MY Cephei

MY Cephei (IRC +60375) is a red supergiant located in open cluster NGC 7419 in the constellation of Cepheus. It is a semiregular variable star with a maximum brightness of magnitude 14.4 and a minimum of magnitude 15.5.

Not to be confused with Mu Cephei.
MY Cephei

MY Cephei is the brightest star in this infrared image of NGC 7419.
Credit: 2MASS
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
Right ascension 22h 54m 31.7s[1]
Declination +60° 49′ 38.97″[1]
Apparent magnitude (V) 14.4–15.5[2]
Characteristics
Evolutionary stage Extreme[3] OH/IR red supergiant[4]
Spectral type M7–7.5 I[5] (M6–7Iab[2])
Apparent magnitude (G) 10.2686[1]
Apparent magnitude (H) 2.98[6]
Apparent magnitude (K) 2.14[6]
Variable type SRc[2]
Astrometry
Proper motion (μ) RA: –2.635[1] mas/yr
Dec.: –1.719[1] mas/yr
Parallax (π)0.9284 ± 0.1404[1] mas
Distance3,000+350
−290[7] pc
Details
Mass14.5[8] M☉
Radius1,134[9][lower-alpha 1]–2,061[5][lower-alpha 2] R☉
Luminosity129,000[7]–310,000[5] L☉
Temperature3,000[5]–3,400[9] K
Age9[5] Myr
Other designations
MY Cep, IRC +60375, 2MASS J22543171+6049388, IRAS 22525+6033, RAFGL 2987
Database references
SIMBADdata

MY Cephei has an unusual spectral type of M7.5, one of the latest spectral types of any supergiant, and is one of the most luminous and coolest red supergiants, as well as one of the largest known stars. If placed at the center of the Solar System, the star's surface would engulf the orbit of Jupiter and possibly even the orbit of Saturn.

Observations and variability

Observations of the open cluster NGC 7419 in 1954 showed that four of its members were luminous red stars, most likely red supergiants. In addition, an unusually red star was found to be variable and probably an even more luminous supergiant.[10] This star was given the variable star designation MY Cephei in 1973 in the 59th name-list of variable stars.[11]

MY Cephei is classified as semiregular variable star of sub-type SRc, indicating it is a cool supergiant, although its pulsational period is not known. It has been observed as bright as magnitude 14.4 and as faint as magnitude 15.5.[2] The star, along with another late red supergiant star, S Persei, are sometimes considered prototypes for the class of M6–7 supergiants.[12]

Distance

The distance of MY Cephei is assumed to be around 9,780+1,140
−950 light years or 3,000+350
−290 parsecs based on it being a member of the NGC 7419 open cluster.[5][7] Gaia Data Release 2 gives a parallax of 0.9284±0.1404 mas for MY Cep,[1] implying a much closer distance of 1,071+210
−152 pc and a luminosity of 10,000–13,300 L☉ with a corresponding radius of 363 R☉ based on a temperature of 3,025±213 K for the spectral type M7.5 respectively,[13] but that value is considered unreliable due to a very high level of astrometric noise.[1]

Stellar properties

The spectral type of MY Cephei is given in the General Catalogue of Variable Stars as M6–7 Iab, indicating the star is an intermediate-size luminous supergiant star,[2] although most authors gives M7–M7.5 I.[5] Classification is difficult because of the lack of comparable standard stars, but its spectrum appears to be later than M5, earlier than VX Sagittarii when at M9, and more luminous than M7 giant stars.[12]

MY Cephei is a very luminous, cool and large extreme supergiant star, with a luminosity more than 100,000 times that of the Sun (L☉) and a radius in excess of a thousand times the Sun's radius (R☉). It is likely the most luminous, coolest, and the largest supergiant star in its open cluster,[5] and occupies the upper-right hand corner of the Hertzsprung–Russell diagram.

A 2018 paper gives the star a temperature of 3,400 K, corresponding a radius of 1,134 R☉ based on a luminosity of 155,000 L☉.[9] The mass of MY Cephei is uncertain, but expected to be around 14.5 times the Sun's mass (M☉).[8] Mass is being lost at (2.3±0.3)×10−5 M☉ per year, one of highest mass loss rates known for a supergiant star.[5]

A newer calculation, based on SED integration, gives an unexpectedly higher bolometric luminosity of 310,000±70,000 L☉, close to the empirical upper luminosity limit of red supergiants (i.e. Humphreys–Davidson limit). This implies a higher radius of 2,061 R☉ based on an effective temperature of 3,000 K derived using the DUSTY model.[5] Older studies frequently calculated even more lower temperatures and an estimated radius of 2,400 R☉.[12]

See also

Notes
  1. Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772 K:
  2. Applying the Stefan-Boltzmann Law with a nominal solar effective temperature of 5,772 K:

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. "GCVS Query=MY Cep". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2020-08-06.
  3. Davies, Ben; Beasor, Emma R. (2019). "The distances to star clusters hosting Red Supergiants: χ per, NGC 7419, and Westerlund 1". Monthly Notices of the Royal Astronomical Society: Letters. 486: L10–L14. arXiv:1903.12506. doi:10.1093/mnrasl/slz050. S2CID 88517447.
  4. 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.
  5. Humphreys, Roberta M.; Helmel, Greta; Jones, Terry J.; Gordon, Michael S. (August 2020). "Exploring the Mass Loss Histories of the Red Supergiants". The Astronomical Journal. 160 (3): 145. arXiv:2008.01108. Bibcode:2020AJ....160..145H. doi:10.3847/1538-3881/abab15. S2CID 220961677.
  6. Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally Published in: 2003yCat.2246....0C. 2246: 0. Bibcode:2003yCat.2246....0C.
  7. Davies, Ben; Beasor, Emma R. (March 2020). "The 'red supergiant problem': the upper luminosity boundary of Type II supernova progenitors". MNRAS. 493 (1): 468–476. arXiv:2001.06020. Bibcode:2020MNRAS.493..468D. doi:10.1093/mnras/staa174. S2CID 210714093.
  8. 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. S2CID 53723223.
  9. 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". Monthly Notices of the Royal Astronomical Society. 475 (1): 55. arXiv:1712.01852. Bibcode:2018MNRAS.475...55B. doi:10.1093/mnras/stx3174. S2CID 55822928.
  10. Blanco, V.; Nassau, J. J.; Stock, J.; Wehlau, W. (1955). "M-Type Stars in NGC 7419". The Astrophysical Journal. 121: 637. Bibcode:1955ApJ...121..637B. doi:10.1086/146029.
  11. Kukarkin, B. V.; Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (1973). "59th Name-List of Variable Stars". Information Bulletin on Variable Stars. 834: 1. Bibcode:1973IBVS..834....1K.
  12. 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.
  13. Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
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