# Bellatrix

For other uses, see Bellatrix (disambiguation).
Observation data Characteristics Epoch J2000      Equinox J2000 Location of γ Orionis (circled) Constellation Orion Pronunciation Right ascension 05h 25m 07.86325s[1] Declination +06° 20′ 58.9318″[1] Apparent magnitude (V) 1.64[2] Spectral type B2 III[3] U−B color index –0.86[2] B−V color index –0.21[2] Variable type Eruptive[citation needed] Radial velocity (Rv) +18.2[4] km/s Proper motion (μ) RA: –8.11[1] mas/yr Dec.: –12.88[1] mas/yr Parallax (π) 12.92 ± 0.52[1] mas Distance 250 ± 10 ly (77 ± 3 pc) Mass 8.4+0.3 −0.1[5] M☉ Radius 6[6] R☉ Luminosity ~6,400[7] L☉ Surface gravity (log g) 3.60[8] cgs Temperature 22,000[8] K Metallicity [Fe/H] –0.25[9] dex Rotational velocity (v sin i) 46 ± 8[8] km/s Age 20+2 −4[5] Myr Bellatrix, γ Orionis, Amazon Star, warrioress, 24 Ori, Al Najid, HR 1790, BD +06°919, HD 35468, SAO 112740, FK5 201, HIP 25336.[10]

Bellatrix, also known by its Bayer designation Gamma Orionis (γ Ori, γ Orionis), is the third brightest star in the constellation Orion, 5° right of the red giant α Ori (Betelgeuse). Just between the 1st and 2nd magnitude, it is the 27th brightest star in the night sky.

## Observational history

Since 1963, Bellatrix was included with a set of bright stars that astronomers employ as a luminosity standard. 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. However, when an all-sky photometry survey was carried out in 1988, this star was itself found to be variable. It ranges in apparent magnitude from 1.59 to 1.64.[11]

## Properties

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

Bellatrix is a massive star with about 8.4 times the Sun's mass. It has an estimated age of approximately 20 million years;[5] long 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.[7] The effective temperature of the outer envelope of this star is 22,000 K,[8] 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.[12] The measured angular diameter of this star, after correction for limb darkening, is 0.72 ± 0.04 mas.[13] At an estimated distance of 250 light-years (77 parsecs),[1] this yields a physical size of about six times the radius of the Sun.[6][7]

Bellatrix was once thought to belong to the Orion OB1 Association of stars that share a common motion through space, along with the "Orion's Belt" stars ζ Ori (Alnitak), ε Ori (Alnilam), and δ Ori (Mintaka). 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.[7] It is not known to have a stellar companion,[14] although researchers Maria-Fernanda Nieva and Norbert Przybilla raised the possibility it might be a spectroscopic binary composed of two very similar stars after detailed analysis of its spectrum, adding that this would explain its unexpected brightness.[15] 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.[5]

## Etymology and cultural significance

The name Bellatrix is Latin for "female warrior", and first appeared in the works of Abu Ma'shar al-Balkhi and John of Seville. The name 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] It was also called the Amazon Star, which Richard Hinckley Allen proposed came from a loose translation of the Arabic name Al Najīd, the Conqueror.[17] A c.1275 Arabic celestial globe records the name as المرزم "the lion".[18] Bellatrix is one of the four navigational stars in Orion that are used for celestial navigation.[19] The Chinese name for the star is 参宿五 ("The Fifth of the Three Stars").

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.[20]

J.K. Rowling named one of the Death Eaters "Bellatrix Lestrange". The Latin translation alludes to the character's nature in the Harry Potter series.

The marooned astronauts in the original 1968 film of Planet of the Apes initially believe that they are on an unknown planet orbiting Bellatrix, before the sole survivor realizes their true location in the final scene.

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.[21]

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.[22]

## 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.
2. ^ a b c 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
3. ^ Morgan, W. W.; Keenan, P. C., "Spectral Classification", Annual Review of Astronomy and Astrophysics 11: 29, Bibcode:1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333
4. ^ Wilson, R. E. (1953), General Catalogue of Stellar Radial Velocities, Carnegie Institute of Washington, D.C., Bibcode:1953GCRV..C......0W
5. ^ a b c d 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
6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
\begin{align} 2\cdot R_* & = \frac{(10^{-3}\cdot 77\cdot 0.72)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 12\cdot R_{\bigodot} \end{align}
7. ^ a b c d Kaler, James B., "BELLATRIX (Gamma Orionis)", Stars (University of Illinois), retrieved 2012-12-27
8. ^ a b c d 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
9. ^ Massarotti, Alessandro et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
10. ^ "BELLATRIX -- Variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg)
11. ^ Krisciunas, K. (May 1994), "Further Photometry of alpha Ori and gamma Ori", Information Bulletin on Variable Stars 4028: 1, Bibcode:1994IBVS.4028....1K
12. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
13. ^ Richichi; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
14. ^ 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
15. ^ 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.
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.
17. ^ 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.
18. ^ Dorn, B. (1829). "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 (1): 371–392. doi:10.1017/S0950473700000513. edit
19. ^ Bennett, George G. (2011), Complete On-Board Celestial Navigation 2011-2015, DoctorZed Publishing, p. 172, ISBN 0-9870924-0-5
20. ^ 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: 429. Bibcode:1895MNRAS..55..429K.
21. ^ 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.
22. ^ 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.