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X-ray fluorescence (XRF) is qualitative and quantitative analytical tool for elemental analysis of many types of materials; it is non-destructive, fast and is suitable for the analysis of the wide range of elements. The method is based on the excitation of an analyte by a beam of primary X-rays to induce the emission of X-ray fluorescence from the sample. The goal of the quantitative XRF analysis is to relate the elemental concentrations to the measured fluorescence intensities. However, this task is not straightforward since the apparent fluorescence intensities are dependent on the weight fraction of an analyte, matrix composition, geometry of the experimental setup, parameters of the primary X-ray source and detection system, etc.. The quantitative information can be obtained applying theoretical or empirical approaches. One of the aims of this thesis is to investigate the performances of the miniaturised XRF setup intended to the analysis of actinides by their L X-ray lines (12 keV < E < 17 keV) installed in the analysis laboratory within ATALANTE facility (CEA Marcoule). The experimental setup includes an Ag-anode X-ray tube which irradiates a sample, a silicon drift detector (SDD) and a cylindrical HOPG monochromator. The latter element is positioned between the sample and the detection system and in such a geometry, it acts as a bandpass filter modifying the spectral distribution of the fluorescence radiation. In this manner, the spectra can be recorded in the energy range of interest reducing the burden on the detection system from an unwanted radiation. The HOPG monochromator of the experimental setup cover the energy range of interest and permits to analyse analysis of medium-Z (Se, Rb, Sr, Y, etc.) and high-Z (mainly U, Np, Pu, Am, and Cm) elements by their K and L X-ray lines, respectively. The second goal of this work is to refine the classical quantification algorithm based on the fundamental parameters taking into account the modifications of the spectral distribution by the HOPG crystal. Indeed, spectra measured with a classical XRF system can be successfully processed using a theoretical method based on mathematical equations without standards. Such method is called the fundamental parameters (FP) method. However, in order to process accurately the spectra measured with the present setup, it arises the necessity to know the transmission function of the HOPG filter. The detailed investigation of the miniature setup and of the physical phenomena involved was performed utilizing the Monte Carlo method for the radiation transport with the PENELOPE code. In addition, to establish a better understanding of the reflection properties of the HOPG crystal, ray-tracing simulations were performed using the dedicated the ray-tracing package XRT to model the cylindrical HOPG crystal and represent step by step the entire detection channel. The response of the developed optical system was simulated applying the experimental spectra recorded without the HOPG monochromator as an input data. The validity of the simulation model has been approved through the comparison with experimental data for different liquid samples containing medium-Z elements (a few tens of mg.L-1),what allowed to define the HOPG transfer function. Next, the estimated transfer function could be successfully applied in the FP-based software PyMCA to provide quantitative results. To conclude, it is demonstrated that the coupling of the PENELOPE Monte Carlo code and XRT simulations can be used to predict the spectral responses of the miniature setup under different geometrical conditions in order to help to improve it.; La fluorescence des rayons X (XRF) est un outil analytique qualitatif et quantitatif pour la caractérisation élémentaire de nombreux types de matériaux ; elle est non destructive, rapide et convient à l'analyse d'une large gamme d'éléments. La méthode est basée sur l'excitation d'un analyte par un faisceau primaire de rayons X qui induit l'émission de la fluorescence X de l'échantillon. L'objectif de l'analyse quantitative par fluorescence X est d’établir la relation entre la concentration des éléments avec les intensités de fluorescence mesurées. Cependant, cette tâche n'est pas simple puisque les intensités de fluorescence apparentes dépendent de la fraction pondérale de l’élément dans l'analyte, de la composition de la matrice, de la géométrie du dispositif expérimental, des paramètres de la source de rayons X primaires et du système de détection, etc. Les informations quantitatives peuvent être obtenues en appliquant des approches théoriques ou empiriques. Un des objectifs de cette thèse est d'étudier les performances d’une installation miniaturisée de fluorescence X destinée à l'analyse des actinides par leurs raies XL (12 keV < E < 17 keV), implantée dans le laboratoire d’analyses de l’installation ATALANTE (CEA Marcoule). Le dispositif expérimental comprend un tube à rayons X à anode d'Ag qui irradie un échantillon, un détecteur au silicium à dérive (SDD) et un monochromateur HOPG cylindrique. Ce dernier élément est placé entre l'échantillon et le système de détection et agit comme un filtre passe-bande en modifiant la distribution spectrale du rayonnement de fluorescence. De cette manière, les spectres peuvent être enregistrés dans la gamme d'énergie d'intérêt, tout en réduisant le taux de comptage dû aux rayonnements parasites. Le monochromateur HOPG du dispositif expérimental couvre la gamme d'énergie d'intérêt qui permet d'analyser les éléments de Z moyen (Se, Rb, Sr, Y, etc.) et Z élevé (principalement U, Np, Pu, Am et Cm) par leurs raies K et L, respectivement. Le second objectif de ce travail est d'affiner l'algorithme classique de quantification basé sur les paramètres fondamentaux en tenant compte des modifications de la distribution spectrale par le cristal HOPG. En effet, les spectres mesurés avec un système de fluorescence classique peuvent être traités avec succès en utilisant une méthode théorique basée sur des équations mathématiques sans nécessiter d’étalons. Il s’agit de la méthode dite des paramètres fondamentaux (PF). Cependant, pour traiter avec précision les spectres mesurés avec la présente configuration, il est nécessaire de connaître la fonction de transmission du cristal HOPG. L'étude détaillée de l’instrumentation miniature et des phénomènes physiques mis en jeu a été réalisée en utilisant la méthode de Monte Carlo pour le transport des rayonnements, avec le code PENELOPE. Ensuite, pour mieux comprendre les propriétés de réflexion du cristal de HOPG, des simulations d’optique des rayons X ont été réalisées à l'aide du logiciel XRT afin de modéliser la réponse du cristal cylindrique de HOPG et représenter pas à pas l'ensemble de détection. La réponse du système optique développé a été simulée en utilisant des spectres expérimentaux enregistrés sans le monochromateur HOPG comme données d'entrée. Le modèle de simulation a été validé par la comparaison avec des données expérimentales pour différents échantillons liquides contenant des éléments Z moyens (quelques dizaines de mg.L-1), ce qui a permis de caractériser la fonction de transfert du cristal HOPG. Ensuite, celle-ci a pu être importée avec succès dans le logiciel PyMCA, basé sur les paramètres fondamentaux, afin de fournir des résultats quantitatifs. Pour conclure, il est démontré que le couplage du code Monte Carlo PENELOPE et des simulations XRT peut être utilisé pour prédire les réponses spectrales de l’instrumentation de fluorescence miniature pour différentes conditions géométriques dans le but de contribuer à l'améliorer.

