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HD 166 or V439 Andromedae (ADS 69 A) is a 6th magnitude star in the constellation Andromeda, approximately 45 light years away from Earth. It is a variable star of the BY Draconis type,〔 with a variation in brightness smaller than 0.2 magnitude. It is a dwarf star like our Sun, yet cooler and dimmer, having a stellar classification of spectral type G8V and a surface temperature of 5,327 kelvin.〔 It is within one degree of the star Alpha Andromedae.〔''Autostar Suite Astronomer Edition''. CD-ROM. Meade, April 2006.〕 It is located at celestial (X,Y,Z) coordinates of 39.1, 1.13, 21.7 galactic (X,Y,Z) coordinates in ly: -14.1, 34.9, -24.1 and is found at right ascension and declination 0h6m36.75s, +29°1'17.6". The star has a proper motion of 0.422 arcsecond per year (114.1° from north). It has an estimated visual luminosity of 61% of Sol. It has a diameter that is about 0.91 x Sol and has a radial velocity of -5.5 km/s. It is estimated to be about 200 million years old based on its chromospheric activity.〔 X-ray emission has been detected from this star, with an estimated luminosity of .〔 An infrared excess has been detected around this star, most likely indicating the presence of a circumstellar disk at a radius of 7.5 AU. The temperature of this dust is 90 K.〔 The habitable zone for an Earth-like planet would be about 0.77 AU from the star. ==References== 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「HD 166」の詳細全文を読む スポンサード リンク
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