Alpha Hydri
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydrus |
| Right ascension | 01h 58m 46.19467s |
| Declination | −61° 34′ 11.4948″ |
| Apparent magnitude (V) | +2.90 |
| Characteristics | |
| Spectral type | F0 IV |
| U−B color index | +0.189 |
| B−V color index | +0.290 |
| Astrometry | |
| Radial velocity (Rv) | +7 km/s |
| Proper motion (μ) | RA: +263.66 mas/yr Dec.: +26.77 mas/yr |
| Parallax (π) | 45.43±0.44 mas |
| Distance | 71.8 ± 0.7 ly (22.0 ± 0.2 pc) |
| Absolute magnitude (MV) | +1.153 |
| Details | |
| Mass | 2.10+0.17 −0.03 M☉ |
| Radius | 3.27+0.11 −0.04 R☉ |
| Luminosity | 21.00±0.75 L☉ |
| Surface gravity (log g) | 3.64±0.05 cgs |
| Temperature | 7,059+21 −56 K |
| Metallicity [Fe/H] | 0.21+0.10 −0.08 dex |
| Rotational velocity (v sin i) | 118 km/s |
| Age | 810 Myr |
| Other designations | |
| α Hyi, CD−62°71, GJ 83, HIP 9236, HR 591, SAO 248474 | |
| Database references | |
| SIMBAD | data |
Alpha Hydri, Latinized from α Hydri, is the second brightest star in the southern circumpolar constellation of Hydrus. It is readily visible to the naked eye in locations south of 28°N with an apparent visual magnitude of +2.9. It is sometimes informally known as the Head of Hydrus. This should not be confused with Alpha Hydrae (Alphard) in the constellation Hydra. Alpha Hydri is one of only three stars in the constellation Hydrus that are above the fourth visual magnitude. This star can be readily located as it lies to the south and east of the prominent star Achernar in the constellation Eridanus.
Based upon parallax measurements from the Hipparcos mission, Alpha Hydri is located at a distance of about 71.8 light-years (22.0 parsecs) from Earth. This subgiant star is 3.3 times larger and 2.1 as massive as the Sun, with a stellar classification of F0 IV. It is about 810 million years old and is radiating 21 times the Sun's luminosity from its outer atmosphere at an effective temperature of 7,059 K. Alpha Hydri emits X-rays similar to Altair. The space velocity components of this star are [U, V, W] = [−14, −14, -2] km/s.