Using Asteroseismology to Measure Masses of Evolved Stars in M4

Asteroseismology provides a new avenue to study stellar evolution and globular cluster (GC) formation. Using photometry from the K2 mission, we have measured asteroseismic masses for 39 evolved stars in the GC M4, and found the integrated mass loss along the red giant branch and red horizontal branch. M4 remains the only GC for which it is possible to measure mass loss with the current available photometry. This study reports the largest ever seismic analysis of GC stars, and also the first detection of oscillations in early asymptotic giant branch stars in GCs. Interestingly, we discovered a weak bi-modal mass distribution along each branch. With future spectroscopic measurements, we aim to determine if the bi-modality reflects the multiple populations of M4. If the mass difference is confirmed to track the multiple populations, then this is strong independent evidence for the inferred He differences between populations. This He variation will correspond to different population ages, which supports the hypothesis that the sub-populations in a GC are different generations.