The table below gives the Harvard spectral types and their corresponding
effective surface temperature ranges, absolute V magnitudes, B-V colours, and
spectral descriptions. Magnitudes and colours are given for main sequence
stars; giants and supergiants are brighter and bluer than the main sequence
stars. Each Harvard type is further divided into 10 subtypes which are marked
with numbers 0, 1 ... 9 (in the order from hottest to coolest) after the
lettered type. (A hint for beginners: Before C type was added to the list,
students of astronomy developed this mnemonic for the spectral types
from hottest to coolest: Oh, Be A Fine Girl, Kiss Me.)
Below the main spectral classification there is a MKK or Yerkes class by
Morgan, Keenan, and Kellman from Yerkes Observatory and
further below some additional prefixes/suffixes. These classes are usually
written in this order (Harvard class, Yerkes class, suffix); e.g. the full
spectral type of the Sun is G2V.
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 supargiants
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
xxxxxxxxxxxx
xxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Created by Rami T. F. Rekola