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Upsilon Andromedae b, occasionally referred to as Upsilon Andromedae Ab (to distinguish it from the red dwarf Upsilon Andromedae B), is an extrasolar planet approximately 44 light-years away from Earth in the constellation of Andromeda (the Chained Maiden). The planet was discovered orbiting the Solar twin star, Upsilon Andromedae, approximately every five days. Discovered in June 1996 by Geoffrey Marcy and R. Paul Butler, it was one of the first hot Jupiters to be discovered. It is also one of the first non-resolved planets to be detected directly. Upsilon Andromedae b is the innermost known planet in its planetary system. The planet and its host star is one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star (where no proper name already exists).〔(NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars ). IAU.org. 9 July 2014〕〔(NameExoWorlds ).〕 The process involves public nomination and voting for the new names, and the IAU plans to announce the new names in mid-November 2015.〔(NameExoWorlds ).〕 == Discovery == Like the majority of known extrasolar planets, Upsilon Andromedae b was detected by the variations in its star's radial velocity caused by the planet's gravity. The variations were detected by making sensitive measurements of the Doppler shift of Upsilon Andromedae's spectrum. The planet was announced in January 1997, together with 55 Cancri b and the planet orbiting Tau Boötis. Like 51 Pegasi b, the first extrasolar planet discovered around a normal star, Upsilon Andromedae b orbits very close to its star, closer than Mercury does to our Sun. The planet takes 4.617 days to complete an orbit, with a semimajor axis of 0.0595 AU.〔 ((web version ))〕 A limitation of the radial velocity method used to detect Upsilon Andromedae b is that only a lower limit on the mass can be found. In the case of Upsilon Andromedae b, this lower limit is 68.7% of the mass of Jupiter, though depending on the inclination of the orbit, the true mass may be much greater. However, astronomers found recently that inclination of the orbital plane is around 25° and the true mass may be about .〔 Coplanarity is not to be assumed; the mutual inclination between c and d is 35 degrees. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Upsilon Andromedae b」の詳細全文を読む スポンサード リンク
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