Sigma Aquarii
Star in the constellation Aquarius
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Sigma Aquarii is a double star in the equatorial constellation of Aquarius, positioned about 1.3° to the south of the ecliptic.[10] Its name is a Bayer designation that is Latinized from σ Aquarii, and abbreviated Sigma Aqr or σ Aqr. Due to its proximity to the ecliptic, this star is subject to occultation by the Moon.[11] It has a white hue and is visible to the naked eye with an apparent visual magnitude of 4.81.[2] Based upon parallax measurements, the distance to this star is approximately 206 light-years (63 pc).[1] It is drifting further away with a radial velocity of +11 km/s.[12]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 30m 38.821s[1] |
| Declination | −10° 40′ 40.51″[1] |
| Apparent magnitude (V) | 4.81[2] |
| Characteristics | |
| Evolutionary stage | main sequence[3] |
| Spectral type | A0 IVs[4] |
| U−B color index | −0.14[2] |
| B−V color index | −0.08[2] |
| Astrometry | |
| Radial velocity (Rv) | +11.7±0.6[5] km/s |
| Proper motion (μ) | RA: −4.095 mas/yr[1] Dec.: −38.019 mas/yr[1] |
| Parallax (π) | 15.8247±0.4146 mas[1] |
| Distance | 206 ± 5 ly (63 ± 2 pc) |
| Absolute magnitude (MV) | 0.29±0.23[6] |
| Details | |
| Mass | 2.87[3] M☉ |
| Radius | 2.87[6] R☉ |
| Luminosity | 105[3] L☉ |
| Surface gravity (log g) | 4.07[7] cgs |
| Temperature | 10,115[3] K |
| Metallicity [Fe/H] | +0.44[7] dex |
| Rotational velocity (v sin i) | 21[8] km/s |
| Age | 30[6] Myr |
| Other designations | |
| σ Aqr, 57 Aquarii, BD–11°5850, FK5 1591, GC 31440, HD 213320, HIP 111123, HR 8573, SAO 165134, PPM 240380[9] | |
| Database references | |
| SIMBAD | data |
The stellar classification of Sigma Aquarii is A0 IVs,[4] suggesting that it is a subgiant star. The s qualifier means that its absorption lines are sharp (narrow) in comparison with standard stars, caused by a relatively slow rotation. This star is an estimated 30[6] million years old and is spinning with a projected rotational velocity of 21 km/s.[8] It has 2.87[3] times the mass and 2.87 times the radius of the Sun.[6] Sigma Aquarii is radiating 105[3] times the luminosity of the Sun from its photosphere at an effective temperature of 10,115 K.[3]
Sigma Aquarii has been categorized as a hot Am star,[13] meaning that it is a chemically peculiar, although this is now considered doubtful.[14] The spectrum displays at least double the normal abundances of elements like magnesium, aluminum and silicon, while helium and scandium are under-abundant. Calcium, normally deficient in Am stars, has near-normal abundance.[13]
The Hipparcos catalogue identified Sigma Aquarii as a possible astrometric binary with an orbital period of 654 days.[15]