NGC 6231

NGC 6231
NGC 6231 (top) with Zeta2 and Zeta1 Scorpii (bottom)
Observation data (J2000.0 epoch)
Right ascension16h 54m
Declination−41° 48′
Distance5,600±400 ly (1,700±130 parsec[1])
Apparent magnitude (V)2.6
Apparent dimensions (V)15.0′
Physical characteristics
Estimated age2–7 million years[2][3]
Other designationsNGC 6171, Caldwell 76, Collinder 315, Melotte 153, De Cheseaux 9, Dunlop 499, Ha. I.7, Lacaille II.13
Associations
ConstellationScorpius
See also: Open cluster, List of open clusters

NGC 6231 (also known as Caldwell 76 or the Baby Scorpion Cluster[4][5]) is an open cluster in the southern sky located half a degrees north of Zeta Scorpii. NGC 6231 is part of a swath of young, bluish stars in the constellation Scorpius known as the Scorpius OB1 association.[6] The star Zeta1 (HR 6262) is a member of this association, while its brighter apparent partner, Zeta2 (HR 6271), is only 150 ly from Earth and so is not a member.[citation needed]

This cluster is estimated to be about 2–7 million years old,[2][3] and is approaching the Solar System at 22 km/s. The cluster and association lie in the neighboring Sagittarius Arm of the Milky Way. Zeta1 Scorpii (spectral type O8 and magnitude 4.71.[7]) is the brightest star in the association, and one of the most radiant stars known in the galaxy.[8] NGC 6231 was used to measure the binary fraction of B-type stars: 52 ± 8%, indicating that B-type stars are commonly found in binary systems, but not as commonly as in O-type stars.[3]

NGC 6231 also includes three Wolf-Rayet stars: HD 151932, HD 152270,[9] and HD 152408.[10]

  1. ^ Kuhn, Michael A.; Hillenbrand, Lynne A.; Sills, Alison; Feigelson, Eric D.; Getman, Konstantin V. (2018). "Kinematics in Young Star Clusters and Associations with Gaia DR2". The Astrophysical Journal. 870 (1): 32. arXiv:1807.02115. Bibcode:2019ApJ...870...32K. doi:10.3847/1538-4357/aaef8c. S2CID 119328315.
  2. ^ a b Kuhn, M. A.; Medina, N.; Getman, K. V.; et al. (2017). "The Structure of the Young Star Cluster NGC 6231. I. Stellar Population". The Astronomical Journal. 154 (3): 87. arXiv:1706.00017. Bibcode:2017AJ....154...87K. doi:10.3847/1538-3881/aa76e8. S2CID 119435797.
  3. ^ a b c Banyard, G.; Sana, H.; Mahy, L.; Bodensteiner, J.; Villaseñor, J. I.; Evans, C. J. (2022). "The observed multiplicity properties of B-type stars in the Galactic young open cluster NGC 6231". Astronomy & Astrophysics. 658: A69. arXiv:2108.07814. Bibcode:2022A&A...658A..69B. doi:10.1051/0004-6361/202141037. S2CID 237194742.
  4. ^ Goldstein, Alan (2024-01-01). "NGC 6231". Astronomy Magazine. Retrieved 2024-06-10.
  5. ^ Stoyan, Ronald; Schurig, Stephan (2014). interstellarum Deep Sky Atlas. Erlangen: Cambridge University Press; Oculum-Verlag GmbH. ISBN 978-1-107-50338-0. OCLC 920437579.
  6. ^ Reipurth, B. (2008). "Young Stars in NGC 6231 and the Sco OB1 Association". In Reipurth, B. (ed.). Handbook of Star Forming Regions, Volume II: The Southern Sky ASP Monograph Publications. Vol. 5. Astronomical Society of the Pacific. p. 401. Bibcode:2008hsf2.book..401R. ISBN 978-1-58381-670-7.
  7. ^ Sky Catalogue 2000.0
  8. ^ Crossen & Tirion, Binocular Astronomy, p. 119.
  9. ^ Shylaja, B. S (1988). "Study of the Wolf-Rayet members of the cluster NGC 6231". Journal of Astrophysics and Astronomy. 9 (3): 161–172. Bibcode:1988JApA....9..161S. doi:10.1007/BF02715061. S2CID 121125488.
  10. ^ The distinction between OIafpe and WNLha stars. A spectral analysis of HD 151804, HD 152408 and HDE 313846.