Sigma Canis Majoris (σ Canis Majoris, abbreviated Sigma CMa, σ CMa), also named Unurgunite , is a

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 ...

in the southern constellation of

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 t ...

. It is approximately from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared rad ...

and has an average

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of +3.41.

Nomenclature

''σ Canis Majoris'' ( Latinised to ''Sigma Canis Majoris'') is the system's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. T ...

. The star is identified with the nganurganity "

Jacky lizard The jacky dragon (''Amphibolurus muricatus'') is a type of lizard native to southeastern Australia. It was one of the first Australian reptiles to be named by Europeans, originally described by English zoologist George Shaw in Surgeon-General ...

" in the culture of the Boorong, a clan of the indigenous

Maligundidj The Wergaia or Werrigia people are an Aboriginal Australian group in the Mallee and Wimmera regions of north-Western Victoria, made up of a number of clans. The people were also known as the Maligundidj (in the Wotjobaluk language) which mea ...

people of northwestern

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

in Australia, who saw it as an ancestral figure who fights the moon, flanked by his wives (the stars

Delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also r ...

and

Epsilon Canis Majoris Epsilon Canis Majoris is a binary star system and the second-brightest object in the constellation of Canis Major. Its name is a Bayer designation that is Latinised from ε Canis Majoris, and abbreviated Epsilon CMa or ε CMa. This is ...

). The name was transcribed by settler William Stanbridge as "Unurgunite" in the 1850s. (Initial ''ng-'', which does not occur in English, was typically ignored in transcription of that era.) In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize List of proper names of stars, proper names for stars for the international astronomical community. It operates under ...

(WGSN) to catalog and standardize proper names for stars. The WGSN approved the name ''Unurgunite'' for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.

Properties

Sigma Canis Majoris is a

giant star A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

with a

stellar classification 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 t ...

of K4 III. This is a type of star that is in the late stages of its

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

, having consumed the hydrogen at its core and ballooned out to 399 times the Sun's radius. At 1.86

Astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbi ...

s, this radius is nearly double the average distance of the Earth from the Sun. It is currently radiating more than 20,000 times the

luminosity of the Sun The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nomin ...

from its outer envelope at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of around 3,710 K. This gives it the cool orange-red hue of an M-type star.

Variability

Sigma Canis Majoris was noted as a likely

in a list of bright southern stars studied at the

Cape Observatory South African Astronomical Observatory (SAAO) is the national centre for optical and infrared astronomy in South Africa. It was established in 1972. The observatory is run by the National Research Foundation of South Africa. The facility's funct ...

. The variability was confirmed in 1963, and it was formally catalogued as a variable star. It is classified as 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 catego ...

star and its brightness varies from magnitude +3.43 to +3.51. The

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

of this star has a strength below 1 G. It is suspected of being a member of 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 stars. The stars share a common origin, but have become gravitationally ...

of co-moving stars, but this is disputed.

Pre-supernova

Sigma Canis Majoris is listed as a possible

type II supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the mass of the Sun () to undergo this ...

. Instruments are capable of measuring the pre-supernova

neutrino A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...

flux which would act as an alert that the supernova explosion was starting.

References

{{DEFAULTSORT:Sigma Canis Majoris Canis Majoris, Sigma Canis Major Slow irregular variables K-type giants 2646 052877 Unurgunite 033856 Durchmusterung objects Canis Majoris, 22