- For other uses, see Class O.
An O-class (or O-type) star is a stellar classification for stars composed of ionized atoms, especially helium, emitting high amounts of ultraviolet radiation, generally referred to as being blue-violet or dark blue in color. O-type stars in the main sequence tend to be extremely hot in temperature (in the neighborhood of 28,000 to 50,000 Kelvin) and bright in terms of absolute magnitude, the "dark" and "violet" descriptors of their name are as such because of the large output of non-visible heat radiation. (ST reference: Star Charts)
- O9.5II: Delta Orionis Aa1 (part of the Mintaka system). The Star Charts reference refers to the multiple star Mintaka by its combined spectral class of O1-3III.
|By class and type||class O blue-violet star • class B blue star • class A blue-white star • class F white star (white dwarf) • class G yellow star (yellow dwarf • yellow giant) • class K orange star (orange giant) • class M red star (red dwarf • red giant) • green star • brown dwarf • N-type star • R-type star • S-type star • D-type star|
|By size or makeup||black hole/black star • carbon star • collapsar • dwarf star (brown dwarf • red dwarf • white dwarf • yellow dwarf) • giant star (blue giant • red giant • orange giant • yellow giant) • Lazarus star • neutron star • protostar • pulsar • supergiant star • Wolf-Rayet star|