Surface Brightness-Color Relations (SBCRs) are a key tool for characterizing stars and calibrating distance scales in the Universe. These relations link the stellar flux (integrated per solid angle unit) to its color (the difference between the magnitudes calculated in two distinct photometric bands). Their ease of use is a major advantage in modern astronomy. Although widely used for decades, there are, however, differences in the calibration according to the spectral type and the luminosity class of stars. My thesis aims to calibrate precise SBCRs for early- and late-type stars in order to estimate the stellar angular diameter that allows to characterize exoplanets host stars and calibrate extragalactic distances using detached eclipsing binaries in neighboring galaxies such as the Magellanic clouds, M31 or M33.As a first step, I made use of a catalog that lists all the interferometric measurements made so far, namely the JMDC, in order to calibrate an accurate SBCR for late-type stars. The interest of such calibration relates to the characterization of exoplanets host stars, since these relations are intended to be used within the framework of the PLATO space mission. For that purpose, I have developed selection criteria based on the stellar activity, the photometry of stars but also on the quality of the interferometric measurements in order to avoid any bias in the calibration of the relation. In this work, I show a dependence of SBCRs on the spectral type and the luminosity class of stars, and develop four relations allowing to estimate the angular diameter of stars with a precision ranging between 1% and 2%. I also carry out tests proving the consistency of such selection criteria for the calibration of these relations.In order to cover a large sample of stars with different spectral types, I devoted two years of my thesis to the observation of early-type stars using the VEGA instrument installed at the CHARA array, at Mount Wilson, in the United States. In the same way as for late-type stars, I used selection criteria to properly construct my sample of 18 stars to observe. I measured the angular diameter of these stars with an accuracy between 0.8% and 5%, and calibrated a SBCR for early-type stars that allows to estimate their angular diameter with a precision of 2.4%, namely three times more precise than the relations calibrated so far for this type of stars. I also made a detailed study on the infrared photometry of stars. I used conversion relations between K and Ks photometries in order to transform the infrared photometries of stars into an uniform sample. I show that the use of these relations for early-type stars faces some limits, especially for stars with V – K < - 0.3 mag.A part of my thesis has finally been devoted to the development of so-called "theoretical" SBCRs using MARCS atmosphere models, in order to study the physics of SBCRs, and to understand their dependencies and the differences observed in their calibration. I find a dependence of SBCRs on the luminosity class and the spectral type of stars, but also on the metallicity. I show an average agreement of about 3% with my empirical SBCRs, and I suggest solutions to improve this consistency.The SPICA 6-telescope instrument will soon make it possible to carry out interferometric observations of a very large number of stars, and therefore to refine the calibration of SBCRs and access a more precise study of fundamental parameters of stars., Les relations brillance de surface-couleur (SBCRs, en anglais) sont un outil clé pour la caractérisation des étoiles et l'étalonnage des distances dans l'Univers. La SBCR est une relation entre le flux de l'étoile, intégré par unité d'angle solide, et sa couleur, c'est-à-dire la différence entre les magnitudes calculées dans deux bandes photométriques distinctes. Leur facilité d'utilisation représente un atout majeur au sein de l'astronomie moderne. Bien que largement utilisées depuis des décennies, on constate cependant des incohérences selon le type spectral et la classe de luminosité des étoiles. Ma thèse a pour objectif d'étalonner des SBCRs précises pour les étoiles précoces (types spectraux O, B et A) et tardives (types spectraux plus tardifs que F) dans le but d'estimer le diamètre angulaire des étoiles, qui serviront à la caractérisation des étoiles hôtes d'exoplanètes mais aussi pour la détermination de distance des binaires à éclipses extragalactiques.En premier lieu, j'ai utilisé le catalogue répertoriant toutes les mesures interférométriques réalisées jusqu'à maintenant, le Jean-Marie Mariotti Center Measured stellar Diameters Catalog (JMDC), afin de développer des SBCRs précises pour les étoiles tardives. Ces relations visent à préparer la mission spatiale PLAnetary Transits and Oscillations of Stars (PLATO). Pour ce faire, j'ai élaboré des critères de sélection basés sur l'activité stellaire (variabilité, multiplicité, rotation, etc.), la photométrie des étoiles mais également sur la qualité des mesures afin d'éviter le maximum de biais éventuels sur l'étalonnage de la relation. J'ai développé quatre relations permettant d'estimer le diamètre angulaire des étoiles tardives entre 1% et 2% de précision, et j'ai montré une dépendance des SBCRs en fonction du type spectral et de la classe de luminosité des étoiles.J'ai consacré deux années de ma thèse à l'observation d'étoiles de types précoces à l'aide de l'instrument "Visible spEctroGraph and polArimeter" (VEGA) installé au centre d'observation "Center for High Angular Resolution Astronomy" (CHARA), au Mont Wilson, aux États-Unis. De la même manière que pour les étoiles tardives, j'ai eu recours à des critères de sélection pour finalement construire mon échantillon de 18 étoiles à observer. J'ai mesuré le diamètre angulaire de ces étoiles avec une précision comprise entre 0.8% et 5%, et j'ai développé une SBCR permettant d'estimer leur diamètre angulaire avec une précision de 2.4%, à condition que la relation soit appliquée à des étoiles dépourvues d'activité stellaire. J'ai également réalisé une étude détaillée sur la photométrie infrarouge des étoiles. J'ai utilisé des relations de conversion entre les photométries Johnson-K et 2MASS-Ks afin de transformer les photométries infrarouges des étoiles en un échantillon uniforme. Je montre que l'utilisation de ces relations pour ce type d'étoiles présente des limites, notamment pour les étoiles avec des couleurs V – K < - 0.3 mag.Une partie de ma thèse a finalement eu pour objectif de développer des SBCRs dites "théoriques" à l'aide de modèles d'atmosphères MARCS, afin de comprendre physiquement les différences observées entre les SBCRs correspondant à différentes classes d'objets. Je trouve une différence d'environ 0.025 mag entre la brillance de surface des étoiles géantes (log g = 3) et naines (log g = 4.5) pour une couleur V – K autour de 4 mag. Je trouve également des différences dans les SBCRs selon la métallicité des étoiles, et montre un accord moyen d'environ 3% avec mes relations empiriques. L'instrument 6-télescopes SPICA permettra prochainement de réaliser des observations interférométriques d'un très grand nombre d'étoiles, et donc d'affiner l'étalonnage des SBCRs, mais aussi d'accéder à une étude plus précise des paramètres fondamentaux des étoiles.

