Zeta Hydri

Zeta Hydri, Latinized from ζ Hydri, is a single,^[7] white-hued star in the southern constellation of Hydrus. It is faintly visible to the naked eye with an apparent magnitude of 4.83.^[2] This distance to this star can be estimated from its annual parallax shift of 11.47 mas,^[1] showing it to be about 284 light years away. It is moving further away from the Sun with a radial velocity of +3.6 km/s.^[4]

ζ Hydri

Location of ζ Hydri (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Hydrus
Right ascension	02h 45m 32.63435s[1]
Declination	−67° 36′ 59.8268″[1]
Apparent magnitude (V)	4.83[2]
Characteristics
Spectral type	A2IV[2]
U−B color index	+0.09[3]
B−V color index	+0.06[3]
Astrometry
Radial velocity (Rv)	+3.60[4] km/s
Proper motion (μ)	RA: +66.41[1] mas/yr Dec.: +43.38[1] mas/yr
Parallax (π)	11.47±0.17 mas[1]
Distance	284 ± 4 ly (87 ± 1 pc)
Absolute magnitude (MV)	0.13[2]
Details
Mass	2.44[5] M☉
Radius	3.9[5] R☉
Luminosity	79.55[2] L☉
Surface gravity (log g)	3.72[6] cgs
Temperature	9,144[6] K
Rotational velocity (v sin i)	116[6] km/s
Other designations
ζ Hyi, CPD−68°169, FK5 2191, GC 3354, HD 17566, HIP 12876, HR 837, SAO 248644
Database references
SIMBAD	data

The spectrum of this star matches a stellar classification of A2 IV,^[2] suggesting it is a subgiant star that is in the process of evolving away from the main sequence as the supply of hydrogen at its core becomes exhausted. It has a high rate of spin, showing a projected rotational velocity of 116 km/s.^[6] This is giving the star a slight oblate shape with an equatorial bulge that is 5% larger than the polar radius.^[8] It has 2.4 times the mass of the Sun and nearly four times the Sun's radius.^[5] Zeta Hydri is radiating 80^[2] times the Sun's luminosity into space from its photosphere at an effective temperature of 9,144 K.^[6]