Flare frequency in M dwarfs belonging to young moving groups

¹ Centre for Planetary Habitability (PHAB), University of Oslo, 0315 Oslo, Norway
² National Solar Observatory, University of Colorado Boulder, 3665 Discovery Drive, Boulder, CO 80303, USA
³ Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, 2000 Colorado Ave, CO 80305, USA
⁴ Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, 3665 Discovery Drive, Boulder, CO 80303, USA
⁵ Rosseland Centre for Solar Physics, University of Oslo, 0315 Oslo, Norway
⁶ Institute of Theoretical Astrophysics, University of Oslo, 0315 Oslo, Norway

^⋆ Corresponding author.

Received: 18 March 2025
Accepted: 29 May 2025

Abstract

Context. M stars are preferred targets for upcoming studies of terrestrial exoplanets aimed at obtaining their atmosphere spectra over the next decade. However, M dwarfs have long been known for their strong magnetic activity and the ability to frequently produce optical and broadband emission flares.

Aims. We aim to characterise the flaring behaviour of young M dwarfs in the temporal, spectral, and energy dimensions, as well as examine the stellar parameters governing this behaviour. In this way, we aim to improve our understanding of the energy and frequency of the flare events capable of shaping the exoplanet atmosphere.

Methods. Members of young moving groups (YMGs) provide a unique age-based perspective on stellar activity. By examining their flare behaviour in conjunction with rotation, mass, and Hα data, we can obtain a comprehensive understanding of flare-activity drivers in young stars.

Results. We demonstrate that young stars sharing similar stellar parameters could also exhibit a broad range of flare frequency distributions. We also find that the flare behaviour shows indications of difference between optical and far ultraviolet (FUV). We propose that the period of rotation (and not the age of the star) can serve as a good proxy for assessing flaring activity. Furthermore, we recommend that instead of a simple power law for describing the flare frequency distribution, a piecewise power law can be used to describe mid-size and large flare distributions in young and active M dwarfs.

Conclusions. Using known periods of rotation and fine-tuned power laws governing the flare frequency, we can produce a realistic sequence of flare events to study whether the atmosphere of small exoplanets orbiting M dwarf could withstand such activity until the emergence of life.