双星团

双星团
双星团
观测数据 (J2000.0 历元)
星座	英仙座
赤经	2h 20m
赤纬	57° 08′
距离	7.5 kly (2300 秒差距)
视星等 (V)	3.7和3.8
视直径 (V)	60′
物理性质
其他名称（标示）	科德韦尔 14
	相关条目：疏散星团、疏散星团列表

双星团（也称为科德韦尔14）是裸眼可见的疏散星团 NGC 869和 NGC 884（经常被错误的称为英仙座h和χ，其实h是邻近的一颗恒星，而χ就是这两个星团）的合称^[1]，在英仙座内靠得很近。NGC 869和NGC 884 两者至地球的距离都是7,600光年^[2]。NGC 869的质量约为3,700太阳质量，而NGC 884的质量大约是2,800太阳质量；然而后来的研究显示这两个星团有很多的晕星环绕着，所以它们的总质量至少是20,000太阳质量^[3]。依据对个别恒星的研究，这两个星团相对来说都很年轻，大约都只有1,280万岁^[4]。相较之下，昴宿星团的年龄估计是7,500万至15,000万岁。这两个星团各自都有300颗以上的蓝白色超巨星。这两个星团都有蓝移，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]。星团中最热主序星的光谱类型是B0。

神话

珀耳修斯是冒险神话的象征，他是宙斯（众神和人的父亲）的儿子，母亲是凡人达娜厄。珀耳修斯是半神半人，但无不死之身。他接受塞浦路斯国王波利得特克斯的挑战，要杀死蛇发女妖美杜莎，但目光与美杜莎接触的人就会变成石头。雅典娜、荷米斯、和其它的众神，提供珀耳修斯头盔、盾牌、和握把上镶嵌了珠宝的弯刀，并教导他如何面对挑战。在斩下美杜莎的首级之后，珀耳修斯执行了其他的英雄事迹。例如，拯救了被绑在石头上，要献祭给海怪（鲸鱼座）的公主（仙女座）。由于他伟大的成就，众神将珀耳修斯安置在繁星之间，一只手高举镶著宝石的弯刀，另一只手提着美杜莎的头，成为英仙座。双星团就是镶在珀耳修斯弯刀握把上的宝石^{[来源请求]}。

历史

早在公元前130年，希腊天文学家喜帕恰斯就记录了这两个星团（英仙座内的光斑）。然而，双星团的真实性质在望远镜发明之后好几个世纪才被发现。在19世纪初期，威廉·赫歇尔首度辨识出这个天体是分离的两个星团。双星团被收录在科德韦尔深空天体表内，但没有收录在最受欢迎的空天体表，梅西尔目录中^[6]^[7]。

位置

在温带的高纬度地区，双星团是拱极的星团（全年都在地平线上）。它属于英仙座，但在靠近仙后座的边界处。双星团也很靠近每年8月12/13日达到峰值的英仙座流星雨的辐射点。虽然很容易就能够在北方的天空找到，但要观察这两个星团聚集的恒星，还是要借助于望远镜。它们被描述为令人惊讶、赞叹的景象，并经常被列为天文观测指南中指定的目标^[8]。

参考资料

^ 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]. （原始内容存档于2019-03-27）.
^ The Star Formation History and Mass Function of the Double Cluster h and χ Persei (PDF). [8 April 2013]. （原始内容 (PDF)存档于2017-07-22）.
^ Astrophysical parameters of Galactic open clusters. [8 April 2013]. （原始内容存档于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]. （原始内容存档于2014-12-14）.
^ Chaple, Glenn. A double take 39 (1). Astronomy. January 2011.

外部链接

[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]. （原始内容存档于2019-03-27）.

[4] The Star Formation History and Mass Function of the Double Cluster h and χ Persei (PDF). [8 April 2013]. （原始内容 (PDF)存档于2017-07-22）.

[5] Astrophysical parameters of Galactic open clusters. [8 April 2013]. （原始内容存档于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]. （原始内容存档于2014-12-14）.

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

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