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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.
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]
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 ...
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.
Theoretical calculations of stellar structure and the evolution of stars produce plots that match those from observations. This type of diagram could be called temperature-luminosity diagram, but this term is hardly ever used; when the distinction is made, this form is called the theoretical Hertzsprung–Russell diagram instead. A peculiar ...
The revised Yerkes Atlas system [7] listed a dense grid of A-type dwarf spectral standard stars, but not all of these have survived to this day as standards. The "anchor points" and "dagger standards" of the MK spectral classification system among the A-type main-sequence dwarf stars, i.e. those standard stars that have remained unchanged over years and can be considered to define the system ...
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.
For simplicity, the stellar structure equations are written without explicit time dependence, with the exception of the luminosity gradient equation: = Here L is the luminosity, ε is the nuclear energy generation rate per unit mass and ε ν is the luminosity due to neutrino emission (see below for the other quantities). The slow evolution of ...