UW Canis Majoris

UW Canis Majoris is a star in the constellation Canis Major. It is classified as a Beta Lyrae eclipsing contact binary and given the variable star designation UW Canis Majoris. Its brightness varies from magnitude +4.84 to +5.33 with a period of 4.39 days.[8] Bode had initially labelled it as Tau2 Canis Majoris, but this designation had been dropped by Gould and subsequent authors.[9]

UW Canis majoris
Location of UW CMa (circled)
Observation data
Epoch J2000.0      Equinox
Constellation Canis Major
Right ascension 07h 18m 40.37940s[1]
Declination 24° 33′ 31.3206″[1]
Apparent magnitude (V) 4.95[2] (4.82 - 5.33[3])
Characteristics
Spectral type O7.5Iabf + O9.7Ib[4]
U−B color index −1.00[2]
B−V color index −0.15[2]
Variable type Beta Lyrae[3]
Astrometry
Radial velocity (Rv)20[5] km/s
Proper motion (μ) RA: −2.21[1] mas/yr
Dec.: 3.16[1] mas/yr
Parallax (π)1.71 ± 0.27[1] mas
Distance5k ly
(1.5k[6] pc)
Absolute magnitude (MV)-6.1[6]
Orbit[7]
PrimaryUW CMa A
CompanionUW CMa B
Period (P)4.39 days
Semi-major axis (a)34-48 R☉
Eccentricity (e)0
Inclination (i)71.0-71.6°
Longitude of the node (Ω)3.3-4.5°
Details
UW CMa A
Mass11-44[7] M☉
Radius12-20[7] R☉
Luminosity170,000-450,000[7] L☉
Temperature33,750[7] K
UW CMa B
Mass17-33[7] M☉
Radius14-17[7] R☉
Luminosity240,000-330,000[7] L☉
Temperature33,300-33,700[7] K
Other designations
UW Canis Majoris, 29 Canis Majoris, HR 2781, HD 57060, CD−24°5173, HIP 35412, SAO 173444, GC 9734
Database references
SIMBADdata

UW Canis Majoris A is a rare blue supergiant of spectral type O7.5-8 Iab. The precise characteristics of the system are still uncertain, in part because the spectral signature of the secondary is very hard to disentangle from the spectrum of the primary and the surrounding envelope of stellar wind. A detailed spectral study by Gies et al. found that the primary had a diameter 13 times that of the Sun, while its secondary companion is a slightly cooler, less evolved and less luminous supergiant of spectral type O9.7Ib that is 10 times the Sun's diameter. According to this study, the brighter star is the more luminous, its luminosity 200,000 times that of the Sun as opposed to the secondary's 63,000 times. However the secondary is the more massive star at 19 Solar masses to the primary's 16.[4]

However, a more recent photometric analysis finds several configurations of mass and luminosity ratios that match the observed data.[7]

Parallax measurements showed it to be approximately 3000 light years from Earth, but this is unexpectedly close for a star of its spectral type and brightness. Recent more accurate Hipparcos parallax data gives an even closer result around 2000 light years. It is thought to be a distant member of NGC 2362 which would place it about 5000 light years and more closely match its expected luminosity. The contradiction between the different distance results is still a subject of research.[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. S2CID 18759600.
  2. 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. Bibcode:2002yCat.2237....0D.
  3. 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.
  4. Bagnuolo, William G. , Jr.; Gies, Douglas R.; Hahula, Michael E.; Wiemker, Rafael; Wiggs, Michael S. (1994). "Tomographic Separation of Composite Spectra. 2: The Components of 29 UW Canis Majoris". The Astrophysical Journal. 423: 446–55. Bibcode:1994ApJ...423..446B. doi:10.1086/173822.
  5. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
  6. Kaltcheva, N. T.; Hilditch, R. W. (2000). "The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way". Monthly Notices of the Royal Astronomical Society. 312 (4): 753. Bibcode:2000MNRAS.312..753K. doi:10.1046/j.1365-8711.2000.03170.x.
  7. Antokhina, E. A.; Srinivasa Rao, M.; Parthasarathy, M. (2011). "Light curve analysis of Hipparcos data for the massive O-type eclipsing binary UW CMa". New Astronomy. 16 (3): 177–182. arXiv:1011.1739. Bibcode:2011NewA...16..177A. doi:10.1016/j.newast.2010.09.008. S2CID 118460690.
  8. Hutchings, J.B. (1977). "The Massive Hot Binary 29 Canis Majoris". Publications of the Astronomical Society of the Pacific. 89 (531): 668–74. Bibcode:1977PASP...89..668H. doi:10.1086/130206. JSTOR 40677088.
  9. Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, VA: The McDonald & Woodward Publishing Company. p. 74. ISBN 978-0-939923-78-6.
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