Sigma Scorpii
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| Observation data Epoch J2000.0 |
|
|---|---|
| Constellation (pronunciation) |
Scorpius |
| Right ascension | 16h 21m 11.3s |
| Declination | −25° 35' 34" |
| Apparent magnitude (V) | +2.90 |
| Distance | 735 ± 134 ly (225 ± 41 pc) |
| Spectral type | B1III + O9.5V + B9V |
| Other designations | |
Sigma Scorpii (σ Sco / σ Scorpii) is a star system in the constellation Scorpius. It also has the traditional name Al Niyat, although this name is sometimes also applied to Tau Scorpii, or to the asterism formed by both Sigma and Tau. Sigma Scorpii is 735 light years from the Sun.
The primary component of the system, Sigma Scorpii A, is classified as a blue-white B-type giant. It is a variable star of the Beta Cephei type. Its apparent brightness varies hardly perceptibly between +2.86 and +2.94 with multiple periods of 0.2468429, 0.239671, and 8.2 days. It is itself an eclipsing binary, and has a nearby O-type companion which makes an orbit once every 33 days.
Orbiting this binary at a separation half an arcsecond, or at least 120 Astronomical Units (AU), four times the Sun–Neptune distance, is the magnitude +5.2 Sigma Scorpii C which has an orbital period of over a hundred years. Even farther out at 20 arcseconds, or more than 4500 AU, is Sigma Scorpii B with a magnitude of +8.7. It is classified as a B9 dwarf.
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