UW Canis Majoris

From Wikipedia, the free encyclopedia
Jump to: navigation, search
UW Canis Majoris
Observation data
Epoch J2000.0      Equinox
Constellation Canis Major
Right ascension 07h18m40.37940s
Declination 24°33′31.3206″
Apparent magnitude (V) 4.84 - 5.33
Spectral type O7.5Iabf + O9.7Ib[1]
U−B color index -1.02
B−V color index -0.15
Variable type Beta Lyrae
Radial velocity (Rv) -11 km/s
Proper motion (μ) RA: -2.21 mas/yr
Dec.: 3.16 mas/yr
Parallax (π) 1.71 ± 0.27 mas
Distance 5k ly
(1.5k[2] pc)
Absolute magnitude (MV) -6.1[2]
Mass 16 / 19[1] M
Radius 13 / 10[1] R
Luminosity 200,000 / 63,000[1] L
Temperature 33,750 / 29,000[1] K
Other designations
UW Canis Majoris, HR 2781, HD 57060, CD−24°5173, HIP 35412, SAO 173444, GC 9734
Database references

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.[3] Bode had initially labelled it as Tau2 Canis Majoris, but this designation had been dropped by Gould and subsequent authors.[4]

UW Canis Majoris A is a rare blue supergiant of spectral type O7.5-8 Iab with a diameter 13 times that of the Sun, while its companion is a slightly cooler, less evolved and less luminous supergiant of spectral type O9.7Ib that is 10 times the Sun's diameter. 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.[1] 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 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.[2]


  1. ^ a b c d e f 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. 
  2. ^ a b c 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. 
  3. ^ Hutchings, J.B. "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. 
  4. ^ 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.