Omega Hydrae
Star in the constellation Hydra
From Wikipedia, the free encyclopedia
Omega Hydrae, Latinised from ω Hydrae, is a golden-hued star in the equatorial constellation of Hydra, located to the west-southwest of the brighter star Zeta Hydrae.[10] Based upon an annual parallax shift of just 3.64 mas as seen from Earth, it is located roughly 900 light-years from the Sun. It is faintly visible to the naked eye with an apparent visual magnitude of 5.00.[2]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 05m 58.36642s[1] |
| Declination | +05° 05′ 32.3360″[1] |
| Apparent magnitude (V) | 5.00[2] |
| Characteristics | |
| Evolutionary stage | horizontal branch[3] |
| Spectral type | K2 II-III[4] |
| U−B color index | +1.22[2] |
| B−V color index | +1.22[2] |
| Astrometry | |
| Radial velocity (Rv) | +24.3±0.8[5] km/s |
| Proper motion (μ) | RA: −19.58[1] mas/yr Dec.: −11.07[1] mas/yr |
| Parallax (π) | 3.64±0.31 mas[1] |
| Distance | 900 ± 80 ly (270 ± 20 pc) |
| Absolute magnitude (MV) | −2.19[6] |
| Details[3] | |
| Mass | 4.32±0.37 M☉ |
| Radius | 48.49±5.55 R☉ |
| Luminosity | 944.3±178.3 L☉ |
| Surface gravity (log g) | 1.74±0.12 cgs |
| Temperature | 4,789[7] K |
| Metallicity [Fe/H] | −0.12±0.10 dex |
| Rotational velocity (v sin i) | 2.3[8] km/s |
| Age | 180±70 Myr |
| Other designations | |
| ω Hya, 18 Hydrae, BD+05°2116, HD 77996, HIP 44659, HR 3613, SAO 117420[9] | |
| Database references | |
| SIMBAD | data |
This is an evolved K-type star with a stellar classification of K2 II-III,[4] which indicates a spectrum showing traits intermediate between the giant and bright giant stages. It is most likely (98% chance) on the horizontal branch, indicating that the star is generating energy through the thermonuclear fusion of helium at its core. With 4.32 times the Sun's mass, it has expanded to around 48 times the radius of the Sun. Omega Hydrae is about 180[3] million years old and spinning with a leisurely projected rotational velocity of 2.3 km/s.[8] The star is radiating roughly 944[3] times the solar luminosity from its photosphere at an effective temperature of 4,789 K.[7]