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Eta Andromedae : ウィキペディア英語版 | Eta Andromedae
Eta Andromedae (Eta And, η Andromedae, η And) is a spectroscopic binary star in the constellation of Andromeda. It consists of two G-type subgiant or giant stars orbiting each other with a period of 115.7 days and has an overall apparent visual magnitude of approximately 4.403.〔〔The spectroscopic binary eta Andromedae: Determination of the orbit by optical interferometry, C. A. Hummel et al., ''Astronomical Journal'' 106, #6 (December 1993), pp. 2486–2492, , .〕 ==History==
Eta Andromedae was discovered to be a double-lined spectroscopic binary in a series of spectra taken in 1899 and 1900.〔A list of nine stars whose velocities in the line of sight are variable, W. W. Campbell and W. H. Wright, ''Astrophysical Journal'' 12 (November 1900), pp. 254–257, , .〕 Its orbit was computed in 1946 from spectroscopic observations.〔The Spectroscopic Binary η Andromedae, Katherine C. Gordon, ''Astrophysical Journal'' 103 (January 1946), pp. 13–15, .〕 Because spectroscopy only reveals the radial velocity of a star towards or away from the viewer, such a computation does not determine all orbital elements. In observations made from 1990 to 1992, Eta Andromedae was resolved interferometrically by the Mark III Stellar Interferometer at Mount Wilson Observatory, California, United States. This allowed a more complete orbit to be computed and, in 1993, published.〔
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