NGC 6440

NGC 6440
HST image of NGC 6440
Observation data (J2000 epoch)
ClassV[1]
ConstellationSagittarius
Right ascension17h 48m 52.67s[2]
Declination−20° 21′ 34.5″[2]
Distance27.1 ± 1.3 kly (8.3 ± 0.4 kpc)[3]
Apparent magnitude (V)9.3[4]
Apparent dimensions (V)4.4′[4]
Physical characteristics
Mass> 4.42×105[3] M☉
Metallicity = −0.56[3] dex
Estimated age≈11 Gyr[5]
Other designationsNGC 6440[6]
See also: Globular cluster, List of globular clusters

NGC 6440 is a globular cluster of stars in the southern constellation of Sagittarius. It was discovered by German-English astronomer William Herschel on 28 May 1786. With an apparent visual magnitude of 9.3 and an angular diameter of 4.4′, it can be observed as a fuzzy blob when viewed through a small telescope.[4] Its Shapley–Sawyer Concentration Class is V.[1]

This cluster is located at a distance of 27.1 ± 1.3 kly (8.3 ± 0.4 kpc) from the Sun.[3] It is situated toward the galactic bulge of the Milky Way,[3] about 26 kly (8.0 kpc) from the Galactic Center. The center of the cluster is fairly concentrated, but does not appear to have undergone a core collapse.[7] It has a core radius of 0.85 ly (0.26 pc), and a half-mass radius of 6.6 ly (2.02 pc). Observations suggest it is one of the most metal–rich globular clusters in the galaxy, and it is close to solar metallicity.[3] NGC 6440 is a rich target for Astrophysical X-ray sources. As of 2022, thirteen pulsars have been discovered in NGC 6440.[3]

References

  1. ^ a b Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin. 849: 11–14. Bibcode:1927BHarO.849...11S.
  2. ^ a b 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.
  3. ^ a b c d e f g Vleeschower, L.; et al. (June 2022). "Discoveries and timing of pulsars in NGC 6440". Monthly Notices of the Royal Astronomical Society. 513 (1): 1386–1399. arXiv:2204.00086. Bibcode:2022MNRAS.513.1386V. doi:10.1093/mnras/stac921.
  4. ^ a b c O'Meara, Stephen James (2007). Herschel 400 Observing Guide. Cambridge University Press. p. 233. ISBN 9780521858939.
  5. ^ Origlia, L.; et al. (November 2008). "Probing the Galactic Bulge with Deep Adaptive Optics Imaging: The Age of NGC 6440". The Astrophysical Journal Letters. 687 (2): L79 – L82. arXiv:0809.3939. Bibcode:2008ApJ...687L..79O. doi:10.1086/593351.
  6. ^ "NGC 6440". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 8 January 2017.
  7. ^ Ortolani, S.; et al. (December 1994). "The low galactic latitude metal-rich globular cluster NGC 6440". Astronomy and Astrophysics Supplement. 108: 653–659. Bibcode:1994A&AS..108..653O.