Bellatrix is a bright star in the constellation of Orion (top right).
The traditional nameBellatrix is from theLatinbellātrix "female warrior". It first appeared in the works ofAbu Ma'shar al-Balkhi andJohannes Hispalensis, where it originally referred toCapella, but was transferred to Gamma Orionis by the Vienna school of astronomers in the 15th century, and appeared in contemporary reprints of theAlfonsine tables.[17] In 2016, theInternational Astronomical Union organized aWorking 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 includedBellatrix for this star. It is now so entered in the IAU Catalog of Star Names.[20] The designation of Bellatrix as γ Orionis (Latinized to Gamma Orionis) was made byJohann Bayer in 1603. The "gamma" designation is commonly given to the third-brightest star in each constellation.
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 theUBV magnitude system. These are used for comparison with other stars to check for variability, and so by definition, theapparent magnitude of Bellatrix was set to 1.64.[21] However, when an all-skyphotometry 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,[22] and appears to be a low amplitude, possibly irregular variable.[23]
From left to right, the stars Bellatrix, the Sun, andAlgol 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.[5] 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 B2main 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 8.6 times the mass[9] and 6.4 times the radius of the Sun.[10] As a massive star, this star willevolve faster than the Sun, currently it has an estimated age of approximately 25 million years.[9] Thehydrogen should be exhausted in seven million years, after that Bellatrix will expand and cool. It may end its life in asupernova.[26] Theeffective temperature of the outer envelope of this star is22,000 K,[11] which is considerably hotter than the 5,772 K on the Sun. This high temperature gives this star the blue-white hue that occurs withB-type stars.[27] It shows aprojected rotational velocity of around 52 km/s.[14]
Bellatrix was thought to belong to theOrion OB1 association of stars that share a common motion through space, along with the stars ofOrion's Belt:Alnitak (Zeta Orionis),Alnilam (Epsilon Orionis), andMintaka (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 aproper motion with Bellatrix. Three nearby candidates were all found to be background stars.[29]
Some researchers suspected that Bellatrix was a member of the32 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] Theproper 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 ablack hole companion orbiting~100 AU from the star with a period measured in centuries could account for the discrepancy.[31]
Bellatrix was also called theAmazon Star, which Richard Hinckley Allen proposed came from a loose translation of the Arabic nameAl Najīd, the Conqueror.[15] A c.1275 Arabic celestial globe records the name as المرزم "the lion".[32] Bellatrix is one of the fournavigational stars in Orion that are used forcelestial navigation.[33]
In the 17th century catalogue of stars in theCalendarium ofAl Achsasi al Mouakket, this star was designatedMenkib al Jauza al Aisr, which was translated intoLatin asHumerus Sinister Gigantis (The Left Shoulder of the Giant).[34]
TheWardaman people of northern Australia know Bellatrix asBanjan, 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 isYa-jungin "Owl Eyes Flicking", watching the ceremonies.[35]
To theInuit, 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 asAkuttujuuk "those (two) placed far apart", referring to the distance between them, mainly to people from North Baffin Island and Melville Peninsula.[36]
^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.ISBN978-1-931559-44-7.
^abcCrawford, 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.
^abSamus, 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.
^Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities".Washington. Carnegie Institute of Washington, D.C.Bibcode:1953GCRV..C......0W.
^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.
^Johnson, H. L. (1963). "Photometric Systems".Basic Astronomical Data: Stars and Stellar Systems: 204.Bibcode:1963bad..book..204J.
^Krisciunas, K. (May 1994). "Further Photometry of alpha Ori and gamma Ori".Information Bulletin on Variable Stars.4028: 1.Bibcode:1994IBVS.4028....1K.
^Krisciunas, K. (May 1994). "Further Photometry of alpha Ori and gamma Ori".Information Bulletin on Variable Stars.4028: 1.Bibcode:1994IBVS.4028....1K.
^abNieva, 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.S2CID119206639.
^"The Colour of Stars".Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. Archived fromthe original on 2012-03-18. Retrieved2012-01-16.
^Harney, Bill Yidumduma; Cairns, Hugh C. (2004) [2003].Dark Sparklers (Revised ed.). Merimbula, New South Wales: Hugh C. Cairns. pp. 139–40.ISBN0-9750908-0-1.
