ON THE USE OF CA-I TRIPLET LINES AS LUMINOSITY INDICATORS

Many strong lines formed in stellar atmospheres are well known to be d ominated by pressure broadening, therefore their wings are a precious help for determining the surface gravities of dwarf or subgiant stars. In this paper, we explore the possibility for using the wings of the Ca I triplet lines 6102, 6122, 6162 Angstrom for which recent theoreti cal computations of the damping are available. A NLTE code for radiati ve transfer was used to check these new computations against the integ rated Solar Spectrum. We report here that (i) there is a spectacular i mprovement in the fit of the computed profile with the observed one wh en the new quantum mechanical computations are used instead of the cla ssical Unsold's expression of the Van der Waals damping constant (ii) the departures from LTE in the computation of the wings of these lines are negligible, and this justifies the use of LTE computations for th e determination of the surface gravities of G type stars, by this meth od.