Psi Hydrae

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Psi Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 13h 09m 03.27026s[1]
Declination −23° 07′ 05.0501″[1]
Apparent magnitude (V) 4.97[2]
Spectral type K0 III[3]
U−B color index +0.95[2]
B−V color index +1.05[2]
Radial velocity (Rv)−17.2±0.6[4] km/s
Proper motion (μ) RA: −20.08[1] mas/yr
Dec.: −39.81[1] mas/yr
Parallax (π)14.09 ± 0.48[1] mas
Distance231 ± 8 ly
(71 ± 2 pc)
Absolute magnitude (MV)+0.54[5]
Radius10.6[6] R
Luminosity56[7] L
Surface gravity (log g)2.72[5] cgs
Temperature4,680[5] K
Metallicity [Fe/H]−0.19±0.04[5] dex
Other designations
ψ Hya, 45 Hya, BD−22° 3515, HD 114149, HIP 64166, HR 4958, SAO 181410.[8]
Database references

Psi Hydrae (ψ Hya) is a star in the equatorial constellation of Hydra. Based upon an annual parallax shift of 14.09 mas as seen from Earth, it is located around 231 light years away from the Sun. It is faintly visible to the naked eye with an apparent magnitude of 4.97.[2]

This is a probable astrometric binary system.[9] The primary, component A, is an evolved giant star with a stellar classification of K0 III.[3] It is a red clump star that is generating energy through the fusion of helium at its core.[10] The measured angular diameter is 1.39±0.02 mas,[11] which, at the estimated distance of Psi Hydrae, yields a physical size of about 10.6 times the radius of the Sun.[6] It is radiating 56[7] times the solar luminosity from its photosphere at an effective temperature of 4,680. K.[5]


  1. ^ a b c d e van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV data, SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b Houk, Nancy; Smith-Moore, M. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor: Dept. of Astronomy, University of Michigan, 
  4. ^ 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:1208.3048Freely accessible, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61. 
  5. ^ a b c d e McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527. 
  6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1.  The radius (R*) is given by:
  7. ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037Freely accessible, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x. 
  8. ^ "* psi Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-17. 
  9. ^ Makarov, V. V.; Kaplan, G. H. (May 2005), "Statistical Constraints for Astrometric Binaries with Nonlinear Motion", The Astronomical Journal, 129 (5): 2420–2427, Bibcode:2005AJ....129.2420M, doi:10.1086/429590. 
  10. ^ Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329Freely accessible, Bibcode:2000ApJ...539..732A, doi:10.1086/309278. 
  11. ^ Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.