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 [Fe/H] = −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]

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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