Xi Hydrae

Xi Hydrae, Latinised from ξ Hydrae, is a solitary^[10] star in the equatorial constellation of Hydra. With an apparent magnitude of 3.54^[3] it is visible to the naked eye. Based on parallax measurements, the tar is situated 130 light-years from Earth.

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	10.28±0.11[6] R☉
Luminosity	61.0±1.5[6] L☉
Surface gravity (log g)	2.78±0.07[6] cgs
Temperature	5,034±34[6] K
Metallicity [Fe/H]	+0.16±0.20[5] dex
Rotational velocity (v sin i)	2.7[7] km/s
Other designations
ξ Hya, 288 G. Hydrae,[8] CD−31°9083, HD 100407, HIP 56343, HR 4450, SAO 202558[9]
Database references
SIMBAD	data

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.^[11]

Charactertistics

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] The star has 10.28 times the Sun's radius, 61 times the Sun's luminosity and an effective temperature of 5,034 K.^[6]

One possible non-radial oscillation mode of Xi Hydrae

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.^[13]