NGC 7160

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NGC 7160
NGC 7160 map.png
The location of NGC 7160 in the sky
Observation data (J2000 epoch)
ConstellationCepheus
Right ascension 21h 53m 40s[1]
Declination+62° 36′ 12″[1]
Distance2,570 ly (789 pc[2])
Apparent magnitude (V)6.1 [1]
Apparent dimensions (V)13'
Physical characteristics
Mass105[3] M
Estimated age15 million years[4]
Notable featuresPart of Cepheus OB2
Other designationsOCl 236
See also: Open cluster, List of open clusters

NGC 7160 is an open cluster in the constellation Cepheus. It was discovered by William Herschel on November 9, 1789. The cluster was also observed by John Herschel on October 7, 1829. It is a poor cluster and with little central concentration, with Trumpler class II3p.[5] It is part of the stellar association Cepheus OB2, located one degree south-southwest of VV Cephei.[6]

NGC 7160 is a young cluster, whose age is estimated to be between 10[7] and 19 million years.[2] The cluster presents no extented infrared emission when observed by Spitzer Space Telescope and Herschel Space Telescope which suggests that the molecular cloud in which it was formed has been removed.[8] NGC 7160 lies within the Cepheus Bubble, an expanding dusty shell with a diameter of about 10 degrees, which corresponds to 120 pc (390 ly) at the distance of NGC 7160. It is bordered by HII regions like IC 1396, in which is located the open cluster Trumpler 37. The total mass of molecular gas in the Cepheus Bubble is estimated to be 105 M based on CO emission mapping. The bubble is believed to have been formed by the stellar wind and photoionisation from OB stars that have exploded as supernovae. Mu Cephei, Nu Cephei, and NGC 7160 may have been companions of those stars. It has been suggested that Lambda Cephei and 68 Cygni are runaway stars from that area.[9]

The core radius of the cluster is 0.73 parsec (2.4 light years), while the tidal radius is 5.7 parsecs (18.5 light years) and represents the average outer limit of NGC 7160, beyond which a star is unlikely to remain gravitationally bound to the cluster core.[4] 16 stars, probable members of the cluster, are located within the central part of the cluster, and 71 probable members are located within the angular radius of the cluster.[4] Among the members is EM Cephei (mag 7.03), a variable star whose spectrum switches between B and Be star states. It is suggested it is a Be star with a variable circumstellar disk with mass losses (6±3)×10−11 M per year.[10] One low mass member, with spectral type K4.5 is accreting, suggesting the presence of a protoplanetary disk. It is characterised by very low far-IR flux with a high accretion rate.[7][8]

References[edit]

  1. ^ a b c "NGC 7160". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2015-06-19.
  2. ^ a b WEBDA: NGC 7160
  3. ^ Piskunov, A. E.; Schilbach, E.; Kharchenko, N. V.; Röser, S.; Scholz, R.-D. (6 November 2007). "Tidal radii and masses of open clusters". Astronomy & Astrophysics. 477 (1): 165–172. Bibcode:2008A&A...477..165P. doi:10.1051/0004-6361:20078525.
  4. ^ a b c Kharchenko, N. V.; Piskunov, A. E.; Schilbach, E.; Röser, S.; Scholz, R.-D. (3 October 2013). "Global survey of star clusters in the Milky Way". Astronomy & Astrophysics. 558: A53. arXiv:1308.5822. Bibcode:2013A&A...558A..53K. doi:10.1051/0004-6361/201322302.
  5. ^ Seligman, Courtney. "NGC 7160 (= OCL 236)". Celestial Atlas. Retrieved 19 November 2018.
  6. ^ Crossen, Craig; Rhemann, Gerald (2012). Sky Vistas: Astronomy for Binoculars and Richest-Field Telescopes. Springer Science & Business Media. p. 167. ISBN 9783709106266.
  7. ^ a b Sicilia-Aguilar, Aurora; Hartmann, Lee W.; Hernández, Jesús; Briceño, César; Calvet, Nuria (July 2005). "Cepheus OB2: Disk Evolution and Accretion at 3–10 Myr". The Astronomical Journal. 130 (1): 188–209. Bibcode:2005AJ....130..188S. doi:10.1086/430748.
  8. ^ a b Sicilia-Aguilar, Aurora; Roccatagliata, Veronica; Getman, Konstantin; Rivière-Marichalar, Pablo; Birnstiel, Tilman; Merín, Bruno; Fang, Min; Henning, Thomas; Eiroa, Carlos; Currie, Thayne (10 December 2014). "The Herschel/PACS view of the Cep OB2 region: Global protoplanetary disk evolution and clumpy star formation". Astronomy & Astrophysics. 573: A19. arXiv:1410.2713. doi:10.1051/0004-6361/201424669.
  9. ^ Patel, Nimesh A.; Goldsmith, Paul F.; Heyer, Mark H.; Snell, Ronald L.; Pratap, Preethi (November 1998). "Origin and Evolution of the Cepheus Bubble". The Astrophysical Journal. 507 (1): 241–253. Bibcode:1998ApJ...507..241P. doi:10.1086/306305.
  10. ^ Kjurkchieva, Diana; Marchev, Dragomir; Sigut, T. A. A.; Dimitrov, Dinko (18 August 2016). "The B and Be states of the star EM Cepheus". The Astronomical Journal. 152 (3): 56. arXiv:1606.04815. Bibcode:2016AJ....152...56K. doi:10.3847/0004-6256/152/3/56.

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