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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).
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.
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]
It groups stars into five main luminosity groups designated by roman numerals: I supergiant; II bright giant; III giant; IV subgiant; V dwarf (main sequence). 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.
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.
Disc of debris around an F-type star, HD 181327. [1]An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. . These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600
Various methods and tools are involved in stellar age estimation, an attempt to identify within reasonable degrees of confidence what the age of a star is. These methods include stellar evolutionary models , membership in a given star cluster or system , fitting the star with the standard spectral and luminosity classification system , and the ...