Eta Piscium
Eta Piscium (η Piscium, abbreviated Eta Psc, η Psc) is a binary star and the brightest star in the constellation of Pisces, with an apparent visual magnitude of +3.6. Based upon a measured annual parallax shift of 9.33 mas as seen from Earth, it is located roughly 350 light-years distant from the Sun in the thin disk population of the Milky Way.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Pisces |
| Right ascension | 01h 31m 29.01026s |
| Declination | +15° 20′ 44.9685″ |
| Apparent magnitude (V) | +3.611 (3.83 + 7.51) |
| Characteristics | |
| Spectral type | G7 IIIa |
| U−B color index | +0.730 |
| B−V color index | +0.976 |
| Variable type | γ Cas |
| Astrometry | |
| Radial velocity (Rv) | 13.60±0.42 km/s |
| Proper motion (μ) | RA: +27.14 mas/yr Dec.: −2.64 mas/yr |
| Parallax (π) | 9.33 ± 0.72 mas |
| Distance | 350 ± 30 ly (107 ± 8 pc) |
| Absolute magnitude (MV) | −1.52 |
| Orbit | |
| Period (P) | 850.5±66.5 yr |
| Semi-major axis (a) | 1.228±0.144″ |
| Eccentricity (e) | 0.469±0.053 |
| Inclination (i) | 58.5±2.5° |
| Longitude of the node (Ω) | 32.8±2.0° |
| Periastron epoch (T) | 2040.3±66.9 |
| Argument of periastron (ω) (secondary) | 86.9±4.0° |
| Details | |
| η Psc A | |
| Mass | 3.78±0.16 M☉ |
| Radius | 26.48±2.15 R☉ |
| Luminosity | 457 L☉ |
| Surface gravity (log g) | 2.20±0.14 cgs |
| Temperature | 4,937±40 K |
| Metallicity [Fe/H] | −0.13±0.06 dex |
| Rotational velocity (v sin i) | 8.4 km/s |
| Age | 220±30 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The two components are designated Eta Piscium A (formally named Alpherg /ˈælfɜːrɡ/, the traditional name of the system) and B.
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