Astronomy:NGC 6522

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NGC 6522
File:250px
Observation data (J2000 epoch)
ClassVI[citation needed]
ConstellationSagittarius
Right ascension 18h 03m 34.08s[1]
Declination−30° 02′ 02.3″[1]
Distance25.1 kly (7.7 kpc)[2]
Apparent magnitude (V)8.3[3]
Apparent dimensions (V)9.4′[3]
Physical characteristics
Absolute magnitude−7.67[1]
Mass5.93×104[4] M☉
Metallicity[Fe/H] = –1.34[2] dex
Estimated age12.0 Gyr[5]
Other designationsGCl 82, C 1800-300[6]
See also: Globular cluster, List of globular clusters

NGC 6522 is a globular cluster of stars in the southern constellation of Sagittarius. It was discovered by German-British astronomer William Herschel on June 24, 1784. The cluster has an apparent visual magnitude of 8.3 and an angular diameter of 9.4′.[3] It is located at a distance of 25.1 kly (7.7 kpc) from the Sun,[2] and lies in the Milky Way's central bulge,[7] about 2.0 kly (0.6 kpc) from the Galactic Center.[1] The cluster is centered in a region of the sky known as Baade's Window.[8] It is highly impacted by reddening due to interstellar dust and the view is heavily contaminated by field stars, making it more difficult to identify members.[9]

NGC 6522 is possibly the oldest star cluster in the Milky Way,[10] with an age of more than 12 billion years.[11][12] It is a core collapsed cluster with a core radius of 0.5′ and a 1.0′ half-light radius.[9] The cluster formed four billion years before the Milky Way galactic bar appeared, and may have been confined to the bar for a period of time. At present it trails the bar in its orbit around the core.[13]

This is a low mass globular cluster with an estimated 5.93×104 times the mass of the Sun. Distinctive chemical abundances among the members indicate the cluster has multiple populations of stars, with the younger populations exhibiting pollution from earlier generations.[4] Twenty variable stars have been identified as members of NGC 6522, consisting of eight RR Lyrae, three type II Cepheids, and nine long-period variable stars.[9] Six pulsars have been discovered.[14]

  • The globular clusters NGC 6528 (lower left) is close to NGC 6522 (upper right)
    The globular clusters NGC 6528 (lower left) is close to NGC 6522 (upper right)
  • The cluster is located in Baade's Window, a region of night sky that is not clouded by dust from the Milky Way.
    The cluster is located in Baade's Window, a region of night sky that is not clouded by dust from the Milky Way.

References

  1. ↑ 1.0 1.1 1.2 1.3 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. 
  2. ↑ 2.0 2.1 2.2 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. 
  3. ↑ 3.0 3.1 3.2 O'Meara, Stephen James (2013). Deep-Sky Companions: Southern Gems. Cambridge University Press. p. 367. ISBN 9781107015012. https://books.google.com/books?id=S5QIEKns33sC&pg=367. 
  4. ↑ 4.0 4.1 Fernández-Trincado, J. G. et al. (July 2019). "H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia". Astronomy & Astrophysics 627: id. A178. doi:10.1051/0004-6361/201834391. Bibcode: 2019A&A...627A.178F. 
  5. ↑ Koleva, M. et al. (April 2008). "Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting". Monthly Notices of the Royal Astronomical Society 385 (4): 1998–2010. doi:10.1111/j.1365-2966.2008.12908.x. Bibcode: 2008MNRAS.385.1998K. 
  6. ↑ "SIMBAD Astronomical Database". Results for NGC 6522. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+6522. 
  7. ↑ Ness, Melissa et al. (December 2014). "NGC 6522: a typical globular cluster in the Galactic bulge without signatures of rapidly rotating Population III stars". Monthly Notices of the Royal Astronomical Society 445 (3): 2994−2998. doi:10.1093/mnras/stu2144. Bibcode: 2014MNRAS.445.2994N. 
  8. ↑ "NGC 6522". Students for the Exploration and Development of Space. http://spider.seds.org/spider/MWGC/n6522.html. 
  9. ↑ 9.0 9.1 9.2 Arellano Ferro, A. et al. (October 2023). "Variable stars in the field of the Galactic bulge globular cluster NGC 6522". Astrophysics and Space Science 368 (10): id. 91. doi:10.1007/s10509-023-04249-4. Bibcode: 2023Ap&SS.368...91A. 
  10. ↑ Barbuy, B. et al. (November 2009). "VLT-FLAMES Analysis of 8 giants in the Bulge Metal-poor Globular Cluster NGC 6522: Oldest Cluster in the Galaxy?". Astronomy and Astrophysics 507 (1): 405–415. doi:10.1051/0004-6361/200912748. Bibcode: 2009A&A...507..405B. 
  11. ↑ Shiga, David (30 April 2011). "The universe's first stars were whirling dervishes". New Scientist: 20. https://www.newscientist.com/article/dn20426-the-universes-first-stars-were-whirling-dervishes.html. Retrieved 2024-09-09. 
  12. ↑ Chiappini, Cristina et al. (28 April 2011). "Imprints of fast-rotating massive stars in the Galactic Bulge". Nature 472 (7344): 454–457. doi:10.1038/nature10000. PMID 21525928. Bibcode: 2011Natur.472..454C. 
  13. ↑ Barbuy, B. et al. (October 2021). "UVES analysis of red giants in the bulge globular cluster NGC 6522". Astronomy & Astrophysics 654: id. A29. doi:10.1051/0004-6361/202140815. Bibcode: 2021A&A...654A..29B. 
  14. ↑ Abbate, F. et al. (December 2023). "A MeerKAT view of the pulsars in the globular cluster NGC 6522". Astronomy & Astrophysics 680: id. A47. doi:10.1051/0004-6361/202347725. Bibcode: 2023A&A...680A..47A. 



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