Xi Hydrae

Xi Hydrae, Latinised from ξ Hydrae, is a solitary^[9] star in the equatorial constellation of Hydra. It was also given the Flamsteed designation 19 Crateris. This magnitude 3.54^[3] star is situated 130 light-years from Earth and has a radius about 10 times that of the Sun. It is radiating 58 times as much luminosity as the Sun.^[6]

Xi Hydrae

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Hydra[1]
Right ascension	11h 33m 00.11505s[2]
Declination	−31° 51′ 27.4435″[2]
Apparent magnitude (V)	3.54[3]
Characteristics
Spectral type	G7 III[3]
Astrometry
Radial velocity (Rv)	−4.90±0.30[4] km/s
Proper motion (μ)	RA: −209.62[2] mas/yr Dec.: −40.84[2] mas/yr
Parallax (π)	25.16±0.16 mas[2]
Distance	129.6 ± 0.8 ly (39.7 ± 0.3 pc)
Absolute magnitude (MV)	+0.54[1]
Details
Mass	2.94±0.15[5] M☉
Radius	10.2±0.1[6] R☉
Luminosity	57.65±2.39[6] L☉
Surface gravity (log g)	2.87±0.02[5] cgs
Temperature	5,044±40[5] K
Metallicity [Fe/H]	+0.16±0.20[5] dex
Rotational velocity (v sin i)	2.7[6] km/s
Other designations
ξ Hya, 288 G. Hydrae,[7] CD−31°9083, HD 100407, HIP 56343, HR 4450, SAO 202558[8]
Database references
SIMBAD	data

One possible non-radial oscillation mode of Xi Hydrae

Flamsteed gave Xi Hydrae the designation 19 Crateris. He included a number of stars now within the IAU boundaries of Hydra as part of a Hydra & Crater constellation overlapping parts of both modern constellations.^[10]

The star Xi Hydrae is particularly interesting in the field of asteroseismology since it shows solar-like oscillations. Multiple frequency oscillations are found with periods between 2.0 and 5.5 hours.^[11]

Xi Hydrae has left the main sequence, having exhausted the supply of hydrogen in its core. Its spectrum is that of a red giant. Modelling its physical properties against theoretical evolutionary tracks shows that it has just reached the foot of the red giant branch for a star with an initial mass around 3 M_☉. This puts its age at about 510 myr.^[12]