Dear Erik,

      Please receive the requested short report on on-going activities 
for GAIA photometry. 
      With my best wishes for an happy new year 2002 and regards,
      Michel

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      During the past months - as indicated at Barcelona - little effort 
could be dedicated to GAIA photometry (this until the end of January 2002. 
The prospection of observing sites and of performances of existing instru-
mentation at La Palma, La Silla, Paranal, Hawaii etc., has confirmed the
limited capabilities of new ground-based spectra to help significantly the
selection or the fine-tuning of medium-band system for GAIA.

      The main limitations are the spectral range - UV is often not accessible 
below 360-380nm -, the problem of chromatic losses, the difficulty to monitor
with sufficient time resolution the changes of H2O absorption bands and the
emission of OH bands in the red and near IR.

      The main effects to minimize in GAIA MBP are now the cosmic spread in
metallicity induced by variations of [alpha/Fe] on one hand and the effects 
of drege-up contaminations in the atmospheres of evolved late type-stars. 
These effects lead to systemmatic errors, age or mass dependent, on the
temperatures and [M/H] if the band locations are not finely optimized. Other
parameters as emission features, stellar rotation, chemical anomalies are
limitations to the GAIA classification capabilities which have to be adressed
although they have little or no impact on the number and location of MBP
filters.

     The fine tuning of the band locations requires the knowledge of the
various C,N,O molecular components, namely the NH, OH, CH, CN bands intensi-
ties, plus the corresponding changes of the overall flux distribution due to
changes of blocking and backwarming of the stellar atmospheres. The same is
true for alpha-element abundance changes which lead to a redistribution of 
the flux in the wavelength intervall covered by GAIA MBP.

     Detailed energy distributions (and not just relative spectra) over the
whole range  250-1050nm are hence needed, with various enhancement levels of 
N or alpha-element abundances at given Teff, gravity and overall metallicity.
Observed spectra are of little use for the band tuning since they do not
provide a range of enhancements whereas we look for subtle differential
effects.

     The final number of bands for MBP and their exact location will depend 
on the capability to disentangle [Fe/H], [N/Fe], [alpha/Fe]. The knowledge of
clean [Fe/H] is a requisite to derive the age - metallicity - birthplace
relations from GAIA photometry. The total number of bands is fixed by the
number of astrophysical parameters to be determined. The number of bands in 
the F system was defined by the various scientific goals to address and has 
not been changed since the edition of the ESA-SCI (2000)4. At this time we
tried to minimize dredge-up effects but notalpha-element ehancement effects. 
A modification by +/- 1 band will then wait until reliable synthetic spectra
are available in the course of 2002.

     In parallel the absolute calibration (by M Grenon) of the Geneva photo-
meter P7-2000, now installed at the 1.20 Mercator telescope at La Palma, is 
in progress and should be achieved in early 2002. Absolute fluxes for GAIA
spectroscopic targets could so become available in a near future.

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Addition by Hoeg on 14 Jan.:
At the PWG meeting in Barcelona Grenon took the action to provide a
list of missing photometric targets (MPT) before the end of Dec. 2001,
especially to Kolka for observations in Tartu.

This list has not been produced.
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