Bellatrix

For other uses, see Bellatrix (disambiguation).

Bellatrix

Location of γ Orionis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Orion
Pronunciation	/ˈbɛlətrɪks/ /bɛˈleɪtrɪks/[1]
Right ascension	05^h 25^m 07.86325^s[2]
Declination	+06° 20′ 58.9318″[2]
Apparent magnitude (V)	1.64[3] (1.59 - 1.64[4])
Characteristics
Spectral type	B2 III[5] or B2V[6]
U−B color index	−0.86[3]
B−V color index	−0.21[3]
Variable type	Suspected[4]
Astrometry
Radial velocity (Rv)	+18.2[7] km/s
Proper motion (μ)	RA: −8.11[2] mas/yr Dec.: −12.88[2] mas/yr
Parallax (π)	12.92 ± 0.52 mas[2]
Distance	250 ± 10 ly (77 ± 3 pc)
Absolute magnitude (MV)	−2.78[8]
Details
Mass	7.7[9] M☉
Radius	5.75[9] R☉
Luminosity	9,211[9] L☉
Surface gravity (log g)	3.60[10] cgs
Temperature	21,800[9] K
Metallicity [Fe/H]	−0.07[9] dex
Rotational velocity (v sin i)	52[11] km/s
Age	25.2[12] Myr
Other designations
Bellatrix, BenAnna[13], Al Najīd[14], Amazon Star[14], γ Orionis, Gamma Ori, γ Ori, 24 Ori, NSV 1972, BD+06°919, FK5 201, HD 35468, HIP 25336, HR 1790, SAO 112740[15]
Database references
SIMBAD	data

Bellatrix is the third-brightest star in the constellation of Orion, positioned 5° west of the red supergiant Betelgeuse (Alpha Orionis). It has the Bayer designation γ Orionis, which is Latinized to Gamma Orionis. With a slightly variable magnitude of around 1.6, it is typically the 25th-brightest star in the night sky. Located at a distance of 250±10 light-years from the Sun, it is a blue giant star around 7.7 times as massive as the sun with 5.75 times its diameter.

Nomenclature

Bellatrix is a bright star in the constellation of Orion (top right).

The traditional name Bellatrix is from the Latin bellātrix "female warrior". It first appeared in the works of Abu Ma'shar al-Balkhi and Johannes Hispalensis, where it originally referred to Capella, but was transferred to Gamma Orionis by the Vienna school of astronomers in the 15th century, and appeared in contemporary reprints of the Alfonsine tables.^[16] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[17] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016^[18] included a table of the first two batches of names approved by the WGSN; which included Bellatrix for this star. It is now so entered in the IAU Catalog of Star Names.^[19] The designation of Bellatrix as γ Orionis (Latinized to Gamma Orionis) was made by Johann Bayer in 1603. The "gamma" designation is commonly given to the third-brightest star in each constellation.

Standard star

Bellatrix has been used as both a photometric and spectral standard star, but both characteristics have been shown to be unreliable.

In 1963, Bellatrix was included with a set of bright stars used to define the UBV magnitude system. These are used for comparison with other stars to check for variability, and so by definition, the apparent magnitude of Bellatrix was set to 1.64.^[20] However, when an all-sky photometry survey was carried out in 1988, this star was suspected to be variable. It was measured ranging in apparent magnitude from 1.59 to 1.64,^[21] and appears to be a low amplitude, possibly irregular variable.^[22]

Physical properties

From left to right, the stars Bellatrix, the Sun, and Algol B

The spectral types for O and early B stars were defined more rigorously in 1971 and Bellatrix was used as a standard for the B2 III type.^[23] The expected brightness of Bellatrix from this spectral type is about one magnitude brighter than calculated from its apparent magnitude and Hipparcos distance.^[24] Analysis of the observed characteristics of the star indicate that it should be a B2 main sequence star, not the giant that it appears from its spectral type.^[6] Close analysis of high resolution spectra suggest that it is a spectroscopic binary composed of two similar stars less luminous than a B2 giant.^[25]

Bellatrix is a massive star with about 7.7 times the mass and 5.8 times the radius of the Sun.^[9] It has an estimated age of approximately 25 million years^[12]—old enough for a star of this mass to consume the hydrogen at its core and begin to evolve away from the main sequence into a giant star.^[26] The effective temperature of the outer envelope of this star is 22,000 K,^[10] which is considerably hotter than the 5,778 K on the Sun. This high temperature gives this star the blue-white hue that occurs with B-type stars.^[27] It shows a projected rotational velocity of around 52 km/s.^[11] Bellatrix may have sufficient mass to end its life in a supernova explosion.^[26]

