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O B A F G K M Hottest to Coldest (Temperature sequence)

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)

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O B A F G K M Hottest to Coldest (Temperature sequence)

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  1. 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. 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. Atmospheric temperature: > 33,000 K Hydrogen Balmer lines: weak Other spectral features: Ionized Helium (He+) featuressometimes 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 O stars

  4. 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 B stars

  5. 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 A stars

  6. 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 F stars

  7. 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 G stars

  8. 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 K stars

  9. 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 M stars

  10. 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. Other stars

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