Bellatrix
 Location of γ Orionis (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Orion |
| Pronunciation | /ˈbɛlətrɪks/ |
| Right ascension | 05h 25m 07.86325s |
| Declination | +06° 20′ 58.9318″ |
| Apparent magnitude (V) | 1.64(1.59 - 1.64) |
| Characteristics | |
| Spectral type | B2 III |
| U−B color index | –0.86 |
| B−V color index | –0.21 |
| Variable type | suspected |
| Astrometry | |
| Radial velocity (Rv) | +18.2 km/s |
| Proper motion (μ) |
RA: –8.11 mas/yr Dec.: –12.88 mas/yr |
| Parallax (π) | 12.92 ± 0.52mas |
| Distance | 250 ± 10 ly (77 ± 3 pc) |
| Absolute magnitude (MV) | −2.78 |
| Details | |
| Mass | 8.6 M☉ |
| Radius | 5.75 R☉ |
| Luminosity | 9,211 L☉ |
| Surface gravity (log g) | 3.60 cgs |
| Temperature | 22000 K |
| Metallicity [Fe/H] | –0.07 dex |
| Rotational velocity (v sin i) | 46±8 km/s |
| Age | 25.2 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Bellatrix, also designated Gamma Orionis (γ Orionis, abbreviated Gamma Ori, γ Ori), is the third-brightest star in the constellation of Orion, 5° west of the red giant Alpha Orionis (Betelgeuse). Just between the first and second magnitude and slightly variable, it is about the 25th-brightest star in the night sky.
Bellatrix is a massive star with about 8.6 times the Sun's mass. It has an estimated age of approximately 25 million years; 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. The effective temperature of the outer envelope of this star is 22000 K, 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. At an estimated distance of 250 light-years (77 parsecs), this yields a physical size of about six times the radius of the Sun.
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 Zeta Orionis (Alnitak), Epsilon Orionis (Alnilam), and Delta Orionis (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. It is not known to have a stellar companion, although researchers Maria-Fernanda Nieva and Norbert Przybilla raised the possibility it might be a spectroscopic binary. 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.
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