UW Canis Majoris is a star in the constellation Canis Major. It is classified as a

Beta Lyrae Beta Lyrae (β Lyrae, abbreviated Beta Lyr, β Lyr) officially named Sheliak (Arabic: الشلياق, Romanization: ash-Shiliyāq) ( IPA: ), the traditional name of the system, is a multiple star system in the constellation of Lyra. Ba ...

eclipsing contact binary and given the

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

designation UW Canis Majoris. Its brightness varies from magnitude +4.84 to +5.33 with a period of 4.39 days. Bode had initially labelled it as Tau² Canis Majoris, but this designation had been dropped by Gould and subsequent authors. UWCMaLightCurve

UW Canis Majoris A is a rare

blue supergiant A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They have luminosity class I and spectral class B9 or earlier. Blue supergiants are found towards the top left of the Hertzsprung–Russell diagram, above ...

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

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 A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

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. However, a more recent photometric analysis finds several configurations of mass and luminosity ratios that match the observed data. Parallax measurements showed it to be approximately 3000

light years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, 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 NGC 2362, also known as Caldwell 64, is an open cluster of stars in the southern constellation of Canis Major. It was discovered by the Italian court astronomer Giovanni Batista Hodierna, who published his finding in 1654. William Herschel called ...

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.

References

{{DEFAULTSORT:UW Canis Majoris Beta Lyrae variables O-type supergiants Canis Major Canis Majoris, 29 Canis Majoris, UW 035412 Durchmusterung objects 057060 2781 Emission-line stars