The GAIA photometry The GAIA mission, the next ESA Cornerstone 6 (launch ), will create a precise three dimensional map of about one billion stars throughout our Galaxy and beyond. To reach the scientific goals, that is to quantify the dynamical, chemical and star formation evolution of the Milky Way, it is crucial to also accurately determine astrophysical parameters through the measured flux for the observed objects (effective temperature, luminosities, global metallicity, ages, chemical anomalies,...). The spectrophotometric instrument on board GAIA, combined with the two astrometric instruments, will provide this information. The medium and broad band photometric systems proposed for GAIA are presented. We discuss their capability to characterize the galactic populations than can be observed. The accuracy expected in the derivation of astrophysical parameters using jointly astrometry and medium band GAIA photometry is also presented. For more information please contact C. Jordi GAIA: Derivation of Stellar Parameters C. Jordi, J.M. Carrasco, F. Figueras, J. Torra, X. Luri, E. Masana Universitat de Barcelona - IEEC, Avda. Diagonal 647, Barcelona, Spain T eff = 3500 K (3 filter combinations) Scientific goals Accuracies:  4  as at V =  as at V = mas at V = 20  complete astrophysical sample: one billion stars  1 km/s radial velocities complete to V = 17.5  sky survey at ~ 0.25 arcsec spatial resolution to V = 20  multi-colour multi-epoch photometry to V = 20  dense quasar link to inertial reference frame Main performances and capabilities Astrometric accuracy in  as Capabilities:  10  as  10% at 10 kpc  1 AU at 100 kpc  10  as/yr at 20 kpc  1 km/s  every star in the Galaxy and Local Group will be seen to move  GAIA will quantify 6-D phase space for over 300 million stars and 5-D phase-space for over 10 9 stars Galactic Structure: origin and history of our Galaxy - tests of hierarchical structure formation - inner bulge/bar dynamics - disk/halo interactions – Star Formation and Evolution: dynamics of star forming regions - luminosity function - complete and detailed local census down to single brown dwarfs Distance Scale and Reference Frames: parallax calibration of all distance scale indicators - definition of the local, kinematically non-rotating metric Local Group and Beyond: rotational parallaxes for Local Group galaxies - kinematical separation of stellar populations - internal dynamics of Local Group dwarfs - detection of supernovae Solar System: new minor planets - taxonomy and evolution Extra-Solar Planetary Systems: complete census of large planets out to pc - orbital characteristics of several thousand planets Fundamental Physics: determination of space curvature parameter  to 1 part in The scientific goals of GAIA require complementary astrometry, photometry and radial velocity data Correct chromatic aberrations in the astrometric focal plane to achieve microarcsec accuracy level (BBP) Characterization of the observed objects in terms of astrophysical parameters. (BBP+MBP) Classification: star (single/multiple), solar system object, galaxy, QSO Stellar astrophysics parameters: T eff, luminosity, chemical composition ([Fe/H], [α/Fe], C/O,...), peculiarities, emssion,… Solar system: taxanomy classification, variability,... QSO: photometric redshif Galaxies: colours,… G magnitude accuracy (mag) G band in the astrometric fields Very broad band: ~ nm Small bolometric correction 11 CCDs per passage (3.3s per CCD) 82 observations The best S/N for variability detection G lim ~ 20 V lim ~ G-V is a function of SP and reddening Light curves: precision at V~20 as Hipparcos at V~9 Goals Broad band system Example of a BBP colour- colour diagram for different gravities and metallicities. Arrow indicates reddening for A v =1. Error bars indicate end- of-mission errors for a source with G=18. The four (or five) broad band photometric filters will provide multi- colour, multi-epoch photometric measurements for each object observed in the astrometric field. Several filter transmision curves are being designed and tested to optimize the BBP system for chromaticity calibration. Artificial neural networks (among other techniques) are being used for this purpouse. Although somewhat redundant in terms of astrophysical information content, BBP will supply higher S/N and angular resolution than MBP, so useful for QSO and galaxy photometry aplications. The figures show some examples and the accuracy achivable Medium band system Photometric accuracy (in mag) in the spectro telescope in each of the relevant colour indices derived from the 11 medium photometric bands (2F system). The accuracy has been computed for an unreddened star. The abundance of  -elements is measured through the MgH reddening free index (QIMg) in the F and G stars and through the QITiO reddening free index for later (K and early M) stars. QICN is used to measure the N abundance of red stars with Teff < 4200 K. Considerable effort is being devoted to the design of an optimum system for GAIA, taking into account the spectral energy distribution of the main galactic stellar populations, as derived from model atmosheres and spectrophotometric observations), as well as the experience with existing photometric systems. At present, 2F (shown in the figure) is the base-line photometric system for GAIA (final system by mid-2005). Temperature determination Precision of 1-3% in T eff, is achievable at G~19 Several passbands to measure the continuum (An error of 0.02 mag in E(b-y) is assumed) Brown dwarfs: Chamaeleon #7 (M8 V) V= 22.2, (V-I) = 5.3, G = 18.8 mag A v =0.26 mag, T eff ~ 2700 K, M= 0.05 M sun Δπ/π = σ M = σ Teff = 20-30K Good derivation of Mass and age Observed spectra of Chamaeleon #7 (provided by F. Comerón). GAIA 75,78,83,89 filters are overploted Expected accuracy of the location of Chamaeleon #7 in the HR diagram. Models from Baraffe et al. (1998). Chemical composition determination Oxigen rich and Carbon rich classification (variation with phase) dex precision is achievable at G~19 K giant (T eff = 4500 K, log g=3.0)M dwarf (T eff = 3500 K, log g=4.5) Satellite & system (April 2002 design status) ASTRO telescopes and focal plane SPECTRO telescope and focal plane Entrance pupil0.5 x 0.5 m 2 Optical transmission> 0.92 Pixel size10 x 15 μm 2 Pixel size (angular)1 x 1.5 arcsec 2 MBPRVS Sample size (in pixels)1 x 41 x 3 Number of CCDs2 x (1+15)1+6 TDI integration time per chip5.5 s16.8 s Average total obs./object 2 x Spectral range nm Spectral sampling0.375 Å/pixel Entrance pupil1.4 x 0.5 m 2 Optical transmission> 0.86 Pixel size10 x 30 μm 2 Pixel size (angular)44.2 x 133 mas 2 Sample size (in pixels)1 x 10 Number of CCDS in Astro11 x 10 Number of CCDS in BBP5 x 10 TDI integration time per chip3.3 s, 1.9 s Average total obs/object2 x 41 ASM: astrometric sky mappers AF1-11: astrometric field BBP: broad-band photometer MBP: medium-band photometer RVS: radial velocity spectrometer Mission livetime: 5 years Mean number of observations per object during mission: Astrometric field: 82 x 11 CCDs Broad-band phot: 82 x 4 passbands Medium-band phot: 204 x 11 passbands Radial velocity: 102 single observations Launch: Proton Orbit: Sun-Earth L2 (Lissajous) Continuous scanning Two astrometric instruments Monolithic mirrors Non-deployable, 3-mirror, SiC optics Astro focal plane: TDI CCDs Radial velocity/photometry telescope Astrophysically driven payload: faint stars, to V=20 mag radial velocities broad-band photometry: chromaticity medium-band photometry: astrophysics Survey principles: revolving scanning on-board detection complete and unbiased sample