Sigma Scorpii
Sigma Scorpii (or σ Scorpii, abbreviated Sigma Sco or σ Sco), is a multiple star system in the constellation of Scorpius, located near the red supergiant Antares, which outshines it. This system has a combined apparent visual magnitude of +2.88, making it one of the brighter members of the constellation. Based upon parallax measurements made during the Hipparcos mission, the distance to Sigma Scorpii is roughly 696 light-years (214 parsecs). North et al. (2007) computed a more accurate estimate of 568+75
−59 light years (174+23
−18 parsecs).
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Scorpius |
| Right ascension | 16h 21m 11.31571s |
| Declination | −25° 35′ 34.0515″ |
| Apparent magnitude (V) | +2.88 |
| Characteristics | |
| Spectral type | B1 III + B1 V |
| U−B color index | −0.70 |
| B−V color index | +0.13 |
| Astrometry | |
| Radial velocity (Rv) | −0.4 km/s |
| Proper motion (μ) | RA: −10.60 mas/yr Dec.: −16.28 mas/yr |
| Distance | 568+75 −59 ly (174+23 −18 pc) |
| Absolute magnitude (MV) | −4.12±0.34 / −3.32±0.34 |
| Orbit | |
| Primary | σ Sco Aa1 |
| Companion | σ Sco Aa2 |
| Period (P) | 33.010±0.002 days |
| Semi-major axis (a) | 3.62±0.06 mas |
| Eccentricity (e) | 0.3220±0.0012 |
| Inclination (i) | 158.2±2.3° |
| Longitude of the node (Ω) | 104±5° |
| Periastron epoch (T) | 34889.0±1.0 MJD |
| Argument of periastron (ω) (secondary) | 283±5° |
| Details | |
| σ Sco Aa1 | |
| Mass | 18.4±5.4, 17.2-18.0 M☉ |
| Radius | 12.7±1.8 R☉ |
| Luminosity | 29,000±8,000, 95,500 L☉ |
| Surface gravity (log g) | 3.85 cgs |
| Temperature | 26,150±1,070, 27,700 K |
| Metallicity [Fe/H] | −0.20±0.20 dex |
| Rotational velocity (v sin i) | 25 km/s |
| Age | 8.0±0.2, 8-10 Myr |
| σ Sco Aa2 | |
| Mass | 11.9±3.1 M☉ |
| Radius | 11 R☉ |
| Luminosity | 16000±4000 L☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
The system consists of a spectroscopic binary with components designated Sigma Scorpii Aa1 (officially named Alniyat /ælˈnaɪjæt/, the traditional name for the entire star system) and a Beta Cephei variable) and Aa2; a third component (designated Sigma Scorpii Ab) at 0.4 arcseconds from the spectroscopic pair, and a fourth component (Sigma Scorpii B) at about 20 arcseconds.