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Cluster of stars in the southern constellation of Ara
NGC 6250 is a open cluster of stars in the southern constellation of Ara, near the border with Scorpius. It was discovered by English astronomer John Herschel on July 1, 1834. This cluster has an apparent visual magnitude of 5.9 and spans an angular diameter of 18′, with the brightest member being of magnitude 7.6. About 15 members are visible with binoculars or a small telescope. NGC 6250 is located at a distance of 2,820 ly (865 pc) from the Sun, and is approaching with a mean radial velocity of −10±6 km/s.
The Trumpler classification of NGC 6250 is II 3 r, indicating a rich cluster of stars (r) with a slightly disparate grouping (II) and a large brightness range (3). This is a young cluster with an estimated age of 14 million years. Seven cluster members are B-type stars, and three are illuminating reflection nebulae. Two magnetic chemically peculiar stars (CP2) and two candidate Lambda Boötis stars have been identified as members. The metallicity of the cluster members is consistent with the Sun.
References
^ Dias, W. S.; et al. (September 2001), "Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue", Astronomy and Astrophysics, 376 (2): 441–447, Bibcode:2001A&A...376..441D, doi:10.1051/0004-6361:20011021.
^ Bayer, C.; et al. (November 2000), "CCD photometric search for peculiar stars in open clusters. I. NGC 2169, Melotte 105 and NGC 6250", Astronomy and Astrophysics Supplement, 147: 99–109, Bibcode:2000A&AS..147...99B, doi:10.1051/aas:2000294.
McSwain, M. Virginia; Gies, Douglas R. (November 2005), "The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters", The Astrophysical Journal Supplement Series, 161 (1): 118–146, arXiv:astro-ph/0505032, Bibcode:2005ApJS..161..118M, doi:10.1086/432757.
Herbst, W. (November 1977), "Extinction law in dust clouds and the young southern cluster NGC 6250: further evidence for high values of R", Astronomical Journal, 82: 902–907, Bibcode:1977AJ.....82..902H, doi:10.1086/112144.