Astronomy:NGC 6539

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NGC 6539
File:240px
Globular cluster NGC 6539
Observation data (J2000 epoch)
ClassX:[1]
ConstellationSerpens
Right ascension 18h 04m 49.74s[2]
Declination–07° 35′ 09.1″[2]
Distance26.63 kly (8.165 kpc)[3]
Apparent magnitude (V)9.6[4]
Apparent dimensions (V)6.9′[4]
Physical characteristics
Absolute magnitude−8.21[2]
Mass5.36×105[5] M☉
Metallicity[Fe/H] = −0.66[2] dex
Other designationsGCL 85
See also: Globular cluster, List of globular clusters

NGC 6539, or GCL 85, is a globular cluster of stars in the constellation Serpens. It was discovered by Danish astronomer Theodor Brorsen in 1856.[6][7] This cluster is visible with a small amateur telescope, having an apparent visual magnitude of 9.6 and an angular size of 6.9″.[4] It is located at a distance of 26.63 kly (8.165 kpc) from the Sun,[3] and 10 kly (3.1 kpc) from the Galactic Center.[2]

This cluster is located in the outer parts of the Galactic bulge. There is a large dark cloud complex located in the fore of this cluster, causing reddening from extinction.[8] NGC 6539 has a core radius of 0.54′, a half-mass radius of 1.67′, and a tidal radius of 21.5′. Compared to other globular clusters, NGC 6539 is considered metal rich, indicating that it has a relatively higher abundance of elements more massive than helium. Thirteen variable stars have been detected within 7′ of the core, of which a dozen are long period variables.[9] A millisecond pulsar was discovered in 1990.[10]

References

  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. ↑ 2.0 2.1 2.2 2.3 2.4 Di Criscienzo, M. et al. (February 2006), "RR Lyrae-based calibration of the Globular Cluster Luminosity Function", Monthly Notices of the Royal Astronomical Society 365 (4): 1357–1366, doi:10.1111/j.1365-2966.2005.09819.x, Bibcode: 2006MNRAS.365.1357D. 
  3. ↑ 3.0 3.1 Baumgardt, H.; Vasiliev, E. (2021), "Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data", Monthly Notices of the Royal Astronomical Society 505 (4): 5957–5977, doi:10.1093/mnras/stab1474, Bibcode: 2021MNRAS.505.5957B. 
  4. ↑ 4.0 4.1 4.2 Gilmour, Jess K. (2012), The Practical Astronomer's Deep-sky Companion, Springer London, p. 120, ISBN 9781447100713, https://books.google.com/books?id=HyMRBwAAQBAJ&pg=PA120. 
  5. ↑ Boyles, J. et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal 742 (1): 51, doi:10.1088/0004-637X/742/1/51, Bibcode: 2011ApJ...742...51B. 
  6. ↑ Normandin, George (October 20, 2000), "Globular Star Cluster NGC 6539", Kopernik Space Images, http://www.kopernik.org/images/archive/n6539.htm, retrieved 2006-09-28. 
  7. ↑ Patterson, Bill (June 20, 2008), "Global CLusters 2007 Gallery", LAAstro, http://www.laastro.com/Glob2007_spec.html, retrieved 2012-04-09. 
  8. ↑ Origlia, L. et al. (November 2005), "Near-infrared photometry and spectroscopy of NGC 6539 and UKS 1: two intermediate metallicity bulge globular clusters", Monthly Notices of the Royal Astronomical Society 363 (3): 897–904, doi:10.1111/j.1365-2966.2005.09490.x, Bibcode: 2005MNRAS.363..897O. 
  9. ↑ Baker, JoDee M. et al. (January 2007), "Variable Stars in Metal-Rich Globular Clusters. III. NGC 6539", The Astronomical Journal 133 (1): 139–146, doi:10.1086/509638, Bibcode: 2007AJ....133..139B. 
  10. ↑ D'Amico, N. et al. (May 1990), Green, D. W. E., ed., "Millisecond Pulsar in NGC 6539", IAU Circular 5013: 1, Bibcode: 1990IAUC.5013....1D. 



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