EDP Sciences
Free access
Volume 399, Number 1, February III 2003
Page(s) 337 - 342
Section The solar system
DOI http://dx.doi.org/10.1051/0004-6361:20021785

A&A 399, 337-342 (2003)
DOI: 10.1051/0004-6361:20021785

Testing general relativity by micro-arcsecond global astrometry

A. Vecchiato1, 2, 3, M. G. Lattanzi4, B. Bucciarelli4, M. Crosta4, 2, 3, F. de Felice1, 2, 3 and M. Gai4

1  Istituto di Fisica "G. Galilei", Via Marzolo 8, 35100 Padova, Italy
2  Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Padova
3  Centro per gli Studi e le Attività Spaziali "G. Colombo" (CISAS), Padova
4  INAF, Osservatorio Astronomico di Torino, 10025 Pino Torinese TO, Italy

(Received 24 October 2002 / Accepted 27 November 2002)

The global astrometric observations of a GAIA-like satellite were modeled within the PPN formulation of Post-Newtonian gravitation. An extensive experimental campaign based on realistic end-to-end simulations was conducted to establish the sensitivity of global astrometry to the PPN parameter  $\gamma$, which measures the amount of space curvature produced by unit rest mass. The results show that, with just a few thousands of relatively bright, photometrically stable, and astrometrically well behaved single stars, among the ~ 109 objects that will be observed by GAIA, $\gamma$ can be estimated after 1 year of continuous observations with an accuracy of ~ 10-5 at the $3\sigma$ level. Extrapolation to the full 5-year mission of these results based on the scaling properties of the adjustment procedure utilized suggests that the accuracy of $\simeq$ $ 2\times 10^{-7}$, at the same $3\sigma$ level, can be reached with ~ 106 single stars, again chosen as the most astrometrically stable among the millions available in the magnitude range V=12-13. These accuracies compare quite favorably with recent findings of scalar-tensor cosmological models, which predict for $\gamma$ a present-time deviation, $\left\vert 1 - \gamma \right\vert$, from the General Relativity value between 10-5 and  10-7.

Key words: astrometry -- relativity -- gravitation -- space vehicles: instruments

Offprint request: M. G. Lattanzi, lattanzi@to.astro.it

© ESO 2003

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