Eta Hydrae
Eta Hydrae (η Hydrae) is a star in the equatorial constellation of Hydra. With an apparent visual magnitude of 4.3, it is visible to the naked eye. However, it is the faintest of the five stars that form the "head" of the hydra. Based upon an annual parallax shift of 5.56 mas, it is located roughly 590 light years from the Sun.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 08h 43m 13.47499s |
| Declination | +03° 23′ 55.1867″ |
| Apparent magnitude (V) | 4.294 |
| Characteristics | |
| Spectral type | B3 V |
| U−B color index | −0.726 |
| B−V color index | −0.187 |
| Variable type | Candidate β Cep |
| Astrometry | |
| Proper motion (μ) | RA: −19.39 mas/yr Dec.: −1.08 mas/yr |
| Parallax (π) | 5.56 ± 0.24 mas |
| Distance | 590 ± 30 ly (180 ± 8 pc) |
| Absolute magnitude (MV) | −1.48 |
| Details | |
| Mass | 7.0±0.1 M☉ |
| Radius | 3.9 R☉ |
| Luminosity (bolometric) | 2,680 L☉ |
| Surface gravity (log g) | 3.933 cgs |
| Temperature | 18,630±411 K |
| Rotational velocity (v sin i) | 101±5 km/s |
| Age | 31.6±3.9 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is a B-type main sequence star with a stellar classification of B3V. It has been classified as a candidate Beta Cephei variable with a period of 2.2 days, although this designation was rejected by Stankov and Handler (2005). The spectrum shows a slight underabundance of carbon, compared to the Sun. The star is around 32 million years old and is spinning with a projected rotational velocity of 101 km/s. It has an estimated seven times the mass of the Sun and nearly four times the Sun's radius. Eta Hydrae radiates 2,680 times the solar luminosity from its outer atmosphere at an effective temperature of 18,630 K.