International audience; We present an energy-dispersive X-ray fluorescence (EDXRF) instrumentation mainly intended for the quantitative analysis of actinides based on their intense L X-ray lines. The experimental setup is equipped with a highly oriented pyrolytic graphite (HOPG) optic as a bandpass filter placed between a sample and a detection system. In such an arrangement, it modifies the spectral distribution of the fluorescence radiation and allows recording of a spectrum in the energy range from 10 keV to 18 keV, while suppressing parts considered to be useless. In order to perform accurate quantitative analysis of the recorded spectra, the classical quantification algorithm based on the fundamental parameters must be adapted to take into account the effect of the HOPG optic on the measured intensities. This requires to determine the transmission function of the HOPG filter and implement it in the algorithm. The validity of this approach is checked in different application examples.

Context. The nearby and young β Pictoris system hosts a well resolved disk, a directly imaged massive giant planet orbiting at ≃9 au, as well as an inner planet orbiting at ≃2.7 au, which was recently detected through radial velocity (RV). As such, it offers several unique opportunities for detailed studies of planetary system formation and early evolution. Aims. We aim to further constrain the orbital and physical properties of β Pictoris b and c using a combination of high contrast imaging, long base-line interferometry, and RV data. We also predict the closest approaches or the transit times of both planets, and we constrain the presence of additional planets in the system. Methods. We obtained six additional epochs of SPHERE data, six additional epochs of GRAVITY data, and five additional epochs of RV data. We combined these various types of data in a single Markov-chain Monte Carlo analysis to constrain the orbital parameters and masses of the two planets simultaneously. The analysis takes into account the gravitational influence of both planets on the star and hence their relative astrometry. Secondly, we used the RV and high contrast imaging data to derive the probabilities of presence of additional planets throughout the disk, and we tested the impact of absolute astrometry. Results. The orbital properties of both planets are constrained with a semi-major axis of 9.8 ± 0.4 au and 2.7 ± 0.02 au for b and c, respectively, and eccentricities of 0.09 ± 0.1 and 0.27 ± 0.07, assuming the HIPPARCOS distance. We note that despite these low fitting error bars, the eccentricity of β Pictoris c might still be over-estimated. If no prior is provided on the mass of β Pictoris b, we obtain a very low value that is inconsistent with what is derived from brightness-mass models. When we set an evolutionary model motivated prior to the mass of β Pictoris b, we find a solution in the 10–11 MJup range. Conversely, β Pictoris c’s mass is well constrained, at 7.8 ± 0.4 MJup, assuming both planets are on coplanar orbits. These values depend on the assumptions on the distance of the β Pictoris system. The absolute astrometry HIPPARCOS-Gaia data are consistent with the solutions presented here at the 2σ level, but these solutions are fully driven by the relative astrometry plus RV data. Finally, we derive unprecedented limits on the presence of additional planets in the disk. We can now exclude the presence of planets that are more massive than about 2.5 MJup closer than 3 au, and more massive than 3.5 MJup between 3 and 7.5 au. Beyond 7.5 au, we exclude the presence of planets that are more massive than 1–2 MJup. Conclusions. Combining relative astrometry and RVs allows one to precisely constrain the orbital parameters of both planets and to give lower limits to potential additional planets throughout the disk. The mass of β Pictoris c is also well constrained, while additional RV data with appropriate observing strategies are required to properly constrain the mass of β Pictoris b.

