of planetary detection in the corresponding CoRoT fields (Gazzano et al. 2010). Using MATISSE atmospheric parameters, we determined distances and combining them with kinematics information (proper motions from PPMXL catalogue - Roeser et al. (2010) and astrometry), we derived Galactic kinematics components : position, velocities and orbits. This allowed me to study the stellar populations in the CoRoT /Exoplanet fields and quantify the metallicity gradient in the Galaxy (Gazzano et al. in preparation). I also participated to the spectroscopic follow-up observations of CoRoT planetary candidates with high resolution spectroscopy, to the spectroscopic analysis, with the VWA software (Bruntt et al. 2010b,a), of planet hosting stars for the CoRoT space mission and to their characterisation and publication. Indeed, the determination of the fundamental parameters of the star is a mandatory step for the complete characterisation of the planet
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Martinez, Arturo O., Ian J. M. Crossfield, Joshua E. Schlieder, Courtney D. Dressing, Christian Obermeier, John Livingston, Simona Ciceri, et al. "Stellar and Planetary Parameters for K2's Late-type Dwarf Systems from C1 to C5." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623204.
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The NASA K2 mission uses photometry to find planets transiting stars of various types. M dwarfs are of high interest since they host more short-period planets than any other type of main-sequence star and transiting planets around M dwarfs have deeper transits compared to other main-sequence stars. In this paper, we present stellar parameters from K and M dwarfs hosting transiting planet candidates discovered by our team. Using the SOFI spectrograph on the European Southern Observatory's New Technology Telescope, we obtained R approximate to 1000 J-, H-, and K-band (0.95-2.52 mu m) spectra of 34 late-type K2 planet and candidate planet host systems and 12 bright K4-M5 dwarfs with interferometrically measured radii and effective temperatures. Out of our 34 late-type K2 targets, we identify 27 of these stars as M dwarfs. We measure equivalent widths of spectral features, derive calibration relations using stars with interferometric measurements, and estimate stellar radii, effective temperatures, masses, and luminosities for the K2 planet hosts. Our calibrations provide radii and temperatures with median uncertainties of 0.059 R-circle dot (16.09%) and 160 K (4.33%), respectively. We then reassess the radii and equilibrium temperatures of known and candidate planets based on our spectroscopically derived stellar parameters. Since a planet's radius and equilibrium temperature depend on the parameters of its host star, our study provides more precise planetary parameters for planets and candidates orbiting late-type stars observed with K2. We find a median planet radius and an equilibrium temperature of approximately 3 R-circle plus and 500 K, respectively, with several systems (K2-18b and K2-72e) receiving near-Earth-like levels of incident irradiation.
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Neilson, Hilding R., and Richard Ignace. "Period Change and Stellar Evolution of β Cephei Stars." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/2689.
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The β Cephei stars represent an important class of massive star pulsators that probe the evolution of B-type stars and the transition from main sequence to hydrogen-shell burning evolution. By understanding β Cep stars, we gain insights into the detailed physics of massive star evolution, including rotational mixing, convective core overshooting, magnetic fields, and stellar winds, all of which play important roles. Similarly, modeling their pulsation provides additional information into their interior structures. Furthermore, measurements of the rate of change of pulsation period offer a direct measure of β Cephei stellar evolution. In this work, we compute state-of-the-art stellar evolution models assuming different amounts of initial rotation and convective core overshoot and measure the theoretical rates of period change, that we compare to rates previously measured for a sample of β Cephei stars. The results of this comparison are mixed. For three stars, the rates are too low to infer any information from stellar evolution models, whereas for three other stars the rates are too high. We infer stellar parameters, such as mass and age, for two β Cephei stars: ξ1 CMa and δ Cet, which agree well with independent measurements. We explore ideas for why models may not predict the higher rates of period change. In particular, period drifts in β Cep stars can artificially lead to overestimated rates of secular period change.
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Posbic, Hélène. "Automatic stellar parameters determination : chemical characterization of the Galactic thick disk and preparation to the Gaia mission." Observatoire de Paris, 2012. https://hal.science/tel-02095129.
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La formation de la Voie Lactée est toujours une question ouverte. Plusieurs scénarios sont proposés. Les différents scénarios prédisent différentes caractéristiques chimiques du disque. Cette thèse a pour but de caractériser chimiquement le disque de la Voie Lactée, dans et en dehors du voisinage solaire, pour contraindre les scénarios de formation de disque. Ceci sera possible grâce à des spectres stellaires de haute résolution de 200 étoiles qui ont été observées avec le spectographe Giraffe sur le Very Large Telescope (VLT). Ces étoiles ont été sélectionnées de sorte à avoir des altitudes galactiques ǀZǀ qui couvrent en espace le disque mince et le disque épais (ǀZǀ jusqu'à 2 kpc). Un nouveau logiciel d'analyse automatique de spectres a été dévoloppé pour déterminer les paramètres stellaires de ces étoiles, plus particulièrement leurs abondances individuelles. SPADES (Stellar PArameters DEtermination Software) est basé sur une analyse raie par raie qui utilise une grille de spectres de référence synthétiques. Une des particularités de SPADES est sa capacité à calculer des spectres synthétiques à la volée. Une fois testé pour déterminer les erreurs internes et externes de la méthode, SPADES a été utilisé pour déterminer les vitesses radiales, températures effectives, gravités de surface, métallicités et abondances individuelles de l'chantillon d'étoiles. Les distances de ces étoiles ont également été déterminées. La fonction de distribution de métallicité du disque a été calculée en utilisant cet échantillon d'étoiles. Elle montre une majorité d'étoiles du disque épais, avec une transition lisse de la métallicité au niveau de l'interface disque épais/halo. Le comportement vertical de la fonction de distribution de métallicité a aussi été étudié. Un grandient vertical de metallicité dans le disque de valeur 0. 19 +/- 0. 14 dex/kpc a été marginalement détecté avec un niveau sigma de 1. 4. Les tendance de [Ti/Fe] et [Ca/Fe] par à [Fe /H] pour les étoiles à moinns de 1 kpc au dessus du plan sont en bon accord avec celles d'études précédentes. Ceci fut la conclusion de la comparaison entre ce travail et celui des auteurs : Bensby et al. (2005), Takeda (2007), et Neves et al. (2009). Le résultat principal de l'analyse est que les tendances de [Ca/Fe] vs [Fe/H] et [Ti/Fe] vs [Fe/H] sont similaires aux basses altitudes (i. E. ǀZǀ < 1 kpc) et aux altitudes plus hautes (1 < ǀZǀ < 2. 5 kpc). Ceci laisse suggérer que les gaz et les étoiles du disque épais ont été enrichis par la même proportion de super novae de type II et type I proche du plan Galactique et jusqu'à des altitudes de 2. 5 kpc et plus. Ces résultats appuient les scénarios de formation du disque épais du genre "collapse" ou accrétion de gaz défavorisant l'idée d'un disque épais formé par capture pendant la fusionThe formation of the Milky Way disk is still an open question. Many scenarios are proposed. Different formation scenarios predict different disk chemical trends. This thesis aims to chemically characterize the Milky Way disk inside and outside the solar neighbourhood, to better constrain its formation scenario. This is possible thanks to high resolution spectra of 200 disk stars observed using the Giraffe spectograph on the Very Large Telescope (VLT). They were selected to have galactic altitudes ǀZǀ that cover both the thin and tick disk (ǀZǀ up to 2 kpc). A new automatic spectra analysis software was developed to determine the stellar parameters, and most importantly, the elemental abundances of these stars. SPADES (Stellar PArameters DEtermination Software) is based on a line-by-line analysis using a reference grid of synthetic stellar spectra. One of its particularities is its ability to calculate synthetic spectra on-the-y. Once tested for internal and external errors, it was used to determine the radial velocity, effective temperature, surface gravity, metallicity and elemental abundances of the smple stars. The distances of these stars were also determined. The metallicity distribution function of the disk using this sample was calculated. It showed a large contribution of the disk stars and a smooth transition at the metallicity of the thick disk/halo interface. The vertivcal behaviour of the metallicity distribution function was also studied. A vertical metallicity grandient in the disk of 0. 19 +/- 0. 14 dex/kpc was marginally detected at the 1. 4 sigma level. The [Ti/Fe] and [Ca/Fe] vs [Fe/H] trends for stars located at less than 1 kpc above the plane were found to be in good agreement with previous studies. This is conclusion from the comparison of this work with author's like Bensky et al. (2005), Takeda (2007), and Neves et al. (2009). The main result of the analysis is that the trends of [Ca/Fe] vs [Fe/H] and [Ti/He] vs [Fe/H] show no significant difference close (i. E. ǀZǀ < 1 kpc) and farther away (1 < ǀZǀ < 2. 5 kpc) from the Galactic plane. This suggests that the thick disk gas and stars have been enriched by the same proportion of type II and type I super-novae from the galactic plane up to at least 2. 5 kpc. These results support thick disk formation scenarios like collapse or gas-rich accretion and disfavour a thick disc formed of stars captured during merger event
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Ekanayake, Gemunu. "Determination of Stellar Parameters through the Use of All Available Flux Data and Model Spectral Energy Distributions." UKnowledge, 2017. http://uknowledge.uky.edu/physastron_etds/44.
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Basic stellar atmospheric parameters, such as effective temperature, surface gravity, and metallicity plays a vital role in the characterization of various stellar populations in the Milky Way. The Stellar parameters can be measured by adopting one or more observational techniques, such as spectroscopy, photometry, interferometry, etc. Finding new and innovative ways to combine these observational data to derive reliable stellar parameters and to use them to characterize some of the stellar populations in our galaxy is the main goal of this thesis.
