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Eta Canis Majoris

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η Canis Majoris
Location of η Canis Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Canis Major
Right ascension 07h 24m 05.70228s[1]
Declination −29° 18′ 11.1798″[1]
Apparent magnitude (V) 2.38 – 2.48[2]
Characteristics
Evolutionary stage Blue supergiant, likely a post-red supergiant[3]
Spectral type B5 Ia[4]
U−B color index −0.708[5]
B−V color index −0.087[5]
Variable type α Cyg[2]
Astrometry
Radial velocity (Rv)41.1[6] km/s
Proper motion (μ) RA: −4.14 mas/yr[1]
Dec.: 5.81 mas/yr[1]
Parallax (π)1.64±0.40 mas[1]
Distanceapprox. 2,000 ly
(approx. 600 pc)
Absolute magnitude (MV)−7.0[7]
Details
Mass5.5 or 9.5[3] M☉
Radius54[8] R☉
Luminosity163,800+4,200
−15,900[3] L☉
Surface gravity (log g)1.95+0.02
−0.03[8] cgs
Temperature15,800+100
−400[3] K
Rotational velocity (v sin i)51.5±5.0[3] km/s
Age8.3[9] Myr
Other designations
Aludra, η Canis Majoris, 31 Canis Majoris, CD−29°4328, FK5 283, HD 58350, HIP 35904, HR 2827, SAO 173651
Database references
SIMBADdata

Eta Canis Majoris is a blue supergiant star in the constellation of Canis Major. It has the proper name Aludra, pronounced /əˈluːdrə, əˈljuːdrə/;[10] Eta Canis Majoris is its Bayer designation. This star has an apparent visual magnitude that varies between 2.38 and 2.48, which makes it the fifth-brightest in the constellation. Parallax measurements from the Hipparcos mission estimate a large distance of 2,000 light-years. It is drifting further away from the Sun with a line of sight velocity of 41 km/s.[6]

Nomenclature

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η Canis Majoris, Latinised to Eta Canis Majoris, is the star's Bayer designation, abbreviated Eta CMa or η CMa.

The traditional name Aludra originates from the Arabic: العذراء al-adhraa, 'the virgin'. This star, along with Epsilon Canis Majoris (Adhara), Delta Canis Majoris (Wezen) and Omicron2 Canis Majoris (Thanih al Adzari), were Al 'Adhārā (العذاري), 'the Virgins'.[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[13] included a table of the first two batches of names approved by the WGSN; which included Aludra for this star.

In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow,[14] refers to an asterism consisting of Eta Canis Majoris, Delta Canis Majoris, HD 63032, HD 65456, Omicron Puppis, k Puppis, Epsilon Canis Majoris, Kappa Canis Majoris and Pi Puppis. Consequently, Eta Canis Majoris itself is known as 弧矢二 (Hú Shǐ èr, English: the Second Star of Bow and Arrow).[15]

Properties

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A light curve for Eta Canis Majoris, plotted from Hipparcos data[16]

Eta Canis Majoris is a blue supergiant star with a spectral type of B5Ia.[3] It has been the standard for this spectral class in the Morgan–Keenan system, and since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[17][18]

This is likely a post-red supergiant, a star which left its red supergiant phase and is near the end of its life. As a consequence, Aludra has lost significant part of its mass. It formed with a mass of 22 M☉ and now has either 5.5 or 9.5 M☉, depending on the estimate.[3] The present day mass loss rate is estimated at (0.12±0.01)×10−6 M☉·yr−1, or one solar mass every 8.3 million years.[8]

Aludra shines brightly in the skies in spite of a large distance from Earth due to being intrinsically many times brighter than the Sun. It has a luminosity over 100,000 times and a radius around 54 times that of the Sun. The star has only existed for a fraction of the time the Sun has, less than 10 million years, yet is already in the final stages of its life.[8][3]

The star is classified as an Alpha Cygni-type variable star and its brightness varies from magnitude +2.38 to +2.48 over a period of 4.7 days.[2][19]

Namesakes

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Both USS Aludra (AF-55), an Alstede-class stores ship, and USS Aludra (AK-72), a Crater-class cargo ship, were U.S. Navy vessels named after the star.