Recent work has used spectra of about 5000 stars in NGC 6397 that were extracted from a MUSE mosaic to determine the atmospheric parameters for these stars by fitting the spectra against the Goettingen Spectral Library. A significant change in metallicity between the turn off and the red giant branch was found and was discussed as a possible manifestation of predicted effects of atomic diffusion. However, the small amplitude of the effect and inconsistency with earlier measurements call for more attention before this result is interpreted. Systematic effects due to the interpolation or to the synthetic spectra cannot be ruled out at this level of precision. We reanalyze the data with the ELODIE and MILES reference libraries in order to assess the robustness of the result. These empirical libraries have a finer metallicity coverage down to approximately the cluster metalicity turn-off. We used the ULySS full-spectrum fitting package, together with the library interpolators to remeasure the three atmospheric parameters effective temperature, surface gravity, and [Fe/H] metallicity. We find a very low [Fe/H] dispersion along the isochrone (0.07 dex), consistent with our error estimate (0.05 dex). However, the [Fe/H] trend is not reproducible. This shows that the data have the potential to reveal patterns of the magnitude of the expected physical effects, but the analysis methods need to be refined to cull systematic effects that currently dominate the patterns., 9 pages, 5 figures. Accepted for publication in Astronomy and Astrophysics

Mt. Abu Faint Object Spectrograph and Camera (MFOSC-P) is an in-house developed instrument for Physical Research Laboratory (PRL) 1.2m telescope at Mt. Abu India, commissioned in February 2019. Here we present the first science results derived from the low resolution spectroscopy program of a sample of M Dwarfs carried out during the commissioning run of MFOSC-P between February-June 2019. M dwarfs carry great significance for exoplanets searches in habitable zone and are among the promising candidates for the observatory's several ongoing observational campaigns. Determination of their accurate atmospheric properties and fundamental parameters is essential to constrain both their atmospheric and evolutionary models. In this study, we provide a low resolution (R$\sim$500) spectroscopic catalogue of 80 bright M dwarfs (J$, Comment: Accepted for Publication in MNRAS

We present the photometric properties of 2210 newly identified dwarf galaxy candidates in the MATLAS fields. The Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) deep imaging survey mapped $\sim$142 deg$^2$ of the sky around nearby isolated early type galaxies using MegaCam on the Canada-France-Hawaii Telescope, reaching surface brightnesses of $\sim$ 28.5 - 29 in the g-band. The dwarf candidates were identified through a direct visual inspection of the images and by visually cleaning a sample selected using a partially automated approach, and were morphologically classified at the time of identification. Approximately 75% of our candidates are dEs, indicating that a large number of early type dwarfs also populate low density environments, and 23.2% are nucleated. Distances were determined for 13.5% of our sample using pre-existing $z_{spec}$ measurements and HI detections. We confirm the dwarf nature for 99% of this sub-sample based on a magnitude cut $M_g$ = -18. Additionally, most of these ($\sim$90%) have relative velocities suggesting that they form a satellite population around nearby massive galaxies rather than an isolated field sample. Assuming that the candidates over the whole survey are satellites of the nearby galaxies, we demonstrate that the MATLAS dwarfs follow the same scaling relations as dwarfs in the Local Group as well as the Virgo and Fornax clusters. We also find that the nucleated fraction increases with $M_g$, and find evidence of a morphology-density relation for dwarfs around isolated massive galaxies., 21 pages, 16 figures, 1 table. Accepted for publication in MNRAS; minor corrections to the text, and updated Figures 8 and 9 to match published version

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).; 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).; 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).; 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).

International audience; This paper describes a protocol for quantification of heritage copper alloys by energy-dispersive X-ray fluorescence spectroscopy (ED-XRF). The protocol, nicknamed CHARMed PyMca, is designed for users who wish to maximize inter-laboratory reproducibility of quantitative ED-XRF results for the wide range of copper alloys found in heritage materials. By maximizing reproducibility, this protocol should facilitate collaboration and allow the rigorous use of shared data and databases. The protocol uses free, open-source, fundamental parameters software called PyMca. PyMca allows for a consistent and transparent application of the fundamental parameters approach independent of the ED-XRF instrumentation used. The proposed protocol calls for calibration of standardless PyMca results against a set of certified reference materials designed specifically for use with heritage copper alloys, the so-called copper CHARM set. Finally, this protocol calls for the calibration-to-standards to be carried out following a consistent strategy, including error modelling and the incorporation of a validation procedure. A reproducibility study was conducted using CHARMed PyMca and eight different ED-XRF instruments of six different types. In comparison to a 2010 study conducted according to the same method, CHARMed PyMca showed a dramatic improvement in reproducibility and method sensitivity

The knowledge of accurate values of effective temperature, surface gravity, and luminosity of stars in open clusters is very important not only to derive cluster distances and ages but also to discuss the stellar structure and evolution. Unfortunately, stellar parameters are still very scarce. Aims. Our goal is to study five open clusters to derive stellar parameters of the B and Be star population and discuss the cluster properties. In a near future, we intend to gather a statistically relevant samples of Be stars to discuss their origin and evolution. Methods. We use the Barbier-Chalonge-Divan spectrophotometric system, based on the study of low-resolution spectra around the Balmer discontinuity, since it is independent of the interstellar and circumstellar extinction and provides accurate Hertzsprung-Russell diagrams and stellar parameters. Results. We determine stellar fundamental parameters, such as effective temperatures, surface gravities, spectral types, luminosity classes, absolute and bolometric magnitudes and colour gradient excesses of the stars in the field of Collinder 223, Hogg 16, NGC 2645, NGC 3114, and NGC 6025. Additional information, mainly masses and ages of cluster stellar populations, is obtained using stellar evolution models. In most cases, stellar fundamental parameters have been derived for the first time. We also discuss the derived cluster properties of reddening, age and distance. Conclusions. Collinder 223 cluster parameters are E(B–V) = 0.25 ± 0.03 mag and (mv–Mv)0 = 11.21 ± 0.25 mag. In Hogg 16, we clearly distinguish two groups of stars (Hogg 16a and Hogg 16b) with very different mean true distance moduli (8.91 ± 0.26 mag and 12.51 ± 0.38 mag), mean colour excesses (0.26 ± 0.03 mag and 0.63 ± 0.08 mag), and spectral types (B early-type and B late-/A-type stars, respectively). The farthest group could be merged with Collinder 272. NGC 2645 is a young cluster (v–Mv)0 = 12.18±0.30 mag. The cluster parameters of NGC 3114 are E(B–V) = 0.10±0.01 mag and (mv–M-v)0 = 9.20±0.15 mag. This cluster presents an important population of Be star, but it is difficult to define the cluster membership of stars because of the high contamination by field stars or the possible overlapping with a nearby cluster. Finally, we derive the following cluster parameters of NGC 6025: E(B–V) = 0.34 ±0.02 mag, (mv–Mv)0= 9.25±0.17 mag, and an age between 40 Myr and 69 Myr. In all the cases, new Be candidate stars are reported based on the appearance of a second Balmer discontinuity., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. High-resolution FEROS and HARPS spectra were obtained as part of the ground-based follow-up campaigns for 19 targets holding great asteroseismic potential. These data are used to accurately estimate their fundamental parameters and the abundances of 16 chemical species in a self-consistent manner. Some powerful probes of mixing are investigated (the Li and CNO abundances, as well as the carbon isotopic ratio in a few cases). The information provided by the spectroscopic and seismic data is combined to provide more accurate physical parameters and abundances. The stars in our sample follow the general abundance trends as a function of the metallicity observed in stars of the Galactic disk. After an allowance is made for the chemical evolution of the interstellar medium, the observational signature of internal mixing phenomena is revealed through the detection at the stellar surface of the products of the CN cycle. A contamination by NeNa-cycled material in the most massive stars is also discussed. With the asteroseismic constraints, these data will pave the way for a detailed theoretical investigation of the physical processes responsible for the transport of chemical elements in evolved, low- and intermediate-mass stars., Accepted for publication in A&A, 25 pages, 13 colour figures (revised version after language editing)