Our initial work, based on the spectroscopic and photometric data available in literature, had the objective of calibrating the stellar parameters from a range of available flux observations from far-UV to far-IR. Much effort has been made to estimate probability distributions of the stellar parameters using Bayesian inference, rather than point estimates.
We applied these techniques to blue straggler stars (BSSs) in the galactic field, which are thought to be a product of mass transfer mechanism associated with binary stars. Using photometry available in SDSS and GALEX surveys we identified 85 stars with UV excess in their spectral energy distribution (SED) : indication of a hot white dwarf companion to BSS. To determine the parameter distributions (mass, temperature and age) of the WD companions, we developed algorithms that could fit binary model atmospheres to the observed SED. The WD mass distribution peaks at 0.4M , suggests the primary formation channel of field BSSs is Case-B mass transfer, i.e. when the donor star is in red giant phase of its evolution. Based on stellar evolutionary models, we estimate the lower limit of binary mass transfer efficiency β ~ 0.5.
Next, we have focused on the Canis Major overdensity (CMO), a substructure located at low galactic latitude in the Milky Way, where the interstellar reddening (E(B-V )) due to dust is significantly high. In this study we estimated the reddening, metallicity distribution and kinematics of the CMO using a sample of red clump (RC) stars. The averageE(B-V)(~0.19)is consistent with that measured from Schlegel maps (Schlegal et.al. 1998). The overall metallicity and kinematic distribution is in agreement with the previous estimates of the disk stars. But the measured mean alpha element abundance is relatively larger with respect to the expected value for disk stars.
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Bruno, Giovanni. "Characterization of transiting exoplanets : analyzing the impact of the host star on the planet parameters." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4746/document.
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Dans le cadre de ma thèse, j’ai analysé les spectres de neuf étoiles Kepler obtenus avec les relevés de vitesse radiale (VR). Cela a permis la caractérisation de leur compagnons planétaires. J’ai analysé les spectres de 21 autres étoiles CoRoT et Kepler, probablement hôtes de naines M à faible masse. Cela a permis d’'élargir l'échantillon des étoiles à faible masse avec masse et rayon mesurés. J’ai calculé l’indice d’activité chromosphérique de 31 étoiles observées avec SOPHIE/OHP, en aidant l’étude des interactions étoile-planète. J’ai étudié le comportement de SOPHIE à bas signal à bruit (S/B). J’ai déterminé l’intervalle de S/B dans lequel un spectre stellaire est fiable pour la mesure des paramètres stellaires.Dans le cadre du consortium SOPHIE, j’ai suivi l’analyse complète du système Kepler-117. Ce système multi-planétaire montre variations des périodes orbitaux dues aux échanges dynamiques entre les planètes (TTV). Pour déterminer les paramètres du système, un approche spécifique a été développé pour l’ajustement simultané de transits, VR et TTV (Bruno et al. 2015).Finalement, je me suis intéressé à l’activité stellaire dans la photométrie de transit. J’ai impl ́ementé deux logiciels de modélisation de tâches stellaires dans un code MCMC, en ajoutant l’évolution des tâches dans l’un d’eux. J’ai appliqué les logiciels au Soleil, à CoRoT-7 et à CoRoT-2. J’ai amené un étude détaillé de la courbe de lumière de CoRoT-2, et exploré les effets des tâches dans les paramètres du transit (Bruno et al., en prep.). Avec la méthode FF’ (Aigrain et al. 2012), j’ai contribué à l’exploration du lien entre la signature des tâches de CoRoT-7 et dans la photométrie et dans les VRDuring my PhD, I analyzed the spectra of nine Kepler stars obtained by radial velocity (RV) observations. This allowed the characterization of their planetary companions. I analyzed the spectra of twenty-one other CoRoT and Kepler stars, likely orbited by low-mass M dwarfs. This helped widening the sample of low-mass stars with measured mass and radius. I calculated the chromospheric activity indfex of thirty-one stars observed with SOPHIE/OHP, helping the study of star-planet interactions. I studied the behavior of SOPHIE in low signal-to-noise ratio (SNR) regime. I determinhed the SNR range in which a stellar spectrum is reliable for the measure of the stellar parameters.Within the SOPHIE consortium, I followed the complete analysis of the Kepler-117 system. This multi-planetary system presents variations in the planetary orbital periods due to their mutual dynamical interacion (TTVs). To fit the system parameters, a specific fitting approach including TTV modeling was developed. We derived the system parameters by the simultaneous fit of transits, RVs, and TTVs (Bruno et al. 2015).Finally, I addressed the problem of stellar activity in transit photometry. I implemented two starspot modeling codes into an MCMC algorithm, adding spot evolution to oneof them. I applied the codes to the Sun, CoRoT-7, and CoRoT-2. I carried an extensive study on the light curve of CoRoT-2, and explored the effects of the spots on the transit parameters (Bruno et al., in prep.). With the FF’ method (Aigrain et al. 2012), I contributed to explore the connection between the photometric and RV signature of starspots in CoRoT-7
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Rajpurohit, Arvind Singh. "Low-mass stars as tracers of the milky way populations : investigating the effects of metallicity in cool atmosphere." Thesis, Besançon, 2013. http://www.theses.fr/2013BESA2023/document.
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Les étoiles de petite masse (naines M) forment la composante stellaire dominante de notre galaxie et contribuent à la majeure partie de la matière baryonique dans la galaxie. Notre compréhension de la galaxie repose donc sur la connaissance de cette composante peu lumineuse. Par ailleurs, un nombre grandissant d’exoplanètes sont découverte autour de naines M, y compris des super-terres. L’étude des naines M a ainsi des implications importantes sur la physique stellaire, permettant de comprendre les processus en jeu dans ces atmosphères froides. Ces astres restent cependant peu connus du fait de leur faible luminosité intrinsèque. La description de ces étoiles nécessite une validation empirique fort, notamment en ce qui concerne les effets de l’abondance chimique sur la physique des atmosphères froides.Le but de cette thèse est de déterminer les paramètres fondamentaux des naines M et de tester les modèles d’atmosphères d’étoiles froides.Dans la première partie nous comparons des spectres calibrés dans le visible et l’infrarouge des composantes de système triple LHS 1070 avec des spectres synthétiques. Cette étude permet d’améliorer notre compréhension de la formation de la poussière dans les atmosphères très froides. Ce travail est étendu à un échantillon de naines M et permet de déterminer l’échelle de température des naines M. La seconde partie présente l’analyse des spectres à haute résolution de 21 naines M de faible métallicité (sous naines). Nous analysons en détail les signature moléculaires et atomiques dans le spectre. La comparaison avec des spectres synthétiques permet de mesurer les paramètres stellaires des étoiles et de déterminer avec précision leur métallicité. Ce travail doit initier des recherches futures. En particulier nous voulons étendre cette étude dans le domaine proche-infrarouge pour s’assurer que les résultats obtenus sont cohérents du domaine optique jusqu’à l’infrarouge procheVery Low-Mass stars (M dwarfs) are an important source of information for probing the lowmass end of the main sequence, down to the hydrogen burning limit. They are the dominantstellar component of the Galaxy and make up the majority of baryonic matter in the Galaxy.Moreover, an increasing number of M dwarfs are now known to host exoplanets, includingsuper-Earth exoplanets. The determination of accurate fundamental parameters for M dwarfshas therefore relevant implications for both stellar and Galactic astronomy as well as planetology.Despite their large number in the Galaxy, M dwarfs remain elusive objects and themodelling of their photosphere has long remained a challenge (molecular opacities, dust cloudformation). The description of these stars therefore need a strong empirical basis, or validation.In particular, the effect of metallicity on the physics of cool atmospheres are still poorly known,even for early-type M-dwarfs.[...]
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McCarthy, Kyle. "Characterizing the Nearest Young Moving Groups." UKnowledge, 2015. http://uknowledge.uky.edu/physastron_etds/30.
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Moving groups are associations of stars which originated from the same star forming region. These groups are typically young (< 200 Myr) since they have not dissipated into the galactic field population. Over the last 15 years, roughly 10 such moving groups have been found with distances < 150 pc (7 with distances < 100 pc), each with a unique velocity and position.
This work first investigates the likelihood to resolve star from two moving groups (AB Doradus and Beta Pictoris) using high spacial resolution optical interferrometry and found 5 AB Doradus stars and 1 Beta Pictoris star with declinations > -30 could be spacially resolved.
To more deeply characterize individual groups, we used the 2.7m telescope at the McDonald Observatory to observe 10 proposed AB Doradus stars and 5 proposed Octans-Near stars (3 probable members, 2 possible) with high resolution (R ~60,000) optical spectroscopy. Each group is characterized in three ways: (1) Chemical analysis to determine the homogeneity among members, (2) Kinematic traceback to determine the origin, and (3) Isochrone fitting to determine the age. We find the 8 stars in our AB Doradus sample are chemically homogeneous with [M/H] = -0.03 ± 0.06 dex, traceback to an age of 125 Myr, and the stars in this mass range are on the main sequence. The two deviants are a metal rich, potentially younger member and a metal poor, young star likely not associated with AB Doradus.
In our Octans-Near sample, we find the 3 probable members have [M/H] = -0.06 ± 0.11, the stars do not trace back to a common origin, and the probable members are on the main sequence. In addition to these tests, we found that the probable members are slightly more lithium depleted than the Pleiades, implying an age between 125 and 200 Myr.
Finally, we investigate systematic trends in fundamental stellar parameters from the use of different techniques. Preliminary results find differences in temperatures between interferrometric and spectroscopic techniques to be a function of temperature with a interferrometric temperatures being cooler by an average of 36 ± 115 K. We also calculated the chemical abundances as a function of condensation temperature for our moving group sample and predict 2 stars in AB Doradus could represent the initial star forming environment and discuss the implications for planet hosting stars in nearby moving groups.
