NGC 2360

NGC 2360 (also known as Caroline's Cluster[3] or Caldwell 58) is an open cluster in the constellation Canis Major. It was discovered on 26 February 1783,[4] by Caroline Herschel who wrote, "A beautiful cluster of pretty compressed stars near 1/2 degree in diameter."[5] Her notes were overlooked until her brother William included the cluster in his 1786 catalogue of 1000 clusters and nebulae and acknowledged her as the discoverer.[4] The cluster lies 3.5 degrees east of Gamma Canis Majoris and less than one degree northwest of the eclipsing binary star R Canis Majoris; it has a combined apparent magnitude of 7.2.[5] It is 13 arc minutes in diameter.[2] By the western edge of the cluster is the unrelated star, 5.5-magnitude HD 56405.[6]

NGC 2360
Observation data (J2000 epoch)
ConstellationCanis Major
Right ascension 07h 17m 43s[1]
Declination−15° 38′ 29″[1]
Apparent magnitude (V)7.2[2]
Apparent dimensions (V)13′[2]
Physical characteristics
Other designationsCaroline's Cluster,[3] Caldwell 58, Cr 134, Mel 64[3]
Map showing the location of NGC 2360

American astronomer Olin J. Eggen surveyed the cluster in 1968, concluding that the brightest star in the field, magnitude-8.96 HD 56847, is likely to lie in the field and not a true member of the cluster. He also identified one or possibly two blue stragglers.[7] These are unexpectedly hot and luminous stars that appear younger than surrounding stars, and have likely developed by sucking matter off companion stars.[8] Four are now recognised to be in the cluster.[9] By analysing the masses of the smallest stars that have evolved into red giants—namely, stars of 1.8 or 1.9 solar masses—Swiss astronomers Jean-Claude Mermilliod and Michel Mayor were able to date the age of the cluster at 2.2 billion years.[10] The cluster has a diameter of around 15 light-years and is located 3700 light-years from Earth.[5]


Sirius and M41 (lower right), M50 (upper left), and NGC 2360 (lower left)

Notes
  1. "Results for NGC 2360". NGC/IC Project Database. Archived from the original on 2012-05-20. Retrieved 2010-12-03.
  2. "SEDS Online NGC Database". Results for NGC 2360. Retrieved 2010-12-03.
  3. "NGC 2360". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-12-03.
  4. Hoskin, Michael (2005). "Caroline Herschel as observer" (PDF). Journal for the History of Astronomy. 36 (4): 373–406. Bibcode:2005JHA....36..373H. doi:10.1177/002182860503600402.
  5. O'Meara, Stephen James (2002). The Caldwell Objects. Cambridge University Press. pp. 231–33. ISBN 978-0-521-82796-6.
  6. Streicher, Magda (April 2006). "Caroline Herschel's Deepsky Discoveries" (PDF). Deepsky Delights. The Astronomical Society of Southern Africa. pp. 234–36. Retrieved 16 March 2014.
  7. Eggen, Olin J. (1968). "The Intermediate-Age Cluster NGC 2360" (PDF). The Astrophysical Journal. 152: 83–87. Bibcode:1968ApJ...152...83E. doi:10.1086/149526.
  8. Fellman, Megan (17 October 2011). "Astronomers Explain 'Blue Stragglers'". News. Evanston, Illinois: Northwestern University. Retrieved 18 March 2014.
  9. Ahumada, J. A.; Lapasset, E. (2007). "New catalogue of blue stragglers in open clusters" (PDF). Astronomy and Astrophysics. 463 (2): 789–97. Bibcode:2007A&A...463..789A. doi:10.1051/0004-6361:20054590.
  10. Mermilliod, Jean-Claude; Mayor, Michel (1990). "Red Giants in Open Clusters. III – Binarity and Stellar Evolution in Five Intermediate-age Clusters: NGC 2360, 2423, 5822, 6811, and IC 4756" (PDF). Astronomy and Astrophysics. 273 (1): 61–72. Bibcode:1990A&A...237...61M.
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