Inferring the Helium abundance of extragalactic Globular Clusters using
  Integrated Spectra
  The leading method for the determination of relevant stellar population
parameters of unresolved extragalactic Globular Clusters is through the study
of their integrated spectroscopy, where Balmer line-strength indices are
considered to be age sensitive. Previously, a splitting in the highly optimised
spectral line-strength index H$\beta_o$ was observed in a sample of Galactic
globular clusters at all metallicities resulting in an apparent "upper branch"
and "lower branch" of globular clusters in the H$\beta_o$ - [MgFe] diagram.
This was suggested to be caused by the presence of hot Blue straggler stars
(BSSs), resulting in an underestimation of 'spectroscopic' ages in the upper
branch. Over a decade on, we look to re-evaluate these findings. We make use of
new, large Galactic Globular Cluster integrated spectroscopy datasets. To
produce a large, homogeneously combined sample we have considered a number of
factors including the radial dependence of Balmer and metal lines. Using this
new sample, in disagreement with previous work, we find the splitting in
H$\beta_o$ only occurs at intermediate to high metallicities ([M/H]$>-1$), and
is not the result of an increased fraction of BSSs, but rather is due to an
increased Helium abundance. We explore the possible impact of varying Helium on
simple stellar population models to provide a theoretical basis for our
hypothesis and then use the relationship between upper branch candidacy and
enhanced Helium to predict the Helium content of three M31 clusters. We discuss
what this can tell us about their mass and fraction of first generation stars.
