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Star Classification

Spectral Classification

  • Originally we used a system based on the strength of hydrogen absorption lines
  • A new system was introduced based on decreasing temperature
    • Introduced by Annie Jump Cannon
    • Each class is further subdivided into 10 subclasses
      • Using numbers 0 through 9
    • Mnemonic for remembering:
      • Oh Be A Fine Girl, Kiss Me

Spectral Classes

Spectral Class Colour Approximate Temperature Principle Features
O Blue >30,000 K Neutral and ionized helium lines, weak hydrogen lines
B Blue-white 10,0000-30,000 K Neutral helium lines, strong hydrogen lines
A White 7500-10,000 K Strongest hydrogen lines, weak ionized calcium lines, weak ionized metal lines
F Yellow-white 6000-7500 K Strong hydrogen lines, strong ionized calcium lines, weak sodium lines, many ionized metal lines
G Yellow 5200-6000 K Weaker hydrogen lines, strong ionized calcium lines, strong sodium lines, many lines of ionized and neutral metals
K Orange 3700-5200 K Very weak hydrogen lines, strong ionized calcium lines, strong sodium lines, many lines of neutral metals
M Red 2400-3700 K Strong lines of neutral metals and molecular bands of titanium oxide dominate
L Red 1300-2400 K Metal hydride lines, alkali metal lines
T Magenta 700-1300 K Methane lines
Y Infrared < 700 K Ammonia lines

Luminosity Classes

Astronomy Star