This updated characterization technique allows for a deeper understanding of the moving group environment. As future, high precision instruments emerge in astronomy (Jame Webb Space Telescope, GAIA, 30m class telescopes), moving groups are ideal targets since these associations will help us understand star forming regions, stellar evolution at young ages, constrain stellar evolutionary models, and identify planetary formation and evolution mechanisms.
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Neyskens, Pieter. "Exploring S stars: stellar parameters, abundances and constraints on the s-process from a new grid of model atmospheres." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209358.
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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
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Levenhagen, Ronaldo S., Marcos P. Diaz, Paula R. T. Coelho, and Ivan Hubeny. "A Grid of Synthetic Spectra for Hot DA White Dwarfs and Its Application in Stellar Population Synthesis." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624926.
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In this work we present a grid of LTE and non-LTE synthetic spectra of hot DA white dwarfs (WDs). In addition to its usefulness for the determination of fundamental stellar parameters of isolated WDs and in binaries, this grid will be of interest for the construction of theoretical libraries for stellar studies from integrated light. The spectral grid covers both a wide temperature and gravity range, with 17,000 K <= T-eff <= 100,000 K and 7.0 <= log g <= 9.5. The stellar models are built for pure hydrogen and the spectra cover a wavelength range from 900 angstrom to 2.5 mu m. Additionally, we derive synthetic HST/ACS, HST/WFC3, Bessel UBVRI, and SDSS magnitudes. The grid was also used to model integrated spectral energy distributions of simple stellar populations and our modeling suggests that DAs might be detectable in ultraviolet bands for populations older than similar to 8 Gyr.
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van, der Wel A., K. Noeske, R. Bezanson, C. Pacifici, A. Gallazzi, M. Franx, J. C. Muñoz-Mateos, et al. "THE VLT LEGA-C SPECTROSCOPIC SURVEY: THE PHYSICS OF GALAXIES AT A LOOKBACK TIME OF 7 Gyr." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/614714.
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The Large Early Galaxy Census (LEGA-C-16) is a Public Spectroscopic Survey of similar to 3200 K-band selected galaxies at redshifts z. =. 0.6 - 1.0 with stellar masses M-* > 10(10) M-circle dot, conducted with VIMOS on ESO's Very Large Telescope. The survey is embedded in the COSMOS field (R.A. = 10h00; decl. = +2 deg). The 20 hr long integrations produce high-signal-to-noise ratio continuum spectra that reveal ages, metallicities and velocity dispersions of the stellar populations. LEGA-C's unique combination of sample size and depth will enable us for the first time to map the stellar content at large lookback time, across galaxies of different types and star formation activity. Observations started in 2014 December and are planned to be completed by mid 2018, with early data releases of the spectra and value-added products. In this paper we present the science case, the observing strategy, an overview of the data reduction process and data products, and a first look at the relationship between galaxy structure and spectral properties, as it existed 7 Gyr ago.
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Guo, Yicheng, David C. Koo, Yu Lu, John C. Forbes, Marc Rafelski, Jonathan R. Trump, Ricardo Amorín, et al. "STELLAR MASS–GAS-PHASE METALLICITY RELATION AT 0.5 ≤ z ≤ 0.7: A POWER LAW WITH INCREASING SCATTER TOWARD THE LOW-MASS REGIME." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621237.
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We present the stellar mass (M-*)-gas-phase metallicity relation (MZR) and its scatter at intermediate redshifts (0.5 <= z <= 0.7) for 1381 field galaxies collected from deep spectroscopic surveys. The star formation rate (SFR) and color at a given M-* of this magnitude-limited (R less than or similar to 24 AB) sample are representative of normal star-forming galaxies. For masses below 10(9) M-circle dot, our sample of 237 galaxies is similar to 10 times larger than those in previous studies beyond the local universe. This huge gain in sample size enables superior constraints on the MZR and its scatter in the low-mass regime. We find a power-law MZR at 10(8) M-circle dot < M-* < 10(11) M-circle dot: 12 + log (O/H) = (5.83 +/- 0.19)+(0.30 +/- 0.02) log (M-*/M-circle dot). At 10(9) M-circle dot < M-* < 10(10.5) M-circle dot, our MZR shows agreement with others measured at similar redshifts in the literature. Our power-law slope is, however, shallower than the extrapolation of the MZRs of others to masses below 10(9) M-circle dot. The SFR dependence of the MZR in our sample is weaker than that found for local galaxies (known as the fundamental metallicity relation). Compared to a variety of theoretical models, the slope of our MZR for low-mass galaxies agrees well with predictions incorporating supernova energy-driven winds. Being robust against currently uncertain metallicity calibrations, the scatter of the MZR serves as a powerful diagnostic of the stochastic history of gas accretion, gas recycling, and star formation of low-mass galaxies. Our major result is that the scatter of our MZR increases as M-* decreases. Our result implies that either the scatter of the baryonic accretion rate (sigma((M) over dot)) or the scatter of the M-*-M-halo relation (sigma(SHMR)) increases as M-* decreases. Moreover, our measure of scatter at z = 0.7 appears consistent with that found for local galaxies. This lack of redshift evolution constrains models of galaxy evolution to have both sigma((M) over dot) and sigma(SHMR) remain unchanged from z = 0.7 to z = 0.
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Watson, Victor. "Estimation de paramètres physiques à partir de leur description par une base de mesure de très grande dimension." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30091/document.
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Cette thèse contribue au développement de diverses méthodes permettant la détermination des paramètres stellaires fondamentaux (température effective, gravité de surface et "métallicité" i.e., la composition chimique globale), ainsi que de la vitesse de rotation projetée (vsini), à partir de l'analyse de spectres à haute résolution. Plusieurs méthodes seront présentées, et leurs performances respectives en terme d'extraction des paramètres fondamentaux seront discutées. Nous mettrons en particulier l'accent sur une mise en œuvre originale de la méthode dite Sliced Inverse Regression (SIR, Watson et al. 2017)This thesis contributes to the development of various methods for the determination of the stellar fundamental parameters (effective temperature, surface gravity and "metallicity" ie, the overall chemical composition), as well as the projected rotation speed (vsini), from the analysis of high resolution spectra. Several methods will be presented, and their respective performances in terms of extraction of the fundamental parameters will be discussed. In particular, we will focus on an original implementation of the Sliced Inverse Regression method (SIR, Watson et al., 2017)
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Neilson, Hilding R., Joseph T. McNeil, Richard Ignace, and John B. Lester. "Limb Darkening and Planetary Transits: Testing Center-to-limb Intensity Variations and Limb-darkening Directly from Model Stellar Atmospheres." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/2684.
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The transit method, employed by Microvariability and Oscillation of Stars (MOST), Kepler, and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough to begin to measure planet atmosphere composition, planetary oblateness, starspots, and other phenomena at the level of a few hundred parts per million. However, these results depend on our understanding of stellar limb darkening, that is, the intensity distribution across the stellar disk that is sequentially blocked as the planet transits. Typically, stellar limb darkening is assumed to be a simple parameterization with two coefficients that are derived from stellar atmosphere models or fit directly. In this work, we revisit this assumption and compute synthetic planetary-transit light curves directly from model stellar atmosphere center-to-limb intensity variations (CLIVs) using the plane-parallel Atlas and spherically symmetric SAtlas codes. We compare these light curves to those constructed using best-fit limb-darkening parameterizations. We find that adopting parametric stellar limb-darkening laws leads to systematic differences from the more geometrically realistic model stellar atmosphere CLIV of about 50–100 ppm at the transit center and up to 300 ppm at ingress/egress. While these errors are small, they are systematic, and they appear to limit the precision necessary to measure secondary effects. Our results may also have a significant impact on transit spectra.
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Larson, Ana Marie. "A study of high quality, near-infrared spectra of eight spectral type of K stars: precise radial velocities, chromospheric emission, and fundamental stellar parameters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21938.pdf.
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Queiroz, Anna Bárbara de Andrade. "Star horse : a Bayesian tool for determining masses, ages, distances and extinction for field stars." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/180515.
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Nos encontramos em uma localização vantajosa para o estudo da formação e evolução de galáxias espirais. Situados no disco da Via-Láctea, somos capazes de fazer observações detalhadas sobre as estrelas individuais que a compõem. Com o avanço tecnológico das últimas décadas, foi possível coletar um grande conjunto de informações, (e.g. composição química, cinemática, astrometria e parâmetros atmosféricos), com alta resolução para uma vasta parte do volume Galáctico. Com o objetivo de compreender melhor a nossa Galáxia, desenvolvemos uma ferramenta, chamada StarHorse, que estima parâmetros como distâncias, idades, massas e avermelhamento utilizando informação disponível em levantamentos espectroscópicos, fotométricos e astrométricos. O código StarHorse estima os parâmetros através de um método Bayesiano, que constrói uma distribuição de probabilidade a partir do cálculo de verossimilhança entre observações e modelos de evolução teórica e a partir de priores Galácticos bem conhecidos. Os parâmetros que o StarHorse estima são cruciais para estudos de arqueologia Galáctica. Com eles é possível investigar a estrutura, o histórico de formação estelar, a função de massa inicial, o mapa tridimensional da nossa Galáxia e também adicionar vínculos a modelos quemodinâmicos da Via Láctea Neste trabalho, focaremos na descrição e validação do método, testando sua aplicabilidade em levantamentos recentes de espectroscópica, astrometria e fotometria. Também disponibilizamos catálogos com distâncias e extinção para comunidade astronômica. As nossas distâncias e extinções se tornaram referência dentro da colaboração APOGEE e foram liberadas junto com o seu Data Release 14. Ademais, catálogos foram liberados para os surveys RAVE, Gaia-ESO e GALAH. Neste trabalho, exploramos os resultados do StarHorse, especialmente os resultados APOGEE, em um contexto amplo de arqueologia Galáctica.We are in an advantageous position to study the formation and evolution of disk galaxies. By being inside the Milky Way, we are able to make detailed observations about the individual stars that compose it. With the technological revolution of the latest years, it has been possible to collect a massive set of information, (e.g. chemical composition, kinematics, astrometry, and atmospheric parameters), with high resolution for a large portion of the Galactic volume. With the goal to understand better our Galaxy, we developed a tool, called StarHorse, that can estimate distances, ages, masses, and extinction from the available spectroscopic, astrometric, and photometric information. StarHorse makes these estimates through a Bayesian method, that builds a probability distribution over the models by calculating a likelihood function between observation and stellar evolution models, and by using common knowledge about our Galaxy as priors. The parameters that StarHorse estimates are crucial to Galactic archaeology studies. With them, we can investigate the structure, the star formation history, the initial mass function, the three-dimensional dust map of our Galaxy, and provide constraints to chemodynamical models of the Milky Way. In this work, we focus on the description and validation of the method, testing its applicability in recent spectroscopic and astrometric surveys. We also make available catalogs with distances and extinctions to the astronomy community. Our distances and extinctions became a reference inside the APOGEE-team and were released as part of the SDSS Data Release 14. Moreover, we made available catalogs also to other spectroscopic surveys such as Gaia-ESO, RAVE, and GALAH. In this work, we also explore these results, especially for APOGEE, in a broad Galactic archaeology context.
