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 J2000      Equinox
Constellation	Orion
Right ascension	05h 33m 31.44649s[1]
Declination	−01° 09′ 21.8595″[1]
Apparent magnitude (V)	5.31 (- 5.55) - 5.66[2]
Characteristics
Evolutionary stage	B1V + B7V[3]
U−B color index	−0.09[4]
B−V color index	−0.18[4]
Variable type	Eclipsing,[5] β Cephei[3]
Astrometry
Radial velocity (Rv)	22.2[6] km/s
Proper motion (μ)	RA: −1.088[1] mas/yr Dec.: −1.183[1] mas/yr
Parallax (π)	2.2654 ± 0.1138 mas[1]
Distance	1,210 ± 39 ly (371 ± 12[3] pc)
Absolute bolometric magnitude (Mbol)	−5.36 + −1.65[3]
Orbit[3]
Period (P)	1.4853784 days
Semi-major axis (a)	13.51 R☉
Eccentricity (e)	0
Inclination (i)	78.28°
Details[3]
VV Ori A
Mass	9.52 M☉
Radius	4.958 R☉
Luminosity	10,400 L☉
Surface gravity (log g)	4.026 cgs
Temperature	26,200 K
VV Ori B
Mass	3.80 M☉
Radius	2.360 R☉
Luminosity	339 L☉
Surface gravity (log g)	4.272 cgs
Temperature	16,100 K
Other designations
HR 1868, HD 36695, HIP 26063, BD−01°943, SAO 132255, TYC 4766-2449-1
Database references
SIMBAD	data

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.[5] However, there are also additional cycles in the lightcurve that suggest that at least one of the stars is pulsating.[3]

A light curve for VV Orionis, plotted from TESS data[7]

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,[8] but this is unproven. A circular orbit with the stars only 13.5 R_☉ apart can account for the observed brightness and radial velocity changes,[5] while a third body may explain the decreasing orbital inclination.[3]

The two stars are both on the main sequence. The primary, a β Cephei pulsator, has a spectral type of B1 and temperature of about 26,000 K, while the secondary (possibly a slowly pulsating B-type star) has a spectral type of B7 and a temperature of about 16,000 K. The secondary has a mass of 3.8 M_☉, radius of 2.4 R_☉, and bolometric luminosity of 340 L_☉. The primary is over twice the mass, twice the radius, and thirty times the luminosity of its companion.[3]