1. Spectral Classification of Stars JPH 02/01/08 O B A F G K M Hottest to Coldest (Temperature sequence) Classification scheme due to Annie Jump Cannon (Harvard) (non-alphabetic ordering merely an historical accident) Within each letter class also a numerical class 0-9 (Hot to Cold) for further refinement. Then a Roman Numeral (e.g., I, II, V) for luminosity class Sun = G2V A0 – A9 Early to late A-type

2. Spectral Classification of Stars JPH 02/01/08 Luminosity classes (LC) Second parameter (pressure-dependent) Super-supergiants 0 0-Ia Ia-0 Supergiants: Ia Iab Ib Bright giants: IIa IIab IIb Normal giants: IIIa IIIab IIIb Subgiants IVa IVab IVb Main Sequence V (also “dwarfs”) a,ab,b: subclasses (in decreasing luminosity order) Transition classes (Ib-II also used)

3. Spectral Classification of Stars JPH 02/01/08

4. Spectral Classification of Stars JPH 02/01/08 O stars Atmospheric temperature: > 33,000 K Hydrogen Balmer lines: weak Other spectral features: Ionized Helium (He+) features sometimes in emission, strong UV continuum Parameters (in solar units) –Mass 20-60 –Radius 9-15 –Luminosity 90,000 – 800,000 Lifetime (M.S.): 10-1 Myr

5. Spectral Classification of Stars JPH 02/01/08 B stars Atmospheric temperature: 10,500-30,000 K Hydrogen Balmer lines: medium Other spectral features: Neutral He absorption Parameters (in solar units): –Mass 3-18 –Radius 3.0-8.4 –Luminosity 95-52,000 Lifetime (M.S.): 400-11 Myr

6. Spectral Classification of Stars JPH 02/01/08 A stars Atmospheric temperature: 7,500-10,000 K Hydrogen Balmer lines: strong Other spectral features: H features maximum at A0, some features of heavy elements, eg Ca+ Parameters (in solar units): –Mass 2.0-3.0 –Radius 1.7-2.7 –Luminosity 8-55 Lifetime (M.S.): 3 Gyr – 440 Myr

7. Spectral Classification of Stars JPH 02/01/08 F stars Atmospheric temperature: 6,000-7,200 K Hydrogen Balmer lines: medium Other spectral features: Ca+ lines continue to increase as Balmer lines weaken thru class (from 0 to 9) Parameters (in solar units): –Mass 1.1-1.6 –Radius 1.2-1.6 –Luminosity 2.0-6.5 Lifetime (M.S.): 7-3 Gyr

8. Spectral Classification of Stars JPH 02/01/08 G stars Atmospheric temperature: 5,500-6,000 K Hydrogen Balmer lines: weak Other spectral features: Ca+ H&K, Na "D" Sun is G2V Parameters (in solar units): –Mass 0.9-1.05 –Radius 0.85-1.1 –Luminosity 0.66-1.5 Lifetime (M.S.): 15-8 Gyr

9. Spectral Classification of Stars JPH 02/01/08 K stars Atmospheric temperature: 4,000-5,250 K Hydrogen Balmer lines: very weak Other spectral features: Ca+, Fe, strong molecules, eg CH, CN Parameters (in solar units): –Mass 0.6-0.8 –Radius 0.65-0.8 –Luminosity 0.10-0.42 Lifetime (M.S.): 17 Gyr

10. Spectral Classification of Stars JPH 02/01/08 M stars Atmospheric temperature: 2,600-3,850 K Hydrogen Balmer lines: very weak Other spectral features: Molecules, eg TiO, very red continuum Parameters (in solar units): –Mass 0.08-0.5 –Radius 0.17-0.63 –Luminosity 0.001-0.08 Lifetime (M.S.): 56 Gyr

11. Spectral Classification of Stars JPH 02/01/08 Other stars W = Wolf-Rayet (WR) stars – very massive – earlier than O-type – losing mass at high rate –WN = nitrogen rich –WC = carbon rich L = “stars” redder than M. May not be true stars (i.e., H burning) – brown dwarfs. "R", "N", "S" stars are cool stars with particular types of molecular bands.