The ratio of α-elements to iron in early-type galaxies from TiO and Mg2

In order to derive the ratio of alpha-elements to iron in galaxies, we have observed the strongest TiO band heads of the gamma and gamma' systems at 7000-7500 Angstrom in a sample of a dozen early-type galaxies. The equivalent widths of the TiO bands are compared with synthetic spectra for single-aged stellar populations and composite galaxy models, all computed with [alpha/Fe] = 0.0 and +0.3. The same method is also applied to the (Fe) and Mg-2 Lick indices for the sample galaxies. The results obtained are [Ti/Fe] approximate to [Mg/Fe] approximate to +0.3, indicating a clear enhancement of the alpha-elements-to-iron ratio for our sample of early-type galaxies.