luminosity class

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A classification of stars according to their luminosity, which can vary widely for a given spectral type. Luminosity class indicates, for example, whether a star is a supergiant, a giant, or a dwarf. The luminosity class is assigned by examination of the star's spectrum, looking at luminosity-sensitive lines or line ratios. The luminosity classes generally used are:Ia–0 Extreme supergiants (sometimes called hypergiants)

Ia  Luminous supergiants

Iab  Normal supergiants

Ib  Underluminous supergiants

II   Bright giants

III    Giants

IV    Subgiants

V   Dwarfs (main-sequence stars)

The accompanying diagram shows the luminosity classes on a Hertzsprung–Russell diagram. See also spectral classification.

luminosity class: A plot of the absolute magnitude of stars against their spectral type shows different luminosity classes.

Subjects: Astronomy and Astrophysics.

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