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.
| NGC 6540 | |
|---|---|
 Hubble Space Telescope image of NGC 6540 | |
| Observation data (J2000 epoch) | |
| Constellation | Sagittarius |
| Right ascension | 18h 06m 08.60s[1] |
| Declination | −27° 45′ 55.0″[1] |
| Distance | 12.07 ± 0.98 kly (3.7 ± 0.3 kpc)[2] |
| Apparent magnitude (V) | 9.30[3] |
| Physical characteristics | |
| Absolute magnitude | −5.38[1] |
| Radius | 4.75′ × 4.75′[3] |
| Metallicity | = −1.20[1] dex |
| Other designations | C 1803-278, NGC 6540, Cr 364[4] |
![{\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4c0821bd80891e071c08e7c7ee8e022baedf522c)
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
edit- ^ a b c d e 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.
- ^ a b 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.
- ^ a b c "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
edit- 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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