Synthetic spectroscopic indices for identifying multiple stellar
  populations in globular clusters
  We present an investigation of synthetic spectroscopic indices that can
plausibly help in identifying the presence of multiple stellar populations in
globular clusters. The study is based on a new grid of stellar model
atmospheres and high-resolution (R=500,000) synthetic spectra, that consider
chemical partitions that have been singled out in Galactic globular clusters.
The database is composed of 3472 model atmospheres and theoretical spectra
calculated with the collection of Fortran codes DFSYNTHE, ATLAS9 and SYNTHE,
developed by Robert L. Kurucz. They cover a range of effective temperature from
4300 to 7000 K, surface gravity from 2.0 to 5.0 dex and four different chemical
compositions. A set of 19 spectroscopic indices were calculated from a degraded
version (R=2500) of the theoretical spectra dataset. The set includes five
indices previously used in the context of globular clusters analyses and 14
indices that we have newly defined by maximizing the capability of
differentiating the chemical compositions. We explored the effects of
atmospheric parameters on the index values and identified the optimal spectral
diagnostics that allow to trace the signatures of objects of different stellar
populations, located in the main sequence, the red giant branch and the
horizontal branch. We found a suitable set of indices, that mostly involve
molecular bands (in particular NH, but also CH and CN), that are very promising
for spectroscopically identifying multiple stellar populations in globular
clusters.
