NGC 1261

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NGC 1261
Ngc 1261.jpg
NGC 1261 from Hubble Legacy Archive
Observation data (J2000.0 epoch)
Class II [1]
Constellation Horologium
Right ascension 03h 12m 16.21s [2]
Declination –55° 12′ 58.4″ [2]
Distance 53.5  kly (16.4  kpc) [3]
Apparent magnitude (V)8.63 [4]
Apparent dimensions (V)12.9′
Physical characteristics
Absolute magnitude −7.81 [5]
Mass3.41×105 [6]   M☉
Metallicity  = −1.38±0.14 [5] dex
Estimated age10.24  Gyr [7]
Other designationsGCL 5, [4] ESO 155-SC11, Caldwell 87, Melotte 19
See also: Globular cluster, List of globular clusters

NGC 1261 (also known as Caldwell 87) is a globular cluster of stars in the southern constellation of Horologium, first discovered by Scottish astronomer James Dunlop in 1826. The cluster is located at a distance of 53 kilolight-years from the Sun, and 59 kilolight-years from the Galactic Center. [3] It is about 10.24 [7]  billion years old with 341,000 [6] times the mass of the Sun. The cluster does not display the normal indications of core collapse, but evidence suggests it may have instead passed through a post core-collapse bounce state within the past two billion years. The central luminosity density is 2.22  L☉·pc−3, which is low for a globular cluster. [8] Despite this, it has a Shapley–Sawyer Concentration Class of II, [1] indicating a dense central concentration.

A total of 22 RR Lyrae variables have been discovered in this cluster, along with two long-period variables, three SX Phoenicis variables, and an eclipsing binary. [9] It was determined to be an Oosterhoff type I cluster, based on the periods of fourteen of the RR Lyrae variables. [10] 18 probable blue straggler candidates have been identified. [5]

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NGC 4147 is the New General Catalogue identifier for a globular cluster of stars in the northern constellation of Coma Berenices. It was discovered by English astronomer William Herschel on March 14, 1784, who described it as "very bright, pretty large, gradually brighter in the middle". With an apparent visual magnitude of 10.7, it is located around 60,000 light years away from the Sun at a relatively high galactic latitude of 77.2°.

References

  1. 1 2 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. 1 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. 1 2 Paust, Nathaniel E. Q.; et al. (February 2010), "The ACS Survey of Galactic Globular Clusters. VIII. Effects of Environment on Globular Cluster Global Mass Functions", The Astronomical Journal, 139 (2): 476–491, Bibcode:2010AJ....139..476P, doi:10.1088/0004-6256/139/2/476, hdl: 2152/34371 , S2CID   120965440.
  4. 1 2 "NGC 1261". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2020-04-08.
  5. 1 2 3 Kravtsov, V.; et al. (June 2010), "Wide-field multi-color photometry of the Galactic globular cluster NGC 1261", Astronomy and Astrophysics, 516: 8, arXiv: 1005.0007 , Bibcode:2010A&A...516A..23K, doi:10.1051/0004-6361/200913449, S2CID   55542820, A23.
  6. 1 2 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.
  7. 1 2 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.
  8. ↑ Simunovic, Mirko; et al. (November 2014), "The Blue Straggler Star Population in NGC 1261: Evidence for a Post-core-collapse Bounce State", The Astrophysical Journal Letters, 795 (1): 5, arXiv: 1410.0693 , Bibcode:2014ApJ...795L..10S, doi:10.1088/2041-8205/795/1/L10, S2CID   119294014, L10.
  9. ↑ Salinas, R.; et al. (September 2016), "An AO-assisted Variability Study of Four Globular Clusters", The Astronomical Journal, 152 (3): 10, arXiv: 1605.06517 , Bibcode:2016AJ....152...55S, doi: 10.3847/0004-6256/152/3/55 , S2CID   119304354, 55.
  10. ↑ Wehlau, A.; Demers, S. (May 1977), "NGC 1261 and the Oosterhoff type I systems", Astronomy and Astrophysics, 57: 251–256, Bibcode:1977A&A....57..251W.
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