雙星團

雙星團
雙星團
觀測數據 (J2000.0 曆元)
星座	英仙座
赤經	2h 20m
赤緯	57° 08′
距離	7.5 kly (2300 秒差距)
視星等 (V)	3.7和3.8
視直徑 (V)	60′
物理性質
其他名稱（標示）	科德韋爾 14
	相關條目：疏散星團、疏散星團列表

雙星團（也稱為科德韋爾14）是裸眼可見的疏散星團 NGC 869和 NGC 884（經常被錯誤的稱為英仙座h和χ，其實h是鄰近的一顆恆星，而χ就是這兩個星團）的合稱^[1]，在英仙座內靠得很近。NGC 869和NGC 884 兩者至地球的距離都是7,600光年^[2]。NGC 869的質量約為3,700太陽質量，而NGC 884的質量大約是2,800太陽質量；然而後來的研究顯示這兩個星團有很多的暈星環繞著，所以它們的總質量至少是20,000太陽質量^[3]。依據對個別恆星的研究，這兩個星團相對來說都很年輕，大約都只有1,280萬歲^[4]。相較之下，昴宿星團的年齡估計是7,500萬至15,000萬歲。這兩個星團各自都有300顆以上的藍白色超巨星。這兩個星團都有藍移，NGC 869以39 km/s（24 mi/s）接近地球，NGC 884也以相似的速度，38 km/s（24 mi/s）朝向地球接近^[5]。星團中最熱主序星的光譜類型是B0。

神話

珀耳修斯是冒險神話的象徵，他是宙斯（眾神和人的父親）的兒子，母親是凡人達娜厄。珀耳修斯是半神半人，但無不死之身。他接受賽普勒斯國王波利得特克斯的挑戰，要殺死蛇髮女妖美杜莎，但目光與美杜莎接觸的人就會變成石頭。雅典娜、荷米斯、和其它的眾神，提供珀耳修斯頭盔、盾牌、和握把上鑲嵌了珠寶的彎刀，並教導他如何面對挑戰。在斬下美杜莎的首級之後，珀耳修斯執行了其他的英雄事蹟。例如，拯救了被綁在石頭上，要獻祭給海怪（鯨魚座）的公主（仙女座）。由於他偉大的成就，眾神將珀耳修斯安置在繁星之間，一隻手高舉鑲著寶石的彎刀，另一隻手提著美杜莎的頭，成為英仙座。雙星團就是鑲在珀耳修斯彎刀握把上的寶石^{[來源請求]}。

歷史

早在西元前130年，希臘天文學家喜帕恰斯就記錄了這兩個星團（英仙座內的光斑）。然而，雙星團的真實性質在望遠鏡發明之後好幾個世紀才被發現。在19世紀初期，威廉·赫歇爾首度辨識出這個天體是分離的兩個星團。雙星團被收錄在科德韋爾深空天體表內，但沒有收錄在最受歡迎的空天體表，梅西爾目錄中^[6]^[7]。

位置

在溫帶的高緯度地區，雙星團是拱極的星團（全年都在地平線上）。它屬於英仙座，但在靠近仙后座的邊界處。雙星團也很靠近每年8月12/13日達到峰值的英仙座流星雨的輻射點。雖然很容易就能夠在北方的天空找到，但要觀察這兩個星團聚集的恆星，還是要藉助於望遠鏡。它們被描述為令人驚訝、讚嘆的景象，並經常被列為天文觀測指南中指定的目標^[8]。

參考資料

^ Some confusion surrounds what Bayer intended by these designations. It is sometimes claimed that Bayer could not have resolved the pair into two patches of nebulosity, and that Chi refers to the Double Cluster and h to a nearby star; see Stephen James O'Meara and Daniel W.E. Green, 2003, "The Mystery of the Double Cluster", Sky and Telescope, Vol. 105, No. 2 (February 2003), p. 116–119. Bayer's Uranometria chart for Perseus does not show them as nebulous objects, but his chart for Cassiopeia does, and they are described as Nebulosa Duplex in Schiller's Coelum Stellatum Christianum, which was assembled with Bayer's help; see Morton Wagman, Lost Stars, McDonald & Woodward, 2003, ISBN 0939923785, p. 240.
^ UBVI and Hα Photometry of the h and χ Persei Cluster. [8 April 2013].
^ The Stellar Population of h and χ Persei: Cluster Properties, Membership, and the Intrinsic Colors and Temperatures of Stars. [13 July 2013]. （原始內容存檔於2019-03-27）.
^ The Star Formation History and Mass Function of the Double Cluster h and χ Persei (PDF). [8 April 2013]. （原始內容 (PDF)存檔於2017-07-22）.
^ Astrophysical parameters of Galactic open clusters. [8 April 2013]. （原始內容存檔於2014-12-13）.
^ O'Meara, Stephen James. The Caldwell Objects. Cambridge University Press. 2002. ISBN 978-0-521-82796-6.
^ Caldwell Club Introduction. [2006-09-08]. （原始內容存檔於2014-12-14）.
^ Chaple, Glenn. A double take 39 (1). Astronomy. January 2011.

外部連結

[1] Some confusion surrounds what Bayer intended by these designations. It is sometimes claimed that Bayer could not have resolved the pair into two patches of nebulosity, and that Chi refers to the Double Cluster and h to a nearby star; see Stephen James O'Meara and Daniel W.E. Green, 2003, "The Mystery of the Double Cluster", Sky and Telescope, Vol. 105, No. 2 (February 2003), p. 116–119. Bayer's Uranometria chart for Perseus does not show them as nebulous objects, but his chart for Cassiopeia does, and they are described as Nebulosa Duplex in Schiller's Coelum Stellatum Christianum, which was assembled with Bayer's help; see Morton Wagman, Lost Stars, McDonald & Woodward, 2003, ISBN 0939923785, p. 240.

[2] UBVI and Hα Photometry of the h and χ Persei Cluster. [8 April 2013].

[3] The Stellar Population of h and χ Persei: Cluster Properties, Membership, and the Intrinsic Colors and Temperatures of Stars. [13 July 2013]. （原始內容存檔於2019-03-27）.

[4] The Star Formation History and Mass Function of the Double Cluster h and χ Persei (PDF). [8 April 2013]. （原始內容 (PDF)存檔於2017-07-22）.

[5] Astrophysical parameters of Galactic open clusters. [8 April 2013]. （原始內容存檔於2014-12-13）.

[The_Caldwell_Objects-6] O'Meara, Stephen James. The Caldwell Objects. Cambridge University Press. 2002. ISBN 978-0-521-82796-6.

[caldwellclubweb-7] Caldwell Club Introduction. [2006-09-08]. （原始內容存檔於2014-12-14）.

[Astronomy-8] Chaple, Glenn. A double take 39 (1). Astronomy. January 2011.

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