Spectral Type | Teff | MV (main sequence) | B-V (main sequence) | Description (of the spectrum) |
O | > 25000 K | < -4.1 | < -0.31 | Relatively few absorption lines. Lines of ionized He, doubly ionized N, triply ionized Si. H lines weak. |
B | 11000 - 25000 K | 0.7 - -4.1 | 0.0 - -0.31 | Lines of neutral He, singly ionized O and Mg. H lines stronger than in O stars. |
A | 7500 - 11000 K | 2.6 - 0.7 | 0.27 - 0.0 | Strong H lines. Lines of singly ionized Mg, Si, Fe, Ti, Ca etc. and some neutral metals. |
F | 6000 - 7500 K | 4.4 - 2.6 | 0.58 - 0.27 | H lines weaker and neutral metal lines stronger than in A stars. Lines of singly ionized Ca, Fe, Cr. |
G | 5000 - 6000 K | 5.9 - 4.4 | 0.89 - 0.58 | Lines of ionized Ca most conspicuous features. Many lines of ionized and neutral metals. CH bands. |
K | 3500 - 5000 K | 9.0 - 5.9 | 1.45 - 0.89 | Neutral metal lines predominate. CH bands present. |
M | < 3500 K | > 9.0 | > 1.45 | Strong lines of neutral metals and molecular bands of TiO. |
C | 2000 - 5400 K | CARBON STARS. Strong bands of molecular carbon, CN, CH, or other carbon compounds; no TiO. | ||
MKK / Yerkes class | Description | |||
Ia | luminous supergiants | |||
Ib | less luminous supergiants | |||
II | bright giants | |||
III | normal giants | |||
IV | sub giants | |||
V | dwarfs (main sequence stars) | |||
rarely used: | VI | subdwarfs | ||
rarely used: | VII | white dwarfs | ||
Additional info: | prefix / suffix | Description | ||
c | sharp lines | |||
d | dwarf (main sequence star) | |||
D | white dwarf | |||
e | emission (hydrogen emission in O stars) | |||
em | emission in metal lines | |||
ep | peculiar emission | |||
eq | emission with shorter wavelength absorption | |||
f | emission by helium and neon in O stars | |||
g | giant | |||
k | interstellar lines | |||
m | strong metallic lines | |||
n | diffuse lines | |||
nn | very diffuse lines | |||
p | peculiar spectrum | |||
s | sharp lines | |||
sd | subdwarf | |||
wd | white dwarf | |||
wk | weak lines | |||
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