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We demonstrate the eclipsing binary detection performance of the Gaia variability analysis and processing pipeline using Hipparcos data. The automated pipeline classifies 1 067 (0.9%) of the 118 204 Hipparcos sources as eclipsing binary candidates. The detection rate amounts to 89% (732 sources) in a subset of 819 visually confirmed eclipsing binaries, with the period correctly identified for 80% of them, and double or half periods obtained in 6% of the cases.
We present the variability processing and analysis that is foreseen for the Gaia mission within Coordination Unit 7 (CU7) of the Gaia Data Processing and Analysis Consortium (DPAC). A top level description of the tasks is given.
The ESA space mission Gaia, planned to be launched at the end of 2013, will make astrometric, photometric and spectroscopic measurements of about 1 billion sources in our Galaxy. Amongst these sources will be numerous multiple systems. In the processing chain eclipsing binaries (EBs) will be detected and, if possible, their period and characteristics determined. Here we summarize the various steps that are foreseen to automatically classify and characterise these EBs.
We started a systematic search for periodic variable-star candidates in the EROS-2 database in the context of preparatory work for the Gaia satellite mission. The goal is to evaluate different classification tools and strategies, and to identify a large sample of variable candidates. In this paper we present the results of an assessment study of a three-step identification and classification process. In the study we took a sample of about 80,000 stars from one of the LMC EROS fields.
The measurement of the positions, distances, motions and luminosities of stars represents the foundations of modern astronomical knowledge. Launched at the end of the eighties, the ESA Hipparcos satellite was the first space mission dedicated to such measurements. Hipparcos improved position accuracies by a factor of 100 compared to typical ground-based results and provided astrometric and photometric multi-epoch observations of 118,000 stars over the entire sky. The impact of Hipparcos on astrophysics has been extremely valuable and diverse. Building on this important European success, the ESA Gaia cornerstone mission promises an even more impressive advance. Compared to Hipparcos, it will bring a gain of a factor 50 to 100 in position accuracy and of a factor of 10,000 in star number, collecting photometric, spectrophotometric and spectroscopic data for one billion celestial objects. During its 5-year flight, Gaia will measure objects repeatedly, up to a few hundred times, providing an unprecedented database to study the variability of all types of celestial objects. Gaia will bring outstanding contributions, directly or indirectly, to most fields of research in astrophysics, such as the study of our Galaxy and of its stellar constituents, and the search for planets outside the solar system.
Two upcoming large scale surveys, the ESA Gaia and LSST projects, will bring a new era in astronomy. The number of binary systems that will be observed and detected by these projects is enormous, estimations range from millions for Gaia to several tens of millions for LSST. We review some tools that should be developed and also what can be gained from these missions on the subject of binaries and exoplanets from the astrometry, photometry, radial velocity and their alert systems.
The ESA Gaia mission will provide a multi-epoch database for a billion of objects,
including variable objects that comprise stars, active galactic nuclei and asteroids. We
highlight a few of Gaia’s properties that will benefit the study of variable objects, and
illustrate with two examples the work being done in the preparation of the data processing
and object characterization. The first example relates to the analysis of the nearly
simultaneous multi-band data of Gaia with the Principal Component Analysis techniques, and
the second example concerns the classification of Gaia time series into variability types.
The results of the ground-based processing of Gaia’s variable objects data will be made
available to the scientific community through the intermediate and final ESA releases
throughout the mission.
G. Meynet, Observatoire de Genève, Université de Genève, CH-1290 Sauverny, Switzerland,
N. Mowlavi, ISDC, Observatoire de Genève, Université de Genève, Chemin d'Ecogia 16, CH-1290 Versoix, Switzerland,
A. Maeder, Observatoire de Genève, Université de Genève, CH-1290 Sauverny, Switzerland
After a review of the many effects of metallicity on the evolution of rotating and non-rotating stars, we discuss the consequences of a high metallicity for massive-star populations and stellar nucleosynthesis. The most striking effect of high metallicity is to enhance the amount of mass lost by stellar winds. Typically, at a metallicity of Z = 0.001 only 9% of the total mass returned by non-rotating massive stars is ejected by winds (91% by supernova explosions), whereas at Solar metallicity this fraction may amount to more than 40%. High metallicity favors the formation of Wolf–Rayet stars and Type-Ib supernovae, but militates against the occurrence of Type-Ic supernovae. We estimate empirical yields of carbon on the basis of the observed population of WC stars in the Solar neighborhood, and obtain that WC stars eject 0.2%–0.4% of the mass initially locked into stars in the form of newly synthesized carbon. Models give values well in agreement with these empirical yields. Chemical-evolution models indicate that such carbon yields may have an important impact on the abundance of carbon at high metallicity.
The carbon isotopic ratio, 12C/13C, is a tracer of the mixing events during the evolution along the giant branch, due to the conversion of 12C into 13C (and 14N) via the CN cycle. A decrease of this ratio from 90, the solar value, to 20–25, is expected due to the first dredge-up. However, ratios down to 3–4, the CN cycle equilibrium value, have been observed in giants of the field, of globular and of open clusters. Observations seem to indicate a non-standard mixing in the RGB, probably beginning in the luminosity bump, when the outward moving hydrogen burning shell crosses the molecular weight barrier left by the convective layer in its maximum extent. We are currently analyzing a sample of 24 giants in 8 open clusters for which we determined 12C/13C from high resolution, high signal to noise spectra using spectrum synthesis. In this work we discuss the general characteristics of our results in comparison to previous analyses of giants in open clusters available in the literature.
Two examples of stellar predictions from models of asymptotic giant branch
stars are presented to illustrate the difficulties associated with
astronuclear studies. The first example is the dredge-up process by which
nuclei synthesized in the stellar interior are brought to the
surface; the second is the production of primary sodium. Those examples
illustrate the need for a good understanding of the details
of model calculations from both a physical and a numerical stand point.
They highlight as well some of the current limitations of AGB model
The third dredge-up phenomenon in asymptotic giant branch stars, responsible for the formation of C stars, is discussed based on detailed evolutionary model calculations. The structural readjustment of the star as dredge-up proceeds is analyzed, and its consequences on dredge-up predictions discussed. The question of how to obtain dredge-up in asymptotic giant branch models is also addressed. It is stressed, in particular, that the modeling of dredge-up requires some sort of extra-mixing to be applied below the envelope if the local Schwarzschild criterion is used to delimit convective zones.
The Geneva group has computed a complete grid of stellar models from 0.8 to 60 M⊙ at a metallicity of Z=0.100 (i.e. 5 times solar, Mowlavi et al. 1997). These stellar models present interesting features such as the nearly complete evaporation of the most massive stars due to intense stellar winds. For instance, for Z >> 0.040, final stages of massive stars (M > 60 M⊙) might be white dwarfs rather than neutron stars or black holes.
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