Characterisation of magnetic activity of M dwarfs - Possible impact on surface brightness R. V. Ibañez Bustos, A. P. Buccino, N. Nardetto, D. Mourard, M. Flores and P. J. D. Mauas A&A, 696 (2025) A230 Published online: 28 April 2025 DOI: 10.1051/0004-6361/202450348