| Spectral Type |
Atmospheric
Temperature (K) |
Hydrogen (Balmer) Features |
Other Features | Mass Ratio | Radius
Ratio |
Luminosity
Ratio (Sun = 1) |
Main Sequence Lifetime |
| O | >33,000 | weak | Ionized
Helium (He+) features sometimes in emission Strong UV continuum |
20-60 | 9-15 | 90,000-800,000 | 10-1 Myr |
| B | 10,500-30,000 | medium | Neutral He absorption | 3-18 | 3.0-8.4 | 95-52,000 | 400-11 Myr |
| A | 7,500-10,000 | strong | H
features maximum at A0 Some features of heavy elements, eg Ca+ |
2.0-3.0 | 1.7-2.7 | 8-55 | 3 Gyr - 440 Myr |
| F | 6,000-7,200 | medium | 1.1-1.6 | 1.2-1.6 | 2.0-6.5 | 7-3 Gy | |
| G | 5,500-6,000 | weak | Ca+
H&K, Na "D" Sun is G2V |
0.9-1.05 | 0.85-1.1 | 0.66-1.5 | 15-8 Gy |
| K | 4,000-5,250 | v. weak | Ca+,
Fe, Strong molecules, eg CH, CN |
0.6-0.8 | 0.65-0.80 | 0.10-0.42 | 17 Gy |
| M | 2,600-3,850 | v. weak | Molecules,
eg TiO Very red continuum |
0.08-0.5 | 0.17-0.63 | 0.001-0.08 | 56 Gy |
