Showing papers by "F. Thévenin published in 2013"
Max Planck Society1, University of Cádiz2, University of Nice Sophia Antipolis3, National University of Distance Education4, University of Liège5, National and Kapodistrian University of Athens6, INAF7, Royal Observatory of Belgium8, Pablo de Olavide University9, Centre national de la recherche scientifique10, University of Rennes11, Uppsala University12, Centre National D'Etudes Spatiales13, Niels Bohr Institute14, Tartu Observatory15, University of Catania16, European Southern Observatory17, Institut d'Astrophysique de Paris18, University of Paris19
TL;DR: In this article, the authors describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellite's data, covering single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space.
Abstract: The Gaia satellite will survey the entire celestial sphere down to 20th magnitude, obtaining astrometry, photometry, and low resolution spectrophotometry on one billion astronomical sources, plus radial velocities for over one hundred million stars. Its main objective is to take a census of the stellar content of our Galaxy, with the goal of revealing its formation and evolution. Gaia's unique feature is the measurement of parallaxes and proper motions with hitherto unparalleled accuracy for many objects. As a survey, the physical properties of most of these objects are unknown. Here we describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellite's data. This system covers single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space. Multiple methods are used for many types of stars, producing multiple results for the end user according to different models and assumptions. Prior to its application to real Gaia data the accuracy of these methods cannot be assessed definitively. But as an example of the current performance, we can attain internal accuracies (RMS residuals) on F,G,K,M dwarfs and giants at G=15 (V=15-17) for a wide range of metallicites and interstellar extinctions of around 100K in effective temperature (Teff), 0.1mag in extinction (A0), 0.2dex in metallicity ([Fe/H]), and 0.25dex in surface gravity (logg). The accuracy is a strong function of the parameters themselves, varying by a factor of more than two up or down over this parameter range. After its launch in November 2013, Gaia will nominally observe for five years, during which the system we describe will continue to evolve in light of experience with the real data.
164 citations
TL;DR: Asteroseismic data can be used to determine surface gravities with precisions of < 005 dex by using the global seismic quantities Deltanu and nu_max along with Teff and [Fe/H] as mentioned in this paper.
Abstract: Asteroseismic data can be used to determine surface gravities with precisions of < 005 dex by using the global seismic quantities Deltanu and nu_max along with Teff and [Fe/H] Surface gravity is also one of the four stellar properties to be derived by automatic analyses for 1 billion stars from Gaia data (workpackage GSP_Phot) We explore seismic data from MS F, G, K stars (solar-like stars) observed by Kepler as a potential calibration source for methods that Gaia will use for object characterisation (log g) We calculate log g for bright nearby stars for which radii and masses are known, and using their global seismic quantities in a grid-based method, we determine an asteroseismic log g to within 001 dex of the direct calculation, thus validating the accuracy of our method We find that errors in Teff and mainly [Fe/H] can cause systematic errors of 002 dex We then apply our method to a list of 40 stars to deliver precise values of surface gravity, ie sigma < 002 dex, and we find agreement with recent literature values Finally, we explore the precision we expect in a sample of 400+ Kepler stars which have their global seismic quantities measured We find a mean uncertainty (precision) on the order of <002 dex in log g over the full explored range 38 < log g < 46, with the mean value varying only with stellar magnitude (001 - 002 dex) We study sources of systematic errors in log g and find possible biases on the order of 004 dex, independent of log g and magnitude, which accounts for errors in the Teff and [Fe/H] measurements, as well as from using a different grid-based method We conclude that Kepler stars provide a wealth of reliable information that can help to calibrate methods that Gaia will use, in particular, for source characterisation with GSP_Phot where excellent precision (small uncertainties) and accuracy in log g is obtained from seismic data
67 citations
TL;DR: In this paper, the authors presented new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy and identified 14 new variable stars.
Abstract: We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, four are Anomalous Cepheids (ACs) and two are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dSphs and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters. We use the BV Period--Wesenheit (PW) relation of RRLs together with evolutionary prescriptions and find a true distance modulus of 20.09+/-0.07(intrinsic)+/-0.1(statistical) mag that agrees quite well with similar estimates available in the literature. We identified four peculiar variables. Taking into account their position in the Bailey diagram and in the BV PW relation, two of them (V14, V149) appear to be candidate ACs, while two (V158, V182) might be peculiar RRLs. In particular, the variable V158 has a period and a V-band amplitude very similar to the low-mass RRL ---RRLR-02792---recently identified by Pietrzynski at al. (2012) in the Galactic bulge.
37 citations
TL;DR: In this article, the authors presented new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy and identified 14 new variable stars.
