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Alpha Gruis (α Gruis, α Gru) or Alnair is the brightest star in the southern constellation Grus. Its first depiction in a celestial atlas was in Johann Bayer's ''Uranometria'' of 1603.〔 ==Properties== Alpha Gruis has a stellar classification of B6 V,〔 although some sources give it a classification of B7 IV.〔 The first classification indicates that this is a B-type star on the main sequence of stars that are generating energy through the thermonuclear fusion of hydrogen at the core. However, a luminosity class of 'IV' would suggest that this is a subgiant star; meaning the supply of hydrogen at its core is becoming exhausted and the star has started the process of evolving away from the main sequence. It has no known companions.〔 The measured angular diameter of this star, after correcting for limb darkening, is .〔 At a parallax-measured distance of from Earth, this yields a physical size of 3.4 times the radius of the Sun.〔 It is rotating rapidly, with a projected rotational velocity of about 215 km/s providing a lower bound for the rate of azimuthal rotation along the equator.〔 This star has around four times the Sun's mass and is radiating 263 times the luminosity of the Sun.〔 The effective temperature of Alpha Gruis's outer envelope is 13,920 K,〔 giving it the blue-white hue characteristic of B-type stars.〔 The abundance of elements other than hydrogen and helium, what astronomers term the metallicity, is about 74% of the abundance in the Sun.〔 Based on the estimated age and motion, it may be a member of the AB Doradus moving group that share a common motion through space. This group has an age of about 70 million years,〔 which is consistent with α Gruis's 100-million-year〔 estimated age (allowing for a margin of error). The space velocity components of this star in the Galactic coordinate system are (''V'', ''W'' ) = , , .〔 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「Alpha Gruis」の詳細全文を読む スポンサード リンク
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