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M star

An M star is a cool, red star, of spectral type M, with a surface temperature of less than 3,600°C. Molecular absorption bands are prominent in the spectrum, with bands of titanium oxide becoming dominant at the lower end of the temperature range.

Main sequence M stars, known as red dwarfs, have a mass of less than 0.5 Msun (mass of the Sun) and a luminosity of less than 0.08 Lsun (luminosity of the Sun); examples include the nearby Proxima Centauri and Barnard's Star.

M-type giant stars, known as red giants, occur in the mass range 1.2 to 1.3 Msun and may have luminosities exceeding 300 Lsun. The largest stars of all are M-type supergiants, such as Betelgeuse and Antares, of mass of 13 to 25 Msun and luminosity of 40,000 to 500,000 Lsun.

An Me star is an M star with emission lines in its spectrum. Some Mira stars are of this type, as also are some M-type dwarfs known as dMe stars.

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