M starsStars of spectral type M, cool red stars with a surface temperature (T eff) of about 2400 to 3480 kelvin. There is a greater abundance of oxygen to carbon in their surface layers (compare carbon stars), and the excess oxygen is available for the formation of molecular oxides. The spectra are characterized by broad absorption bands of titanium and vanadium oxides (TiO, VO). Lines of neutral metals are also present. Some show emission lines too, and are classed as Me stars. Antares and Betelgeuse are M stars. See also S stars.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006