References

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  1. ^ a b c d van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  2. ^ a b c Kazarovets, E. V.; et al. (1999). "The 74th Special Name-list of Variable Stars". Information Bulletin on Variable Stars. 4659: 1. Bibcode:1999IBVS.4659....1K.
  3. ^ a b c d e f g h Sánchez Arias, Julieta Paz; et al. (August 2023). "Unveiling the Evolutionary State of Three B Supergiant Stars: PU Gem, ϵ CMa, and η CMa". Galaxies. 11 (5): 93. arXiv:2308.12745. Bibcode:2023Galax..11...93S. doi:10.3390/galaxies11050093.
  4. ^ Prinja, R. K.; Massa, D. L. (October 2010). "Signature of wide-spread clumping in B supergiant winds". Astronomy and Astrophysics. 521: L55. arXiv:1007.2744. Bibcode:2010A&A...521L..55P. doi:10.1051/0004-6361/201015252. S2CID 59151633.
  5. ^ a b Alcaino, Gonzalo (June 1969). "The Globular Clusters NGC 2808 and NGC 1851". Astrophysical Journal. 156: 853. Bibcode:1969ApJ...156..853A. doi:10.1086/150019.
  6. ^ a b Wielen, R.; et al. (1999). "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions". Veröff. Astron. Rechen-Inst. Heidelb. 35 (35). Astronomisches Rechen-Institut Heidelberg: 1. Bibcode:1999VeARI..35....1W.
  7. ^ Underhill, A. B.; et al. (November 1979). "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars". Monthly Notices of the Royal Astronomical Society. 189 (3): 601–605. Bibcode:1979MNRAS.189..601U. doi:10.1093/mnras/189.3.601.
  8. ^ a b c d Haucke, M.; et al. (2018). "Wind properties of variable B supergiants. Evidence of pulsations connected with mass-loss episodes". Astronomy and Astrophysics. 614. arXiv:1902.01341. Bibcode:2018A&A...614A..91H. doi:10.1051/0004-6361/201731678. S2CID 126150688.
  9. ^ Tetzlaff, N.; et al. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
  10. ^ "IAU Catalog of Star Names". International Astronomical Union. Retrieved 28 July 2016.
  11. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. p. 130. ISBN 0-486-21079-0. Retrieved 2010-12-12.{{cite book}}: CS1 maint: ignored ISBN errors (link)
  12. ^ "IAU Working Group on Star Names (WGSN)". International Astronomical Union. Retrieved 22 May 2016.
  13. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). International Astronomical Union. Retrieved 28 July 2016.
  14. ^ 弧矢 (Hú Shǐ) is westernized into Koo She. R.H. Allen had opinion that Koo She refers to the asterism including Delta Velorum and Omega Carinae. AEEA opinion is, Delta Velorum is member of 天社 (Tiān Shè), meaning Celestial Earth God's Temple asterism, and Omega Carinae is not member of any asterisms. 天社 (Tiān Shè) is westernized into Tseen She and R.H. Allen used the term Tseen She for Chinese name of Eta Carinae. See Richard Hinckley Allen: Star Names — Their Lore and Meaning: Argo Navis and (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日 Archived 2012-02-04 at the Wayback Machine.
  15. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 17 日 Archived 2012-02-04 at the Wayback Machine
  16. ^ "Light Curve". Hipparcos ESA. ESA. Retrieved 12 August 2022.
  17. ^ Garrison, R. F. (December 1993). "Anchor Points for the MK System of Spectral Classification". Bulletin of the American Astronomical Society. 25: 1319. Bibcode:1993AAS...183.1710G. Archived from the original on 2019-06-25. Retrieved 2012-02-04.
  18. ^ Morgan, W. W.; et al. (1978). Revised MK Spectral Atlas for stars earlier than the sun. Yerkes Observatory, University of Chicago, and Kitt Peak National Observatory. Bibcode:1978rmsa.book.....M.
  19. ^ Watson, Christopher (May 3, 2013). "Eta Canis Majoris". AAVSO Website. American Association of Variable Star Observers. Retrieved 5 February 2014.
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