A search for solar-like oscillations in K giants in the globular cluster M4

TL;DR

This study conducted a photometry campaign on K giants in globular cluster M4 to detect solar-like oscillations, but found no clear signals, suggesting oscillation amplitudes are lower than expected.

Contribution

First high-precision photometry of K giants in M4 targeting solar-like oscillations, providing constraints on oscillation amplitudes in globular cluster stars.

Findings

No clear oscillation signals detected in K giants.

High-precision photometry achievable in crowded cluster regions.

Oscillation amplitudes are lower than classical predictions.

Abstract

To expand the range in the colour-magnitude diagram where asteroseismology can be applied, we organized a photometry campaign to find evidence for solar-like oscillations in giant stars in the globular cluster M4. The aim was to detect the comb-like p-mode structure characteristic for solar-like oscillations in the amplitude spectra. The two dozen main target stars are in the region of the bump stars and have luminosities in the range 50-140 Lsun. We collected 6160 CCD frames and light curves for about 14000 stars were extracted. We obtain high quality light curves for the K giants, but no clear oscillation signal is detected. High precision differential photometry is possible even in very crowded regions like the core of M4. Solar-like oscillations are probably present in K giants, but the amplitudes are lower than classical scaling laws predict.