Blue supergiant

Hot, luminous star with a spectral type of A9 or earlier

A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They are usually considered to be those with luminosity class I and spectral class B9 or earlier, although sometimes A-class supergiants are also deemed blue supergiants. Blue supergiants are found towards the top left of the Hertzsprung–Russell diagram, above and to the right of the main sequence.

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