Star Classification

Spectral Classification

Originally we used a system based on the strength of hydrogen absorption lines
- Devised by Williamina Fleming
- Strongest hydrogen lines were A --> O
- Hydrogen lines alone are not that useful for classification
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 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