# High-cadence spectroscopy of M-dwarfs - II. Searching for stellar pulsations with HARPS

## TL;DR

This study used high-precision spectroscopic data to search for stellar pulsations in M-dwarfs, finding no significant signals but establishing detection limits and suggesting the potential for future discoveries with improved instruments.

## Contribution

First observational search for M-dwarf pulsations using HARPS data, setting detection thresholds and highlighting the need for more sensitive instruments.

## Key findings

- No significant pulsation signals detected in the targeted M-dwarfs.
- Pulsations with amplitudes above ~0.5 m/s could be detected with 90% completeness.
- Results suggest the presence of low-amplitude or unresolved pulsations in M-dwarfs.

## Abstract

Stellar oscillations appear all across the Hertzsprung-Russell diagram. Recent theoretical studies support their existence also in the atmospheres of M dwarfs. These studies predict for them short periodicities ranging from 20~min to 3~h. Our Cool Tiny Beats (CTB) programme aims at finding these oscillations for the very first time. With this goal, CTB explores the short time domain of M dwarfs using radial velocity data from the HARPS-ESO and HARPS-N high-precision spectrographs. Here we present the results for the two most long-term stable targets observed to date with CTB, GJ~588 and GJ~699 (i.e. Barnard's star). In the first part of this work we detail the correction of several instrumental effects. These corrections are specially relevant when searching for sub-night signals. Results show no significant signals in the range where M dwarfs pulsations were predicted. However, we estimate that stellar pulsations with amplitudes larger than $\sim0.5\,\mathrm{m\,s}^{-1}$ can be detected with a 90% completeness with our observations. This result, along with the excess of power regions detected in the periodograms, open the possibility of non-resolved very low amplitude pulsation signals. Next generation more precise instrumentation would be required to detect such oscillations. However, the possibility of detecting pulsating M-dwarf stars with larger amplitudes is feasible due to the short size of the analysed sample. This motivates the need for completeness of the CTB survey.