Companions

Bellatrix was thought to belong to the Orion OB1 association of stars that share a common motion through space, along with the stars of Orion's Belt: Alnitak (Zeta Orionis), Alnilam (Epsilon Orionis), and Mintaka (Delta Orionis). However, this is no longer believed to be the case, as Bellatrix is now known to be much closer than the rest of the group.^[26] It is not known to have a stellar companion,^[28] although researchers Maria-Fernanda Nieva and Norbert Przybilla raised the possibility it might be a spectroscopic binary.^[25] A 2011 search for nearby companions failed to conclusively find any objects that share a proper motion with Bellatrix. Three nearby candidates were all found to be background stars.^[29]

Some researchers suspected that Bellatrix was a member of the 32 Orionis group. They proposed that the 32 Ori group should instead be termed the Bellatrix Cluster on the basis that the sky position and distance of Bellatrix are similar to those of the 32 Ori group.^[30] The proper motion of Bellatrix deviates significantly from the mean motion of the group, leaving its membership in question. However, it may be possible to reconcile membership if the divergent velocity is the result of an unseen companion. For example, a face-on orbit with a black hole companion orbiting ~100 AU from the star with a period measured in centuries could account for the discrepancy.^[31]

Etymology and cultural significance

Bellatrix was also called the Amazon Star, which Richard Hinckley Allen proposed came from a loose translation of the Arabic name Al Najīd, the Conqueror.^[14] A c.1275 Arabic celestial globe records the name as المرزم "the lion".^[32] Bellatrix is one of the four navigational stars in Orion that are used for celestial navigation.^[33]

In the 17th century catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Menkib al Jauza al Aisr, which was translated into Latin as Humerus Sinister Gigantis (The Left Shoulder of the Giant).^[34]

The Wardaman people of northern Australia know Bellatrix as Banjan, the sparkling pigment used in ceremonies conducted by Rigel the Red Kangaroo Leader in a songline when Orion is high in the sky. The other stars of Orion are his ceremonial tools and entourage. Betelgeuse is Ya-jungin "Owl Eyes Flicking", watching the ceremonies.^[35]

To the Inuit, the appearance of Betelgeuse and Bellatrix high in the southern sky after sunset marked the beginning of spring and lengthening days in late February and early March. The two stars were known as Akuttujuuk "those (two) placed far apart", referring to the distance between them, mainly to people from North Baffin Island and Melville Peninsula.^[36]

See also

• List of brightest stars
• List of nearest bright stars
• Historical brightest stars

