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Stellar classification

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Stellar classification is a classification of stars based on photospheric temperature and its associated spectral characteristics.

Contents

Classification Syntax

The classification system is of form:

{Class}{Subclass}{Luminosity}{Peculiarities}

Class

Harvard one-dimensional (temperature) classification scheme are given in the following table.

Class Temperature Conventional color Apparent color Mass Radius Luminosity Hydrogen lines  % of all Main Sequence Stars
O 30,000–60,000 K blue blue 60 M☉ 15 R☉ 1,400,000 L☉ Weak ~0.00003%
B 10,000–30,000 K blue white blue white to white 18 M☉ 7 R☉ 20,000 L☉ Medium 0.13%
A 7,500–10,000 K white white 3.1 M☉ 2.1 R☉ 80 L☉ Strong 0.6%
F 6,000–7,500 K yellowish white white 1.7 M☉ 1.3 R☉ 6 L☉ Medium 3%
G 5,000–6,000 K yellow yellow 1.1 M☉ 1.1 R☉ 1.2 L☉ Weak 8%
K 3,500–5,000 K orange yellow orange 0.8 M☉ 0.9 R☉ 0.4 L☉ Very weak 13%
M 2,000–3,500 K red orange red 0.3 M☉ 0.4 R☉ 0.04 L☉ Very weak >78%

Luminosity

  • Ia Most luminous supergiants
  • Ib Less luminous supergiants
  • II Luminous giants
  • III Normal giants
  • IV Subgiants
  • V Main sequence stars (dwarfs)

Peculiarity Codes

  • comp Composite spectrum; two spectral types are blended, indicating that the star is an unresolved binary.
  • e Emission lines are present (usually hydrogen).
  • m Abnormally strong "metals" (elements other than hydrogen and helium) for a star of a given spectral type; * usually applied to A stars.
  • n Broad ("nebulous") absorption lines due to fast rotation.
  • nn Very broad lines due to very fast rotation.
  • neb A nebula's spectrum is mixed with the star's.
  • p Unspecified peculiarity, except when used with type A, where it denotes abnormally strong lines of "metals" (related to Am stars).
  • s Very narrow ("sharp") lines.
  • sh Shell star (B to F main sequence star with emission lines from a shell of gas).
  • var Varying spectral type.
  • wl Weak lines (suggesting an ancient, "metal"-poor star)

Example

The sun (Sol) is classified G2V. Therefore it is a yellow star (G) 20% of the way between G and K (2) belonging to the main sequence (V).

External Links

Image:Example.jpg

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