Omicron Hydrae
Blue-hued star in the constellation Hydra
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Omicron Hydrae (ο Hya) is the Bayer designation for a solitary[11] star in the equatorial constellation Hydra. At one time it bore the Flamsteed designation 25 Crateris, but this is no longer used by astronomers so as to avoid confusion.[12] With an apparent visual magnitude of 4.70,[3] this star is visible to the naked eye. Based upon an annual parallax shift of 7.27 mas,[2] it is located around 449 light years from the Sun.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Hydra[1] |
| Right ascension | 11h 40m 12.78970s[2] |
| Declination | −34° 44′ 40.7733″[2] |
| Apparent magnitude (V) | 4.70[3] |
| Characteristics | |
| Spectral type | B9 V[4] |
| U−B color index | −0.20[3] |
| B−V color index | −0.08[3] |
| Astrometry | |
| Radial velocity (Rv) | +5.9[5] km/s |
| Proper motion (μ) | RA: −43.24[2] mas/yr Dec.: −1.61[2] mas/yr |
| Parallax (π) | 7.27±0.16 mas[2] |
| Distance | 449 ± 10 ly (138 ± 3 pc) |
| Absolute magnitude (MV) | −0.99[1] |
| Details | |
| Mass | 3.56±0.04[6] M☉ |
| Radius | 5.5[7] R☉ |
| Luminosity | 309[6] L☉ |
| Surface gravity (log g) | 2.87[8] cgs |
| Temperature | 10,495[6] K |
| Rotation | 27.2 days[8] |
| Rotational velocity (v sin i) | 160[6] km/s |
| Age | 252[9] Myr |
| Other designations | |
| ο Hya, CD−34°7610, FK5 439, HD 101431, HIP 56922, HR 4494, SAO 202695[10] | |
| Database references | |
| SIMBAD | data |
This is a B-type main sequence star with a stellar classification of B9 V.[4] It has completed an estimated 98.4%±1.1% of its lifetime on the main sequence. With 3.56[6] times the mass of the Sun, it radiates 309 times the Sun's luminosity from its outer atmosphere at an effective temperature of 10,495 K.[6] The rate of spin is relatively high, with a projected rotational velocity of 160 km/s.[6]