| NGC 6540 | |
|---|---|
 Hubble Space Telescope image of NGC 6540 | |
| Observation data (J2000 epoch) | |
| Constellation | Sagittarius |
| Right ascension | 18 06 08.60 |
| Declination | −27° 45′ 55.0″ |
| Distance | 12.07 ± 0.98 kly (3.7 ± 0.3 kpc) |
| Apparent magnitude (V) | 9.30 |
| Physical characteristics | |
| Absolute magnitude | −5.38 |
| Radius | 4.75′ × 4.75′ |
| Metallicity | = −1.20 dex |
| Other designations | C 1803-278, NGC 6540, Cr 364 |
| See also: Globular cluster, List of globular clusters | |
= −1.20 NGC 6540 is a globular cluster of stars in the souther constellation Sagittarius, positioned about 4.66° away from the Galactic Center. 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 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, and 14 kly (4.4 kpc) from the Galactic Center. It was originally thought to be an open cluster before being designated a globular. The cluster includes a peculiar X-ray source of uncertain type.
References
- ^ 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.
- ^ 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. arXiv:1804.05781. Bibcode:2018PASA...35...21P. doi:10.1017/pasa.2018.16.
- ^ "NGC 6540". Students for the Exploration and Development of Space. Retrieved 15 January 2016.
- "NGC 6540". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 7 January 2017.
- Bica, E.; et al. (March 1994). "The globular cluster NGC 6540". Astronomy and Astrophysics. 283: 67–75. Bibcode:1994A&A...283...67B.
- 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. arXiv:1805.08057. Bibcode:2018A&A...616A..36M. doi:10.1051/0004-6361/201833086.
External links
- 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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