Exploring the short-term variability of H$\alpha$ and H$\beta$ emissions in a sample of M dwarfs

TL;DR

This study investigates short-term Hα and Hβ emission variability in M dwarfs, revealing that late-type M dwarfs with shorter rotation periods exhibit higher chromospheric activity fluctuations, with flaring events contributing significantly.

Contribution

It provides a comprehensive analysis of short-term emission variability across a wide spectral range of M dwarfs, combining spectroscopic monitoring with archival photometric data to explore activity patterns.

Findings

64% of M dwarfs show significant short-term Hα variability

Late-type M dwarfs with shorter rotation periods are more variable

Flaring events are a primary cause of observed variability

Abstract

The time scales of variability in active M dwarfs can be related to their various physical parameters. Thus, it is important to understand such variability to decipher the physics of these objects. In this study, we have performed the low resolution ($\sim$5.7\AA) spectroscopic monitoring of 83 M dwarfs (M0-M6.5) to study the variability of H$\alpha$ / H$\beta$ emissions; over the time scales from $\sim$0.7 to 2.3 hours with a cadence of $\sim$3-10 minutes. Data of a sample of another 43 late-type M dwarfs (M3.5-M8.5) from the literature are also included to explore the entire spectral sequence. 53 of the objects in our sample ($\sim$64\%) show statistically significant short-term variability in H$\alpha$. We show that this variability in 38 of them are most likely to be related to the flaring events. We find that the early M dwarfs are less variable despite showing higher activity strengths (L$_{H\alpha}$/L$_{bol}$ \& L$_{H\beta}$/L$_{bol}$), which saturates around $\sim$10$^{-3.8}$ for M0-M4 types. Using archival photometric light curves from TESS and Kepler/K2 missions, the derived chromospheric emission (\ha and \hb emission) variability is then explored for any plausible systematics with respect to their rotation phase. The variability indicators clearly show higher variability in late-type M dwarfs (M5-M8.5) with shorter rotation periods ($<$2 days). For 44 sources, their age has been estimated using StarHorse project and possible correlations with variability have been explored. The possible causes and implications for these behaviors are discussed.