Astronomy:NGC 6540

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NGC 6540
Hubble Space Telescope image of NGC 6540
Observation data (J2000 epoch)
ConstellationSagittarius
Right ascension 18h 06m 08.60s[1]
Declination−27° 45′ 55.0″[1]
Distance12.07 ± 0.98 kly (3.7 ± 0.3 kpc)[2]
Apparent magnitude (V)9.30[3]
Physical characteristics
Absolute magnitude−5.38[1]
Radius4.75′ × 4.75′[3]
Metallicity[Fe/H] = −1.20[1] dex
Other designationsC 1803-278, NGC 6540[4]
See also: Globular cluster, List of globular clusters

NGC 6540 is a globular cluster of stars in the souther constellation Sagittarius, positioned about 4.66° away from the Galactic Center.[5] It was discovered by German-British astronomer Wilhelm Herschel on May 24, 1784, with an 18.7-inch mirror telescope, who described the cluster as "pretty faint, not large, crookedly extended, easily resolvable". It has an apparent visual magnitude of 9.3[3] with an angular diameter of about 9.5 arcminutes.

The cluster is located at a distance of 12 kly (3.7 kpc) from the Sun,[2] and 14 kly (4.4 kpc) from the Galactic Center. It was originally thought to be an open cluster before being designated a globular.[1] The cluster includes a peculiar X-ray source of uncertain type.[6]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 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. 
  2. ↑ 2.0 2.1 Pérez-Villegas, A. et al. (May 2018). "Orbits of Selected Globular Clusters in the Galactic Bulge". Publications of the Astronomical Society of Australia 35: id. e021. doi:10.1017/pasa.2018.16. Bibcode: 2018PASA...35...21P. 
  3. ↑ 3.0 3.1 3.2 "NGC 6540". Students for the Exploration and Development of Space. http://spider.seds.org/spider/MWGC/n6540.html. 
  4. ↑ "NGC 6540". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+6540. 
  5. ↑ Bica, E. et al. (March 1994). "The globular cluster NGC 6540". Astronomy and Astrophysics 283: 67–75. Bibcode: 1994A&A...283...67B. 
  6. ↑ Mereghetti, Sandro et al. (August 2018). "EXTraS discovery of a peculiar flaring X-ray source in the Galactic globular cluster NGC 6540". Astronomy & Astrophysics 616: id. A36. doi:10.1051/0004-6361/201833086. Bibcode: 2018A&A...616A..36M. 
  • NGC 6540
  • Robert Burnham Jr., Burnham's Celestial Handbook: An observer's guide to the universe beyond the solar system, vol 3, p. 1556



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