VV Cephei
VV Cephei, also known as HD 208816, is an eclipsing binary star system located in the constellation Cepheus, approximately 5,000 light years from Earth. It is both a B[e] star and shell star.
Location of VV Cephei in Cepheus constellation | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 21h 56m 39.14385s |
| Declination | +63° 37′ 32.0174″ |
| Apparent magnitude (V) | 4.91 (4.80 - 5.36) |
| Characteristics | |
| U−B color index | +0.43 |
| B−V color index | +1.73 |
| Variable type | EA + SRc |
| A | |
| Spectral type | M2 Iab |
| U−B color index | +2.07 |
| B−V color index | +1.82 |
| B | |
| Spectral type | B0-2 V |
| U−B color index | −0.52 |
| B−V color index | +0.36 |
| Astrometry | |
| Proper motion (μ) | RA: −1.066 mas/yr Dec.: −0.425 mas/yr |
| Parallax (π) | 1.0033 ± 0.1073 mas |
| Distance | 4,900 ly (1,500 pc) |
| Absolute magnitude (MV) | −6.93 |
| Orbit | |
| Period (P) | 7,430.5 days |
| Semi-major axis (a) | 16.2 ± 3.7" (24.8 AU) |
| Eccentricity (e) | 0.346 ± 0.01 |
| Inclination (i) | 84° |
| Semi-amplitude (K1) (primary) | 19.43 ± 0.33 km/s |
| Semi-amplitude (K2) (secondary) | 19.14 ± 0.68 km/s |
| Details | |
| A | |
| Mass | 2.5 or 18.2 M☉ |
| Radius | 779.27+77.24 −96.32 1,050 R☉ |
| Luminosity | 72,881±16,307 L☉ |
| Surface gravity (log g) | 0.0 cgs |
| Temperature | 3,396±35 K |
| Metallicity [Fe/H] | −0.06 dex |
| B | |
| Mass | 8 or 18.6 M☉ |
| Radius | 13-25 R☉ |
| Metallicity | −0.14 |
| Age | 25 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
VV Cephei is an eclipsing binary with the third longest known period. A red supergiant, it fills its Roche lobe when closest to a companion blue star, the latter appearing to be on the main sequence. Matter flows from the red supergiant onto the blue companion for at least part of the orbit and the hot star is obscured by a large disk of material. The supergiant primary, known as VV Cephei A, is currently recognised as one of the largest stars in the galaxy although its size is not certain. The best estimate is 1,050 R☉, which is nearly as large as the orbit of Jupiter.