Asteroseismic Masses of Red Giants in the Galactic Globular Clusters M9 & M19

TL;DR

This study uses asteroseismology to measure stellar masses in globular clusters M9 and M19, revealing differences in mass-loss related to metallicity and cluster type, and exploring potential multiple populations.

Contribution

First seismic mass measurements for stars in M9 and M19, establishing a link between mass-loss and metallicity, and highlighting differences between Type I and Type II clusters.

Findings

Mass-loss in M9 is 0.16 solar masses, in M19 is 0.33 solar masses.

M19's higher mass-loss suggests different trends for Type II clusters.

Tentative evidence of two stellar mass populations in the clusters.

Abstract

Asteroseismic masses of globular cluster (GC) stars are invaluable to investigate stellar evolution. Previously, only two GCs have been seismically studied. We present new detections of solar-like oscillations in the clusters M9 and M19, focusing on two key areas: stellar mass loss and GC multiple populations. Using K2 photometry, we detect solar-like oscillations in stars on the red giant branch and early asymptotic giant branch. We measure an integrated mass-loss for M9 of $0.16\pm0.02$(rand)$\pm0.03$(sys)$M_{\odot}$ and M19 of $0.33\pm0.03$(rand)$^{+0.09}_{-0.07}$(sys)$M_{\odot}$. Comparing these to the mass-loss estimates from previous seismically studied clusters, we derive a preliminary relationship between stellar mass-loss and metallicity for Type I GCs. We find that the mass-loss for M19 -- a Type II GC -- is significantly larger, suggesting Type II clusters follow a different mass-loss-metallicity trend. We also examine the mass distributions in each evolutionary phase for evidence of a bimodality that could indicate mass differences between sub-populations. While no clear bimodality is observed, there is tentative evidence suggesting the presence of two mass populations. Classification through spectroscopic abundances into the sub-populations is needed to verify these findings. This study reinforces that asteroseismology of GC stars provides an excellent testbed for studying stellar evolution. However, to advance the field we need high-quality photometry of more GCs, a goal that could be realised with the upcoming Roman Telescope.