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Xi Geminorum (ξ Gem) is a star in the zodiac constellation Gemini with the traditional name Alzirr.〔 It forms one of the four feet of the outline demarcating the Gemini twins.〔 The star has an apparent visual magnitude of 3.35,〔 which is bright enough for it to be seen with the naked eye. From parallax measurements, its distance from the Earth can be estimated as .〔 Alzirr has a stellar classification of F5 IV,〔 which is subgiant star that is in the process of evolving away from the main sequence of stars like the Sun. It has about 162%〔 of the Sun's mass and is radiating more than 11 times the luminosity of the Sun.〔 This energy is being emitted from the outer envelope of the star at an effective temperature of 6,464 K.〔 This causes the star to take on the yellow-white hue common to F-type stars.〔 X-ray emission has been detected from this star, which has an estimated X-ray luminosity of .〔 It has the spectroscopic signature of a rapidly rotating star, with a projected rotational velocity of about 66 km s−1.〔 Although generally considered a single star, there is some evidence that it may instead be a spectroscopic binary system consisting of two component stars of equal mass.〔 ==Name== The proper name of Xi Geminorum is Alzirr, meaning "the button" in Arabic. This star, along with γ Gem (Alhena), μ Gem (Tejat Posterior), ν Gem and η Gem (Tejat Prior) were ''Al Han'ah'', "the brand" (on the neck of the camel). They also were associated in ''Al Nuḥātai'', the dual form of ''Al Nuḥāt'', "a Camel's Hump".〔 In Chinese, (), meaning ''Well (asterism)'', refers to an asterism consisting of ξ Geminorum, μ Geminorum, ν Geminorum, γ Geminorum, ε Geminorum, 36 Geminorum, ζ Geminorum and λ Geminorum.〔 ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.〕 Consequently, ξ Geminorum itself is known as (, (英語:the Fourth Star of Well).)〔 (香港太空館 - 研究資源 - 亮星中英對照表 ), Hong Kong Space Museum. Accessed on line November 23, 2010.〕 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「Xi Geminorum」の詳細全文を読む スポンサード リンク
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