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M 70
M 70
	哈伯太空望遠鏡拍攝的M70；視場為3.3弧分 ; Credit: ESA/Hubble和NASA
觀測數據(J2000 曆元)
分類	V
星座	人馬座
赤經	18h 43m 12.76s
赤緯	–32° 17′ 31.6″
距離	29.4 kly（9.0 kpc）
視星等 (V)	+9.06
視直徑(V)	8.0′
物理性質
Mass	1.79×105 M☉
半徑	34 ly
金屬量	–1.35 dex
估計年齡	12.80 Gyr
其它名稱	GCl 101, M70, NGC 6681
	參見：球狀星團，球狀星團表

M70或梅西耶70，也稱為NGC 6681，是在人馬座南側的一個球狀星團^[a]。梅西耶在1780年8月31日發現它^[5]。著名的海爾·波普彗星在1995年7月23日被發現時，就在它的旁邊^[9]。

它與地球的距離為29,400光年^[4]，並以6,500光年的距離繞著銀河中心運轉^[10]。它的大小和亮度與同在人馬座的鄰居，也是球狀星團的M69大致相同^[11]。M70的核心非常小，半徑大約只有0.22 ly（0.068 pc）^[12]，半光度的半徑則為182.0 ly（55.80 pc）^[13]。該星團經歷了核心崩塌，使其質量集中於中心^[14]，光度分佈遵循幂定律^[10]。

星團中有兩個不同的恒星群體，每一個群體都顯示出獨特的豐度^[15]。已知有五顆變星位於其廣泛的半徑，即潮汐半徑內，所有的這些變星都是天琴座RR型變星^[8]^[16]。這個星團在核心附近可能有兩顆藍離散星 ^[10]。

圖集

哈伯太空望遠鏡拍攝的M70。
以箭頭標示出M70的星圖，在正常狀況下，地平線的位置在圖的南方(下方) (羅伯托·穆拉) 。

參考資料和註解

^ Shapley, Harlow; Sawyer, Helen B., A Classification of Globular Clusters, Harvard College Observatory Bulletin, August 1927, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
^ Goldsbury, Ryan; et al, The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters, The Astronomical Journal, December 2010, 140 (6): 1830–1837, Bibcode:2010AJ....140.1830G, arXiv:1008.2755 , doi:10.1088/0004-6256/140/6/1830.
^ ^3.0 ^3.1 ^3.2 NGC 6681. SIMBAD. 斯特拉斯堡天文資料中心.
^ ^4.0 ^4.1 ^4.2 Boyles, J.; et al, Young Radio Pulsars in Galactic Globular Clusters, The Astrophysical Journal, November 2011, 742 (1): 51, Bibcode:2011ApJ...742...51B, arXiv:1108.4402 , doi:10.1088/0004-637X/742/1/51.
^ ^5.0 ^5.1 Adam, Len, Imaging the Messier Objects Remotely from Your Laptop, The Patrick Moore Practical Astronomy Series, Springer: 304, 2018, Bibcode:2018imor.book.....A, ISBN 978-3319653853
^ distance × sin( diameter_angle / 2 ) = 34 ly. radius
^ ^7.0 ^7.1 Forbes, Duncan A.; Bridges, Terry, Accreted versus in situ Milky Way globular clusters, Monthly Notices of the Royal Astronomical Society, May 2010, 404 (3): 1203–1214, Bibcode:2010MNRAS.404.1203F, arXiv:1001.4289 , doi:10.1111/j.1365-2966.2010.16373.x.
^ ^8.0 ^8.1 Liller, M. H., The variable stars in the field of the globular cluster NGC 6681, Astronomical Journal, October 1983, 88: 1463–1469, Bibcode:1983AJ.....88.1463L, doi:10.1086/113435.
^ Mobberley, Martin, It Came From Outer Space Wearing an RAF Blazer!: A Fan's Biography of Sir Patrick Moore, Springer Science & Business Media: 483, 2013, ISBN 978-3319006093
^ ^10.0 ^10.1 ^10.2 Watson, Alan M.; et al, Far-ultraviolet imaging of the globular cluster NGC 6681 with WFPC2 (PDF), Astrophysical Journal, Part 2, November 1994, 435 (1): L55–L58 [2021-08-12], Bibcode:1994ApJ...435L..55W, doi:10.1086/187593, （原始内容存档 (PDF)于2022-10-06）.
^ Frommert, Hartmut; Kronberg, Christine, Globular Cluster M70, SEDS Messier pages (Students for the Exploration and Development of Space (SEDS)), 2007-08-30 [2018-12-04], （原始内容存档于2015-03-03）.
^ Djorgovski, S., Physical Parameters of Galactic Globular Clusters, Djorgovski, S. G.; Meylan, G. (编), Structure and Dynamics of Globular Clusters. Proceedings of a Workshop held in Berkeley, California, July 15–17, 1992, to Honor the 65th Birthday of Ivan King 50, San Francisco, California: Astronomical Society of the Pacific: 373, January 1993, Bibcode:1993ASPC...50..373D, ISBN 978-0937707692.
^ Forbes, Duncan A.; et al, Uniting old stellar systems: from globular clusters to giant ellipticals, Monthly Notices of the Royal Astronomical Society, October 2008, 389 (4): 1924–1936, Bibcode:2008MNRAS.389.1924F, arXiv:0806.1090 , doi:10.1111/j.1365-2966.2008.13739.x.
^ Pryor, Carlton; et al, Mass-to-light ratios for globular clusters. I - The centrally concentrated clusters NGC 6624, M28 (NGC 6626), and M70 (NGC 6681), Astronomical Journal, August 1989, 98: 596–610, Bibcode:1989AJ.....98..596P, doi:10.1086/115160.
^ O'Malley, Erin M.; et al, High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681, The Astrophysical Journal, September 2017, 846 (1): 15, Bibcode:2017ApJ...846...23O, arXiv:1706.06962 , doi:10.3847/1538-4357/aa7b72, 23.
^ Clement, Christine M.; et al, Variable Stars in Galactic Globular Clusters, The Astronomical Journal, November 2001, 122 (5): 2587–2599, Bibcode:2001AJ....122.2587C, arXiv:astro-ph/0108024 , doi:10.1086/323719.