Absolute Ca II H & K and H-alpha flux measurements of low-mass stars: Extending R′HK to M dwarfs C. J. Marvin, A. Reiners, G. Anglada-Escudé, S. V. Jeffers and S. Boro Saikia A&A, 671 (2023) A162 Published online: 22 March 2023 DOI: 10.1051/0004-6361/201937306