Sigma Arae

Not to be confused with S Arae.

Sigma Arae is a star in the southern constellation of Ara. Its name is a Bayer designation that is Latinized from σ Arae, and abbreviated Sigma Ara or σ Ara. This star is visible to the naked eye with an apparent visual magnitude of +4.575.^[2] The distance to this star, based upon an annual parallax shift of 8.53 mas,^[1] is approximately 382 light-years (117 pc). It is drifting closer to the Sun with a radial velocity of −9 km/s.^[1]

Sigma Arae

The location of σ Arae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ara
Right ascension	17h 35m 39.591s[1]
Declination	−46° 30′ 20.46″[1]
Apparent magnitude (V)	+4.575[2]
Characteristics
Spectral type	A0 V[3]
U−B color index	−0.064[2]
B−V color index	−0.027[2]
Astrometry
Radial velocity (Rv)	−9.28±0.33[1] km/s
Proper motion (μ)	RA: −25.046 mas/yr[1] Dec.: −38.30 mas/yr[1]
Parallax (π)	8.5285±0.1394 mas[1]
Distance	382 ± 6 ly (117 ± 2 pc)
Absolute magnitude (MV)	1.40[4]
Details
Mass	2.56±0.35[5] M☉
Radius	4.90±0.22[5] R☉
Luminosity	215±22[5] L☉
Surface gravity (log g)	3.47±0.07[5] cgs
Temperature	9,986±206[5] K
Other designations
σ Arae, CD−46 11661, GC 23815, HD 159217, HIP 86092, HR 6537, SAO 228162, PPM 323154, TIC 16245795[6]
Database references
SIMBAD	data

This is an A-type main sequence star with a stellar classification of A0 V.^[3] It has 2.6 times the mass of the Sun and 4.9 times the Sun's radius. The star is radiating 215 times the luminosity of the Sun from its photosphere at an effective temperature of 9,986 K.^[5] Unusually for an A-type star, X-ray emissions with a luminosity of 4.6×10²⁹ erg s⁻¹ have been detected from Sigma Arae. Normally this is explained by the presence of a lower mass orbiting companion star. However, such a scenario does not appear to hold true for this star. Instead, the signature of a surface magnetic field has been detected with a strength of roughly 128±73 Gauss, indicating the source of the X-rays may be surface magnetic activity.^[7]