spectral class


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See also: Spectral Classes for Main Sequence Stars (table)Characteristics of Spectral Classes for Main Sequence Stars
Class Color Surface Temperature Strong Lines
O blue-white 35,000°C; ionized helium
B blue-white 21,000°C; helium
A white 10,000°C; hydrogen
F creamy 7,000°C; ionized calcium
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spectral class,

in astronomy, a classification of the stars by their spectrumspectrum,
arrangement or display of light or other form of radiation separated according to wavelength, frequency, energy, or some other property. Beams of charged particles can be separated into a spectrum according to mass in a mass spectrometer (see mass spectrograph).
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 and luminosityluminosity,
in astronomy, the rate at which energy of all types is radiated by an object in all directions. A star's luminosity depends on its size and its temperature, varying as the square of the radius and the fourth power of the absolute surface temperature.
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. In 1885, E. C. Pickering began the first extensive attempt to classify the stars spectroscopically. This work culminated in the publication of the Henry Draper Catalogue (1924), which lists the spectral classes of 255,000 stars. The stars are divided into 7 classes designated by the letters O, B, A, F, G, K, and M; the hottest stars (O and B) are blue-white in color, while the coolest (M) are red. Each of the letter classes has subdivisions indicated by numerals 0 through 9. Thus, a B0 is the hottest B-type star, B5 is halfway between types B and A, and B9 is only slightly hotter than type A. The table entitled Spectral Classes for Main Sequence StarsCharacteristics of Spectral Classes for Main Sequence Stars
Class Color Surface Temperature Strong Lines
O blue-white 35,000°C; ionized helium
B blue-white 21,000°C; helium
A white 10,000°C; hydrogen
F creamy 7,000°C; ionized calcium
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 gives the characteristics of the seven principal types. To the seven main groups, four more groups have since been added. R, N, and S are classes similar to the K and M types but denote somewhat different spectral characteristics; W indicates a Wolf-Rayet star, the hottest type of star that shines with a steady light. According to a system introduced by W. W. Morgan and others, a Roman numeral is added to the spectral class to specify the luminosity, or intrinsic intensity, of a star. A bright supergiant is Ia, a faint supergiant is Ib, a bright giant is II, a normal giant is III, a subgiant is IV, and a normal dwarf or main-sequence star is V. For example, Sirius is classed as A1 V, a main-sequence white star. Betelgeuse, M2 Ia, is a bright red supergiant. See also Hertzsprung-Russell diagramHertzsprung-Russell diagram
[for Ejnar Hertzsprung and H. N. Russell], graph showing the luminosity of a star as a function of its surface temperature. The luminosity, or absolute magnitude, increases upwards on the vertical axis; the temperature (or some temperature-dependent
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.
References in periodicals archive ?
SAO100949 is a spectral class A star, and although it should be white appears greenish in a low power field.
This is the first new spectral class in more than 50 years and will mean that .
This discussion concentrates on the main components: Sirius A, a star of spectral class A twice as massive as the sun; and Sirius B, one of the most massive white dwarfs known.
Astronomers will be able to compare a star's size and possibly some of its surface features with its spectral class and evolutionary stage.
Other possible sources, he says, are novas (another kind of stellar explosion), red giant stars, Wolf-Rayet stars or stars of spectral class O.

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