New response functions for absorption-line indices from high-resolution spectra^*

Department of Astronomy, University of Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: [tantalo;chiosi;piovan]@pd.astro.it

Received: 6 July 2005
Accepted: 4 August 2006

Abstract

Using a huge library of 1-Å resolution spectra over a wide range of ,  and [Fe/H] and for both solar and α-enhanced abundance ratios [ α/Fe] , we present theoretical absorption-line indices in the Lick system. First we derive the response functions (s) for a wide range of , , [Fe/H], and [ α/Fe]  = +0.4 dex. The s are commonly used to correct indices with solar [ α/Fe]  ratios to indices with [ α/Fe]  > 0. The s vary not only with the type of star but also with metallicity. Second, with the aid of this and the fitting functions (s), we derive the indices for single stellar populations and compare them with those obtained by previous authors. The new s not only supersede the old ones, but also show that  increases with the degree of enhancement. The new indices for single stellar populations are used with aid of the recursive minimum-distance method to derive the age, metallicity, and degree of enhancement of a sample of Galactic globular clusters for which these key parameters have been independently derived from the colour–magnitude diagram and/or spectroscopic studies. The agreement is remarkably good.