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A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
Class G main-sequence stars make up about 7.5%, nearly one in thirteen, of the main-sequence stars in the solar neighborhood. There are 21 G-type stars within 10pc. [c] [11] Class G contains the "Yellow Evolutionary Void". [84] Supergiant stars often swing between O or B (blue) and K or M (red).
The stellar classification is a hierarchy with solar twin being most like the Sun followed by solar analog and then solar-type. [1] Observations of these stars are important for understanding better the properties of the Sun in relation to other stars and the habitability of planets.
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.
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 ...
A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. [1] B-type stars are extremely luminous and blue.
Specific to supergiants, the luminosity class is further divided into normal supergiants of class Ib and brightest supergiants of class Ia. The intermediate class Iab is also used. Exceptionally bright, low surface gravity, stars with strong indications of mass loss may be designated by luminosity class 0 (zero) although this is rarely seen. [4]
The primary star, ε Sagittarii A, of this binary star system has a stellar classification of B9.5 III, [3] with the luminosity class of III suggesting it has a luminosity comparable to a giant star for its spectral type. It has about 3.8 times the mass of the Sun and is radiating around 500 times the Sun's luminosity from its photosphere. [6]