Omicron¹ Canis Majoris (ο¹ CMa, ο¹ Canis Majoris) is a

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Canis Major Canis Major is a constellation in the southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin for "greater dog" in contrast to C ...

. It is also a

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

Name

Johann Bayer Johann Bayer (; 1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain in 1572. In 1592, aged 20, he began his study of philosophy and law at the University of Ingolstadt, after which he ...

gave two adjacent stars the

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

of ο Canis Majoris in 1603, but without distinguishing between the stars.

John Flamsteed John Flamsteed (19 August 1646 – 31 December 1719) was an English astronomer and the first Astronomer Royal. His main achievements were the preparation of a 3,000-star catalogue, ''Catalogus Britannicus'', and a star atlas called '' Atlas ...

gave the two omicron stars his own numbered designations of 16 and 24 Canis Majoris in the early 18th century.

Friedrich Wilhelm Argelander Friedrich Wilhelm August Argelander (22 March 1799 – 17 February 1875) was a German astronomer. He is known for his determinations of stellar brightnesses, positions, and distances. Life and work Argelander was born in Memel in the Kingd ...

labelled the stars as ο¹ and ο² in his atlas ''Uranometria Nova''.

Nicolas Louis de Lacaille Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a French astronomer and geodesist who named 14 out of the 88 constellations. From 1750 to 1754, he studied the sky at the Cape of Goo ...

labelled it c Canis Majoris, but this was not upheld by subsequent cartographers. Its

Henry Draper Catalogue The ''Henry Draper Catalogue'' (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the ''Henry Draper Extension'' (HDE), published between 192 ...

designation is HD 50877. The two Omicron stars marked the centre of the Great Dog's body on Bayer's 1603 ''Uranometria''.Wagman, p. 504.

Distance

The distance to ο¹ Canis Majoris is uncertain. It is strongly associated with the Collinder 121

stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Stellar associations will normally contain from 10 to 100 or more visible stars. An association is primarily identified by commonalities in i ...

, located around 3,500 light years (1,085 parsecs) distant. Its original Hipparcos parallax placed it at 610 pc, similar to the distance of

EZ Canis Majoris EZ Canis Majoris (abbreviated to EZ CMa, also designated as WR 6) is binary system in the constellation of Canis Major. The primary is a Wolf-Rayet star and it is one of the ten brightest Wolf-Rayet stars, brighter than a ...

, another member of Cr 121. ο¹ CMa appears to be interacting with the nebula around EZ CMa, implying the two are at the same distance. However, the revised Hipparcos parallax is only 0.22 mas, with a large margin of error of 0.43 mas, so the distance is not well-defined but likely to be large. The distance to EZ CMa is now thought to be around 1,500 pc. Conversely, though only separated by 2 degrees from the blue supergiant ο² Canis Majoris, the two appear to be unrelated. Bailer-Jones ''et al.'' (2021) estimate a distance of 820parsecs, give or take 74parsecs to Omicron Canis Majoris, using a method that use its

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

from

Gaia EDR3 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, espec ...

, its color and apparent magnitude.

Description

The star itself is an orange K-type

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...

of spectral type K2.5 Iab and is an

irregular variable An irregular variable is a type of variable star in which variations in brightness show no regular periodicity. There are two main sub-types of irregular variable: eruptive and pulsating. Eruptive irregular variables are divided into three categ ...

star, varying between

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

s 3.78 and 3.99. A cool star, its surface temperature is around 4,000 K. Around 8 times as massive as the Sun with around 390 times its diameter, it shines with 37,000 times its

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

. Interstellar dust only obscures it slightly, and its apparent magnitude is 0.16 fainter than it would be if unobscured. Thought to be around 18 million years old, ο¹ Canis Majoris is undergoing

nuclear fusion Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...

of helium in its core to generate energy and will one day explode as a

type II supernova A Type II supernova or SNII (plural: ''supernovae'') results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun () to undergo this type ...

References

{{DEFAULTSORT:Omicron1 Canis Majoris Canis Majoris, Omicron1 Canis Major Slow irregular variables K-type supergiants Canis Majoris, 16 2580 050877 Durchmusterung objects 033152