Comparison of Alpha-Element Enhanced Simple Stellar Population Models
  with Milky Way Globular Clusters
  We present simple stellar population (SSP) models with scaled-solar and
alpha-element enhanced abundances. The SSP models are based on the Dartmouth
Stellar Evolution Database, our library of synthetic stellar spectra, and a
detailed systematic variation of horizontal-branch (HB) morphology with age and
metallicity. In order to test the relative importance of a variety of SSP model
ingredients, we compare our SSP models with integrated spectra of 41 Milky Way
Globular Clusters (MWGCs) from Schiavon et al. (2005). Using the Mg b and
Ca4227 indices, we confirm that Mg and Ca are enhanced by about +0.4 and +0.2
dex, respectively, in agreement with results from high resolution spectra of
individual stars in MWGCs. Balmer lines, particularly Hgamma and Hdelta, of
MWGCs are reproduced by our alpha-enhanced SSP models not only because of the
combination of isochrone and spectral effects but also because of our
reasonable HB treatment. Moreover, it is shown that the Mg abundance
significantly influences Balmer and iron line indices. Finally, the
investigation of power-law initial mass function (IMF) variations suggests that
an IMF much shallower than Salpeter is unrealistic because the Balmer lines are
too strong on the metal-poor side to be compatible with observations.
