NGC 7419

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NGC 7419
NGC 7419 2MASS.jpg
NGC 7419 in infrared, highlighting the five red supergiants, plus the foreground Carbon star MZ Cep at lower left
Credit: 2MASS
Observation data (J2000 epoch)
ConstellationCepheus
Right ascension22h 54m 20s[1]
Declination+60° 48′ 54″[1]
Distance(2,300 - 3,300[2])
Apparent magnitude (V)13[1]
Apparent dimensions (V)2′[3]
Physical characteristics
See also: Open cluster, List of open clusters

NGC 7419 is an open cluster in the constellation Cepheus. It is heavily reddened and notable for containing five red supergiants, the highest number known in any cluster until the end of the 20th century, but probably no blue supergiants.

Members[edit]

The most luminous of the five red supergiants is the exceptionally cool MY Cephei.[4] It has a spectral type of M7.5 which is one of the latest spectral types of any supergiant, although analysis is made difficult by the lack of comparable standard stars.[5] It is estimated to have a temperature of 2,600 K[6] and a bolometric luminosity of 180,000 L.[7] MY Cephei is a semiregular variable star with a brightness range of magnitude 14.4 - 15.3.[8]

The brightest hot stars have a spectral type of BC2, indicating B2 stars with enhanced levels of carbon.[9] One has a bright giant luminosity class of II, while the other has a luminosity class of Ib-II, indicating it is either a bright giant or supergiant. The hotter stars of the cluster are visually faint due to around six magnitudes of interstellar extinction.[2]

The lack of blue supergiants, particularly in a cluster of just the right size and age to include five red supergiants, is unusual. Such low ratios of blue:red supergiants occur in low metallicity clusters, but NGC 7419 has young and has near-solar metallicity. Rapidly rotating stars may account for this evolutionary trend, encouraging high mass loss and rapid evolution of massive stars into red supergiants. This conclusion is also consistent with the high proportion of Be stars in the cluster.[4][2]

The age of the cluster is calculated to be 14±2 million years. Clusters of this age are expected to have a main sequence turnoff at spectral type B1, and this is seen in NGC 7419. 1,200 M of B-type stars alone are observed, implying a total cluster mass of 7,000 - 10,000 M.[2]

Non-members[edit]

Visible in the same field and as prominent as the red supergiants in infrared images is the carbon star MZ Cephei, which is much closer to us than NGC 7419.[4] It is a slow irregular variable star with a range of 14.7 - 15.4.[8]

The visually brightest star in the core region of the cluster is a yellow giant, placed at around 500 parsecs by Gaia astrometry.[10] The even brighter nearby star HD 316721 is also a foreground object.[4] Further out still from the centre of the cluster is the 7th magnitude eclipsing binary V453 Cephei, around 250 parsecs distant from us.[11]

References[edit]

  1. 1.0 1.1 1.2 Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  2. 2.0 2.1 2.2 2.3 Marco, A; Negueruela, I (2013). "NGC 7419 as a template for red supergiant clusters". Astronomy & Astrophysics 552: A92. arXiv:1302.5649. Bibcode 2013A&A...552A..92M. doi:10.1051/0004-6361/201220750.
  3. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  4. 4.0 4.1 4.2 4.3 Caron, Genevive; Moffat, Anthony F. J.; St-Louis, Nicole; Wade, Gregg A.; Lester, John B. (2003). "The Lack of Blue Supergiants in NGC 7419, a Red Supergiant-rich Galactic Open Cluster with Rapidly Rotating Stars". The Astronomical Journal 126 (3): 1415–1422. Bibcode 2003AJ....126.1415C. doi:10.1086/377314.
  5. Beauchamp, Alain; Moffat, Anthony F. J; Drissen, Laurent (1994). "The galactic open cluster NGC 7419 and its five red supergiants". Astrophysical Journal Supplement Series 93: 187. Bibcode 1994ApJS...93..187B. doi:10.1086/192051.
  6. Cesetti, M; Pizzella, A; Ivanov, V. D; Morelli, L; Corsini, E. M; Dalla Bontà, E (2013). "The Infrared Telescope Facility (IRTF) spectral library:. Spectral diagnostics for cool stars". Astronomy & Astrophysics 549: A129. arXiv:1211.5572. Bibcode 2013A&A...549A.129C. doi:10.1051/0004-6361/201219078.
  7. Fawley, W. M; Cohen, M (1974). "The open cluster NGC 7419 and its M7 supergiant IRC +60 375". Astrophysical Journal 193: 367. Bibcode 1974ApJ...193..367F. doi:10.1086/153171.
  8. 8.0 8.1 Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports 61: 80. Bibcode 2017ARep...61...80S. doi:10.1134/S1063772917010085.
  9. Walborn, N. R (1976). "The OBN and OBC stars". Astrophysical Journal 205: 419. Bibcode 1976ApJ...205..419W. doi:10.1086/154292.
  10. Gaia Collaboration; Brown, A. G. A; Vallenari, A; Prusti, T; De Bruijne, J. H. J; Mignard, F; Drimmel, R; Babusiaux, C et al. (2016). "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties". Astronomy & Astrophysics 595: A2. arXiv:1609.04172. Bibcode 2016A&A...595A...2G. doi:10.1051/0004-6361/201629512.
  11. Van Leeuwen, F (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.


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