% GaiaSAM aims
% AK, FT

   Calibration of the astrophysical parametrization of Gaia sources.

   Improving the models to the extent needed to allow Gaia to achieve its
   science goals, based on basic parameters (Teff, logg, abundances)
   - e.g.  separation of populations by chemical composition.

   To what extent is this possible?

   The result of this work should be an estimation of needed improvements in
   modelling and the achievable parameter accuracies, taking into account the
   limitations of the Gaia instruments.
   
   What are the limiting factors, concerning models and observations?
   (Do they lead to a limiting magnitude, e.g. because RVS data are needed?)

   Examples for how this estimation will be done and some preliminary results.

   e.g. Cycle 4 simulated data with realistic S/N estimates;
   carry out parametrization using NLTE vs. LTE grids (as training or testing grids);
   correction of radial velocities for convection effects,
   tests of flux distributions (correction for continuum flux 1D--$>$3D for BP/RP).
   
   The result of this work will also form the basis for the calibration of
   extended parameters (e.g. activity index).

   Outlook: Preparation for the era after Gaia and follow-up studies.

   This work will be based on observations and models:

   Observations (of "benchmark stars"):

   * calibration stars for AP reference stars (in the framework of
     GBOG=ground-based observations for Gaia)

   * constraints for modelling (e.g. radius measurements, high-resolution spectra)

   Modelling (development and testing):

   * non-LTE for formation of Ca triplet lines (as well as Mg, Ti and Si lines)

   * 3D hydrodynamical atmosphere models

   * input data for line formation and opacities for models


