Wikipedia

NGC 6522

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 identify members.[9]

NGC 6522
Observation data (J2000 epoch)
ClassVI[citation needed]
ConstellationSagittarius
Right ascension18h 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 = –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 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]

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

References

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  1. ^ a b c d 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. arXiv:astro-ph/0511128. Bibcode:2006MNRAS.365.1357D. doi:10.1111/j.1365-2966.2005.09819.x. S2CID 17838243.
  2. ^ 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.
  3. ^ a b c O'Meara, Stephen James (2013). Deep-Sky Companions: Southern Gems. Cambridge University Press. p. 367. ISBN 9781107015012.
  4. ^ a b 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. arXiv:1801.07136. Bibcode:2019A&A...627A.178F. doi:10.1051/0004-6361/201834391.
  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. arXiv:0801.0871. Bibcode:2008MNRAS.385.1998K. doi:10.1111/j.1365-2966.2008.12908.x. S2CID 17571531.
  6. ^ "SIMBAD Astronomical Database". Results for NGC 6522. Retrieved 2011-03-13.
  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. arXiv:1408.0290. Bibcode:2014MNRAS.445.2994N. doi:10.1093/mnras/stu2144.
  8. ^ "NGC 6522". Students for the Exploration and Development of Space. Retrieved 2020-09-23.
  9. ^ a b c 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. arXiv:2310.16257. Bibcode:2023Ap&SS.368...91A. doi:10.1007/s10509-023-04249-4.
  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. arXiv:0908.3603. Bibcode:2009A&A...507..405B. doi:10.1051/0004-6361/200912748.
  11. ^ Shiga, David (30 April 2011). "The universe's first stars were whirling dervishes". New Scientist: 20. 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. Bibcode:2011Natur.472..454C. doi:10.1038/nature10000. PMID 21525928.
  13. ^ Barbuy, B.; et al. (October 2021). "UVES analysis of red giants in the bulge globular cluster NGC 6522". Astronomy & Astrophysics. 654. id. A29. arXiv:2107.08746. Bibcode:2021A&A...654A..29B. doi:10.1051/0004-6361/202140815.
  14. ^ Abbate, F.; et al. (December 2023). "A MeerKAT view of the pulsars in the globular cluster NGC 6522". Astronomy & Astrophysics. 680. id. A47. arXiv:2310.03800. Bibcode:2023A&A...680A..47A. doi:10.1051/0004-6361/202347725.
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