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Farrington, Christopher Donald. "The Separated Fringe Packet Survey: Updating Multiplicity of Solar-Type Stars within 22 Parsecs." Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/phy_astr_diss/26.
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Over the past half century, multiplicity studies have provided a foundation for the theories of stellar formation and evolution through understanding how likely it is that stars form alone or with companions. If spectroscopic orbits are combined with techniques that can determine visual orbits, we can access the most fundamental parameter of stellar evolution, stellar mass. This dissertation is composed of two main sections. The first involves the investigation of the seminal multiplicity study of Duquennoy & Mayor (1991b) which has been the ``gold standard" for solar-type stars for nearly 20 years. Improvements in technology in the intervening years have improved the measurement accuracy for radial velocities and distances on which the study was based. Using Georgia State University's CHARA Array to search the systems in Duquennoy & Mayor's multiplicity survey for overlooked companions along with a literature search covering regimes unreachable by the CHARA Array, we have found that more than 40% of the Duquennoy & Mayor's sample was further than originally believed and the uncorrected multiplicity percentages change from 57:38:4:1:0% (single:double:triple:quad:quint%) to 48:42.5:7.5:1:1% with the discoveries of multiple previously undiscovered companions. The second part of this project describes the application of separated fringe packets for resolving the astrometric position of secondaries with small angular separations on long-baseline optical interferometers. The longest baselines of the CHARA Array allow access to a previously inaccessible range of separations compared with other techniques (<40 milliarcseconds) and the ability to very accurately angularly resolve a large number of single- and double-lined spectroscopic binaries. Combining astrometric and spectroscopic orbits provides assumption-free stellar masses and using the CHARA Array allows access to many previously unreachable systems available for high-accuracy mass determinations. We report the first angular separation measurements of seven spectroscopic binary systems, five additional separated fringe packet detections, ten systems with probably overlapping fringe packets, four systems with new data on pre-existing orbits, one completely new visual orbit for a SB2 system previously unresolved, and the detection of two previously unknown companions.
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Challouf, Mounir. "Caractérisation interférométrique de la relation brillance de surface-couleur des binaires à éclipse et étalonnage des échelles de distance dans l'univers." Thesis, Nice, 2015. http://www.theses.fr/2015NICE4023/document.
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La mesure des distances aux galaxies proches de notre Voie Lactée a révolutionné notre compréhension de l'échelle de distance et a fourni la preuve de l'expansion de l'univers. Notamment les distances aux Petit et Grand Nuages de Magellan sont deux échelons essentiels de l'échelle des distances cosmiques. De nombreuses méthodes indépendantes (comme celle des RR Lyrae, des Céphéides ou des étoiles Red clump) ont été utilisées pour déterminer ces distances. Le but de mon travail de thèse est d'améliorer notre compréhension de la relation BSC grâce à l'interférométrie optique. Pour cela, j'ai utilisé l'instrument VEGA installé sur l'interféromètre CHARA. Cet instrument fonctionne dans le visible et bénéficie de la plus longue base du monde. VEGA a une résolution spatiale de 0.3 mas, ce qui en fait un outil idéal pour une détermination précise des diamètres des étoiles. Dans un premier temps j'ai déterminé le diamètre de huit étoiles de type OBA avec une précision moyenne de 1.5%. Ensuite j'ai combiné ces diamètres avec d'autres mesures collectées dans la littérature pour ainsi donner une nouvelle relation BSC pour ce type d'étoiles. Dans un second temps, une étude théorique de l'impact de rotation sur la relation BSC a été faite pour comprendre les effets physiques influant sur la précision de cette relation de manière à compenser la dispersion existant actuellement et ce dans le but d'améliorer encore la précision sur les distances extragalactiquesMeasuring distances separating our own Galaxy from nearby ones revolutionized our understanding of the distance scale and provided the evidence for the expansion of the universe. The distances to the Small and Large Magellanic Clouds are critical steps of the cosmic distance ladder, and they have been determined using numerous independent methods (as, RR Lyrae stars, Cepheids and "red clump" stars). The aim of my thesis work is to improve our understanding of the Surface Brightness-Color relation (SBC) using optical interferometry. For this, we use the interferometer VEGA on CHARA. This instrument operates in the visible and benefits from the baselines of the CHARA interferometer. It has a spatial resolution of 0.3 mas, which makes it an ideal tool to determine diameters of stars. At first I determined the diameter of eight OBA-type stars with an average accuracy of 1.5%. Then I combined these diameters with others collected from the literature, to determine a new SBC relation for this type of stars. In a second step, a theoretical study of the impact of the rotation on the SBC relation was made to understand the physical effects affecting the accuracy of this relation and suppress the currently existing dispersion in order to further improve the accuracy of extragalactic distances
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Burnett, Benedict. "Stellar parameter estimation from spectrophotometric data." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526545.
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Correia, Caio F?bio Teixeira. "Par?metros f?sico-qu?micos de estrelas com planetas na miss?o CoRoT." Universidade Federal do Rio Grande do Norte, 2011. http://repositorio.ufrn.br:8080/jspui/handle/123456789/18596.
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In the present study we compute the atmospheric parameters (Teff , log g and vmic, [Fe/H]) and chemical abundance of 16 ions (Fe I, Fe II, O I, Si I, Na I, Mg I, Al I, Ca I, Ti I, Co I, Ni I, Rb I, Zr I, Ba II, La II and Cr I) for 16 solar-like stars with masses between 0:8 and 1:2 Mfi aproximatedly, including 10 planet-host stars detected by the CoRoT Space Mission. For this study, we use data from the ESO public archive: (i) high resolution spectra (R 47000) from the UVES spectrograph on the VLT/UT2-ESO (for 7 stars, covering the wavelength range 3450-4515 ? and 5500-9400 ?) and (ii) high resolution spectra from HARPS spectrograph on the La Silla-ESO 3.60 m telescope (for 9 stars, covering the wavelength range 4200-6865 ?). Our spectral analysis is based on MARCS models of atmosphere and Turbospectrum spectroscopic tools. On the base of the computed parameters, the referred abundances appears to follow the same behavior of the solar curve abundances. Further, one observes a signifficant correlation between the abundance ratio [m/Fe] and condensation temperature (Tc) of refractory elements (Tc > 900 K). The behavior of the projected rotational velocity (v sin i) versus the computed abundances [m/Fe] is also analyzed, presenting no clear trends. This study oers additional constraints to trace the evolutive history of solar-like stars with planets, including the search for chemical dierences between stars with and without transit planets and anomalies in the studied abundances
No presente estudo, n?s determinamos os par?metros atmosf?ricos (Teff , log g, vmic e [Fe/H]) e as abund?ncias qu?micas de 16 ?ons (Fe I, Fe II, O I, Si I, Na I, Mg I, Al I, Ca I, Ti I, Co I, Ni I, Rb I, Zr I, Ba II, La II e Cr I) para 16 estrelas solares, com massas entre 0:8 e 1:2 M , aproximadamente, incluindo 10 estrelas com planetas detectados pelo telesc?pio espacial CoRoT. Para este estudo, foram usados dados do arquivo p?blico do ESO: (i) espectros de alta resolu??o (R 47000) do espectr?grafo UVES localizado no VLT/UT2- ESO (para 7 estrelas, cobrindo o dom?nio espectral de 3450-4515 ? e 5500-9400 ?) e (ii) espectros de alta resolu??o obtidos com o espectr?grafo HARPS localizado no telesc?pio de 3,60 m, em La Silla-ESO (para 9 estrelas, cobrindo a faixa de 4200-6865 ?). Nossa an?lise espectral ? baseada nos modelos de atmosfera MARCS e nas ferramentas espectrosc?picas do Turbospectrum. Com base nos par?metros obtidos, as abund?ncias referidas parecem seguir tend?ncia semelhante ? curva de abund?ncias solares. Adicionalmente, observa-se uma correla??o signi cativa entre a abund?ncia relativa [m/H] e a temperatura de condensa??o (Tc) dos elementos refrat?rios (Tc > 900 K). O comportamento da velocidade rotacional projetada (v sin i) em fun??o das abund?ncias obtidas tamb?m ? analisada, n?o apresentando correla??es claras. Este estudo oferece v?nculos adicionais para o tra?ado da hist?ria evolutiva de estrelas solares com planetas, incluindo a busca por diferen?as qu?micas entre estrelas com e sem planetas em tr?nsito, e por anomalias nas abund?ncias estudadas
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García, Pérez Ana E., Carlos Allende Prieto, Jon A. Holtzman, Matthew Shetrone, Szabolcs Mészáros, Dmitry Bizyaev, Ricardo Carrera, et al. "ASPCAP: THE APOGEE STELLAR PARAMETER AND CHEMICAL ABUNDANCES PIPELINE." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621372.
