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54 Piscium is an orange dwarf star approximately 36 light-years away in the constellation of Pisces. In 2002, an extrasolar planet was confirmed to be orbiting the star, and in 2006, a brown dwarf was also discovered orbiting it. == Stellar components == The Flamsteed designation 54 Piscium originated in the star catalogue of the British astronomer John Flamsteed, first published in 1712. It has an apparent magnitude of 5.86, allowing it to be seen with the unaided eye under suitable viewing conditions.The star has a classification of K0V, with the luminosity class V indicating this is a main sequence star that is generating energy at its core through the thermonuclear fusion of hydrogen into helium. The effective temperature of the photosphere is about 5,062 K,〔 giving it the characteristic orange hue of a K-type star.〔 It has been calculated that the star may have 76 percent〔 of the Sun's mass and 46 percent of the luminosity. The radius has been directly determined by interferometry to be 94 percent that of the Sun's radius using the CHARA array.〔 The rotational period of 54 Piscium is about 40.2 days.〔 The age of the star is about 6.4 billion years, based on chromospheric activity and isochronal analysis.〔 There is some uncertainty in the scientific press about the enriched of elements heavier than hydrogen than the Sun; what astronomers term the metallicity. Santos et al. (2004) report the logarithm of the abundance ratio of iron to hydrogen, (), to be 0.12 dex,〔 whereas Cenarro et al. (2007) published a value of –0.15 dex.〔 Long term observation of this star's magnetic activity levels suggests that it is entering a Maunder minimum period, which means it may undergo an extended period of low starspot numbers. It has a Sun-like activity cycle that has been decreasing in magnitude. As of 2010, the most recent period of peak activity was 1992–1996, which showed a lower level of activity than the previous peak in 1976–1980.〔 In 2006, a direct image of 54 Piscium showed that there was a brown dwarf companion to 54 Piscium A.〔 54 Piscium B is though to be a "methane brown dwarf" of the spectral type "T7.5V". The luminosity of this substellar object suggests that it has a mass of 0.051 that of the Sun (50 times the mass of Jupiter) and 0.082 times the Sun's radius. Similar to Gliese 570 D, this brown dwarf is though to have a surface temperature of about .〔 When 54 Piscium B was directly imaged by NASA's Spitzer Space Telescope, it was shown that the brown dwarf had a projected separation of around 476 astronomical units from the primary star.〔 54 Piscium B was the first brown dwarf to be detected around a star with an already known extrasolar planet (based on radial velocity surveys). 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「54 Piscium」の詳細全文を読む スポンサード リンク
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