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NGC 6388

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NGC 6388
Observation data (J2000 epoch)
ClassIII[1][2]
ConstellationScorpius[3]
Right ascension17h 36m 17.461s[4]
Declination−44° 44′ 08.34″[4]
Distance35.6 ± 1.5 kly (10.90 ± 0.45 kpc)[5]
Apparent magnitude (V)6.8[3]
Apparent dimensions (V)10.4′[3]
Physical characteristics
Mass2.17×106[6] M☉
Tidal radius6.21′[7]
VHB16.85[7]
Metallicity = −0.55[7] dex
Estimated age11.5±1.5 Gyr[8]
See also: Globular cluster, List of globular clusters

NGC 6388 is a globular cluster of stars located in the southern constellation of Scorpius. The cluster was discovered by Scottish astronomer James Dunlop on May 13, 1826 using a 20 cm (9 in) reflector telescope.[3] It was later determined to be a globular cluster by English astronomer John Herschel, who was able to resolve it into individual stars.[3] NGC 6388 is located at a distance of approximately 35,600 light-years (10.90 kpc) from the Sun.[5] Due to its apparent visual magnitude of +6.8,[3] binoculars or a small telescope are required to view it.

This cluster has an age of 11.5±1.5 Gyr and a core radius of 7.2″. The central velocity dispersion is 18.9 km/s,[8] and the central density is 2.19×105 L☉·pc−3.[9] With an estimated mass of 2.17×106 M☉,[6] it is one of the most massive globular clusters in the Milky Way. Multiple stellar populations have been detected.[8] In the past it has been proposed that this cluster was accreted into the Milky Way galaxy. However, the abundance of stellar elements from a large sample of cluster members strongly indicate it was formed within the galaxy.[10][11]

The Hertzsprung–Russell diagram for NGC 6388 shows that the main-sequence turnoff for this cluster is similar to that of the cluster 47 Tucanae. This suggests that the bulk of the stellar components have a similar age and chemical abundances between the two clusters. However, the RR Lyrae variables and hotter members of the horizontal branch in NGC 6388 appear overluminous.[12] It has been suggested that this extended horizontal branch may be the result of a central intermediate mass black hole (IMBH). X-ray observations of the cluster rule out an accreting IMBH, but not a quiescent black hole.[8] The stellar density and radial profiles of velocity dispersion rule out an IMBH with a mass greater than about 2,000 M☉.[13]

The cluster contains a population of blue straggler stars (BSS), which are the result of stellar mergers. The radial distribution of this population is high near the core, decreasing at intermediate distance before increasing again at larger radii. This bimodal distribution is similar to that in other globulars. However, the scale of the population at intermediate distances suggests that dynamic friction in NGC 6388 is less efficient at segregating BSS toward the core.[14]

Examination of NGC 6388 by the Chandra observatory show 61 X-ray sources within a half-mass radius of the core (0.67′), with all having luminosities above 5×1030 erg. Five of these appear to be X-ray binaries.[9]

References

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  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. ^ "NCG 6388". Students for the Exploration and Development of Space. Retrieved 26 September 2015.
  3. ^ a b c d e f O'Meara, Stephen James (2013). Deep-Sky Companions: Southern Gems. Cambridge University Press. pp. 346–347. ISBN 9781107015012.
  4. ^ a b Skrutskie, Michael F.; et al. (February 1, 2006). "The Two Micron All Sky Survey (2MASS)". The Astronomical Journal. 131 (2): 1163–1183. Bibcode:2006AJ....131.1163S. doi:10.1086/498708. ISSN 0004-6256. S2CID 1891333.
  5. ^ a b Watkins, Laura L.; et al. (October 2015). "Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Clusters. III. Dynamical Distances and Mass-to-Light Ratios". The Astrophysical Journal. 812 (2). id. 149. arXiv:1509.00513. Bibcode:2015ApJ...812..149W. doi:10.1088/0004-637X/812/2/149.
  6. ^ a b 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. ^ a b c "NCG 6388". Galactic Globular Clusters Database. Retrieved 26 September 2015.
  8. ^ a b c d Lützgendorf, N.; et al. (September 2011). "Kinematic signature of an intermediate-mass black hole in the globular cluster NGC 6388". Astronomy & Astrophysics. 533. id. A36. arXiv:1107.4243. Bibcode:2011A&A...533A..36L. doi:10.1051/0004-6361/201116618.
  9. ^ a b Maxwell, J. Edward; et al. (September 2012). "X-Ray Binaries in the Ultrahigh Encounter Rate Globular Cluster NGC 6388". The Astrophysical Journal. 756 (2). id. 147. arXiv:1208.1426. Bibcode:2012ApJ...756..147M. doi:10.1088/0004-637X/756/2/147.
  10. ^ Carretta, Eugenio; Bragaglia, Angela (September 2023). "Chemistry of multiple stellar populations in the mono-metallic, in situ, bulge globular cluster NGC 6388". Astronomy & Astrophysics. 677. id. A73. arXiv:2307.05478. Bibcode:2023A&A...677A..73C. doi:10.1051/0004-6361/202346174.
  11. ^ Massari, Davide; et al. (December 2023). "Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). I. The final word on the origin of NGC 6388 and NGC 6441". Astronomy & Astrophysics. 680. id. A20. arXiv:2310.01495. Bibcode:2023A&A...680A..20M. doi:10.1051/0004-6361/202347289.
  12. ^ Catelan, M.; et al. (November 2006). "Deep HST Photometry of NGC 6388: Age and Horizontal-Branch Luminosity". The Astrophysical Journal. 651 (2): L133–L136. arXiv:astro-ph/0609727. Bibcode:2006ApJ...651L.133C. doi:10.1086/509720.
  13. ^ Lanzoni, B.; et al. (June 2013). "The Velocity Dispersion Profile of NGC 6388 from Resolved-star Spectroscopy: No Evidence of a Central Cusp and New Constraints on the Black Hole Mass". The Astrophysical Journal. 769 (2). id. 107. arXiv:1304.2953. Bibcode:2013ApJ...769..107L. doi:10.1088/0004-637X/769/2/107.
  14. ^ Dalessandro, E.; et al. (2008). "Blue straggler stars in the unusual globular cluster NGC 6388". Memorie della Società Astronomica Italiana. 79: 698. Bibcode:2008MmSAI..79..698D.

Further reading

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  • Media related to NGC 6388 at Wikimedia Commons
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