SAC Seminar - Madeline Howell, Monash University, Australia
Title: Studying Stellar Evolution using Asteroseismology of Red Giants in Globular Clusters
Info about event
Asteroseismology provides a new avenue for accurately measuring the individual masses of red giants, with the detection of their solar-like oscillations. By measuring seismic masses of globular cluster (GC) stars, we are able to study stellar evolution. I will present the detections of solar-like oscillations in two GCs; M4 and M80. We investigated two major areas of stellar evolution and GC science; i) stellar mass loss, and ii) the multiple populations in GCs. Mass loss remains a major uncertainty in stellar modelling. By taking the differences in the averaged measured masses in various phases of evolution, an integrated mass loss can be quantified. Mass loss is thought to scale with metallicity, which we test by comparing our results for M80 to the seismic masses from the higher-metallicity GC, M4. From this comparison, we notice that there is a significant metallicity and temperature dependence in the mass loss on the horizontal branch. We also investigate whether there are mass differences between the sub-populations in M80. We detect a distinct bimodality in the early asymptotic giant branch mass distribution. This could be a signature of sub-population membership. If confirmed with spectroscopy, it would be the first direct measurement of a mass difference between sub-populations. We also report strong evidence for mass loss differences between the sub-populations in M80. Differing mass loss rates on the red giant branch has been proposed as the second parameter that could explain the horizontal branch morphology variations between GCs.