Determining PPN gamma with Gaia's astrometric core solution

Abstract:
The ESA space astrometry mission Gala, due for launch in early 2012, will in addition to its huge output of fundamental astrometric and astrophysical data also provide stringent tests of general relativity. In this paper we present an updated analysis of Gaia's capacity to measure the PPN parameter gamma as part of its core astrometric solution. The analysis is based on small-scale astrometric solutions taking into account the simultaneous determination of stellar astrometric parameters and the satellite attitude. In particular, the statistical correlation between PPN gamma and the stellar parallaxes is considered. Extrapolating the results to a full-scale solution using some 100 million stars, we find that PPN gamma could be obtained to about 10(-6), which is significantly better than today's best estimate from the Cassini mission of 2 x 10(-5).