Chemical abundance ratios of galactic globular clusters from modelling
  integrated light spectroscopy
  We use our new, flux-calibrated stellar population model of absorption-line
indices to derive ages, metallicities, and various element abundance ratios
from integrated light spectroscopy of galactic globular clusters. The ages
agree well with the literature and are all consistent with the age of the
universe. There is a considerable scatter, though, and we obtain systematically
larger ages than CMD determinations mostly for metal-rich globular clusters.
The metallicities agree well with literature values on the Zinn & West scale,
if we adopt iron abundance [Fe/H] for those clusters whose ages agree with the
CMD ages. It turns out that the derivation of individual element abundance
ratios is not reliable at [Fe/H]<-1 dex, while the [alpha/Fe] ratio is robust
at all metallicities. We find general enhancement of light and alpha elements,
as expected, with significant variations for some elements. The elements O and
Mg follow the same general enhancement with almost identical distributions of
[O/Fe] and [Mg/Fe]. We obtain slightly lower [C/Fe] and very high [N/Fe]
ratios, instead. This chemical anomaly, commonly attributed to self-enrichment,
is well known in globular clusters from individual stellar spectroscopy. It is
the first time that this pattern is obtained also from the integrated light.
The alpha elements follow a pattern such that the heavier elements Ca and Ti
are less enhanced. More specifically, the [Ca/Fe] and [Ti/Fe] ratios are lower
than [O/Fe] and [Mg/Fe] by about 0.2 dex. This trend is also seen in recent
determinations of element abundances in globular cluster and field stars of the
Milky Way. This suggests that Type Ia supernovae contribute significantly to
the enrichment of the heavier alpha elements as predicted by nucleosynthesis
calculations and galactic chemical evolution models.