Abstract: We present new optical (BVI) time-series data for the evolved variable stars in the Carina dwarf spheroidal galaxy. The quality of the data and the observing strategy allowed us to identify 14 new variable stars. Eight out of the 14 are RR Lyrae (RRL) stars, 4 are Anomalous Cepheids (ACs), and 2 are geometrical variables. Comparison of the period distribution for the entire sample of RRLs with similar distributions in nearby dwarf spheroidal galaxies and in the Large Magellanic Cloud indicates that the old stellar populations in these systems share similar properties. This finding is also supported by the RRL distribution in the Bailey diagram. On the other hand, the period distribution and the Bailey diagram of ACs display significant differences among the above stellar systems. This evidence suggests that the properties of intermediate-age stellar populations might be affected both by environmental effects and structural parameters. We use the BV Period-Wesenheit (PW) relation of RRLs together with evolutionary prescriptions and find a true distance modulus of 20.09 ± 0.07 (intrinsic) ± 0.1 (statistical) mag that agrees quite well with similar estimates available in the literature. We identified four peculiar variables. Taking into account their position in the Bailey diagram and in the BV PW relation, two of them (V14 and V149) appear to be candidate ACs, while two (V158 and V182) might be peculiar RRLs. In particular, the variable V158 has a period and a V-band amplitude very similar to the low-mass RRL—RRLR-02792—recently identified by Pietrzynski et al. in the Galactic bulge.
31 citations
Max Planck Society1, University of Cádiz2, University of Nice Sophia Antipolis3, National University of Distance Education4, University of Liège5, National and Kapodistrian University of Athens6, INAF7, Royal Observatory of Belgium8, Pablo de Olavide University9, University of Rennes10, Centre national de la recherche scientifique11, Uppsala University12, Centre National D'Etudes Spatiales13, Niels Bohr Institute14, Tartu Observatory15, University of Catania16, European Southern Observatory17, Institut d'Astrophysique de Paris18, University of Paris19
TL;DR: In this article, the authors describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellite's data, covering single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space.
Abstract: The Gaia satellite will survey the entire celestial sphere down to 20th magnitude, obtaining astrometry, photometry, and low resolution spectrophotometry on one billion astronomical sources, plus radial velocities for over one hundred million stars. Its main objective is to take a census of the stellar content of our Galaxy, with the goal of revealing its formation and evolution. Gaia's unique feature is the measurement of parallaxes and proper motions with hitherto unparalleled accuracy for many objects. As a survey, the physical properties of most of these objects are unknown. Here we describe the data analysis system put together by the Gaia consortium to classify these objects and to infer their astrophysical properties using the satellite's data. This system covers single stars, (unresolved) binary stars, quasars, and galaxies, all covering a wide parameter space. Multiple methods are used for many types of stars, producing multiple results for the end user according to different models and assumptions. Prior to its application to real Gaia data the accuracy of these methods cannot be assessed definitively. But as an example of the current performance, we can attain internal accuracies (RMS residuals) on F,G,K,M dwarfs and giants at G=15 (V=15-17) for a wide range of metallicites and interstellar extinctions of around 100K in effective temperature (Teff), 0.1mag in extinction (A0), 0.2dex in metallicity ([Fe/H]), and 0.25dex in surface gravity (logg). The accuracy is a strong function of the parameters themselves, varying by a factor of more than two up or down over this parameter range. After its launch in November 2013, Gaia will nominally observe for five years, during which the system we describe will continue to evolve in light of experience with the real data.
24 citations
TL;DR: Gaia as mentioned in this paper will reveal the origin and history of the Milky Way as the major goal and reveal the intrinsic properties of stars that large surveys combined together like Gaia, Kepler, PLATO will reveal.
Abstract: Beyond the extraordinary three dimensional map that Gaia will create for a billion of stars, it will reveal the origin and history of the Milky Way as the major goal. This does not weakness the fantastic impact of Gaia on the stellar physic. It will put constraints on the modeling of stars to an extreme that consequently new input physics will be mandatory to understand a Gaia HR diagram. Stars are formed in populations and evolve as collection of objects revealing important clues on how they formed, what kind of mass function is active during the star formation, how frequent is the star formation, all of this is imprinted in the intrinsic properties of stars that large surveys combined together like Gaia, Kepler, PLATO will revealed. The characterization of stars hosting planets is also a goal of such combination of large surveys and in particular of the measure of distances in the Galaxy. The launch of Gaia is for November of 2013 and the output catalogue is expected for 2020. Then will start the beginning of a new Astrophysics touching so many topics that a new age of astrophysics is then foreseen.