Delta Canis Majoris is the third-brightest star in the constellation after
Sirius and
ε Canis Majoris (Adhara), with an
apparent magnitude of +1.83, and is white or yellow-white in colour. Lying about 10 degrees south southeast of Sirius, it only rises to about 11 degrees above the horizon at the latitude of the United Kingdom.[14] The open cluster
NGC 2354 is located only 1.3 degrees east of Delta Canis Majoris.[15] As with the rest of Canis Major, Delta Canis Majoris is most visible in winter skies in the
northern hemisphere, and summer skies in the southern. In Bayer's Uranometria, it is in the Great Dog's hind quarter.[16]
History and naming
δ Canis Majoris (Latinised to Delta Canis Majoris) is the star's
Bayer designation.
The traditional name, Wezen (alternatively Wesen, or Wezea), is derived from the medieval Arabic وزنal-wazn, which means 'weight' in modern
Arabic. The name was for one of a pair of stars, the other being Hadar, which has now come to refer to
Beta Centauri. It is unclear whether the pair of stars was originally
Alpha and Beta Centauri or
Alpha and
Beta Columbae. In any case, the name was somehow applied to both Delta Canis Majoris and Beta Columbae.[17]Richard Hinckley Allen muses that the name alludes to the difficulty the star has rising above the horizon in the northern hemisphere.[16] Astronomer
Jim Kaler has noted the aptness of the traditional name given the star's massive nature.[18]
In 2016, the
International Astronomical Union organized a
Working Group on Star Names (WGSN)[19] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[20] included a table of the first two batches of names approved by the WGSN; which included Wezen for this star.
In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Thalath al Adzari (تالت ألعذاري - taalit al-aðārii), which was translated into
Latin as Tertia Virginum, meaning the third virgin.[23] This star, along with
ε Canis Majoris (Adhara),
η Canis Majoris (Aludra) and
ο2 Canis Majoris (Thanih al Adzari), were Al ʽAdhārā (ألعذاري), the Virgins.[24][25]
Physical properties
Artist's illustration of Wezen, a yellow supergiant 1,600 light-years away in the Canis Major constellation
Delta Canis Majoris is a
supergiant of
class F8. Its surface temperature is around 5,818 K,[26] and it is 14 times more massive than the Sun.[8] Its absolute magnitude is −5.97,[4] and it lies around 1,600
light-years away. It is rotating at a speed of around 28 km/s, and hence may take a year to rotate fully. Only around 10 million years old, Delta Canis Majoris has stopped fusing
hydrogen in its core. Its outer envelope is beginning to expand and cool, and in the next 100,000 years it will become a red supergiant as its core fuses heavier and heavier elements. Once it has an
iron core, it will collapse and explode as a
supernova.[18]
The
angular diameter of Wezen has been measured using
interferometry, giving a
limb-darkened diameter of 3.633±0.026
milliarcseconds. J Davis et al. (2007) used this angular diameter and calculated a physical radius of 215±66
R☉ using a
parallax of 1.82±0.56 milliarcseconds measured by the
Hipparcos specrcaft, which implies a distance of 1800±550
light-years.[26] Since then, the 2007 Hipparcos reduction refined the parallax to 2.03±0.38 mas, corresponding a distance of about 1600±300 ly (493
parsecs).[1] This distance gives a smaller radius of 193 R☉ using the angular diameter.[27] A 2010 study gives a luminosity and temperature implying a radius of 173 R☉,[10][a] while a 2017 study published a radius of 188 R☉.[9]
If Delta Canis Majoris were as close to Earth as Sirius is, it would be as bright as a half-full moon.[28]
^
abGutierrez-Moreno, Adelina; et al. (1966). "A System of photometric standards". Publ. Dept. Astron. Univ. Chile. 1. Publicaciones Universidad de Chile, Department de Astronomy: 1–17.
Bibcode:
1966PDAUC...1....1G.
^Evans, D. S. (June 20–24, 1966). Batten, Alan Henry; Heard, John Frederick (eds.). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and Their Applications, Proceedings from IAU Symposium No. 30. 30. University of Toronto: International Astronomical Union: 57.
Bibcode:
1967IAUS...30...57E.
^
abcdeLyubimkov, Leonid S.; Lambert, David L.; Korotin, Sergey A.; Rachkovskaya, Tamara M.; Poklad, Dmitry B. (2015-02-01), "Carbon abundance and the N/C ratio in atmospheres of A-, F- and G-type supergiants and bright giants", Monthly Notices of the Royal Astronomical Society, 446 (4): 3447–3460,
arXiv:1411.2722,
doi:
10.1093/mnras/stu2299,
ISSN1365-2966
^Arellano Ferro, A.; Giridhar, S.; Rojo Arellano, E. (April 2003). "A Revised Calibration of the MV-W(O I 7774) Relationship using Hipparcos Data: Its Application to Cepheids and Evolved Stars". Revista Mexicana de Astronomía y Astrofísica. 39: 3–15.
arXiv:astro-ph/0210695.
Bibcode:
2003RMxAA..39....3A.
^Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.).
Cambridge,
MA:
Sky Pub. p. 23.
ISBN978-1-931559-44-7.
^
abKaler, James B.
"Wezen". Stars website. University of Illinois. Retrieved 28 May 2010.
^ε CMa as Aoul al Adzari or Prima Virginum (the first virgin),
ο2 CMa as Thanih al Adzari or Secunda Virginum (the second virgin) and δ CMa as Thalath al Adzari or Tertia Virginum (the third virgin).
η CMa should be Rabah al Adzari or Quarta Virginum (the fourth virgin) consistently, but it was given by the name Aludra, meaning 'the virgin' (same meaning with Adhara (
ε CMa) or Al ʽAdhārā)