NGC 7419

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.

NGC 7419
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 ascension 22h 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
Other designationsCollinder 453

Members

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 between 2,600 to 3,400 K[6][7] and a bolometric luminosity of 155,000 L☉ and a radius as large as 1,134 to 2,440 R☉, making it one of largest known stars and one of most luminous and coolest cool supergiants.[7][8] MY Cephei is a semiregular variable star with a brightness range of magnitude 14.4 - 15.3.[9]

The brightest hot stars have a spectral type of BC2, indicating B2 stars with enhanced levels of carbon.[10] 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

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.[9]

The visually brightest star in the core region of the cluster is a yellow giant, placed at around 500 parsecs by Gaia astrometry.[11] 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.[12]

References
  1. "NGC 7419". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-01-03.
  2. 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. "SEDS Online NGC Database". Results for NGC 7419. Retrieved 2018-01-03.
  4. Caron, Geneviève; 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. Beasor, Emma R; Davies, Ben; Arroyo-Torres, B; Chiavassa, A; Guirado, J. C; Marcaide, J. M; Alberdi, A; De Wit, W. J; Hofmann, K. -H; Meilland, A; Millour, F; Mohamed, S; Sanchez-Bermudez, J (2018). "The evolution of red supergiant mass-loss rates" (PDF). Monthly Notices of the Royal Astronomical Society. 475 (1): 55. Bibcode:2018MNRAS.475...55B. doi:10.1093/mnras/stx3174.
  8. 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.
  9. 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 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085.
  10. Walborn, N. R. (1976). "The OBN and OBC stars". Astrophysical Journal. 205: 419. Bibcode:1976ApJ...205..419W. doi:10.1086/154292.
  11. Gaia Collaboration; Brown, A. G. A.; Vallenari, A.; Prusti, T.; De Bruijne, J. H. J; Mignard, F.; Drimmel, R.; Babusiaux, C.; Bailer-Jones, C. A. L.; Bastian, U.; Biermann, M.; Evans, D. W.; Eyer, L.; Jansen, F.; Jordi, C.; Katz, D.; Klioner, S. A.; Lammers, U.; Lindegren, L.; Luri, X.; O'Mullane, W.; Panem, C.; Pourbaix, D.; Randich, S.; Sartoretti, P.; Siddiqui, H. I.; Soubiran, C.; Valette, V.; Van Leeuwen, F.; Walton, N. A. (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.
  12. Van Leeuwen, Floor (2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.


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