Omicron Hydrae

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.

Omicron Hydrae

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]