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The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has built the largest moderately high-resolution (R approximate to 22,500) spectroscopic map of the stars across the Milky Way, and including dust-obscured areas. The APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) is the software developed for the automated analysis of these spectra. ASPCAP determines atmospheric parameters and chemical abundances from observed spectra by comparing observed spectra to libraries of theoretical spectra, using. 2 minimization in a multidimensional parameter space. The package consists of a FORTRAN90 code that does the actual minimization and a wrapper IDL code for book-keeping and data handling. This paper explains in detail the ASPCAP components and functionality, and presents results from a number of tests designed to check its performance. ASPCAP provides stellar effective temperatures, surface gravities, and metallicities precise to 2%, 0.1 dex, and 0.05 dex, respectively, for most APOGEE stars, which are predominantly giants. It also provides abundances for up to 15 chemical elements with various levels of precision, typically under 0.1 dex. The final data release (DR12) of the Sloan Digital Sky Survey III contains an APOGEE database of more than 150,000 stars. ASPCAP development continues in the SDSS-IV APOGEE-2 survey.
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Trahin, Boris. "Étalonnage de l'échelle des distances dans l'ère Gaia : les étoiles pulsantes RR Lyrae et Céphéides." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEO018.
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Les étoiles pulsantes sont utilisées pour estimer les distances dans l’Univers, au moyen de la relation liant leur période de pulsation à leur magnitude absolue. La calibration de cette relation période-luminosité est réalisée via la détermination de distances indépendantes, notamment par la méthode de la parallaxe de pulsation. Cependant, la précision de cette méthode est aujourd’hui encore principalement limitée par le facteur de projection (p-facteur), un paramètre permettant de remonter à la vitesse pulsante de l’étoile à partir des vitesses radiales mesurées par spectroscopie. Mon travail de thèse a consisté à utiliser le code SPIPS (Spectro-Photo-Interferometry of Pulsating Stars) afin de parvenir à une détermination précise du p-facteur. Reprenant le principe de la parallaxe de pulsation, ce code permet d’obtenir une meilleure précision statistique des paramètres fondamentaux d’une étoile pulsante, grâce à une modélisation simultanée des observables spectroscopique, photométrique et interférométrique. L’utilisation de cette méthode en fixant une distance mesurée indépendamment permet alors de remonter à la valeur du p-facteur. En vue d’une utilisation à grande échelle du code SPIPS, j’ai effectué dans un premier temps un important travail d’optimisation et de collecte de données de la littérature. Ces catalogues ainsi que diverses observations réalisées tout au long de ces trois années (avec entre autres l’instrument PIONIER du VLTI) m’ont permis de construire une base de données complète et homogène de plus de 300 étoiles. L’objectif de ma thèse fût alors d’appliquer le code SPIPS à un large échantillon d’étoiles, en utilisant les parallaxes du second catalogue du satellite Gaia. Au moyen de ces parallaxes, j’ai tout d’abord pu calculer avec précision le p-facteur de quelques variables de type RR Lyrae. Appliqué dans un second temps à un plus grand échantillon de Céphéides, le code SPIPS m’a permis de déterminer une relation linéaire entre le p-facteur et la période de pulsation, aboutissant à un nouvel étalonnage de la relation période-luminosité. Ces résultats prometteurs du code SPIPS laissent envisager que les prochaines publications de données du satellite Gaia permettront de lever le voile sur la nature du p-facteur, remettant ainsi au premier plan la méthode de la parallaxe de pulsation dans l’étalonnage de l’échelle des distances et la détermination de la constante de HubblePulsating stars are used to determine distances in the Universe owing to the relation between their pulsation period and absolute magnitude. The calibration of this period-luminosity relation is performed through the determination of independant distances, in particular with the parallax of pulsation method. However, the accuracy of this method is still mainly limited by the projection factor, a parameter used to convert radial velocities measured from spectroscopy into the true pulsating velocity of the star. The objective of this thesis is to use the SPIPS (Spectro-Photo-Interferometry of Pulsating Stars) algorithm to precisely determine this p-factor. Based on the parallax of pulsation approach, this code allows to obtain a better precision on the fundamental parameters of a pulsating star, thanks to a simultaneous modeling of the observables (spectroscopy, photometry and interferometry). Using this method while fixing an independent distance estimate allowed me to retrieve the value of the p-factor. In view of a large scale use of the SPIPS code, I first did an important work of optimization and data collection. These catalogs as well as various observations I made throughout these three years (with among others the PIONIER instrument of the VLTI) allowed me to create a complete and heterogeneous database of more than 300 stars. I then apply the SPIPS algorithm to a large sample of stars using the parallaxes from the second data release of the Gaia satellite. Using these parallaxes, I was first able to accurately calculate the p-factor of some RR Lyrae type variables. Applied to a larger sample of Cepheids, the SPIPS code allowed me to determine a linear relation between the p-factor and the pulsation period, resulting in a new calibration of the period-luminosity relation. These promising results of the SPIPS code suggest that the future releases of the Gaia satellite will unveil the nature of the p-factor, bringing the parallax of pulsation method to the forefront of in the calibration of the distance scale and the determination of the Hubble constant
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Lee, Young Sun. "The SEGUE Stellar Parameter Pipeline and the alpha elements of stars in the Milky Way." Diss., Connect to online resource - MSU authorized users, 2008.
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Thesis (Ph.D.)--Michigan State University. Dept. of Physics and Astronomy, 2008.Title from PDF t.p. (viewed on July 22, 2009) Includes bibliographical references (p. 243-249). Also issued in print.
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Rusomarov, Naum. "Magnetic fields and chemical maps of Ap stars from four Stokes parameter observations." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-278535.
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Our knowledge of stellar magnetic fields relies almost entirely on circular polarization observations, which has historically limited our understanding of the stellar magnetic field topologies. Recently, it has become possible to obtain phase-resolved high-resolution spectropolarimetric observations in all four Stokes parameters for early-type magnetic stars. Interpretation of such observations with the Magnetic Doppler imaging technique has uncovered a new, previously unknown, level of complexity of surface stellar magnetic fields. This new insight is critical for understanding the origin, evolution and structure of magnetic fields in early-type stars. In this study we observed the magnetic, chemically peculiar Ap stars HD 24712 (DO Eri, HR 1217) and HD 125248 (CS Vir, HR 5355) in all four Stokes parameters with the HARPSpol spectropolarimeter at the ESO 3.6-m telescope. The resulting spectra have high signal-to-noise ratio and superb resolving power, by far surpassing the quality of any existing stellar Stokes parameter observations. We studied variation of the spectrum and magnetic observables of HD 24712 as a function of rotational phase (paper I). In the subsequent magnetic Doppler imaging investigation of this star, we interpreted the phase-resolved Stokes line profile observations (paper II). This analysis showed that HD 24712, unlike more massive Ap stars studied in all four Stokes parameters, has a dominant dipolar field component with a negligible contribution of small-scale magnetic structures. Simultaneously with magnetic mapping we derived surface abundance distributions of Fe, Nd, Na, and Ca. Building upon the technique of Magnetic Doppler imaging, we developed the first three-dimensional abundance inversion code and applied it to reconstruct the abundance distributions of Fe and Ca in three dimensions in the atmosphere of HD 24712 (paper III). We also performed Magnetic Doppler imaging analysis of the spectropolarimetric observations of HD 125248 (paper IV). The reconstructed detailed maps of the surface abundance distribution and magnetic field topology of HD 125248 revealed a magnetic field with significant deviations from the canonical dipolar field geometry, and strong surface abundance inhomogeneities for Cr and several rare earth elements. We assessed our inversion results in the context of magnetic Doppler imaging studies of other magnetic, chemically peculiar Ap stars and latest theoretical research on the evolution and stability of magnetic fields in radiative stellar interiors. Our analysis suggests that old or less massive Ap stars have predominantly dipolar magnetic fields while more massive or younger stars exhibit more complicated field topologies. We also compared our three-dimensional chemical abundance maps of HD 24712 to the predictions of theoretical atomic diffusion calculations in magnetized stellar atmospheres, generally finding a lack of agreement between theory and observations.
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Okeng'o, Geoffrey Onchong’a. "A theoretical study of stellart pulsations in young brown dwarfs." Thesis, University of the Western Cape, 2011. http://hdl.handle.net/11394/2567.
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Magister Scientiae - MscThis thesis reports the results of a twofold study on the recently proposed phenomenon of ‘stellar pulsations’ in young brown dwarfs by the seminal study of Palla and Baraffe (2005) (PB05, thereafter). The PB05 study presents results of a non-adiabatic linear stability analysis showing that young brown dwarfs should become pulsationally unstable during the deuterium burning phase of their evolution.
South Africa
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Jones, Caitlin Dawn. "Stellar variance for asteroseismic parameter estimation and inferences on the evolutionary state and binary population of red giant stars." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8444/.
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The latest generation of space missions have performed large scale observations of stars and this has been revolutionary in the field of asteroseismology. The ability to characterise thousands of stars has been instrumental in understanding the interiors of stars and the evolution of the Galaxy. This thesis focuses on studying red giant stars, both on an individual basis and as a population, using a robust asteroseismic metric we define based on the bandpass filtered estimate of the stellar variance. Here we present results of testing asteroseismic scaling relations, and the assumptions needed to create realistic simulated power spectra. The resulting synthetic datasets then inform three other investigations. We present the results of an investigation into determining the binary population of Kepler red giant branch stars using our variance metric. The inferred fraction of 57.4 +/- 2.5% is consistent with previous work on main sequence stars. Results of using our variance metric as part of an analysis pipeline, designed to automate the detection of solar-like oscillations and determine global asteroseismic parameters in K2 and CoRoT data are presented. Finally, we present a discussion of using ourvariance metric to highlight structural differences between red giant branch and red clump stars.
