VILNIUS GAIA GROUP
         Report: GAIA-VIL-006, 25 MAY 2001

   MAIN GAIA PARAMETERS RELEVANT TO THE PHOTOMETRY

        Vladas Vansevicius(*) and Erik Hoeg(**)

 * Institute of Physics, Gostauto 12, 2600 Vilnius, Lithuania
** Copenhagen University Observatory, Juliane Mariesvej 28-32,
   DK-2100 Copenhagen, Denmark


Abstract.
We present main parameters of the GAIA instruments relevant
to the broad and medium band photometry, and optimization
of the photometric systems. It is rather time consuming
task to retrieve these data from the GSR or scattered
sources, therefore, we believe that this table will
serve as a quick reference for potential designers.

(Please report any possible corrections to V.V.: wladas@astro.lt)

TABLE 1. MAIN PARAMETERS OF THE GAIA INSTRUMENTS.
         See GSR, Fig.3.7 about sampling.
===================================================================
Parameter                                          Value
===================================================================

ASTRO-1,2
===================================================================
Optical transmittance (250-1100 nm)                 0.9
Rectangular pupil size along scan (m)               1.70
Rectangular pupil size across scan (m)              0.70
Focal plane scale 1 arcsec (um)                     242
CCD chip #1B
CCD pixel size along scan (um)                      9
CCD pixel size across scan (um)                     27
TDI integration time per 1 CCD (s)                  0.86
Number of transits per star in each Astro telesc.   67

ASTRO-1
Sample size along scan (pix)                        1
Sample size across scan (pix)                       8
RON (e/sample, as read out)                         6.2
Samples for photometry of the star, read out        6
Samples for photometry of the star, transmitted     6
Samples to derive the sky, read out                 10
Samples to derive the sky, transmitted              4

ASTRO-2
Sample size along scan (pix)                        6
Sample size across scan (pix)                       8
RON (e/sample, as read out)                         5.0
Samples for photometry of the star, read out        2
Samples for photometry of the star, transmitted     2
Samples to derive the sky, read out                 8
Samples to derive the sky, transmitted              8
===================================================================

SPECTRO
===================================================================
Optical transmittance (250-1100nm)                  0.81
Rectangular pupil size along scan (m)               0.75
Rectangular pupil size across scan (m)              0.70
Focal plane scale 1 arcsec (um)                     20
CCD chip #1B (<600 nm)
CCD chip #2  (>600 nm)
CCD pixel size along scan (um)                      10
CCD pixel size across scan (um)                     10
TDI integration time per 1 CCD (s)                  3.04
Number of transits per star                         100
Sample size along scan (pix)                        1
Sample size across scan (pix)                       4
RON (e/sample, as read out)                         3.0
Samples for photometry of the star, read out        4
Samples for photometry of the star, transmitted     4
Samples to derive the sky, read out                 10
Samples to derive the sky, transmitted              4
===================================================================



TABLE 2. MISCELLANEOUS INFORMATION (proposal to unify)
===================================================================
1. Sky background model SED:
     (Teff=5750 K, log g=4.5, [Fe/H]=0.0, Kurucz)
     (V_Johnson mag/arcsec^2)                       22.5
2. Magnitude normalization: V_Johnson filter
3. Color indices set to 0.0 for the model SED:
     (Teff=40000 K, log g=4.5, [Fe/H]=0.0, Kurucz)
===================================================================



TABLE 3. SUPPLEMENTARY INFORMATION OF THE GAIA INSTRUMENTS
         See also GSR, Table 3.16.
===================================================================
Parameter                             BBP1    BBP2    MBP     RVS
===================================================================
Number of CCDs along scan             5       5       16      1
Total number of chips                 50      50      16      2
TDI lines per chip                    2780    2780    730     3650
Columns per chip                      2150    2150    7300    1220
Pixel size, [um]                      9x27    9x27    10x10   20x20
Sample binning, [pixels]              1x8     6x8     1x4     1x1
Samples per star read out             16      10      14      930
Samples per star transmitted          10      10      8       930
RON, [e/sample, as read out]          6.2     5.0     3.0     3.0
TDI integration time per CCD, [s]     0.86    0.86    3.0     30
Limiting magnitude, [G]               20      20      20      17
Average star density, [deg^{-2}]      25000   25000   25000   2900
Readout rate, [stars/s]               2200    2200    11700   100
===================================================================
Notes:
BBP1, BBP2 - broad band photometric system for ASTRO-1,2.
MBP - medium band photometric system for SPECTRO.
RVS - radial velocity spectrometer.