JF is supported by JNICT (BPD/9919/96). This work was partially supported by the France-Portugal co-operation (project 059-B0). We gratefully thank Pierre Morel for his help with CESAM, and H.-G. Ludwig for having made available results prior to publication. MNP is grateful to R. Canavaggia for her help in the selection of target stars of the Hipparcos proposal 132.
© European Southern Observatory (ESO) 1999
Online publication: October 4, 1999