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Rosetti, Lorenzo. "Calibrazione di un banco prova per la determinazione d'assetto di un satellite tramite sensore di stelle." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14321/.
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La possibilità di determinare l'assetto di un satellite tramite comparazione di foto del cielo stellato è sempre più in voga. Per fare ciò ci si avvale di sistemi cosiddetti "star tracker". Essi si basano su fotocamere commerciali che necessitano di un'approfondita calibrazione da eseguire a terra. In questo lavoro di tesi si è replicato, in laboratorio, il set-up dei componenti costitutivi di uno star tracker.
Dopo l'esposizione del metodo matematico della proiezione dei punti dallo spazio 3D al piano immagine della CCD, si è proceduto con la calibrazione della camera, sfruttando il software nativo di Image processing, in ambiente Matlab, e si è eseguito l'allineamento della camera con il monitor. Sono stati, quindi, discussi i risultati sia della calibrazione, sia dell'allineamento.
Infine si è presentato un possibile algoritmo da implementare in Matlab (a valle della calibrazione) per ottenere i 3 angoli di Eulero che determinano l'assetto del satellite.
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Titarenko, Anastasia. "Indicateurs chimiques d’âge stellaire à l’ère de Gaia." Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4065/document.
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Les étoiles enregistrent le passé dans leurs âges, leurs compositions chimiques et leur cinématique. Elles peuvent fournir des contraintes détaillées sur les premières époques de la formation des galaxies, jusqu’aux redshifts supérieurs à deux (un recul d’environ 10 milliards d’années). En particulier, les âges stellaires sont essentiels pour la compréhension de l’histoire de la Voie Lactée et pour la comparaison avec les modèles d’évolution galactique.L’avènement de la mission spatiale Gaia ouvre la voie à l’estimation de l’âge pour de grands échantillons d’étoiles. En particulier, les méthodes basées sur l’ajustement d’isochrones peuvent être utilisées. En plus, les distances précises mesurées par Gaia permettent de développer les estimateurs d’âge indirects basés sur l’horloge d’évolution de la population stellaire. En fait, les schémas d’abondance chimique, imprimés sur les atmosphères stellaires, représentent les conditions du gaz au moment de la formation des étoiles à des redshifts supérieurs à deux. Les produits d’évolution chimique de différents canaux nucléosynthétiques peuvent donc fournir une approximation temporelle, qui, après l’étalonnage, peut être utilisé comme un estimateur d’âge.Cette thèse est centrée sur l’utilisation d’horloge chimique particulière : l’abondance [Y/Mg]. À cette fin, les premières données astrométriques de la mission Gaia ont été combinées avec des données spectroscopiques à haute résolution du catalogue AMBRE HARPS. Tout d’abord, l’identification des objets d’AMBRE a été améliorée grâce à la correspondance avec le catalogue 2MASS et la Gaia DR1. Au total, 6776 étoiles ont été identifiées.Deuxièmement, afin d’obtenir des estimations précises du rapport d’abondance [Y/Mg] pour les étoiles du disque galactique, l’outil automatisé GAUGUIN, intégré à la chaîne Gaia DPAC APSIS, a été optimisé et testé. En particulier, les capacités d’estimation d’abondances chimiques ont été améliorées pour des grilles de spectres synthétiques irrégulières, couvrant une large gamme de paramètres atmosphériques stellaires.Troisièmement, le ratio [Y/Mg] a été estimé pour environ 2000 étoiles à partir des données spectroscopiques d’AMBRE HARPS. Les erreurs internes et externes des abondances ont été soigneusement analysées. Les étoiles étudiées appartiennent principalement aux disques mince et épais galactique, dans la gamme de métallicité allant de –1,0 dex à 0,5 dex.Quatrièmement, grâce à l’estimation d’âge basée sur l’adaptation des isochrones pour 342 "turn-off" étoiles d’échantillon, la sensibilité à l’âge du rapport [Y/Mg] a été étudié. L’analyse révèle une corrélation claire entre [Y/Mg] et l’âge pour les étoiles du disque mince de différentes métallicités. Cela correspond aux études antérieures sur les étoiles de type solaire. De plus, aucune dépendance à la métallicité avec l’âge stellaire n’est détectée, donc le ratio [Y/Mg] peut être utilisé comme un indicateur fiable d’âge. Enfin, la relation [Y/Mg] versus l’âge présente une discontinuité entre les étoiles du disque épais autour de 9–10 Gyrs. Pour ces étoiles, la corrélation est différente et a une tendance probablement plus forte avec l’âge. Cela reflète la différence dans les histoires d’évolution chimique pour les deux composantes du disqueStars record the past in their ages, chemical compositions and kinematics. They can provide unprecedented detailed constraints on the early epochs of galaxy formation, back to redshifts greater than two (a look-back time of around 10 billion years). In particular, stellar ages are crucial to the understanding of the Milky Way history and for comparison with galactic evolution models. The advent of the Gaia space mission has opened the path to stellar age estimations for large samples of stars, in particular, based on isochrone fitting methods. In addition, Gaia precise distances allow to develop indirect age estimations based on the stellar population chemical evolution clock. In fact, the chemical abundance patterns imprinted on stellar atmospheres represent the gas conditions at the time of the stars’ formation back to redshifts greater than two. The chemical evolution products of different nucleosynthetic channels can therefore provide a time proxy. After calibration, it can be used as an age estimator.This thesis is focussed on the use of a particular chemical clock, the [Y/Mg] abundance. To this purpose, the astrometric Gaia mission data from the first data release was combined with high resolution spectroscopic data from the AMBRE-HARPS catalogue. First of all, the object identification of the AMBRE archival data was improved, thanks to a cross match with the 2MASS catalog, and later the Gaia DR1. In total, 6776 different stars have been identified.Secondly, in order to obtain precise estimations of the [Y/Mg] abundance ratio for galactic disc stars, the automated GAUGUIN tool integrated in the Gaia DPAC APSIS chain, has been optimized and tested. In particular, the abundance estimation capabilities of the APSIS GAUGUIN tool have been improved for irregularly distributed synthetic spectra grids, spanning a large range in stellar atmospheric parameters.Thirdly, the [Y/Mg] abundance ratio has been estimated for about 2000 stars from the AMBRE HARPS spectroscopic data. In addition, the internal and external errors of the abundances were carefully analysed. The studied stars belong mainly to the galactic thin and thick disc, in the metallicity range from --1.0 dex to 0.5 dex.Fourth, thanks to the isochrone fitting age estimations of 342 turn-off stars of the sample, the age sensitivity of the [Y/Mg] ratio has been studied. The analysis reveals a clear correlation between [Y/Mg] and age for thin disk stars of different metallicities, in synergy with previous studies of Solar type stars. In addition, no metallicity dependence with stellar age is detected, allowing to use the [Y/Mg] ratio as a reliable age proxy.Finally, the [Y/Mg] vs. age relation presents a discontinuity between thin and thick disk stars around 9–10 Gyrs. For thick disk stars, the correlation has a different zero point and probably a steeper trend with age, reflecting the different chemical evolution histories of the two disk components
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Stelzer, Corinna [Verfasser], and Martin J. [Gutachter] Herrmann. "Effekte der nicht-invasiven aurikulären Vagusnervstimulation auf Hirnaktivierungsmuster, kognitive Parameter und Befindlichkeit / Corinna Stelzer ; Gutachter: Martin J. Herrmann." Würzburg : Universität Würzburg, 2017. http://d-nb.info/1144862604/34.
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Borghi, Nicola. "Una nuova stima del parametro di Hubble a z ∼ 0.7 attraverso i cronometri cosmici." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21447/.
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In questo lavoro di Tesi, è stata studiata una sonda cosmologica alternativa, i cronometri cosmici, per porre vincoli sul tasso di espansione dell'Universo a partire dai dati della survey LEGA-C. Il metodo dei cronometri cosmici consente di ottenere una misura diretta del parametro di Hubble H(z) studiando l'età differenziale di popolazioni omogenee di galassie, senza bisogno di dover assumere alcun modello cosmologico. Questo metodo viene implementato, per la prima volta in letteratura, attraverso lo studio degli indici spettrali di galassie passive individuali sfruttando l'ottima risoluzione R∼3500 e rapporto segnale-rumore S/N∼20 degli spettri della Data Release 2 della survey LEGA-C. 350 galassie massive e passive sono state estratte dal campione parente incrociando criteri spettro-fotometrici per massimizzarne la purezza. Tramite il metodo degli indici spettrali si estraggono età, metallicità stellare e arricchimento α delle popolazioni stellari di ogni singola galassia del campione. La combinazione di indici utilizzata (HδA, Ca4227, G4300, HγA, HγF, Fe4383, Fe4531, C4668) è stata scelta in seguito a un'analisi estensiva volta a massimizzare la robustezza dei risultati. Si derivano età di galassie comprese tra 2.5 e 5 Gyr, in ottimo accordo con l'età dell'Universo per una cosmologia ΛCDM standard. Inoltre, [Z/H] e [α/Fe] sono in accordo con i valori misurati nell'Universo locale e consistenti con un'evoluzione puramente passiva. Attraverso la relazione età-redshift mediana sono stati esplorati vincoli ai parametri cosmologici, ottenendo, per un universo ΛCDM piatto, una stima indipendente della costante di Hubble, H0=70.0^+28.7_-18.5 km/s/Mpc. Applicando il metodo dei cronometri cosmici, è stata derivata una nuova misura del parametro di Hubble, H(z=0.72) = 96.1 ± 35.1 km/s/Mpc, per la prima volta ottenuta tramite il metodo degli indici di assorbimento. Verifiche svolte con altre combinazioni di indici confermano l'attendibilità di questo risultato.
