The cross-correlation between the ROSAT all-sky survey ( sources) and the Tycho mission ( stars) catalogs has selected about 14000 stellar X-ray sources (RasTyc sample, Guillout et al. 1999, A&A 351, 1003). Although most of these soft X-ray sources are expected to be the youngest stars in the solar neighbourhood, neither the contamination by older RS CVn systems nor the fraction of BY Dra binaries are actually known. This information is, however, of fundamental importance for studying the recent local star formation history and, for instance, for putting constrains on the scale height of the spatial distribution of nearby young stars around the galactic plane.
In collaboration with P. Guillout and R. Freire Ferrero of Strasbourg Observatory, A. Frasca, E. Marilli and K. Biazzo started a spectroscopic observation campaign aimed at a deep characterisation of a representative sub-sample of the RasTyc population. Spectroscopic observations were performed both at the Observatoire of Haute Provence (OHP) and at M.G. Fracastoro station of OACt. In particular, with the OACt telescopes, they could monitor both spectroscopically and photometrically the more interesting discovered objects.
They have obtained good radial velocity curves and solved for
the orbits of three double-lined (SB2) and three single-lined (SB1) spectroscopic binaries
An accurate spectral classification, both for SB1 and SB2 systems, was also performed.
In addition, for near all sources they have detected a photometric
modulation ascribable to photospheric surface inhomogeneities and
chromospheric H line variation.