Lambda Cephei

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λ Cephei
Cepheus constellation map.svg
Red circle.svg
Location of λ Cep (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cepheus
Right ascension  22h 11m 30.57571s[1]
Declination +59° 24′ 52.15″[1]
Apparent magnitude (V) +5.050[2]
Spectral type O6.5If(n)p[3]
U−B color index −0.622[2]
B−V color index +0.237[2]
Radial velocity (Rv)-75.10[4] km/s
Proper motion (μ) RA: -7.46[1] mas/yr
Dec.: -11.09[1] mas/yr
Parallax (π)1.65 ± 0.22[1] mas
Distance950[2] pc
Absolute magnitude (MV)-6.43[2]
Mass51.4 M
Radius18[5] - 21[6] R
Luminosity630,000 L
Surface gravity (log g)3.54 cgs
Temperature36,000 K
Age4.0 Myr
Other designations
Lambda Cephei, 22 Cephei, HD 210839, HR 8469, BD+58 2402, HIP 109556, SAO 34149, GSC 03981-01585, GC 31066
Database references

Lambda Cephei (λ Cephei) is a fifth magnitude blue supergiant star in the constellation Cepheus, one of the hottest and most luminous visible to the naked eye.


It is a hot O6.5 supergiant star at a distance of approximately 1,980 light years, whose absolute brightness around half a million times the Sun. Its radius is around 20 times that of the latter, with a mass that has been estimated to be between 45 and 60 solar masses.

Lambda Cephei turns around its axis in less than three days compared to the 24.47 days that the Sun needs to complete a full rotation and seems to be single, with no companions. Its ultimate fate is to explode as a supernova leaving behind a neutron star or perhaps a black hole.

Lambda Cephei is also a runaway star that seems to have been expelled of the stellar association Cepheus OB3, that lies at 2,800 light-years, roughly 2,5 million years ago. Its motion through the interstellar medium is producing a shockwave in front of the gases that surround it and in the direction towards it moves.[7]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. ^ a b c d e f Bouret, J.-C.; Hillier, D. J.; Lanz, T.; Fullerton, A. W. (2012). "Properties of Galactic early-type O-supergiants. A combined FUV-UV and optical analysis". Astronomy & Astrophysics. 544: A67. arXiv:1205.3075. Bibcode:2012A&A...544A..67B. doi:10.1051/0004-6361/201118594.
  3. ^ Sota, A.; Maíz Apellániz, J.; Walborn, N. R.; Alfaro, E. J.; Barbá, R. H.; Morrell, N. I.; Gamen, R. C.; Arias, J. I. (2011). "THE GALACTIC O-STAR SPECTROSCOPIC SURVEY. I. CLASSIFICATION SYSTEM AND BRIGHT NORTHERN STARS IN THE BLUE-VIOLET ATR∼ 2500". The Astrophysical Journal Supplement Series. 193 (2): 24. arXiv:1101.4002. Bibcode:2011ApJS..193...24S. doi:10.1088/0067-0049/193/2/24. ISSN 0067-0049.
  4. ^ Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. ISSN 1063-7737.
  5. ^ Bianchi, L.; Garcia, M. (2002). "The Effective Temperatures of Mid‐O Stars". The Astrophysical Journal. 581: 610. Bibcode:2002ApJ...581..610B. doi:10.1086/343042.
  6. ^ Repolust, T.; Puls, J.; Herrero, A. (2004). "Stellar and wind parameters of Galactic O-stars. The influence of line-blocking/blanketing". Astronomy and Astrophysics. 415 (1): 349–376. Bibcode:2004A&A...415..349R. doi:10.1051/0004-6361:20034594.
  7. ^ Gvaramadze, V. V.; Gualandris, A. (2011). "Very massive runaway stars from three-body encounters". Monthly Notices of the Royal Astronomical Society. 410: 304. arXiv:1007.5057. Bibcode:2011MNRAS.410..304G. doi:10.1111/j.1365-2966.2010.17446.x.

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