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Fanfani, Valentina. "Selezione di un campione ottimizzato di "cronometri standard" per la stima del parametro di Hubble." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17900/.
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Il metodo dei cronometri cosmici consente di misurare H(z) attraverso la datazione differenziale delle età delle popolazioni stellari delle galassie "early-type" massive e passive, che assumono il ruolo di “orologi standard” nell'Universo. Questo lavoro di tesi è incentrato sulla selezione di un campione ottimizzato di "orologi standard" a partire dagli spettri della survey spettroscopica ad alta risoluzione LEGA-C, in quanto una buona selezione consente di ridurre e tenere sotto controllo gran parte degli errori sistematici sulle stime di H(z). La prima parte della tesi descrive la selezione delle galassie effettuata a partire dagli spettri della Data Release 2 della survey, tramite l'uso simultaneo di tre criteri diagnostici (fotometrico, spettroscopico e ispezione visuale degli spettri), che ha fornito un campione di 245 "orologi standard" di cui si sono analizzate anche le proprietà fisiche. Nella seconda parte della tesi, l’analisi è stata svolta su un campione di 65 "orologi standard" estratti dalla Data Release 1 della survey, e si è incentrata sullo studio di diagnostici in grado di quantificare il livello di contaminazione residua da parte di una popolazione giovane sottostante la popolazione vecchia dominante che, se non è opportunamente tenuta in considerazione, può inficiare la stima di H(z) fino ad un valore del 20%. Si è quindi analizzata l'emissione ultravioletta nelle SED fotometriche, dimostrandone la trascurabilità. Si è poi applicato il metodo diagnostico spettroscopico basato sul rapporto delle righe del Ca II H/K per la prima volta a dati reali, sia misurandolo come rapporto tra i minimi delle righe, sia formulandone una nuova definizione basata sul rapporto integrale tra le due righe, tramite le misure di due nuovi "pseudo" indici di Lick da noi definiti. Si è quindi quantificata la contaminazione sul campione di "orologi standard" tramite un confronto con andamenti teorici dei rapporti H/K derivati da una libreria di spettri sintetici.
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Nascimento, Sanzia Alves do. "Propriedades f?sicas de planetas extrasolares." Universidade Federal do Rio Grande do Norte, 2008. http://repositorio.ufrn.br:8080/jspui/handle/123456789/18579.
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ROTATION is one the most important aspects to be observed in stellar astrophysics. Here we investigate that particularly in stars with planets. This physical parameter supplies information about the distribution of angular momentum in the planetary system, as well as its role on the control of dierent phenomena, including coronal and cromospherical emission and on the ones due of tidal effects. In spite of the continuous solid advances made on the study of the characteristics and properties of planet host stars, the main features of their rotational behavior is are not well established yet. In this context, the present work brings an unprecedented study about the rotation and angular momentum of planet-harbouring stars, as well as the correlation between rotation and stellar and planetary physical properties. Our analysis is based on a sample of 232 extrasolar planets, orbiting 196 stars of dierent luminosity classes and spectral types. In addition to the study of their rotational behavior, the behavior of the physical properties of stars and their orbiting planets was also analyzed, including stellar mass and metallicity, as well as the planetary orbital parameters. As main results we can underline that the rotation of stars with planets present two clear features: stars with Tef lower than about 6000 K have slower rotations, while among stars with Tef > 6000 K we and moderate and fast rotations, though there are a few exceptions. We also show that stars with planets follow mostly the Krafts law, namely < J > / v rot. In this same idea we show that the rotation versus age relation of stars with planets follows, at least qualitatively, the Skumanich and Pace & Pasquini laws. The relation rotation versus orbital period also points for a very interesting result, with planet-harbouring stars with shorter orbital periods present rather enhanced rotation
ROTA??O ? um dos importantes aspectos a ser observado na astrof?sica estelar. Por isto, neste trabalho, investigamos este par?metro no estudo das estrelas hospedeiras de planetas. Par?metro f?sico este que fornece informa??o sobre a distribui??o do momentum angular dos sistemas planet?rios, bem como sobre o seu papel nos mais diferentes fen?menos, incluindo emiss?o cromosf?rica e coronal e sobre aqueles decorrentes de efeitos de mar?. Apesar dos cont?nuos avan?os feitos no estudo das caracter?sticas e das propriedades destes objetos, as principais caracter?sticas de seu comportamento rotat?rio ainda n?o est?o bem estabelecidas. Neste contexto, o presente trabalho traz um estudo pioneiro sobre a rota??o e o momentum angular das estrelas hospedeiras de planetas, bem como sobre a correla??o entre rota??o e par?metros f?sicos estelares e planet?rios. Nossa an?lise ? baseada em uma amostra de 232 planetas extrasolares, orbitando 196 estrelas de diferentes classes de luminosidade e tipos espectrais. Al?m do estudo do comportamento rotacional dessas estrelas, re-visitamos o comportamento das propriedades f?sicas destas estrelas e de seus planetas, incluindo a massa estelar e a metalicidade, bem como os par?metros orbitais planet?rios. Como resultados principais, podemos sublinhar que a rota??o das estrelas com planetas apresenta duas claras caracter?sticas: estrelas com Tef inferiores aproximadamente 6000 K possuem rota??es mais baixas, enquanto que entre aquelas com Tef > 6000 K encontramos rota??es modv eradas e altas, embora algumas exce??es. N?s mostramos tamb?m que as estrelas com planetas seguem, em sua maioria, a lei do Kraft, a saber < J > / v rot. Nesta mesma linha n?s mostramos que a rela??o rota??o versus idade das estrelas com planetas segue, ao menos qualitativamente, como qualquer outra estrela de campo ou de aglomerado, a lei de Skumanich e de Pace & Pasquini. Um resultado interessante a ser destacado ? a rela??o rota??o versus per?odo orbital, que aponta para uma tend?ncia de que as estrelas que abrigam planetas com per?odo orbital menores apresentam rota??es mais real?adas
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Deen, Casey Patrick. "An investigation of the physical parameters of young stellar objects." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-12-4679.
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Studies of the temporal evolution of young stars and their associated properties rely upon the ability of astronomers to determine ages and masses of objects in different evolutionary states. The best method for determining the age and mass of a young stellar object is to place the object on the Hertzsprung-Russell (HR) diagram and to compare to theoretical evolutionary tracks. Accurate ages allow the investigation of the temporal evolution of properties associated with stellar youth (accretion rates, X-ray activity, circumstellar excess, etc...). One property intimately linked with stellar youth is the presence (or absence) of an optically thick primordial circumstellar disk. Objects in "young" star forming regions are more likely to show evidence for a disk than objects in "older" clusters. Within a single cluster, the picture is not as clear. There exist objects in very young clusters (~1 Myr) which show no evidence for circumstellar disks, and there exist objects in very old clusters (~10 Myr), which show evidence for robust disks, suggesting a variable other than stellar age is driving the evolution of the disks. To investigate whether these outliers are due to age spreads, initial conditions, or simply appear anomalous due to erroneous age determinations, we must determine better placements in the HR diagram by carefully transforming observable quantities (spectral type and apparent magnitude) into the quantities necessary for comparison evolutionary models (effective temperature and luminosity). In the Ophiuchus star forming region, I investigate whether or not objects with disks are younger than disk-less objects. I find no difference in the ages of the two populations, but the systematic and random uncertainties are large enough to mask all but the largest age differences. In the hope of better determining the physical parameters of young stellar objects, I embark on a spectral synthesis campaign to produce comparison synthetic spectra which account for the effects of magnetic fields. This requires the modification of the MOOG spectral synthesis program to handle the full Stokes vector treatment for polarized radiation through a magnetized medium. I create a grid of synthetic spectra covering ranges in effective temperature, surface gravity, and average magnetic field strength relevant for studies of young stellar objects, and develop a Chi-squared minimization routine to determine the best fit synthetic spectrum for a given observed spectrum at an arbitrary resolving power. This grid of synthetic spectra will be an invaluable complement to future near infrared, large band-pass, high-resolving power spectrographs (i.e. IGRINS). In addition to these observational and theoretical attempts to reduce systematic errors, I also helped to develop a suite of silicon and KRS-5 grisms for use in the FORCAST instrument, a mid infrared camera on the SOFIA telescope. These grisms will afford the imaging instrument a mid infrared spectroscopic capability at wavelengths normally inaccessible from the ground. I also report on my work to help write FG Widget, the quick-look reduction software package developed to support grism observations.text
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"Stellar Abundances in the Solar Neighborhood." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.14765.