At the time of writing of this Thesis more than 900 planets have been announced and about 2700 planets from the Kepler space telescope are waiting to be confirmed. The very precise spectra and light curves obtained in Doppler and transit surveys, allows the in-depth study of the parameters of the host stars, and opens the possibility to investigate the star-plant correlations. Also, determining the stellar parameters with precision is critical for more precise determinations of the planetary parameters, namely, mass, radius, and density.In the case of the FGK dwarfs, the determination of stellar parameters is well established and can be used with confidence to study the star-planet relation as well as to obtain precise planetary parameters. However, this is not the case for M dwarfs, the most common stars in the Galaxy. Compared to their hotter cousins, M dwarfs are smaller, colder, and fainter, and therefore harder to study. The biggest challenge regarding M dwarfs is related to the presence of billions of molecular lines that depress the continuum making a classical spectral analysis almost impossible. Finding new and innovative ways to overcome this obstacle in order to obtain precise stellar parameters is the goal of this Thesis.To achieve this goal I focused my research into two main avenues: photometric and spectroscopic methods. My initial work had the objective of establishing a precise photometric metallicity calibration, but I could not reach this goal, as I did not have enough FGK+M binaries with good photometric data. However, it was possible, with the available data, to compare the already established photometric calibrations and slightly improve the best one, as described in Chapter 3.Then, I focused on spectroscopic approaches with the aim of obtaining precise M dwarf parame- ters. To this end I used HARPS high-resolution spectra and developed a method to measure the spectral lines disregarding the continuum completely. Using this method I established a new visible calibration with a precision of 0.08 dex for [Fe/H] and 80 K for Te f f . This work is detailed in Chapter 4.Finally, I also participated in the refinement of the parameters of the star GJ3470 and its planet, where my expertise in stellar parameters of M dwarfs had an important role. The details regarding this investigation are shown in Chapter 5.; Au moment d'écrire ma Thèse plus de 900 exoplanètes été annoncées et plus de 2700 planètes détectées par le télescope spatial Kepler sont en attente d'être confirmées. La haute précision des spectres et des courbes de lumière obtenue dans les relevés Doppler et transit, permet l'étude détaillée des paramètres des étoiles hôtes, et ouvre la possibilité d'enquêter sur les corrélations étoile planètes. En outre, la détermination des paramètres stellaires avec précision est un besoin critique pour déterminer les paramètres planétaires, à savoir, la masse, le rayon et la densité.Dans le cas des naines FGK, la détermination des paramètres stellaires est bien établie et peut être utilisée avec confiance pour étudier la relation planète-étoile ainsi que pour obtenir les paramètres planétaires avec une grande precision. Cependant, ce n'est pas le cas pour les naines M, les étoiles les plus communes de la Galaxie. Par rapport à leurs cousines plus chaudes, les naines M sont plus petites, plus froides, et plus faiblement lumineuses, et donc plus difficile à étudier. Le plus grand défi qui concerne les naines M est lié à la présence de milliards de lignes moléculaires qui gomme le continuum et rend l'analyse spectrale classique presque impossible. Trouver des fac ̧ons nouvelles et novatrices pour surmonter cet obstacle et obtenir une mesure des paramètres stellaires est l'objectif principal de cette Thèse .Pour l'atteindre, j'ai concentré mes recherches sur deux approches méthodologiques, photométrique et spectroscopiques. Mon premier travail avait pour objectif d'établir l'étalonnage de métallicité pho- tométrique précis. Par manque de binaires FGK+M avec de bonnes données photométriques je ne pouvais pas atteindre cet objectif. Il m'a cependant était possible, avec les données disponibles, de comparer les étalonnages photométriques déjà établies et légèrement améliorer le meilleur d'entre eux, comme décrit au Chapitre 3.Puis, je me suis concentré sur les approches spectroscopiques pour obtenir des paramètres stel- laires plus précis pour les naines M. À cette fin, j'ai utilisé des spectres HARPS de haute résolution et développé une méthode pour mesurer les lignes spectrales sans tenir compte du continuum . En utilisant cette méthode, je créé un nouvel étalonnage visible avec une précision de 0.08 dex pour [Fe/H] et 80 K pourTeff .Ce travail est détaillé dans le Chapitre 4.Finalement , j'ai également participé à l'amélioration des paramètres de l'étoile GJ3470 et de sa planète, où mon expertise dans les paramètres stellaires de naines M avait un rôle important. Les détails concernant cette enquête sont présentés dans le Chapitre 5; No momento em que escrevo esta Tese, o número de planetas anunciados já ultrapassou os 900 e os cerca de 2700 candidatos detectados pelo telescópio espacial Kepler esperam por confirmação. Os espectros e as curvas de luz obtidos nos programas de procura de planetas permitem, também, o estudo em profundidade dos parâmetros das estrelas com planetas e abrem a possibilidade de investigar a relação estrela-planeta. Neste contexto, a determinação com precisão dos parâmetros estelares é crítica na determinação precisa dos parâmetros planetários, nomeadamente, a massa, o raio e a densidade.No caso das anãs FGK, os métodos de determinação dos parâmetros estelares estão bem estabelecidos e podem ser usados com confiança no estudo da relação estrela-planeta, assim como na obtenção de parâmetros planetários precisos. No entanto, não é esse o caso para as anãs M, as estrelas mais comuns da nossa Galáxia. Ao contrário das suas primas, as estrelas M são mais pequenas, frias e ténues e, assim sendo, mais difíceis de estudar. O grande entrave no estudo das estrelas M está relacionado com a presença de biliões de linhas moleculares que deprimem o contínuo espectral, fazendo com que uma análise espectral clássica se torne quase impossível. A procura de métodos inovadores que possibilitem ultrapassar este obstáculo, tendo em vista a obtenção de parâmetros precisos, é o objectivo desta Tese.Tendo em conta esse objetivo, foquei os meus esforços em duas linhas principais de pesquisa, baseadas em métodos fotométricos e métodos espectroscópicos. O meu trabalho inicial tinha como objetivo o estabelecimento de uma calibração fotométrica para a metalicidade, mas não me foi possível atingir esse objetivo, pois não tinha sistemas binários FGK+M suficientes com bons dados fotométricos. No entanto, foi possível, com os dados disponíveis, comparar as calibrações fotométricas existentes e refinar ligeiramente a melhor delas, como descrito no Capítulo 3.Após este trabalho passei a concentrar-me em técnicas espectroscópicas de obtenção de parâmetros estelares em estrelas M. Tendo em mente esse objetivo, usei espectros HARPS de alta resolução para desenvolver um novo método de medição de linhas espectrais independente do contínuo espectral. Seguidamente, usei este método no desenvolvimento de uma nova calibração de metalicidade e temperatura efectiva em estrelas M na região do visível, através da qual consegui atingir uma precisão de 0.08 dex para a [Fe/H] e de 80 K para a temperatura. Este trabalho está descrito no Capítulo 4.Ao mesmo tempo colaborei na determinação com precisão dos parâmetros da estrela GJ3470 e do seu planeta, onde a minha proficiência na determinação de parâmetros estelares em anãs M teve um papel importante. Os detalhes relacionados com este trabalho de investigação estão descritos no Capítulo 5.

