Balmer decrement F_Hα/F_Hβ vs. the effective temperature. Possible young stars are shown with filled symbols. Green stars denote pre-MS M stars from Stelzer et al. (2013a), red triangles correspond to the active M dwarf templates from the Sloan Digital Sky Survey (Bochanski et al. 2007), while data from Frasca et al. (2015) is shown in purple squares. Typical ranges of solar plages and prominences are shown as hatched areas. Typical uncertainties are also shown.