Reevaluating Old Stellar Populations
  Determining the properties of old stellar populations (those with age >1 Gyr)
has long involved the comparison of their integrated light, either in the form
of photometry or spectroscopic indexes, with empirical or synthetic templates.
Here we reevaluate the properties of old stellar populations using a new set of
stellar population synthesis models, designed to incorporate the effects of
binary stellar evolution pathways as a function of stellar mass and age. We
find that single-aged stellar population models incorporating binary stars, as
well as new stellar evolution and atmosphere models, can reproduce the colours
and spectral indices observed in both globular clusters and quiescent galaxies.
The best fitting model populations are often younger than those derived from
older spectral synthesis models, and may also lie at slightly higher
metallicities.