Using the wide multi-band photometry available in the COSMOS field we explore the host galaxy properties of a large sample of Active Galactic Nuclei (AGN) obtained by combining X-ray and optical spectroscopic selections. Based on a careful study of their Spectral Energy Distribution (SED), which has been parametrized using a 2-component (AGN+galaxy) model fit, we derived dust-corrected rest-frame magnitudes, colors, stellar masses and star formation rates (SFRs). We find that AGN hosts span a large range of stellar masses and SFRs. No color-bimodality is seen at any redshift in the AGN hosts, which are found to be mainly massive, red galaxies. Once accounting for the color-mass degeneracy in well defined mass-matched samples, we find a residual marginal enhancement of AGN incidence in redder galaxies with lower specific star formation rates, and we argue that this result might emerge because of our ability to properly account for AGN light contamination and dust extinction. Interestingly, we find that the probability for a galaxy to host a black hole growing at any given "specific accretion rate" (i.e. the ratio of X-ray luminosity to the host stellar mass) is almost independent of the host galaxy mass, while it decreases as a power-law with Lx/M. By analyzing the normalization of such probability distribution, we show how the incidence of AGN increases with redshift as rapidly as (1+z)^4, in close resemblance with the overall evolution of the specific star formation rate of the entire galaxy population. Although AGN activity and star formation in galaxies do appear to have a common triggering mechanism, at least in a statistical sense, within the COSMOS sample we do not find strong evidence of any 'smoking gun' signaling powerful AGN influence on the star-forming properties of their hosts galaxies.

