Bellatrix

Bellatrix (γ Orionis)

Location of γ Orionis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Pronunciation /ˈbɛlətrɪks/
Right ascension 05h 25m 07.86325s[1]
Declination +06° 20′ 58.9318″[1]
Apparent magnitude (V) 1.64[2]
Characteristics
Spectral type B2 III[3]
U−B color index -0.86[2]
B−V color index -0.21[2]
Variable type Eruptive
Astrometry
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)
Details
Mass 8.4+0.3
−0.1[5] M☉
Radius 6[6] R☉
Surface gravity (log g) 3.60[7]
Luminosity ~6,400[8] L☉
Temperature 22,000[7] K
Metallicity [Fe/H] –0.25[9] dex
Rotational velocity (v sin i) 46 ± 8[7] km/s
Age 20+2
−4 × 106[5] years
Other designations
Bellatrix, γ Orionis, Amazon Star, warrioress, 24 Ori, Al Najid, HR 1790, BD +06°919, HD 35468, SAO 112740, FK5 201, HIP 25336.[10]
For other uses, see Bellatrix (disambiguation).

Bellatrix, also known by its Bayer designation Gamma Orionis (γ Ori, γ Orionis), is the third brightest star in the constellation Orion, the twenty-seventh brightest star in the night sky, and one of the brightest second-magnitude stars. The name Bellatrix is Latin for female warrior. In the Alfonsine tables, it was also called the Amazon Star, a loose translation of the Arabic name Al Najīd, the Conqueror. It forms the left shoulder of Orion the Hunter.[11] Bellatrix is one of the four navigational stars in Orion that are used for celestial navigation.[12] The Chinese name for the star is 参宿五 ("The Fifth of the Three Stars").

This 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.[8] The effective temperature of the outer envelope of this star is 22,000 K,[7] 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. 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][8]

Since 1963, Gamma Orionis 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 Gamma Orionis 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.[14]

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 Gamma Orionis is now known to be much closer than the rest of the group.[8] It is not known to have a stellar companion.[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]

References

  1. ^ a b c d e f van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. 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. (1973), "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, 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 3540296921, http://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41 . The radius (R*) is given by:
    2R_*\ =\ \frac{10^{-3}\ \times\ 77 \times 0.72\ \text{AU}}{0.0046491\ \text{AU} / R_{\bigodot}}\ \approx\ 12\ R_{\bigodot}
  7. ^ 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, Bibcode 2010A&A...515A..74L, doi:10.1051/0004-6361/200911956 
  8. ^ a b c d Kaler, James B., "BELLATRIX (Gamma Orionis)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/bellatrix.html, retrieved 2012-12-27 
  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), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+Orionis 
  11. ^ Allen, Richard H. (1963). [books.google.com/books?id=5xQuAAAAIAAJ&pg=PA313 Star Names: Their Lore and Meaning] (reprint ed.). New York, NY: Dover Publications Inc.. p. 237. ISBN 0-486-21079-0. books.google.com/books?id=5xQuAAAAIAAJ&pg=PA313. 
  12. ^ Bennett, George G. (2011), Complete On-Board Celestial Navigation 2011-2015, DoctorZed Publishing, p. 172, ISBN 0987092405, http://books.google.com/books?id=cLHeY3bbLbMC&pg=PA172&lpg=PA172 
  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. ^ Krisciunas, K. (May 1994), "Further Photometry of alpha Ori and gamma Ori", Information Bulletin on Variable Stars 4028: 1, Bibcode 1994IBVS.4028....1K 
  15. ^ 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, Bibcode 2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x 

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Coordinates: 05h 25m 07.9s, +06° 20′ 59″