Astrophysics (Index)About

M-type star

(M, M-class star)
(spectral class of star with a temperature in the vicinity of 2500 K)

An M-type star is within the M-class, a spectral class indicating stars with very weak hydrogen absorption lines and with molecular lines (particularly titanium oxide), a red color, and a surface temperature in the 2400-3700 K range. The spectral energy distribution peaks in the near infrared. These include some red dwarves (M-dwarf main sequence stars) and red giants (a type of post-main-sequence star), and some hotter brown dwarfs. (The terms red giant also includes spectral types cooler than M class, and sometimes the terms red dwarf and even m dwarf are similarly used for stars cooler than the M class.) Some M dwarfs are AD Leonis, AU Microscopii, Barnard's Star, G239-25, Kapteyn's Star, Lacaille 9352, Lalande 21185, LHS 1140, Luyten 726-8, Proxima Centauri, Ross 154, Ross 248, Scholz's Star, Teegarden's Star, TRAPPIST-1, Wolf 359, and Gliese 581. Some characteristics of main-sequence (MS) M dwarfs:

< 0.7radius(solar)
8-20absolute magnitude(visual)
< 0.08bolometric luminosity(solar)
70 billion-5 trillion yearsmain-sequence lifetime

M-class spectral types, with mass, radius and luminosity of main-sequence M dwarfs as a fraction of the solar values:

typetemp(K)MS solar massesMS radius(solar)MS luminosity(solar)
M13600 0.490.490.035
M23400 0.440.440.023
M33250 0.360.390.015

A Roman numeral V suffix (e.g., M7V) is a luminosity class indicating a main sequence (i.e., dwarf, meaning non-giant) star.

An example M-class red giant is Betelgeuse (an especially large/bright one, i.e., a supergiant). Stars of hotter spectral classes (e.g., the Sun) eventually spend time in a giant phase following their time on the main sequence, in many cases as a red giant. Their luminosity rises and the internal heat puffs them up, resulting in a surface so large that the heat at the surface is diluted, and the surface temperature is lower, often in the M-class range. Such a red giant phase can last up to a billion years, the least massive of such stars having the longest such phase.

(star type,spectral class)
Further reading:

Referenced by pages:
AU Microscopii (AU Mic)
brown dwarf (BD)
calcium (Ca)
infrared (IR)
K-type star (K)
L-type star (L)
M dwarf
solar mass (MSun)
planet demographics
red dwarf
red giant
red-giant branch (RGB)
Scholz's Star
spectral class
Spectroscopic Properties of Cool Stars (SPOCS)
star formation (SF)
stellar demographics
Transiting Exoplanet Survey Satellite (TESS)
TW Hydrae association (TWA)
ultracool dwarf
Wilson-Bappu effect