NGC 1817

NGC 1817 is an open cluster of stars in the constellation Taurus. It was discovered by English astronomer William Herschel in February 1784.[5] With an apparent magnitude of 7 and spanning 17 arc minutes across the sky, it is separated from the NGC 1807 cluster by just a few degrees.[3] Indeed, the two may actually be parts of a single extended cluster.[5]

NGC 1817
NGC 1817 as seen by the DSS
Observation data (J2000 epoch)
ConstellationTaurus
Right ascension05h 12m 15.(0)s[1]
Declination+16° 41′ 2(4)″[1]
Distance6,430 ly (1,972 pc)[2]
Apparent magnitude (V)7.0[3]
Apparent dimensions (V)17.0′[3]
Physical characteristics
Estimated age0.8−1.2[4] Gyr
Other designationsC 0509+166, Collinder 60

The NGC 1817 cluster is around the same age as the Hyades, or perhaps a little younger at 0.8−1.2 billion years. The turnoff point for this cluster—where stars above a certain mass are evolving through the red giant stage—is twice the mass of the Sun.[6] The cluster is situated in the opposite side of the sky from the Galactic Core at a separation of 32 kly (9.9 kpc) from the core,[6] and is around 1.3 kly (0.4 kpc) away from the Galactic plane.[4]

Measurements of the proper motion of 810 stars within a 1.5° region centered on the cluster suggest that it has at least 169 members.[7] Of these, there is a total of 26 variable stars, including three candidate Gamma Doradus variable stars and sixteen Delta Scuti variables.[8] This unusually high proportion of Delta Scuti variables is likely the result of the turnoff point being located within the instability strip.[5]

References
  1. Wu, Zhen-Yu; et al. (November 2009), "The orbits of open clusters in the Galaxy", Monthly Notices of the Royal Astronomical Society, 399 (4): 2146–2164, arXiv:0909.3737, Bibcode:2009MNRAS.399.2146W, doi:10.1111/j.1365-2966.2009.15416.x.
  2. Kharchenko, N. V.; et al. (August 2005). "Astrophysical parameters of Galactic open clusters". Astronomy and Astrophysics. 438 (3): 1163–1173. arXiv:astro-ph/0501674. Bibcode:2005A&A...438.1163K. doi:10.1051/0004-6361:20042523.
  3. Gilmour, Jess K. (2012), The Practical Astronomer's Deep-sky Companion, The Patrick Moore Practical Astronomy Series, Springer Science & Business Media, p. 123, ISBN 978-1447100713.
  4. Donati, P.; et al. (January 2014), "NGC 1817, NGC 2141 and Berkeley 81: three BOCCE clusters of intermediate age", Monthly Notices of the Royal Astronomical Society, 437 (2): 1241–1258, arXiv:1311.2469, Bibcode:2014MNRAS.437.1241D, doi:10.1093/mnras/stt1944.
  5. O'Meara, Stephen James (2011), Deep-Sky Companions: The Secret Deep, 4, Cambridge University Press, p. 84, ISBN 978-1139500074.
  6. Reddy, Arumalla B. S.; et al. (January 2012), "Comprehensive abundance analysis of red giants in the open clusters NGC 752, 1817, 2360 and 2506", Monthly Notices of the Royal Astronomical Society, 419 (2): 1350–1361, arXiv:1109.2678, Bibcode:2012MNRAS.419.1350R, doi:10.1111/j.1365-2966.2011.19791.x.
  7. Balaguer-Núñez, L.; Jordi, C.; Galadí-Enríquez, D.; Zhao, J. L. (November 2004), "New membership determination and proper motions of NGC 1817. Parametric and non-parametric approach", Astronomy and Astrophysics, 426 (3): 819–826, arXiv:astro-ph/0407455, Bibcode:2004A&A...426..819B, doi:10.1051/0004-6361:20041332.
  8. Andersen, M. F.; et al. (July 2009), "NGC 1817: the richest population of delta Scuti stars", Communications in Asteroseismology, 160: 9, Bibcode:2009CoAst.160....9A, doi:10.1553/cia160s9.
  • Media related to NGC 1817 at Wikimedia Commons


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