The Spectral Classification of Stars
The spectral classification of stars consists of three components. A letter-number combination denotes temperature as well as color. A Roman numeral indicates luminosity, which correlates to size. Finally, lower case letters indicate any special conditions. A complete description follows.
Spectral Types
O Blue 40,000-25,000 degrees C.
B Blue 25,000-11,000
A Blue-white 11,000- 7,500
F White 7,500- 6,000
G Yellow-white 6,000- 5,000
K Orange 5,000- 3,500
M Red 3,500- 3,000
Each type is further subdivided by appending numbers between 0 and 9 with 0 being the hotter. For example, a B2 star is hotter than a B7 star.
Luminosity Classes
Ia Bright supergiant
Iab Less bright supergiant
Ib Supergiant
II Bright giant
III Giant
IV Subgiant
V Main sequence (dwarf)
VI Subdwarf
VII White dwarf
Special Cases
p - peculiar
e - hydrogen emission
m - strong metallic lines
f - broad non-hydrogen emission
n or nn - unusually broad lines (due to rotation)
Sources
"Universe Guide to Stars and Planets ", Ian Ridpath and Wil Tirion, Universe
Books, 1985
"Observer’s Handbook 1998", Edited by Roy Bishop, The Royal Astronomical
Society of Canada, 1997
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