Abstract
The European Gaia astrometry mission is due for launch in 2011. Gaia will rely on the proven principles of the ESA Hipparcos mission to create an all-sky survey of about one billion stars throughout our Galaxy and beyond, by observing all objects down to 20 mag. Through its massive measurement of stellar distances, motions and multicolour photometry, it will provide fundamental data necessary for unravelling the structure, formation and evolution of the Galaxy. This paper presents the design and performance of the broad- and medium-band set of photometric filters adopted as the baseline for Gaia. The 19 selected passbands (extending from the UV to the far-red), the criteria and the methodology on which this choice has been based are discussed in detail. We analyse the photometric capabilities for characterizing the luminosity, temperature, gravity and chemical composition of stars. We also discuss the automatic determination of these physical parameters for the large number of observations involved, for objects located throughout the entire Hertzsprung-Russell diagram. Finally, the capability of the photometric system (PS) to deal with the main Gaia science case is outlined.
Highlights
Gaia has been approved as a cornerstone mission in the ESA scientific programme
When the network is presented with a star to classify, it has no prior knowledge of its astrophysical parameter (AP)
While we show results for these limited AP ranges for clarity, it is important to realize that the model was trained and tested on the full range of APs shown in Fig. 14: there was no prior restriction on the APs of a star presented to the model, even though several combinations of G and APs may not exist in the Galaxy
Summary
The main goal is to provide data to study the formation and subsequent dynamical, chemical and star formation evolution of the Milky Way galaxy (Perryman et al 2001; Mignard 2005). Gaia will achieve this by providing an all-sky astrometric and photometric survey complete to 20 mag in unfiltered light. The full-mission (5-yr) mean-sky parallax accuracies are expected to be around 7 microarcsec (7 μas) at V = 10, 12–25 μas at V = 15 and 100–300 μas at V = 20 (depending on spectral type). Radial velocities will be obtained for 100–150 million stars brighter than V 17–18 mag with accuracies of around 1–15 km s−1, depending on the apparent magnitude and spectral type of the stars and the sky density (for details see Katz et al 2004; Wilkinson et al 2005)
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