| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus [2] |
| Right ascension | 20h 37m 21.5439s [3] |
| Declination | +75° 36′ 01.467″ [3] |
| Apparent magnitude (V) | 7.30 –7.84 [4] |
| Characteristics | |
| A | |
| Spectral type | G8V [5] |
| B | |
| Spectral type | K0V [5] |
| Astrometry | |
| Proper motion (μ) | RA: +308.71 mas/yr [3] Dec.: +540.86 mas/yr [3] |
| Parallax (π) | 36.25±0.58 mas [3] |
| Distance | 91.00 ± 0.95 ly (27.90±0.29 pc) [6] |
| Details | |
| A | |
| Mass | 1.13 [4] M☉ |
| Radius | 0.99 [4] R☉ |
| Temperature | 5,050 [4] K |
| Age | 9.029 [7] Gyr |
| B | |
| Mass | 0.34 [4] M☉ |
| Radius | 0.57 [4] R☉ |
| Temperature | 5,342±15 [4] K |
| Age | 9.029 [7] Gyr |
| C | |
| Mass | 0.74±0.07 [6] M☉ |
| Orbit [4] | |
| Primary | A |
| Companion | B |
| Period (P) | 0.278315349(12) [6] days |
| Semi-major axis (a) | (1.412±0.010)×106 km (2.030±0.014 R☉ ) |
| Inclination (i) | 62.86±0.04° |
| Orbit [6] | |
| Primary | AB |
| Companion | C |
| Period (P) | 29.79±0.08 years |
| Semi-major axis (a) | 4.33±0.20 AU |
| Eccentricity (e) | 0.633±0.007 |
| Inclination (i) | 33.6±1.2° |
| Longitude of the node (Ω) | 17.7±3.1° |
| Argument of periastron (ω) (secondary) | 239.28±2.88° |
| Other designations | |
| VW Cep, LHS 3565, SAO 9828, LTT 16039, BD+75 752, GJ 1255, GJ 9703, HD 197433, HIP 101750 | |
| Database references | |
| SIMBAD | data |
VW Cephei (VW Cep) is a triple star in the constellation Cepheus, located roughly at 90.6 light years from the Sun.
The two inner components form an eclipsing contact binary of W Ursae Majoris-type, whose two component stars share a common outer layer. Both are main-sequence stars smaller than the Sun. They take 0.2783 days (roughly 6.7 hours) to revolve around a common barycentre. [7] Jan Schilt discovered that the star is an eclipsing variable, in 1926. [8]
The third component has been detected by analysing the difference between the observed and the predicted time of eclipses, which is caused by the light-time effect of its orbital motion around the pair, and has been independently detected by astrometry. [6] [4] It has an orbital period of 29.79 years around the inner pair. [4] A fourth component has also been proposed to explain additional changes in eclipse timing, but it was later found that the period variations are more likely caused by mass transfer between components via the Applegate mechanism, rather than the presence of a fourth companion. [4]
