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Messier 70

Coordinates: Sky map 18h 43m 12.64s, −32° 17′ 30.8″
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Messier 70
Globular cluster Messier 70 by Hubble Space Telescope; 3.3′ view
Observation data (J2000 epoch)
ClassV[1]
ConstellationSagittarius
Right ascension18h 43m 12.76s[2]
Declination–32° 17′ 31.6″[3]
Distance29.4 kly (9.0 kpc)[4]
Apparent magnitude (V)7.9[5]
Apparent dimensions (V)8.0′[6]
Physical characteristics
Mass1.79×105[4] M☉
Radius34 ly[7]
Tidal radius11.2′[8]
Metallicity = –1.35[9] dex
Estimated age12.80 Gyr[9]
Other designationsGCl 101, M70, NGC 6681[3]
See also: Globular cluster, List of globular clusters

Messier 70 or M70, also known as NGC 6681, is a globular cluster of stars to be found in the south of Sagittarius.[a] It was discovered by Charles Messier in 1780.[b][6] The famous comet Hale–Bopp was discovered near this cluster in 1995.[10][c]

It is about 29,400[4] light years away from Earth and around 6,500 light-years[11] from the Galactic Center. It is roughly the same size and luminosity as its neighbour in space, M69.[12] M70 has a very small core radius of 0.22 ly (0.068 pc)[13] and a half-light radius of 182.0 ly (55.80 pc).[14] This cluster has undergone core collapse, leaving it centrally concentrated[15] with the luminosity distribution following a power law.[11]

There are two distinct stellar populations in the cluster, with each displaying unique abundances. These likely represent different generations of stars.[16] Five known variable stars lie within the broadest radius, the tidal radius, of it, all of which are RR Lyrae variables.[8][17] The cluster may have two blue stragglers near the core.[11]

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  • Image by Hubble Space Telescope
    Image by Hubble Space Telescope
  • Map showing M70, against a conventional (southern) horizon
    Map showing M70, against a conventional (southern) horizon

See also

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References and footnotes

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  1. ^ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
  2. ^ Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal, 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830, S2CID 119183070.
  3. ^ a b "NGC 6681". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 17 November 2006.
  4. ^ a b c Boyles, J.; et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal, 742 (1): 51, arXiv:1108.4402, Bibcode:2011ApJ...742...51B, doi:10.1088/0004-637X/742/1/51, S2CID 118649860.
  5. ^ "Messier 70". SEDS Messier Catalog. Retrieved 30 April 2022.
  6. ^ a b Adam, Len (2018), Imaging the Messier Objects Remotely from Your Laptop, The Patrick Moore Practical Astronomy Series, Springer, p. 304, Bibcode:2018imor.book.....A, ISBN 978-3319653853
  7. ^ distance × sin( diameter_angle / 2 ) = 34 ly. radius
  8. ^ a b Liller, M. H. (October 1983), "The variable stars in the field of the globular cluster NGC 6681", Astronomical Journal, 88: 1463–1469, Bibcode:1983AJ.....88.1463L, doi:10.1086/113435.
  9. ^ a b Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society, 404 (3): 1203–1214, arXiv:1001.4289, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x, S2CID 51825384.
  10. ^ Mobberley, Martin (2013), It Came From Outer Space Wearing an RAF Blazer!: A Fan's Biography of Sir Patrick Moore, Springer Science & Business Media, p. 483, ISBN 978-3319006093
  11. ^ a b c Watson, Alan M.; et al. (November 1994), "Far-ultraviolet imaging of the globular cluster NGC 6681 with WFPC2" (PDF), Astrophysical Journal, Part 2, 435 (1): L55–L58, Bibcode:1994ApJ...435L..55W, doi:10.1086/187593.{{citation}}: CS1 maint: multiple names: authors list (link)
  12. ^ Frommert, Hartmut; Kronberg, Christine (30 August 2007), "Globular Cluster M70", SEDS Messier pages, Students for the Exploration and Development of Space (SEDS), retrieved 4 December 2018.
  13. ^ Djorgovski, S. (January 1993), "Physical Parameters of Galactic Globular Clusters", in Djorgovski, S. G.; Meylan, G. (eds.), 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, vol. 50, San Francisco, California: Astronomical Society of the Pacific, p. 373, Bibcode:1993ASPC...50..373D, ISBN 978-0937707692.
  14. ^ Forbes, Duncan A.; et al. (October 2008), "Uniting old stellar systems: from globular clusters to giant ellipticals", Monthly Notices of the Royal Astronomical Society, 389 (4): 1924–1936, arXiv:0806.1090, Bibcode:2008MNRAS.389.1924F, doi:10.1111/j.1365-2966.2008.13739.x, S2CID 14108457.
  15. ^ Pryor, Carlton; et al. (August 1989), "Mass-to-light ratios for globular clusters. I - The centrally concentrated clusters NGC 6624, M28 (NGC 6626), and M70 (NGC 6681)", Astronomical Journal, 98: 596–610, Bibcode:1989AJ.....98..596P, doi:10.1086/115160.
  16. ^ O'Malley, Erin M.; et al. (September 2017), "High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681", The Astrophysical Journal, 846 (1): 15, arXiv:1706.06962, Bibcode:2017ApJ...846...23O, doi:10.3847/1538-4357/aa7b72, S2CID 118972140, 23.
  17. ^ Clement, Christine M.; et al. (November 2001), "Variable Stars in Galactic Globular Clusters", The Astronomical Journal, 122 (5): 2587–2599, arXiv:astro-ph/0108024, Bibcode:2001AJ....122.2587C, doi:10.1086/323719, S2CID 38359010.
  1. ^ On the southernmost line of the main (teapot) asterism; its declination means it will not rise (above the horizon) above the 58th parallel north and will need the observer to be as much as a further fifteen degrees of latitude south for detailed, little distorted observation
  2. ^ on 31 August
  3. ^ on 23 July
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