VV Orionis

VV Orionis is an eclipsing binary located in the belt region of the constellation Orion. It is a faint naked eye star.

VV Orionis
Location of VV Orionis (circled) in the Orion's Belt region
Credit: Martin Mutti
Observation data
Epoch       Equinox
Constellation Orion
Right ascension  05h 33m 31.44643s[1]
Declination −01° 09′ 21.8666″[1]
Apparent magnitude (V) 5.31 (- 5.55) - 5.66[2]
Characteristics
Evolutionary stage B1V + B4.5V[3]
U−B color index −0.09[4]
B−V color index −0.18[4]
Variable type Eclipsing binary[3]
Astrometry
Radial velocity (Rv)22.2[5] km/s
Proper motion (μ) RA: -0.82[1] mas/yr
Dec.: -1.07[1] mas/yr
Parallax (π)2.22 ± 0.35[1] mas
Distanceapprox. 1,500 ly
(approx. 450 pc)
Orbit[3]
Period (P)1.48537423 days
Semi-major axis (a)13.49 R☉
Eccentricity (e)0
Inclination (i)85.9°
Details[3]
VV Ori A
Mass10.9 M☉
Radius4.98 R☉
Luminosity10,600 L☉
Surface gravity (log g)4.08 cgs
Temperature26,199 K
VV Ori B
Mass4.09 M☉
Radius2.41 R☉
Luminosity350 L☉
Surface gravity (log g)4.29 cgs
Temperature16,073 K
Other designations
HR 1868, HD 36695, HIP 26063, BD−01° 943, SAO 132255, TYC 4766-2449-1
Database references
SIMBADdata

The brightness of VV Orionis dips regularly every 18 hours. The peak visual magnitude is 5.3, which varies slowly in between the dips. The minimum brightness of the dips alternates between magnitude 5.55 and 5.66. The deep minima have a somewhat rounded bottom, while the less deep minima have flat bottoms with a constant magnitude for several hours.[3]

The VV Orionis system contains two stars which are very close but are not touching. Their orbit is aligned almost perpendicularly to us and there are both primary and secondary eclipses. During secondary eclipse, the primary transits against the secondary, which produces the flat bottom to the secondary minimum. The orbital alignment allows very precise calculation of the orbit and the properties of the stars, but results from different studies have been unusually inconsistent. The lack of a single consistent solution to the orbit has led to suggestions that there is a third star in the system,[6] but this is now thought unlikely. A circular orbit with the stars only 13.5 R☉ apart can account for the observed brightness and radial velocity changes.[3]

The two stars are both on the main sequence. The primary has a spectral type of B1 and temperature of 26,000 K, while the secondary has a spectral type of B4.5 and a temperature of 16,000 K. The secondary has a mass of four M☉, radius of 2.4 R☉, and bolometric luminosity of 350 L☉. The primary is twice the mass, twice the radius, and thirty times the luminosity.

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 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.
  3. Terrell, Dirk; Munari, Ulisse; Siviero, Alessandro (2007). "Observational studies of early-type binary stars: VV Orionis". Monthly Notices of the Royal Astronomical Society. 374 (2): 530. arXiv:astro-ph/0610202. Bibcode:2007MNRAS.374..530T. doi:10.1111/j.1365-2966.2006.11162.x.
  4. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  5. Wilson, Ralph Elmer (1953). "General catalogue of stellar radial velocities". Washington. Bibcode:1953GCRV..C......0W.
  6. Chambliss, Carlson R. (1984). "VV Orionis: A well-behaved early-type eclipsing binary system". Astrophysics and Space Science. 99: 163. Bibcode:1984Ap&SS..99..163C. doi:10.1007/BF00650241.
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