Spectral Classification

The full version of this (with spectra) is at http://cfa-www.harvard.edu/~pberlind/atlas/htmls/note.html

OBAFGKM - At Mount Holyoke: "Only Boys Accepting Feminism Get Kissed Meaningfully"

Spectral Type Surface Temperature Distinguishing Features
O > 25,000K H; HeI; HeII
B 10,000-25,000K H; HeI; HeII absent
A 7,500-10,000K H; CaII; HeI and HeII absent
F 6,000-7,500K H; metals (CaII, Fe, etc)
G 5,000-6,000K H; metals; some molecular species
K 3,500-5,000K metals; some molecular species
M < 3,500K metals; molecular species (TiO!)
C < 3,500K metals; molecular species (C2!)
Within this stars are ranked hotter (subclass 0) to cooler (subclass 9).

Luminosity classes

are determined from spectral features and photometric measurements, coupled with information regarding the distance to the star and theamount of extinction of the starlight from interstellar material. The luminosity class designation describes the size (gravitational acceleration in photosphere) of a star from the atmospheric pressure. For larger stars of a given spectral type, the surface gravity decreases relative to what it was on the main sequence, and this decreases the equivalent widths of the absorption lines.

Luminosity Class Description Comments
0 Hypergiants extreme
Ia Supergiants! large and luminous
Ib Supergiants! less luminous than Ia
II Bright Giants  
III Giants  
IV Sub-Giants  
V Dwarfs Main Sequence
sd Sub-Dwarfs  
D White Dwarfs  

Peculiar features

Peculiarity Code Description
comp composite spectrum
e emission lines present
f NIII and HeII emission (O stars)
m enhanced metal features
n broad absorption features
nn very broad absorption features
neb nebular features present
p other peculiarity
s very narrow absorption lines
sh shell star
var variable spectral features
wl weak features
: uncertainty