Omicron1 Canis Majoris
Epoch J2000 Equinox J2000
|Right ascension||06h 54m 07.9526s|
|Declination||−24° 11′ 03.159″|
|Apparent magnitude (V)||3.851|
|U−B color index||+2.00|
|B−V color index||+1.75|
|Radial velocity (Rv)||+36.3 km/s|
|Proper motion (μ)||RA: −3.83 mas/yr
Dec.: 4.98 mas/yr
|Parallax (π)||0.22 ± 0.43 mas|
|Absolute magnitude (MV)||−4.69|
|Luminosity (bolometric)||560,000 L☉|
|Surface gravity (log g)||0.6 cgs|
|Rotational velocity (v sin i)||12.31 km/s|
Omicron1 Canis Majoris (ο1 CMa, ο1 Canis Majoris) is a star in the constellation Canis Major. Johann Bayer gave two adjacent stars the Bayer designation of Omicron Canis Majoris in 1603, but without distinguishing between the stars. John Flamsteed labelled the stars as Omicron1 and Omicron2 Canis Majoris in the early 18th century, as well as giving them his own numbered designations of 16 and 24 Canis Majoris respectively. Nicolas Louis de Lacaille labelled it c Canis Majoris, but this was not upheld by subsequent cartographers. Its Henry Draper Catalogue designation is HD 50877. The two Omicron stars marked the centre of the Great Dog's body on Bayer's 1603 Uranometria.
The star itself is an orange K-type supergiant of spectral type K2.5Iab that is an irregular variable star, varying between apparent magnitudes 3.78 and 3.99. A cool star, its surface temperature is around 3,900 K. Around 18 times as massive as the Sun with around 530 times its diameter, it shines with 65,000 times its luminosity. Interstellar dust obscures it somewhat, and its apparent magnitude is 1.12 fainter than it would be if unobscured. Thought to be around 18 million years old, Omicron1 Canis Majoris is undergoing nuclear fusion of helium in its core to generate energy and will one day explode as a type II supernova.
Lying approximately 2000 light years from Earth, Omicron1 Canis Majoris shares a common proper motion (and likely origin) with a remote open cluster of stars in the region known as Collinder 121, located around 3,500 light years (1085 parsecs) distant. Conversely, though only separated by 2 degrees from Omicron2 Canis Majoris, the two appear to be unrelated.
- Levesque, E. M.; Massey, P.; Olsen, K. A. G.; Plez, B.; Josselin, E.; Maeder, A.; Meynet, G. (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought". The Astrophysical Journal 628 (2): 973. arXiv:astro-ph/0504337. Bibcode:2005ApJ...628..973L. doi:10.1086/430901.
- Hekker, S.; Meléndez, J. (2007). "Precise radial velocities of giant stars". Astronomy and Astrophysics 475 (3): 1003. doi:10.1051/0004-6361:20078233.
- 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. pp. 73–74. ISBN 978-0-939923-78-6.
- Wagman, p. 504.
- Watson, Christopher (4 January 2010). "Omicron1 Canis Majoris". AAVSO Website. American Association of Variable Star Observers. Retrieved 15 February 2014.
- Kaler, James B. "Omicron1 Canis Majoris". Stars. University of Illinois. Retrieved 24 February 2014.
- Kaltcheva, N. T. (2000). "The region of Collinder 121". Monthly Notices of the Royal Astronomical Society 318 (4): 1023–35.