Sigma Scorpii

"Al Niyat" redirects here. For the other star that traditionally bore this name, see Tau Scorpii.
Sigma Scorpii
Location of σ Scorpii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Scorpius
Right ascension 16h 21m 11.31571s[1]
Declination −25° 35′ 34.0515″[1]
Apparent magnitude (V) +2.88[2]
Characteristics
Spectral type B1 III[3] + B1 V[4]
U−B color index −0.70[2]
B−V color index +0.13[2]
Astrometry
Radial velocity (Rv)−0.4[5] km/s
Proper motion (μ) RA: −10.60[1] mas/yr
Dec.: −16.28[1] mas/yr
Distance568+75
−59 ly
(174+23
−18[4] pc)
Absolute magnitude (MV)−4.12±0.34 / −3.32±0.34[4]
Orbit[4]
Primaryσ Sco Aa1
Companionσ 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
Mass18.4±5.4,[4] 17.2-18.0[6] M☉
Radius12.7±1.8[4] R☉
Luminosity29,000±8,000,[4] 95,500[6] L☉
Surface gravity (log g)3.85[4] cgs
Temperature26,150±1,070,[4] 27,700[6] K
Metallicity [Fe/H]−0.20±0.20[7] dex
Rotational velocity (v sin i)25[8] km/s
Age8.0±0.2,[9] 8-10[6] Myr
σ Sco Aa2
Mass11.9±3.1[4] M☉
Radius11[4] R☉
Luminosity16000±4000[4] L☉
Other designations
Alniyat, Al Niyat, Pekehāwani, 20 Scorpii, ADS 10009, CD-25 11485, FK5 607, HD 147165, HIP 80112, HR 6084, SAO 184336, WDS 16212-2536.[10]
Database references
SIMBADdata

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,[2] 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).[1] North et al. (2007) computed a more accurate estimate of 568+75
−59 light years (174+23
−18 parsecs).[4]

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)[11][12] 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.[13]

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