V636 Scorpii
Spectroscopic binary star system in the constellation Scorpius
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V636 Scorpii is a multiple star system in the constellation Scorpius, 3,000 light years away. The primary is a Classical Cepheid (δ Cephei) variable and its visual magnitude varies from 6.4 to 6.9.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scorpius |
| Right ascension | 17h 22m 46.47796s[2] |
| Declination | −45° 36′ 51.3868″[2] |
| Apparent magnitude (V) | 6.40 - 6.92[3] |
| Characteristics | |
| Cepheid | |
| Spectral type | F7/8Ib/II-G5[3] |
| Variable type | δ Cep[3] |
| companion | |
| Spectral type | B9.5V[4] |
| Astrometry | |
| Radial velocity (Rv) | 9.09 ± 0.17[5] km/s |
| Proper motion (μ) | RA: -3.05 ± 1.03[2] mas/yr Dec.: -2.40 ± 0.38[2] mas/yr |
| Parallax (π) | 1.15±0.76 mas[2] |
| Distance | approx. 3,000 ly (approx. 900 pc) |
| Absolute magnitude (MV) | -3.64[4] |
| Orbit[6] | |
| Period (P) | 1,320.6±1.3 days |
| Semi-major axis (a) | ≥1.401±0.009 au |
| Eccentricity (e) | 0.250±0.004 |
| Periastron epoch (T) | 2,456,865.5±5.7 JD |
| Argument of periastron (ω) (secondary) | 288.0±2.5° |
| Semi-amplitude (K1) (primary) | 11.98±0.06 km/s |
| Details | |
| Cepheid | |
| Mass | 5.6[4] M☉ |
| Radius | ~50[7] R☉ |
| Luminosity | 2,500[4] L☉ |
| Metallicity | +0.07[8] |
| companion | |
| Mass | 2.3±0.3[9] M☉ |
| Other designations | |
| V636 Sco, HIP 85035, CD−45°11441, HD 156979, SAO 227880 | |
| Database references | |
| SIMBAD | data |
V636 Scorpii is a spectroscopic binary, and the fainter companion is thought to itself consist of two stars. The primary is a luminous yellow star and a δ Cephei variable. The less massive companion orbits every 3.6 years and is apparently a B9.5 main sequence star, but the dynamics of the system suggest that it may actually be a pair of stars is a close orbit.[10]
The Cepheid primary pulsates regularly with a period of 6.79671 days. It is a yellow-white supergiant or bright giant that is 5.6 times as massive as the Sun and 2,500 times as luminous.[4]