THE ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, INPRESS, 1997 June

      A NEW CHEMO-EVOLUTIONARY POPULATION SYNTHESIS MODEL FOR EARLY-TYPE
                    GALAXIES. II. OBSERVATIONS AND RESULTS

     A. VAZDEKIS[1], R. PELETIER[1,2], J. E. BECKMAN[1], AND E. CASUSO[1]

                                   ABSTRACT

        We present the results of applying a new chemo-evolutionary stellar
     population model, developed in a previous paper, to new high-quality
     observational data of the nuclear regions of two representative
     elliptical galaxies and the bulge of the Sombrero galaxy. Here we fit
     in detail ~20 absorption lines and six optical and near-infrared
     colors, following two approaches: fitting a single-age,
     single-metallicity model and fitting our full chemical evolutionary
     model. We find that all the iron lines are weaker than the
     best-fitting models predict, indicating that the iron abundance is
     anomalous and deficient. We also find that the Ca I index at 4227 A is
     much lower than predicted by the models. We can obtain good fits for
     all the other lines and observed colors with models of old and
     metal-rich stellar populations and can show that the observed radial
     gradients are due to metallicity decreasing outward. We find that good
     fits are obtained both with fully evolutionary models and with
     single-age, single-metallicity models. This is due to the fact that in
     the evolutionary model more than 80% of the stars form within 1.5 Gyr
     after the formation of the galaxies. The fact that slightly better
     fits are obtained with evolutionary models indicates that these
     galaxies contain a small spread in metallicity.

     Subject headings: galaxies: abundances -- galaxies: evolution --
                       galaxies: nuclei -- galaxies: stellar content