Lick Spectral Indices for Super-Metal-rich Stars

Abstract

We present Lick spectral indices for a complete sample of 139 candidate super-metal-rich stars of different luminosity classes (MK type from I to V). For 91 of these stars we were able to identify, in an accompanying paper, the fundamental atmosphere parameters. This confirms that at least 2/3 of the sample consists of stars with [Fe/H] in excess of +0.1 dex. Optical indices for both observations and fiducial synthetic spectra have been calibrated to the Lick system according to Worthey et al. and include the Fe I indices of Fe5015, Fe5270, and Fe5335 and the Mg I and MgH indices of Mg<SUB>2</SUB> and Mg b at 5180 Å. The internal accuracy of the observations is found to be σ(Fe5015)=+/-0.32 Å, σ(Fe5270)=+/-0.19 Å, σ(Fe5335)=+/-0.22 Å, σ(Mg<SUB>2</SUB>)=+/-0.004 mag, and σ(Mg b)=+/-0.19 Å. This is about a factor of 2 better than the corresponding theoretical indices from the synthetic spectra, the latter being a consequence of the intrinsic limitations in the input physics, as discussed by Chavez et al. By comparing models and observations, we find no evidence for nonstandard Mg versus Fe relative abundance, so [Mg/Fe]=0, on the average, for our sample. Both the Worthey et al. and Buzzoni et al. fitting functions are found to suitably match the data and can therefore confidently be extended for population synthesis application also to supersolar metallicity regimes. A somewhat different behavior of the two fitting sets appears, however, beyond the temperature constraints of our stellar sample. Its impact on the theoretical output is discussed, as far as the integrated Mg<SUB>2</SUB> index is derived from synthesis models of stellar aggregates. A two-index plot, such as Mg<SUB>2</SUB> versus Fe5270, is found to provide a simple and powerful tool for probing distinctive properties of single stars and stellar aggregates as a whole. The major advantage, over a classical CM diagram, is that it is both reddening free and distance independent. Based on observations collected at the Instituto Nacional de Astrofísica, Optica y Electrónica (INAOE) ``G. Haro'' Observatory, Cananea (Mexico).