THE GAIA SATELLITE: A TOOL FOR EMISSION LINE STARS AND HOT STARS

Abstract. The Gaia satellite will be launched at the end of 2011. It will observe at least 1 billion stars,and among them several million emission line stars and hot stars. Gaia will provide parallaxes for each starand spectra for stars till V magnitude equal to 17. After a general description of Gaia, we present the codesand methods, which are currently developed by our team. They will provide automatically the astrophysicalparameters and spectral classification for the hot and emission line stars in the Milky Way and other closelocal group galaxies such as the Magellanic Clouds. 1 Introduction: The Gaia space missionThe Gaia space mission will be launched in 2011/2012. It will orbit at the anti-solar L2 point. Its lifetime isexpected to be 5 years. Onboard, there are 3 different instruments: ASTRO, which will provide astrometricmeasurements (parallaxes, proper-motions) for all stars down to V magnitude 20 with an accuracy 200 timesbetter than Hipparcos. There are 2 spectrophotometers BP/RP (R∼100, 320–660nm and 650–1000nm) and alow/medium resolution spectrograph called the Radial Velocity Spectrometer (R=5000 to 11500, 847-874nm,designed for GK stars). This last one will provide spectra for stars till V magnitude equal to 17, and will be usedto determine the radial velocity of the stars (see Viala et al. 2008). It is expected that 1 billion of stars will beobserved by Gaia, on average 70 times in 5 years (but only 40 times for the RVS). Among them, using the IMFfrom Kroupa (2001), it is estimated that there are, at maximum, 68 million of hot stars (HS), and 6 million ofemission line stars (ELS). Due to the huge quantity of data (200 teraBytes by year), all the data-reduction andthe scientific analysis must be performed automatically via new software based on java programming language.