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abstract: The only elements that were made in significant quantity during the Big Bang were hydrogen and helium, and to a lesser extent lithium. Depending on the initial mass of a star, it may eject some or all of the unique, newly formed elements into the interstellar medium. The enriched gas later collapses into new stars, which are able to form heavier elements due to the presence of the new elements. When we observe the abundances in a stellar regions, we are able to glean the astrophysical phenomena that occurred prior to its formation. I compile spectroscopic abundance data from 49 literature sources for 46 elements across 2836 stars in the solar neighborhood, within 150 pc of the Sun, to produce the Hypatia Catalog. I analyze the variability of the spread in abundance measurements reported for the same star by different surveys, the corresponding stellar atmosphere parameters adopted by various abundance determination methods, and the effect of normalizing all abundances to the same solar scale. The resulting abundance ratios [X/Fe] as a function of [Fe/H] are consistent with stellar nucleosynthetic processes and known Galactic thin-disk trends. I analyze the element abundances for 204 known exoplanet host-stars. In general, I find that exoplanet host-stars are not enriched more than the surrounding population of stars, with the exception of iron. I examine the stellar abundances with respect to both stellar and planetary physical properties, such as orbital period, eccentricity, planetary mass, stellar mass, and stellar color. My data confirms that exoplanet hosts are enriched in [Fe/H] but not in the refractory elements, per the self-enrichment theory for stellar composition. Lastly, I apply the Hypatia Catalog to the Catalog of Potentially Habitable Stellar Systems in order to investigate the abundances in the 1224 overlapping stars. By looking at stars similar to the Sun with respect to six bio-essential elements, I created maps that have located two ``habitability windows'' on the sky: (20.6hr, -4.8deg) and (22.6hr, -48.5deg). These windows may be of use in future targeted or beamed searches.Dissertation/Thesis
Ph.D. Astrophysics 2012
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Andreasen, Daniel Thaagaard. "Determination of stellar parameters for M-dwarf Stars the NIR approach." Tese, 2018. https://hdl.handle.net/10216/134613.
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Andreasen, Daniel Thaagaard. "Determination of stellar parameters for M-dwarf Stars the NIR approach." Doctoral thesis, 2018. https://hdl.handle.net/10216/134613.
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Dieterich, Sergio Bonucci. "Characterization of the Stellar / Substellar Boundary." 2013. http://scholarworks.gsu.edu/phy_astr_diss/66.
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The aim of this dissertation is to address the topic of distinguishing very low mass stars from brown dwarfs through observational means. To that end, we seek to better characterize both populations and establish mechanisms that facilitate establishing an individual object's membership in either the very low mass star or the brown dwarf populations. The dissertation is composed of three separate observational studies. In the first study we report on our analysis of HST/NICMOS snapshot high resolution images of 255 stars in 201 systems within ~10 parsecs of the Sun. We establish magnitude and separation limits for which companions can be ruled out for each star in the sample, and then perform a comprehensive sensitivity and completeness analysis for the subsample of 138 M dwarfs in 126 systems. We calculate a multiplicity fraction of $0.0-0.0+3.5% for L companions to M dwarfs in the separation range of 5 to 70 AU, and $2.3-0.7+5.0% for L and T companions to M dwarfs in the separation range of 10 to 70 AU. Considering these results and results from several other studies, we argue that the so-called "brown dwarf desert" extends to binary systems with low mass primaries and is largely independent of primary mass, mass ratio, and separation.
In the second study we construct a Hertzsprung-Russell diagram for the stellar/substellar boundary based on a sample of 63 objects ranging in spectral type from M6V to L4. We report new VRI photometry for 63 objects and new trigonometric parallaxes for 37 objects. We employ a novel SED fitting algorithm to determine effective temperatures, bolometric luminosities, and radii. We find evidence for the local minimum in the radius-temperature and radius-luminosity trends that may indicate the end of the stellar main sequence and the start of the brown dwarf sequence at $Teff ~2075K, log(L/Lsun) ~ -3.9, and (R/Rsun) ~ 0.086.
The third study is a pilot study for future work and part of a long term search for astrometric binaries that have the potential to yield dynamical masses. We report the discovery of five new multiple systems and discuss their potential for determining dynamical masses: LHS 2071AB, GJ 1215 ABC, LTT 7434 AB, LHS 501 AC, and LHS 3738 AB.
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Turner, Garrison H. "The connection between Delta Scuti stars and close binary parameters." 2011. http://liblink.bsu.edu/uhtbin/catkey/1657875.
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With recent advances in CCD technology, it has become possible to detect low-amplitude variability in stars. Thus, the number of low-amplitude variables has increased at an exceptional rate over the past decade. Many of these low-amplitude variables are pulsating stars such as Delta Scuti or Gamma Doradus stars, whose periods are on the orders of hours and days, respectively. One particular place where these variables are being found is in close binary systems. A close binary system has two components separated on the order of tens of solar radii and whose periods are on the order of days. Eclipsing binary systems occur when the orbital plane of the system is aligned such that the stars eclipse each other with respect to Earth’s line of sight. Soydugan et al. (2006) presented a paper in which a small number of eclipsing systems with a Delta Scuti-type pulsating component were analyzed. The group derived an observational relationship between the pulsation and orbital periods, thus indicating a physical phenomenon. The proposed project herein will seek to further determine whether there is a statistically significant relationship between the pulsation period and orbital
parameters of close binary systems with a Delta Scuti-type pulsating component by searching for such pulsations in close binary systems using the method of high-precision CCD photometry.Stellar dynamics -- Observations -- [Delta] Scuti stars in close binary systems.
Department of Physics and Astronomy
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For, Bi-Qing. "Probing stellar evolution through spectroscopy of horizontal branch stars." Thesis, 2011. http://hdl.handle.net/2152/ETD-UT-2011-08-3759.
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This dissertation describes a new detailed abundance study of field
red horizontal branch stars, RR Lyrae stars and blue horizontal branch stars. To carry out this study, we obtained high-resolution and high signal-to-noise ratio echelle spectra at the McDonald observatory and Las Campanas Observatory. In addition,
new pulsational emphemerides were derived to analyze the spectra
of RR Lyrae stars throughout the pulsational cycles. We find that the abundance ratios are generally consistent with those of field stars of similar metallicity
in different evolutionary
stages and throughout the pulsational cycles for RR Lyrae stars. We also estimated the red and blue edges of the RR Lyrae instability strip using the derived effective temperatures of RHB and BHB stars. New variations between microturbulence and effective temperature are found among the HB population.
For the first time the variation
of microturbulence as a function of phase is empirically shown to be similar to the theoretical calculations. Finally, through the study of a rare eclipsing sdB and M dwarf binary, we discovered an unusually low mass for this type of HB star, which observationally proved the existence of a new group of low-mass sdB stars that was theoretically predicted in the past.text
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Allanson, Steven. "The Star Formation Histories of Red-Sequence Galaxies." Thesis, 2009. http://hdl.handle.net/10012/4794.
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This thesis addresses the challenge of understanding the typical star formation histories of red sequence galaxies, using linestrength indices, mass-to-light ratios and redshift evolution as complementary constraints on their stellar age distribution. We first construct simple parametric models of the star formation history that bracket a range of scenarios,
and fit these models to the linestrength indices of low-redshift cluster red-sequence galaxies. For giant galaxies, we con firm the downsizing trend, i.e. the stellar populations are younger, on average, for lower σ galaxies. We find, however, that this trend flattens or reverses at σ < 70km/s. We then compare predicted stellar mass-to-light ratios with dynamical mass-to-light ratios derived from the Fundamental Plane, or by the SAURON group. For galaxies with σ ~ 70 km/s, models with a late 'frosting' of young stars and
models with exponential star formation histories have stellar mass-to-light ratios that are larger than observed dynamical mass-to-light ratios by factors of 1.7 and 1.4, respectively, and so are rejected. The single stellar population (SSP) model is consistent with the Fundamental Plane, and requires a modest amount of dark matter (between 20% to 30%) to account for the difference between stellar and dynamical mass-to-light ratios. A model in which star formation was 'quenched' at intermediate ages is also consistent with the observations, although in this case less dark matter is required for low mass galaxies. We also find that the contribution of stellar populations to the 'tilt' of the Fundamental Plane is highly dependent on the assumed star-formation history: for the SSP model, the tilt of the FP is driven primarily by stellar-population effects. For a quenched model, two-thirds of the tilt is due to stellar populations and only one third is due to dark matter or non-homology.
Comparing to high redshift cluster data, we find again the SSP and quenched models, as well as a model where strangulation begins at intermediate ages after a period of constant star formation, are preferred. They predict the recent faint-end build up of the red sequence, along with observed dwarf-to-giant ratios. Only the SSP model appears to predict the observed M/L evolution, but only if selection effects are carefully modeled.
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Themeẞl, Nathalie. "Asteroseismic inferences from red-giant stars." Doctoral thesis, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E5F1-E.
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Sarmento, Pedro Ivo Teixeira de Kercadio. "Towards a Comprehensive Understanding of tiny stars in the near-infrared domain - Determining stellar parameters of FGK and M dwarfs from their APOGEE spectra using the spectral synthesis method." Tese, 2020. https://hdl.handle.net/10216/128509.
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Sarmento, Pedro Ivo Teixeira de Kercadio. "Towards a Comprehensive Understanding of tiny stars in the near-infrared domain - Determining stellar parameters of FGK and M dwarfs from their APOGEE spectra using the spectral synthesis method." Doctoral thesis, 2020. https://hdl.handle.net/10216/128509.
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Okeng'o, Geoffrey Onchongâa. "A theoretical study of stellart pulsations in young brown dwarfs." Thesis, 2011. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_4946_1308548503.
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This thesis reports the results of a twofold study on the recently proposed phenomenon of &lsquo
stellar pulsations&rsquo
in young brown dwarfs by the seminal study of Palla and Baraffe (2005) (PB05, thereafter). The PB05 study presents results of a non-adiabatic linear stability analysis showing that young brown dwarfs should become pulsationally unstable during the deuterium burning phase of their evolution.
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Marcos, Ricardo Jorge Pereira Córdova. "Age and gender influences on the rat liver model: quantitative morphological studies of hepatic stellate cells, hepatocytes and kupffer cells and of related functional parameters." Tese, 2013. https://repositorio-aberto.up.pt/handle/10216/74213.
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Marcos, Ricardo Jorge Pereira Córdova. "Age and gender influences on the rat liver model: quantitative morphological studies of hepatic stellate cells, hepatocytes and kupffer cells and of related functional parameters." Doctoral thesis, 2013. https://repositorio-aberto.up.pt/handle/10216/74213.
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