27 Canis Majoris

27 Canis Majoris is a binary star[3] system in the northern constellation of Canis Major,[10] located approximately 1,700 light years away from the Sun.[1] It has the variable star designation EW Canis Majoris;[6] 27 Canis Majoris is the Flamsteed designation. This system is visible to the naked eye as a dim, blue-white hued star with an apparent visual magnitude of +4.65.[2] It is moving away from the Earth with a heliocentric radial velocity of 16 km/s.[5]

27 Canis Majoris
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Right ascension  07h 14m 15.21192s[1]
Declination −26° 21′ 09.0312″[1]
Apparent magnitude (V) +4.65[2] (+4.92 + 5.39)[3]
Characteristics
Spectral type B3 IIIpe[4]
B−V color index −0.17±0.16[5]
Variable type γ Cas + β Cep:[6]
Astrometry
Radial velocity (Rv)16.3±3.6[5] km/s
Proper motion (μ) RA: −6.91[1] mas/yr
Dec.: +3.17[1] mas/yr
Parallax (π)1.88 ± 0.32[1] mas
Distanceapprox. 1,700 ly
(approx. 530 pc)
Absolute magnitude (MV)−4.13[5]
Orbit[7]
Period (P)118.54±11.14 yr
Semi-major axis (a)0.178±0.012″
Eccentricity (e)0.747±0.094
Inclination (i)80.2±1.0°
Longitude of the node (Ω)131.3±3.0°
Periastron epoch (T)1,971.01±0.74
Argument of periastron (ω)
(secondary)		85.0±3.6°
Details
27 CMa A
Mass12.5±2.5[8] M☉
Luminosity (bolometric)15,610[2] L☉
Surface gravity (log g)3.514[9] cgs
Temperature21,061[9] K
Rotational velocity (v sin i)290[9] km/s
Age0.1±0.1[8] Myr
Other designations
27 CMa, EW Canis Majoris, BD−26°4057, GC 9608, HD 56014, HIP 34981, HR 2745, SAO 173264, CCDM J07143-2621, WDS J07143-2621[10]
Database references
SIMBADdata

The pair of stars in this system were first resolved by W. S. Finsen in 1953, and the split has been widening since that time.[11] The system has an orbital period of around 119 years with an eccentricity of 0.7 and a semimajor axis of 0.178″.[7] The magnitude 4.92[3] primary, designated component A, is a Be star with a stellar classification of B3 IIIpe.[4] It is spinning rapidly with a projected rotational velocity of 290 km/s, compared to a critical velocity of 389 km/s.[9] The star appears to be a Beta Cephei variable[12] with a pulsation period of 0.0919 days and an amplitude of 0.0080 in magnitude.[13]

The magnitude 5.39[3] secondary, component B, is classified as a Gamma Cassiopeiae type variable star. Due to its variable nature, the brightness of the system varies from magnitude +4.42 to +4.82.[6]

References
  1. van Leeuwen, F. (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. Hohle, M. M.; et al. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
  3. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  4. Woods, M. L. (1958), "Spectral types of bright southern stars", Memoires of the Mount Stromlo Observatory, 12: 125, Bibcode:1955MmMtS..12..125W.
  5. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  6. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S.
  7. Hartkopf, W. I.; et al. (June 30, 2006), Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, retrieved 2017-06-02.
  8. Tetzlaff, N.; et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  9. Frémat, Y.; Zorec, J.; Hubert, A.-M.; Floquet, M. (2005), "Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars", Astronomy and Astrophysics, 440: 305, arXiv:astro-ph/0503381, Bibcode:2005A&A...440..305F, doi:10.1051/0004-6361:20042229.
  10. "27 CMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 1, 2019.
  11. Mason, Brian D.; et al. (November 1997), "ICCD Speckle Observations of Binary Stars. XVIII. An Investigation of Be Stars", Astronomical Journal, 114: 2112, Bibcode:1997AJ....114.2112M, doi:10.1086/118630.
  12. Balona, L. A.; Krisciunas, K. (May 1994), "Further Confirmation that the Be Star 27 CMa is a beta Cep Variable", Information Bulletin on Variable Stars (4022): 1, Bibcode:1994IBVS.4022....1B.
  13. Stankov, Anamarija; Handler, Gerald (2005), "Catalog of Galactic β Cephei Stars", The Astrophysical Journal Supplement Series, 158 (2): 193–216, arXiv:astro-ph/0506495, Bibcode:2005ApJS..158..193S, doi:10.1086/429408, ISSN 0067-0049.
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