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[2] 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
Right ascension 11h 33m 00.11505s[1]
Declination −31° 51′ 27.4435″[1]
Apparent magnitude (V) 3.54[2]
Spectral type G7 III[2]
Radial velocity (Rv)−4.90±0.30[3] km/s
Proper motion (μ) RA: −209.62[1] mas/yr
Dec.: −40.84[1] mas/yr
Parallax (π)25.16 ± 0.16 mas[1]
Distance129.6 ± 0.8 ly
(39.7 ± 0.3 pc)
Absolute magnitude (MV)+0.54[4]
Mass2.94±0.15[5] M
Radius10.2±0.1[6] R
Luminosity57.65±2.39[6] L
Surface gravity (log g)2.87±0.02[5] cgs
Temperature5,044±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 Lyr, 288 G. Hydrae,[7] CD−31° 9083, HD 100407, HIP 56343, HR 4450, SAO 202558[8]
Database references
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]


  1. ^ a b c d e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  2. ^ a b c Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics, 352: 495–507, Bibcode:1999A&A...352..495M.
  3. ^ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  4. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  5. ^ a b c d Heiter, U.; Jofré, P.; Gustafsson, B.; Korn, A. J.; Soubiran, C.; Thévenin, F. (2015), "Gaia FGK benchmark stars: Effective temperatures and surface gravities", Astronomy & Astrophysics, 582: A49, arXiv:1506.06095, Bibcode:2015A&A...582A..49H, doi:10.1051/0004-6361/201526319, S2CID 53391939.
  6. ^ a b c d Bruntt, H.; et al. (July 2010), "Accurate fundamental parameters for 23 bright solar-type stars", Monthly Notices of the Royal Astronomical Society, 405 (3): 1907–1923, arXiv:1002.4268, Bibcode:2010MNRAS.405.1907B, doi:10.1111/j.1365-2966.2010.16575.x, S2CID 118495267.
  7. ^ "URANOMETRIA ARGENTINA". Archived from the original on 2012-02-27. Retrieved 2012-05-08.
  8. ^ "ksi Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-22.
  9. ^ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  10. ^ Wagman, M. (August 1987), "Flamsteed's Missing Stars", Journal for the History of Astronomy, 18 (3): 216, Bibcode:1987JHA....18..209W, doi:10.1177/002182868701800305, S2CID 118445625.
  11. ^ Frandsen, S.; Carrier, F.; Aerts, C.; Stello, D.; Maas, T.; Burnet, M.; Bruntt, H.; Teixeira, T. C.; De Medeiros, J. R.; Bouchy, F.; Kjeldsen, H.; Pijpers, F.; Christensen-Dalsgaard, J. (2002). "Detection of Solar-like oscillations in the G7 giant star ξ Hya". Astronomy and Astrophysics. 394: L5–L8. arXiv:astro-ph/0209325. Bibcode:2002A&A...394L...5F. doi:10.1051/0004-6361:20021281.
  12. ^ Thévenin, F.; Kervella, P.; Pichon, B.; Morel, P.; Di Folco, E.; Lebreton, Y. (2005). "VLTI/VINCI diameter constraints on the evolutionary status of δ Eri, ξ Hya, η Boo". Astronomy and Astrophysics. 436 (1): 253. arXiv:astro-ph/0501420. Bibcode:2005A&A...436..253T. doi:10.1051/0004-6361:20042075. S2CID 118169489.

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