On the Anomalous Balmer Line Strengths in Globular Clusters
  Spectral feature index diagrams with integrated globular clusters and simple
stellar population models often show that some clusters have weak H beta, so
weak that even the oldest models cannot match the observed feature depths. In
this work, we rule out the possibility that abundance mixture effects are
responsible for the weak indices unless such changes operate to cool the entire
isochrone. We discuss this result in the context of other explanations,
including horizontal branch morphology, blue straggler populations, and nebular
or stellar emission fill-in, finding a preference for flaring in M giants as an
explanation for the H beta anomaly.
