RW Cephei

RW Cephei
Position of RW Cephei
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
Right ascension 22h 23m 07.01657s[1]
Declination +55° 57′ 47.6262″[1]
Apparent magnitude (V) +6.65[2] (6.0 - 7.3[3])
Characteristics
Spectral type K2 0-Ia[4] (G8 - M2Ia-0[3])
Apparent magnitude (K) 1.88[2]
U−B color index 2.38[2]
B−V color index 2.22[2]
Variable type SRd[5]
Astrometry
Radial velocity (Rv)-56.00[6] km/s
Proper motion (μ) RA: -2.74[1] mas/yr
Dec.: -2.66[1] mas/yr
Parallax (π)0.2357 ± 0.0944[7] mas
Distanceapprox. 14,000 ly
(approx. 4,000 pc)
Absolute magnitude (MV)−8.0[8] - −9.4[9]
Details
Mass13.9[10] M☉
Radius1,535 (981-1,758)[lower-alpha 1] R☉
Luminosity550,000[9] L☉
Surface gravity (log g)0.2[11] cgs
Temperature4,015[12] (3,749 - 5,018)[11] K
Age18.7[10] Myr
Other designations
HD 212466, HIP 110504, SAO 34387, BD+55°2737, AAVSO 2219+55A
Database references
SIMBADdata

RW Cephei is an orange hypergiant star in the constellation Cepheus, at the edge of the Sharpless 132 HII region and close to the small open cluster Berkeley 94. One of the largest stars known, RW Cephei is estimated at 1,535 solar radii (1.068×109 km; 7.14 au), which is larger than the orbit of Jupiter.

RW Cephei is also a semi-regular variable star of type SRd, meaning that it is a slowly varying yellow giant or supergiant. The visual magnitude range is from 6.0 to 7.3,[3] while the photographic range is from 8.6 - 10.7.[5] The General Catalogue of Variable Stars gives a period of approximately 346 days, but other studies suggest different periods and certainly no strong periodicity.[13]

The spectral has been classified as early as G8 and as late as M2, but it isn't clear that there has been actual variation. In the first MK spectral atlas, it was listed M0:Ia.[14] RW Cep was later listed as the standard star for spectral type G8 Ia,[15] then as the standard for K0 0-Ia.[16] Based on the same spectra it was adjusted to the standard star for type K2 0-Ia.[17] Molecular bands characteristic of M-class stars are seen in infrared spectra, but not always in optical spectra.[18][19] The temperature is equally uncertain, with contradictory excitation strengths in the spectrum. A simple colour correlation temperature fit gives temperatures around 3,750 K, while a full spectrum fit gives a temperature of 5,000 K.[11]

The distance to RW Cephei has been estimated on the basis of its spectroscopic luminosity and is assumed to be a member of the Cepheus OB1 association at 3,500 parsecs, consistent with the parallax from Gaia Data Release 2.[9][7]

The temperature intermediate between the red supergiants and yellow hypergiants, and itself varying considerably, has led to it being variously considered as a red hypergiant[20] or yellow hypergiant.[21]

