Sigma Aquarii
Sigma Aquarii, Latinized from σ Aquarii, is a double star in the equatorial constellation of Aquarius, positioned about 1.3° to the south of the ecliptic. Due to its proximity to the ecliptic, this star is subject to occultation by the Moon. It has a white hue and is visible to the naked eye with an apparent visual magnitude of 4.81. Based upon parallax measurements, the distance to this star is approximately 175 light-years (54 parsecs). It is drifting further away with a radial velocity of +11 km/s.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 30m 38.82286s |
| Declination | −10° 40′ 40.7031″ |
| Apparent magnitude (V) | 4.81 |
| Characteristics | |
| Spectral type | A0 IVs |
| U−B color index | −0.14 |
| B−V color index | −0.08 |
| Astrometry | |
| Radial velocity (Rv) | +11.7±0.6 km/s |
| Proper motion (μ) | RA: −5.708 mas/yr Dec.: −25.626 mas/yr |
| Parallax (π) | 18.6424 ± 0.6871 mas |
| Distance | 175 ± 6 ly (54 ± 2 pc) |
| Absolute magnitude (MV) | 0.29±0.23 |
| Details | |
| Mass | 2.87 M☉ |
| Radius | 2.87 R☉ |
| Luminosity | 105 L☉ |
| Surface gravity (log g) | 4.07 cgs |
| Temperature | 10,115 K |
| Metallicity [Fe/H] | +0.44 dex |
| Rotational velocity (v sin i) | 21 km/s |
| Age | 30 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The stellar classification of Sigma Aquarii is A0 IVs, indicating 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. It has been categorized as a hot Am star, meaning that it is a chemically peculiar, although this is now considered doubtful. 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.
The Hipparcos catalogue identified Sigma Aquarii as a possible astrometric binary with an orbital period of 654 days.