UW Canis Majoris
A Beta Lyrae eclipsing contact binary in Canis Major.
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UW Canis Majoris is a variable star in the constellation Canis Major. It is classified as a Beta Lyrae eclipsing contact binary and is visible to the naked eye under good observing conditions. The system is notable for its uncertain distance and its association with the giant HII region Sh2-310 and the open cluster NGC 2362.
Quick Facts
- Brightness range
- magnitude +4.84 to +5.33
- Period
- 4.39 days
- Spectral type (primary)
- O7.5-8 Iab
- Spectral type (secondary)
- O9.7Ib
- Primary diameter
- 13 times the Sun
- Secondary diameter
- 10 times the Sun
Facts from the source article.
Lore & Background
The star was initially labelled Tau2 Canis Majoris by Bode, but this designation was dropped by Gould and subsequent authors. Sergai Gaposchnhkin analyzed 376 photographic plates taken over twelve years and announced in 1936 that 29 Canis Majoris is a variable star; it received its variable star designation that same year.
The system consists of a rare blue supergiant primary of spectral type O7.5-8 Iab and a slightly cooler, less evolved secondary supergiant of type O9.7Ib. A detailed spectral study found the primary to have a diameter 13 times that of the Sun and a luminosity 200,000 times that of the Sun, while the secondary is 10 solar diameters across and 63,000 times the Sun's luminosity, though the secondary is the more massive star at 19 solar masses compared to the primary's lower mass. More recent photometric analysis finds several configurations of mass and luminosity ratios that match observed data, leaving the precise characteristics uncertain partly because the secondary's spectral signature is hard to disentangle from the primary and the surrounding stellar wind envelope.
Reader's Guide
UW Canis Majoris is significant as a rare blue supergiant eclipsing binary whose distance remains a subject of research. Parallax measurements have yielded conflicting results: early data suggested approximately 3,000 light years, Hipparcos gave around 2,000 light years, and Gaia Data Release 3 indicates about 3,800 light years.
It is thought to be a distant member of NGC 2362, which would place it about 5,000 light years and better match its expected luminosity. The star is part of the giant HII region Sh2-310 and, along with Tau Canis Majoris, HD 58011, and VY Canis Majoris, is considered a probable source of ionization of gases in that region. The contradictions in distance measurements and the uncertain system parameters continue to make UW Canis Majoris an object of ongoing study, highlighting the challenges in characterizing massive binary systems embedded in complex environments.
More in Emission, Dark and Reflection Nebulae
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: UW Canis Majoris (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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