Definition Red dwarf

proxima centauri, closest star sun @ 4.2 ly, red dwarf

the term red dwarf when used refer star not have strict definition. 1 of earliest uses of term in 1915, used contrast red dwarf stars hotter blue dwarf stars. became established use, although definition remained vague. in terms of spectral types qualify red dwarfs, different researchers picked different limits, example k8–m5 or later k5 . dwarf m star, abbreviated dm, used, included stars of spectral type k.

in modern usage, definition of red dwarf still varies. when explicitly defined, typically includes late k- , mid-m-class stars, in many cases restricted m-class stars. in cases k stars included red dwarfs, , earlier stars.

the coolest true main-sequence stars thought have spectral types around l2 or l3, many objects cooler m6 or m7 brown dwarfs, insufficiently massive sustain hydrogen-1 fusion.