SYNTHESIS OF STELLAR MG AND FE ABSORPTION INDEXES FOR STELLAR POPULATION STUDIES .2. THE EXTENDED AND UP-TO-DATE COLLECTION

This paper is mainly concerned with the prediction of absorption-line spectral features in cool stars, to be used as input in stellar popula tion synthesis projects. From a detailed comparison with the solar int ensity spectrum, we have refined the main parameters of atomic and mol ecular absorption lines that are prominent in the 4850-5400 Angstrom w avelength interval. This line list was used to compute an extensive li brary of synthetic stellar spectra at high resolution in the temperatu re range T-eff = 4000-8000 K, surface gravity interval log g = 1.0-5.0 dex, metallicities ([M/H]) from -1.0 to +0.5 dex, and microturbulent velocity xi = 2 km s(-1). The computations were performed by using the latest release of Kurucz's model atmospheres and numerical codes. The library contains a total of 693 synthetic spectra, from which iron an d magnesium indices were obtained, together with the corresponding ''p seudocontinuum'' fluxes. We illustrate the behavior of five ''Lick-lik e'' spectral indices, namely, Mg-1, Mg-2, Mg b, Fe5270, and Fe5335, in terms of the main atmospheric parameters, namely, effective temperatu re, surface gravity, and metallicity. The trend of the indices with mi croturbulent velocity is also illustrated by means of an additional se t of spectra computed at different microturbulent velocities. Transfor mation equations of the theoretical grid into the Lick/IDS observation al database are presented, showing the full consistency of our grid wi th the empirical database.