References

  1. 1 2 3 4 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.
  2. 1 2 3 4 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  3. 1 2 3 Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W.
  4. ↑ Keenan, P. C.; Yorka, S. B. (1988). "1988 Revised MK Spectral Standards for Stars GO and Later". Bulletin d'Information du Centre de Donnees Stellaires. 35: 37. Bibcode:1988BICDS..35...37K.
  5. 1 2 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  6. ↑ Kharchenko, N. V.; Scholz, R.-D.; Piskunov, A. E.; Röser, S.; Schilbach, E. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ˜55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776.
  7. 1 2 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.
  8. ↑ Stencel, Robert E.; Pesce, Joseph E.; Hagen Bauer, Wendy (1988). "Far-infrared circumstellar 'debris' shell of red supergiant stars". Astronomical Journal (ISSN 0004-6256). 95: 141. Bibcode:1988AJ.....95..141S. doi:10.1086/114622.
  9. 1 2 3 Humphreys, R. M. (1978). "Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way". The Astrophysical Journal Supplement Series. 38: 309. Bibcode:1978ApJS...38..309H. doi:10.1086/190559.
  10. 1 2 Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410: 190. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x.
  11. 1 2 3 Meneses-Goytia, S.; Peletier, R. F.; Trager, S. C.; Falcón-Barroso, J.; Koleva, M.; Vazdekis, A. (2015). "Single stellar populations in the near-infrared. I. Preparation of the IRTF spectral stellar library". Astronomy & Astrophysics. 582: A96. arXiv:1506.07184. Bibcode:2015A&A...582A..96M. doi:10.1051/0004-6361/201423837.
  12. ↑ Davies, Ben; Kudritzki, Rolf-Peter; Figer, Donald F. (2010). "The potential of red supergiants as extragalactic abundance probes at low spectral resolution". Monthly Notices of the Royal Astronomical Society. 407 (2): 1203. arXiv:1005.1008. Bibcode:2010MNRAS.407.1203D. doi:10.1111/j.1365-2966.2010.16965.x.
  13. ↑ Percy, John R.; Kolin, David L. (2000). "Studies of Yellow Semiregular(SRd) Variables". The Journal of the American Association of Variable Star Observers. 28: 1. Bibcode:2000JAVSO..28....1P.
  14. ↑ Morgan, William Wilson; Keenan, Philip Childs; Kellman, Edith (1943). "An atlas of stellar spectra, with an outline of spectral classification". Chicago. Bibcode:1943assw.book.....M.
  15. ↑ Morgan, W. W.; Roman, Nancy G. (1950). "Revised Standards for Supergiants on the System of the Yerkes Spectral Atlas". Astrophysical Journal. 112: 362. Bibcode:1950ApJ...112..362M. doi:10.1086/145351.
  16. ↑ Morgan, W. W.; Keenan, P. C.; Abt, H. A.; Tapscott, J. W. (1981). "Some aspects of the spectroscopic behavior of the stars of highest luminosity in the region of the Hertzsprung gap". Astrophysical Journal. 243: 894. Bibcode:1981ApJ...243..894M. doi:10.1086/158654.
  17. ↑ Keenan, P. C.; Pitts, R. E. (1980). "Revised MK spectral types for G, K, and M stars". Astrophysical Journal Supplement Series. 42: 541. Bibcode:1980ApJS...42..541K. doi:10.1086/190662.
  18. ↑ McCuskey, S. W. (1955). "Stellar Spectra in Milky way REGIONS.III.A Region in Cepheus-Lacerta". Astrophysical Journal Supplement. 2: 75. Bibcode:1955ApJS....2...75M. doi:10.1086/190017.
  19. ↑ Josselin, E.; Plez, B. (2007). "Atmospheric dynamics and the mass loss process in red supergiant stars". Astronomy and Astrophysics. 469 (2): 671. arXiv:0705.0266. Bibcode:2007A&A...469..671J. doi:10.1051/0004-6361:20066353.
  20. ↑ Delgado, A. J.; Djupvik, A. A.; Costado, M. T.; Alfaro, E. J. (2013). "Berkeley 94 and Berkeley 96: Two young clusters with different dynamical evolution". Monthly Notices of the Royal Astronomical Society. 435: 429. arXiv:1307.4290. Bibcode:2013MNRAS.435..429D. doi:10.1093/mnras/stt1311.
  21. ↑ Castro-Carrizo, A.; Quintana-Lacaci, G.; Bujarrabal, V.; Neri, R.; Alcolea, J. (2007). "Arcsecond-resolution 12CO mapping of the yellow hypergiants IRC +10420 and AFGL 2343". Astronomy and Astrophysics. 465 (2): 457. arXiv:astro-ph/0702400. Bibcode:2007A&A...465..457C. doi:10.1051/0004-6361:20066169.

Notes

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