The FEROS--Lick/SDSS observational database of spectral indices of FGK stars for stellar population studies

TL;DR

This paper introduces an empirical database of spectral indices for FGK stars, derived from FEROS spectra, to improve stellar population analysis in galaxies and clusters, and compares observations with synthetic models.

Contribution

It provides a large, validated spectral index database for FGK stars and assesses the accuracy of synthetic models in reproducing observed stellar spectral features.

Findings

Synthetic library reproduces observational indices well for higher temperatures.

Discrepancies observed for low-temperature dwarfs and subgiants, especially below 5000 K.

Discussion of potential causes and improvements for modeling low-temperature stellar spectra.

Abstract

We present FEROS--Lick/SDSS, an empirical database of Lick/SDSS spectral indices of FGK stars to be used in population synthesis projects for discriminating different stellar populations within the integrated light of galaxies and globular clusters. From about 2500 FEROS stellar spectra obtained from the ESO Science Archive Facility we computed line--strength indices for 1085 non--supergiant stars with atmospheric parameter estimates from the AMBRE project. Two samples of 312 {\it dwarfs} and of 83 {\it subgiants} with solar chemical composition and no significant $\alpha$--element abundance enhancement are used to compare their observational indices with the predictions of the Lick/SDSS library of synthetic indices. In general, the synthetic library reproduces very well the behaviour of observational indices as a function of temperature, but in the case of low temperature ($T_{\rm eff}$ $\lesssim $5000\,K) dwarfs; low temperature subgiants are not numerous enough to derive any conclusion. Several possible causes of the disagreement are discussed and promising theoretical improvements are presented.