Xi Hydrae

Xi Hydrae, Latinised from ξ Hydrae, is a solitary star in the equatorial constellation of Hydra. It was also given the Flamsteed designation 19 Crateris. This magnitude 3.54 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.

Xi Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 11h 33m 00.11505s
Declination −31° 51 27.4435
Apparent magnitude (V) 3.54
Characteristics
Spectral type G7 III
Astrometry
Radial velocity (Rv)−4.90±0.30 km/s
Proper motion (μ) RA: −209.62 mas/yr
Dec.: −40.84 mas/yr
Parallax (π)25.16 ± 0.16 mas
Distance129.6 ± 0.8 ly
(39.7 ± 0.3 pc)
Absolute magnitude (MV)+0.54
Details
Mass2.94±0.15 M
Radius10.2±0.1 R
Luminosity57.65±2.39 L
Surface gravity (log g)2.87±0.02 cgs
Temperature5,044±40 K
Metallicity [Fe/H]+0.16±0.20 dex
Rotational velocity (v sin i)2.7 km/s
Other designations
ξ Lyr, 288 G. Hydrae, CD−31° 9083, HD 100407, HIP 56343, HR 4450, SAO 202558
Database references
SIMBADdata

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.

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.

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.

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