Herbig Ae/Be stars are pre-main sequence stars of intermediate mass (2-10 Msun) showing signs of intense activity and strong winds. The origin of their tremendous activity is still not understood in the frame of current theoretical evolutionary models. As of today, growing observational evidences tend to indicate that the energy needed to produce this activity might be of internal origin, but no definite answer has been provided. Solving this still open question is a major concern for testing young stellar evolutionary theory. This could be done by constraining the internal structure of these objects using asteroseismic techniques, i.e. the observation, analysis and modelling of stellar pulsation frequencies and modes. Such a study implies to caracterise and to constrain the theoretical PMS instability strip that Herbig stars cross for a significant fraction of their evolution to the main sequence. Having this aim, I studied first the prototype Ae Herbig star HD 104237. I carried a study of its photospheric fundamental parameters, which was necessary for a further asteroseismic modelling. The analysis of the photospheric line profile variations of this star confirmed the presence of multi-periodic oscillations and enabled the detection of several non-radial pulsations. I could identify some of the pulsation modes and modelled these pulsations in an adiabatic framework. This has supplied interesting leads about the excitation mechanism of the observed pulsations of HD 104237. I then extended my study to 4 others Herbig stars that were observed with HARPS (ESO) in the course of my thesis. Preliminary results of the asteroseismic analysis are presented in my manuscript.; Les étoiles Ae/Be de Herbig sont des étoiles jeunes (pré-séquence principale, PMS), de masse intermédiaire (2-10 Msun) présentant des signes d'une activité intense et de forts vents stellaires, dont l'origine n'est pas expliquée par les théories actuelles d'évolution stellaire. Des travaux observationnels tendent à indiquer que la source énergétique de cette activité serait d'origine interne. Il est donc essentiel d'extraire des informations sur la structure interne des étoiles de Herbig par le biais de l'astérosismologie, c'est-à-dire l'observation, l'analyse et la modélisation des fréquences et des modes d'oscillations des étoiles pulsantes. Une telle étude implique de caractériser et de contraindre la bande d'instabilité PMS théorique, représentant la zone du diagramme Hertzsprung-Russell dans laquelle ces étoiles pulsent, et qui est traversée par les étoiles Ae de Herbig pendant leur trajet évolutif. Dans ce but, je me suis, d'une part, concentrée sur le cas de l'étoile Ae de Herbig prototype HD 104237, en étudiant ses paramètres photosphériques fondamentaux, indispensables à une modélisation astérosismique ultérieure. L'étude des variations de profil de raies photosphériques de cette étoile a confirmé la présence d'oscillations multi-périodiques et a permis de détecter des pulsations non-radiales. Une identification de certains modes de pulsation a été réalisée. La modélisation des pulsations de cette étoile dans le cadre adiabatique a fourni des pistes intéressantes à explorer quant au mécanisme d'excitation des modes de pulsation observés. L'étude a ensuite été étendue à 4 autres étoiles de Herbig observées avec HARPS (ESO), et leur analyse préliminaire est présentée.

Herbig Ae/Be stars are pre-main sequence stars of intermediate mass (2-10 Msun) showing signs of intense activity and strong winds. The origin of their tremendous activity is still not understood in the frame of current theoretical evolutionary models. As of today, growing observational evidences tend to indicate that the energy needed to produce this activity might be of internal origin, but no definite answer has been provided. Solving this still open question is a major concern for testing young stellar evolutionary theory. This could be done by constraining the internal structure of these objects using asteroseismic techniques, i.e. the observation, analysis and modelling of stellar pulsation frequencies and modes. Such a study implies to caracterise and to constrain the theoretical PMS instability strip that Herbig stars cross for a significant fraction of their evolution to the main sequence. Having this aim, I studied first the prototype Ae Herbig star HD 104237. I carried a study of its photospheric fundamental parameters, which was necessary for a further asteroseismic modelling. The analysis of the photospheric line profile variations of this star confirmed the presence of multi-periodic oscillations and enabled the detection of several non-radial pulsations. I could identify some of the pulsation modes and modelled these pulsations in an adiabatic framework. This has supplied interesting leads about the excitation mechanism of the observed pulsations of HD 104237. I then extended my study to 4 others Herbig stars that were observed with HARPS (ESO) in the course of my thesis. Preliminary results of the asteroseismic analysis are presented in my manuscript.; Les étoiles Ae/Be de Herbig sont des étoiles jeunes (pré-séquence principale, PMS), de masse intermédiaire (2-10 Msun) présentant des signes d'une activité intense et de forts vents stellaires, dont l'origine n'est pas expliquée par les théories actuelles d'évolution stellaire. Des travaux observationnels tendent à indiquer que la source énergétique de cette activité serait d'origine interne. Il est donc essentiel d'extraire des informations sur la structure interne des étoiles de Herbig par le biais de l'astérosismologie, c'est-à-dire l'observation, l'analyse et la modélisation des fréquences et des modes d'oscillations des étoiles pulsantes. Une telle étude implique de caractériser et de contraindre la bande d'instabilité PMS théorique, représentant la zone du diagramme Hertzsprung-Russell dans laquelle ces étoiles pulsent, et qui est traversée par les étoiles Ae de Herbig pendant leur trajet évolutif. Dans ce but, je me suis, d'une part, concentrée sur le cas de l'étoile Ae de Herbig prototype HD 104237, en étudiant ses paramètres photosphériques fondamentaux, indispensables à une modélisation astérosismique ultérieure. L'étude des variations de profil de raies photosphériques de cette étoile a confirmé la présence d'oscillations multi-périodiques et a permis de détecter des pulsations non-radiales. Une identification de certains modes de pulsation a été réalisée. La modélisation des pulsations de cette étoile dans le cadre adiabatique a fourni des pistes intéressantes à explorer quant au mécanisme d'excitation des modes de pulsation observés. L'étude a ensuite été étendue à 4 autres étoiles de Herbig observées avec HARPS (ESO), et leur analyse préliminaire est présentée.

In this work we present atmospheric parameters and Li abundances, obtained from a detailed spectroscopic analysis, for a large sample of stars with different evolutionary stages (turn-off, subgiant and giant stars) in the open cluster M67. The observations were carried out with high resolution (R ~ 47,000) and high S/N using the UVES+FLAMES at VLT/UT2. From available photometry and computed synthetic spectra for the region around the lithium line at 6707.75 Å, we derive atmospheric parameters (T eff , log g, [ Fe/H ], v sin i) and Li abundances for each star, in order to better understand the level of mixing and convective dilution of evolved stars in M67.

Abundances of neutron-capture (n - capture) elements in the stars belonging to thin and thick disks are obtained. The separation of thin and thick stars on kinematic criterion was made early. The spectra were obtained with the ELODIE spectrograph at the 1.93-m telescope of the Observatoire de Haute Provence (France). The determination of elemental abundances was carried out in LTE assumption by model atmosphere method, for Ba and Eu taken into account the hyperfine structure. The dependences of n-capture element abundances on metallicity for thin and thick disks are presented.

