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Occasionally, letters a and b are applied to luminosity classes other than supergiants; for example, a giant star slightly less luminous than typical may be given a luminosity class of IIIb, while a luminosity class IIIa indicates a star slightly brighter than a typical giant. [32]
A G-type main-sequence star (spectral type: G-V), also often, and imprecisely, called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about 5,300 and 6,000 K (5,000 and 5,700 °C ; 9,100 and 10,000 °F ).
A star like Deneb, for example, has a luminosity around 200,000 L ⊙, a spectral type of A2, and an effective temperature around 8,500 K, meaning it has a radius around 203 R ☉ (1.41 × 10 11 m). For comparison, the red supergiant Betelgeuse has a luminosity around 100,000 L ⊙ , a spectral type of M2, and a temperature around 3,500 K ...
Intrinsic variable types in the Hertzsprung–Russell diagram showing the Yellow Hypergiants above (i.e. more luminous than) the Cepheid instability strip. A yellow hypergiant (YHG) is a massive star with an extended atmosphere, a spectral class from A to K, and, starting with an initial mass of about 20–60 solar masses, has lost as much as half that mass.
This class of stars was introduced with the Harvard sequence of stellar spectra and published in the Revised Harvard photometry catalogue. The definition of type B-type stars was the presence of non-ionized helium lines with the absence of singly ionized helium in the blue-violet portion of the spectrum. All of the spectral classes, including ...
The luminosity class for such stars is determined from spectral lines that are sensitive to the surface gravity of the star, with more expanded and luminous stars being given I (supergiant) classifications while somewhat less expanded and more luminous stars are given luminosity II or III. [5]
A hypergiant (luminosity class 0 or Ia +) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds.The term hypergiant is defined as luminosity class 0 (zero) in the MKK system.
A K-type main-sequence star, also referred to as a K-type dwarf, or orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ("red dwarfs") and yellow/white G-type main-sequence stars.