References

1. 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, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
2. 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.
3. Crawford, D. L.; Barnes, J. V.; Golson, J. C. (December 1971). "Four-color, Hbeta, and UBV photometry for bright B-type stars in the northern hemisphere". Astronomical Journal. 76: 1058–1071. Bibcode:1971AJ.....76.1058C. doi:10.1086/111220.
4. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
5. Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11 (1): 29. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.
6. Levenhagen, R. S.; Leister, N. V. (2006). "Spectroscopic analysis of southern B and Be stars". Monthly Notices of the Royal Astronomical Society. 371 (1): 252–262. arXiv:astro-ph/0606149. Bibcode:2006MNRAS.371..252L. doi:10.1111/j.1365-2966.2006.10655.x. S2CID 16492030.
7. Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Washington. Carnegie Institute of Washington, D.C. Bibcode:1953GCRV..C......0W.
8. Lamers, H. J. G. L. M.; Harzevoort, J. M. A. G.; Schrijver, H.; Hoogerwerf, R.; Kudritzki, R. P. (1997). "The effect of rotation on the absolute visual magnitudes of OB stars measured with Hipparcos". Astronomy and Astrophysics. 325: L25. Bibcode:1997A&A...325L..25L.
9. Challouf, M.; Nardetto, N.; Mourard, D.; Graczyk, D.; Aroui, H.; Chesneau, O.; Delaa, O.; Pietrzyński, G.; Gieren, W.; Ligi, R.; Meilland, A.; Perraut, K.; Tallon-Bosc, I.; McAlister, H.; Ten Brummelaar, T.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Vargas, N.; Scott, N. (2014). "Improving the surface brightness-color relation for early-type stars using optical interferometry⋆". Astronomy & Astrophysics. 570: A104. arXiv:1409.1351. Bibcode:2014A&A...570A.104C. doi:10.1051/0004-6361/201423772. S2CID 14624307.
10. Lefever, K.; et al. (June 2010). "Spectroscopic determination of the fundamental parameters of 66 B-type stars in the field-of-view of the CoRoT satellite". Astronomy and Astrophysics. 515: A74. arXiv:0910.2851. Bibcode:2010A&A...515A..74L. doi:10.1051/0004-6361/200911956. S2CID 54028925.
11. Simón-Díaz, S.; Herrero, A. (2014). "The IACOB project. I. Rotational velocities in northern Galactic O- and early B-type stars revisited. The impact of other sources of line-broadening". Astronomy & Astrophysics. 562: A135. arXiv:1311.3360. Bibcode:2014A&A...562A.135S. doi:10.1051/0004-6361/201322758. S2CID 119278062.
12. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (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. "Starling Star Registry".
14. Allen, Richard H. (1963). Star Names: Their Lore and Meaning (reprint ed.). New York, NY: Dover Publications Inc. p. 237. ISBN 0-486-21079-0.
15. "BELLATRIX -- Variable Star". SIMBAD. Centre de Données astronomiques de Strasbourg.
16. Kunitzsch, Paul (1986). "The Star Catalogue Commonly Appended to the Alfonsine Tables". Journal for the History of Astronomy. 17 (49): 89–98. Bibcode:1986JHA....17...89K. doi:10.1177/002182868601700202. S2CID 118597258.
17. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
18. "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
19. "IAU Catalog of Star Names". Archived from the original on 7 July 2018. Retrieved 28 July 2016.
20. Johnson, H. L. (1963). "Photometric Systems". Basic Astronomical Data: Stars and Stellar Systems: 204. Bibcode:1963bad..book..204J.
21. Krisciunas, K. (May 1994). "Further Photometry of alpha Ori and gamma Ori". Information Bulletin on Variable Stars. 4028: 1. Bibcode:1994IBVS.4028....1K.
22. Krisciunas, K. (May 1994). "Further Photometry of alpha Ori and gamma Ori". Information Bulletin on Variable Stars. 4028: 1. Bibcode:1994IBVS.4028....1K.
23. Walborn, Nolan R. (1971). "Some Spectroscopic Characteristics of the OB Stars: An Investigation of the Space Distribution of Certain OB Stars and the Reference Frame of the Classification". Astrophysical Journal Supplement. 23: 257. Bibcode:1971ApJS...23..257W. doi:10.1086/190239.
24. Schröder, S. E.; Kaper, L.; Lamers, H. J. G. L. M.; Brown, A. G. A. (2004). "On the Hipparcos parallaxes of O stars". Astronomy and Astrophysics. 428 (1): 149–157. arXiv:astro-ph/0408370. Bibcode:2004A&A...428..149S. doi:10.1051/0004-6361:20047185. S2CID 55115943.
25. Nieva, Maria-Fernanda; Przybilla, Norbert (2012). "Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models". Astronomy & Astrophysics. 539A: 143–63. arXiv:1203.5787. Bibcode:2012A&A...539A.143N. doi:10.1051/0004-6361/201118158. S2CID 119206639.
26. Kaler, James B. "BELLATRIX (Gamma Orionis)". Stars. University of Illinois. Retrieved 2012-12-27.
27. "The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. Archived from the original on 2012-03-18. Retrieved 2012-01-16.
28. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
29. Janson, Markus; et al. (August 2011). "High-contrast Imaging Search for Planets and Brown Dwarfs around the Most Massive Stars in the Solar Neighborhood". The Astrophysical Journal. 736 (2): 89. arXiv:1105.2577. Bibcode:2011ApJ...736...89J. doi:10.1088/0004-637X/736/2/89. S2CID 119217803.
30. Bouy, H.; Alves, J. (December 2015). "Cosmography of OB stars in the solar neighbourhood". Astronomy & Astrophysics. 584: A26. Bibcode:2015A&A...584A..26B. doi:10.1051/0004-6361/201527058. ISSN 0004-6361. S2CID 123265789.
31. Bell, Cameron P. M.; et al. (June 2017). "A stellar census of the nearby, young 32 Orionis group". Monthly Notices of the Royal Astronomical Society. 468 (1): 1198–1220. arXiv:1703.00015. Bibcode:2017MNRAS.468.1198B. doi:10.1093/mnras/stx535.
32. Dorn, Bernhard (July 1830). "Description of the Celestial Globe belonging to Major-General Sir John Malcolm, G.C.B., K.L.S., &c. &c., deposited in the Museum of the Royal Asiatic Society of Great Britain and Ireland". Transactions of the Royal Asiatic Society of Great Britain and Ireland. 2 (2): 371–392. doi:10.1017/S0950473700000513.
33. Bennett, George G. (2011). Complete On-Board Celestial Navigation 2011-2015. DoctorZed Publishing. p. 172. ISBN 978-0-9870924-0-3.
34. Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
35. Harney, Bill Yidumduma; Cairns, Hugh C. (2004) [2003]. Dark Sparklers (Revised ed.). Merimbula, New South Wales: Hugh C. Cairns. pp. 139–40. ISBN 0-9750908-0-1.
36. MacDonald, John (1998). The Arctic sky: Inuit astronomy, star lore, and legend. Toronto, Ontario/Iqaluit, NWT: Royal Ontario Museum/Nunavut Research Institute. pp. 52–54, 119. ISBN 9780888544278.

External links

• Spectrum of Bellatrix
• Navigational Stars