Context.Studies of the effects of environment on galaxy properties and evolution require well defined control samples. Such isolated galaxy samples have up to now been small or poorly defined. The AMIGA project (Analysis of the interstellar Medium of Isolated GAlaxies) represents an attempt to define a statistically useful sample of the most isolated galaxies in the local (z $\leq$ 0.05) Universe., Aims.A suitable large sample for the AMIGA project already exists, the Catalogue of Isolated Galaxies (CIG, Karachentseva, 1973, Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii, 8, 3; 1050 galaxies), and we use this sample as a starting point to refine and perform a better quantification of its isolation properties., Methods.Digitised POSS-I E images were analysed out to a minimum projected radius R $\geq$ 0.5 Mpc around 950 CIG galaxies (those within Vr = 1500 km s-1 were excluded). We identified all galaxy candidates in each field brighter than B = 17.5 with a high degree of confidence using the LMORPHO software. We generated a catalogue of approximately 54 000 potential neighbours (redshifts exist for $\approx$30% of this sample)., Results.Six hundred sixty-six galaxies pass and two hundred eighty-four fail the original CIG isolation criterion. The available redshift data confirm that our catalogue involves a largely background population rather than physically associated neighbours. We find that the exclusion of neighbours within a factor of four in size around each CIG galaxy, employed in the original isolation criterion, corresponds to $\Delta V_r \approx$ 18 000 km s-1 indicating that it was a conservative limit., Conclusions.Galaxies in the CIG have been found to show different degrees of isolation. We conclude that a quantitative measure of this is mandatory. It will be the subject of future work based on the catalogue of neighbours obtained here., This work has been partially supported by DGI Grant AYA 2005-07516-C02-01 and the Junta de Andalucía (Spain). UL acknowledges support by the research project ESP 2004-06870-C02-02. Jack Sulentic is partially supported by a sabbatical grant SAB2004-01-04 of the Spanish Ministerio de Educación y Ciencias. G.B. acknowledges support at the IAA/CSIC by an I3P contract (I3P-PC2005F) funded by the European Social Fund.

We have analysed the light curve of the two brightest X-ray flares from the Galactic Center black hole, one flare observed by XMM-Newton on October 3, 2002 (Porquet et al. 2003), and the other flare observed by Chandra on October 26, 2000 (Baganoff et al. 2001). The power density spectra show five distinct peaks at periods of ~ 100 s, 219 s, 700 s, 1150 s, and 2250 s common to both observations within their estimated measurement uncertainties. The power density spectrum of the recently reported infrared flare of June 16, 2003 (Genzel et al. 2003) shows distinct peaks at two, if not three, periods (including the 1008 +/- 120 s infrared period), which are consistent with the X-ray periods. The remaining two periods could not be covered by the infrared measurements. Each period can be identified with one of the characteristic gravitational cyclic modes associated with accretion disks, i.e. either Lense-Thirring precession, Kepler orbital motion and the vertical and radial epicyclic oscillation modes, in such a way that a consistent value for the black hole mass of M_BH = 2.72^{+0.12}_{-0.19} x 10^6 M_odot and the angular momentum $a$ = 0.9939^{+0.0026}_{-0.0074} is obtained. The available data on M_BH derived from studies of the orbital motion of the S2 (S0-2) star (Schoedel et al. 2002, Ghez et al. 2003) agree with our findings. Finally we discuss some implications of the fairly high value for the angular momentum., In this revised version (accepted by the A&A Editor, 9 pages), we use the formula for the Lense-Thirring precession given by Merloni et al. (1999), which is not restricted to the weak-field limit. Thereby we now obtain a unique solution for the mass and the angular momentum of the supermassive black hole

We present the first results of a spectroscopic survey of faint lensed galaxie s in the core of the galaxy cluster AC114 (z=0.312) obtained from observations w ith the FORS1 spectrograph mounted on the VLT-Antu. The galaxies were chose n in areas close to the high-z critical lines predicted by the gravitational lens model of Natarajan et al (NKSE, 1998) for this cluster, according to both lensing and photometric redshift criteria. All the target galaxies are found to correspond to background galaxies with redshifts values in the [0.7, 3.5] interval. Our spectroscopic observations confirm the predicted lensing redshifts for 3 of the multiple-image galaxies, and together with predictions of the NKSE model led to the discovery of a new 5-image configuration at redshift z=3.347. A revised NKSE model, compatible with the redshift of this new multiple-image system, was generated and employed to calculate the gravitational amplifications of all the observed galaxies. The galaxies corresponding to the multiple-image systems are found to be intrinsically fainter, between 0.5 and 1.5 magnitudes, than the limiting magnitudes of existing blank field studies. When all the observed background galaxies are considered, the resulting intrinsic absolute magnitudes range from M_B~-22 to -19. Therefore, a large gain in sensitivity towards low luminosity high-z objects can actually be obtained, in agreement with theoretical expectations. This method can be used advantageously to probe the high redshift Universe and, in particular, its application to an ensemble of massive cluster cores could constraint the faint end of luminosity function of high redshift galaxies., Comment: 13 pages, Submitted to A&A

This paper represents a collective effort to provide an extensive electronic database useful for the interpretation of galaxy properties.

Cette note concerne l'étude d'un convertisseur d'énergie pyroélectrique réversible. Les paramètres fondamentaux permettant d'optimiser l'énergie électrique récupérée sur une résistance d'utilisation sont étudiés. Un calcul théorique définit les facteurs de qualité pyroélectriques du matériau ainsi que la résistance d'adaptation. Une étude expérimentale de l'énergie électrique récupérée lors d'une attaque thermique impulsionnelle permet de vérifier ces résultats théoriques.