It has been decided that all the Gaia working groups will be dissolved by the end of the year 2005 and will be replaced by
the structure of following Coordination Units (CU):
CU1: System Architecture (William O'Mullane); CU2: Data Simulations (Xavier Luri); CU3: Core Processing (Uli Bastian);
CU4: Object Processing (Dimitri Pourbaix); CU5: Photometric Processing (Floor van Leeuwen); CU6: Spectroscopic Processing (David Katz);
CU7: Variability Processing (Laurent Eyer) ; CU8: Astrophysical Parameters (Coryn Bailer-Jones);
CU9: Catalogue Access (to be activated nearer to launch).
We would like to thank Francesca Figueras (former leader of the VSWG, 2001-2003), Dafydd Evans (co-task leader of the VSWG, 2003-2005),
and all the active members of the VSWG who helped us to make this group lively and fruitful for the Gaia mission.
The Variable star working group objective is to assess the relevance
of GAIA for different variable star types, given the specification of the
satellite, and to develop software in order to be able to cope with
the huge amount of data the mission will provide: that is to efficiently
describe and classify the data.
The aim of this document is to provide a common baseline for the working
group, to engage specialists in order to have some guidances and to
define the working plan to be treated inside this working group during the
forthcoming advanced technology/design consolidation phase, i.e. until about
mid 2004.
GAIA will provide multi-epoch multi-colour photometry for all variable
sources brighter than G = 20. This data will have the precision
necessary to allow a global description of the stellar variability in
terms of physical parameters such as luminosity, temperature and
chemical composition. Furthermore, for variable sources identified as
stellar candles - RR-lyrae, Cepheids, LPV, PN,.. - GAIA will provide
the data needed for determining the extragalactic distance scale (Luri
et al., 2001).
As stated by Paczynski & Pojmanski (1997): A few percent of
all stars are variable, yet more than 90 percent of variables brighter
than 12 magnitude have not been discovered yet . GAIA will make a
revolution in this domain; present estimations from Eyer and Cuypers
(2000), based on conservative hypotheses, indicate that GAIA can
detect about 18 million variables sources, including 5 million classic
periodic variable stars and 2-3 million eclipsing binaries.
On the other hand, and particularly for the variable star domain,
complementary data coming from GAIA and from other ongoing space
missions and ground-based surveys (DENIS, 2mASS, IRAS, ISO,...) will
be fundamental for understanding the complex physical processes
related with these objects.
During the next months and years, the work developed inside the
Variable Stars Working Group will depend on future changes on
instrument design (some specifications, especially for the spectro
instrument, have not yet been settled). It could be optimal if our
working group could provide some guidances on these future changes and
definitions. For example:
Technological challenges i.e. filters and CCD's degradation during mission. How does this affect variability treatment?
Structure of patches and samples for CCDs readout. Are the present design optimal for variable stars detection and treatment?
Choice of Broad and Medium Band Photometric systems. Accuracy reached versus variability detection.
Astrometric and photometric reduction processes and on board detection algorithms. Do variable sources need a special treatment?
The inputs coming from our working group on these and other future
open subjects will suppose an important contribution to the success
of the GAIA mission.