Epsilon Carinae

Epsilon Carinae (ε Carinae, abbreviated Epsilon Car, ε Car), officially named Avior /ˈeɪvjər/,^[13] is a binary star in the southern constellation of Carina. At apparent magnitude +1.86 it is one of the brightest stars in the night sky, but is not visible from most of the northern hemisphere. The False Cross is an asterism formed of Delta Velorum, Kappa Velorum, Iota Carinae and ε Carinae. It is so called because it is sometimes mistaken for the Southern Cross, causing errors in astronavigation.^[14]

Celestia simulation of the ε Carinae system

ε Carinae

Location of ε Carinae (circled in red)
Observation data Epoch J2000      Equinox J2000
Constellation	Carina
Right ascension	08h 22m 30.83526s[1]
Declination	−59° 30′ 34.1431″[1]
Apparent magnitude (V)	1.86[2] (2.01 + 3.85)[3][4]
Characteristics
Spectral type	K3 III[5] + B2 Vp[6]
U−B color index	+0.19[2]
B−V color index	+1.27[2]
Variable type	Eclipsing (suspected)[7]
Astrometry
Radial velocity (Rv)	+11.6[8] km/s
Proper motion (μ)	RA: –25.52[1] mas/yr Dec.: 22.72[1] mas/yr
Parallax (π)	5.39 ± 0.42 mas[1]
Distance	610 ± 50 ly (190 ± 10 pc)
Absolute magnitude (MV)	−4.47[9] (−4.3, −1.8, −1.7)[10]
Details
ε Car A
Mass	10.5[10] M☉
Radius	151 ± 14[11][a] R☉
Luminosity	8,128[11] L☉
Temperature	4,460±90[11] K
Age	31.2 ± 10.1[12] Myr
ε Car B
Mass	7.30[10] M☉
Temperature	20,417[10] K
Age	20[10] Myr
Other designations
Avior, CD−59°1032, FK5 315, HIP 41037, HR 3307, SAO 235932
A: HD 71129
B: HD 71130
Database references
SIMBAD	ε Carinae
	A
	B

Epsilon Carinae is located roughly 560–660 light-years (170–200 parsecs) from the Sun.^[1] Measurements during the Hipparcos mission give the pair an angular separation of 0.46 arcseconds with a difference in magnitude of 2.0.^[6] At their estimated distance, this angle is equivalent to a physical separation of around 4 astronomical units.^[15]

The primary component has an apparent visual magnitude of 2.01,^[3] which by itself would still make it the third-brightest star in the constellation. It is an evolved giant star with a stellar classification of K3 III. However, examination of the ultraviolet flux from this star suggests it may instead be of spectral type K7.^[6] The fainter secondary companion has an apparent visual magnitude of 3.85,^[4] which, if it were a solitary star, would be bright enough to be seen with the naked eye. This is a hot, core hydrogen-fusing B-type main sequence star of spectral class B2 Vp.^[6] The secondary may itself have an orbiting stellar companion of spectral class F8.^[10] This pair may form an eclipsing binary system^[15] with a period of 785 days (2.15 years), resulting in a magnitude change of 0.12 during each eclipse.^[7][16]

Etymology

ε Carinae (Latinised to Epsilon Carinae) is the star's Bayer designation.

The name Avior is not classical in origin. It was assigned to the star by HM Nautical Almanac Office in the late 1930s during the creation of The Air Almanac, a navigational almanac for the Royal Air Force. Of the fifty-seven navigation stars included in the new almanac, two had no classical names: Epsilon Carinae and Alpha Pavonis. The RAF insisted that all of the stars must have names, so new names were invented. Alpha Pavonis was named "Peacock", a translation of Pavo, whilst Epsilon Carinae was called "Avior". Donald Sadler, then Superintendent of HM Nautical Almanac Office, recounted this in his memoirs^[17] but failed to explain the etymology of the invented name. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[18] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016^[19] included a table of the first two batches of names approved by the WGSN; which included Avior for this star.

In Chinese, 海石 (Hǎi Shí), meaning Sea Rock, refers to an asterism consisting of ε Carinae, Iota Carinae, HD 83183, HD 84810 and Upsilon Carinae .^[20] Consequently, ε Carinae itself is known as 海石一 (Hǎi Shí yī, English: the First Star of Sea Rock.)^[21]

Notes

1. Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:

   ${\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{4,460}}{\biggr )}^{4}\cdot 10^{3.91}}}=151\ R_{\odot }}$.

References

1. 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. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
3. "* eps Car A". SIMBAD. Centre de données astronomiques de Strasbourg.
4. "* eps Car B". SIMBAD. Centre de données astronomiques de Strasbourg.
5. Houk, Nancy (1978), "Michigan catalogue of two-dimensional spectral types for the HD stars", University of Michigan Catalogue of two-dimensional spectral types for the HD stars. Volume I. Declinations −90_ to −53_ƒ0, 1, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1975mcts.book.....H.
6. Parsons, Sidney B.; Ake, Thomas B. (November 1998), "Ultraviolet and Optical Studies of Binaries with Luminous Cool Primaries and Hot Companions. V. The Entire IUE Sample", The Astrophysical Journal Supplement Series, 119 (1): 83–104, Bibcode:1998ApJS..119...83P, doi:10.1086/313152.
7. Hoffleit, Dorrit; Warren Jr, W. H., The Bright Star Catalogue (5th revised ed.), Smithsonian Astrophysical Observatory, retrieved 2012-02-12.. See: VizieR V/50
8. Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick (eds.), Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E.
9. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
10. Parsons, Sidney B. (May 2004), "New and Confirmed Triple Systems with Luminous Cool Primaries and Hot Companions", The Astronomical Journal, 127 (5): 2915–2930, Bibcode:2004AJ....127.2915P, doi:10.1086/383546.
11. Charbonnel, C.; Lagarde, N.; Jasniewicz, G.; North, P. L.; Shetrone, M.; Krugler Hollek, J.; Smith, V. V.; Smiljanic, R.; Palacios, A.; Ottoni, G. (2020-01-01), "Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era", Astronomy and Astrophysics, 633: A34, arXiv:1910.12732, Bibcode:2020A&A...633A..34C, doi:10.1051/0004-6361/201936360, ISSN 0004-6361 Epsilon Carinae's database entry at VizieR.
12. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (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.
13. "IAU Catalog of Star Names". Retrieved 28 July 2016.
14. Moore, Patrick (2010). Patrick Moore's Astronomy: Teach Yourself. Hachette. ISBN 978-1444129779.
15. Kaler, James B., "AVIOR (Epsilon Carinae)", Stars, University of Illinois, retrieved 2012-02-12.
16. Hoffleit, Dorrit (1996), "A Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars", The Journal of the American Association of Variable Star Observers, 24 (2): 105–116, Bibcode:1996JAVSO..24..105H
17. Sadler, D. H., Wilkins, G. A. (ed.), A Personal History of H.M. Nautical Almanac Office (PDF), Sidford, Devon: Unpublished, p. 4, archived from the original (PDF) on 2012-04-03, retrieved 2012-02-08.
18. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
19. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
20. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
21. (in Chinese) 香港太空館 – 研究資源 – 亮星中英對照表 Archived 2010-08-11 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.