Young M-dwarfs flare activity model: Towards better exoplanetary atmospheric characterisation

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: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 13 August 2025
Accepted: 20 November 2025

Abstract

Context. Stellar flares can significantly influence the atmospheres and habitability of orbiting exoplanets, especially around young and active M dwarfs. Understanding the temporally and spectrally resolved activity of such stars is essential for assessing their impact on planetary environments.

Aims. We aim to examine in detail state-of-the-art concepts of flare models to identify what is missing in our understanding of energy deposition during the flare event. By comparing synthetic and observed flare spectra, we seek to determine the modelling frameworks best suited for representing flare energetics and spectral far-ultraviolet features while providing a foundation for investigating flare impacts on exoplanet atmospheres.

Methods. In this work, we built the Young M dwarf flare (YMDF) model utilising the combination of radiative-hydrodynamic (RHD) stellar atmosphere models with a high- and low-energy electron beam and corresponding synthetic observables. These models are based on physical principles and were validated with solar and stellar observations.

Results. The newly developed YMDF model reproduces the observed continuum rise in both the TESS photometric band and the FUV-A spectral range. Furthermore, the flare distributions generated within this framework show consistency with those observed in our sample of stars.

Conclusions. We have developed the YMDF model as a tool to reproduce the time-dependent spectra of flaring young M dwarfs, providing a physically motivated description of their spectral and temporal evolution during flare events.