Solar-like oscillations in a metal-poor globular cluster with the HST

TL;DR

This study detects solar-like oscillations in red giant stars within a metal-poor globular cluster using HST data, demonstrating oscillations in an environment with significantly lower metallicity than the Sun.

Contribution

First detection of solar-like oscillations in red giants of a very low metallicity globular cluster using HST data and a novel data reduction technique.

Findings

Evidence of solar-like oscillations in 1-4 stars

Achieved noise levels down to 50 ppm in power spectra

Demonstrated oscillations in stars with metallicity much lower than the Sun

Abstract

We present analyses of variability in the red giant stars in the metal-poor globular cluster NGC6397, based on data obtained with the Hubble Space Telescope. We use an non-standard data reduction approach to turn a 23-day observing run originally aimed at imaging the white dwarf population, into time-series photometry of the cluster's highly saturated red giant stars. With this technique we obtain noise levels in the final power spectra down to 50 parts per million, which allows us to search for low amplitude solar-like oscillations. We compare the observed excess power seen in the power spectra with estimates of the typical frequency range, frequency spacing and amplitude from scaling the solar oscillations. We see evidence that the detected variability is consistent with solar-like oscillations in at least one and perhaps up to four stars. With metallicities two orders of magnitude lower than of the Sun, these stars present so far the best evidence of solar-like oscillations in such a low metallicity environment.