Chi1 Hydrae (χ1 Hydrae) is a binary star[3] in the equatorial constellation of Hydra. It originally received the Flamsteed designation of 9 Crateris before being placed in the Hydra constellation.[10] Based upon an annual parallax shift of 22.8 mas as seen from Earth, it is located about 143 light years from the Sun. It is visible to the naked eye with a combined apparent visual magnitude of 4.94.[2]

Chi1 Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 11h 05m 19.90766s[1]
Declination −27° 17′ 36.9957″[1]
Apparent magnitude (V) 4.94[2]
Spectral type F4 V + F7 V[3]
U−B color index +0.04[2]
B−V color index +0.36[2]
Radial velocity (Rv)+19.1±1.6[4] km/s
Proper motion (μ) RA: −190.728[5] mas/yr
Dec.: −6.273[5] mas/yr
Parallax (π)22.8323 ± 0.1828 mas[5]
Distance143 ± 1 ly
(43.8 ± 0.4 pc)
Absolute magnitude (MV)1.74[6]
Period (P)7.5535±0.0064 yr
Semi-major axis (a)0.1388±0.0016
Eccentricity (e)0.349±0.015
Inclination (i)96.50±0.84°
Longitude of the node (Ω)224.00±0.59°
Periastron epoch (T)1983.455 ± 0.084
Argument of periastron (ω)
χ1 Hya A
Mass1.93[8] M
Radius3.19[5] R
Luminosity17.798[5] L
Temperature6,637[5] K
Metallicity [Fe/H]−0.10[6] dex
Age1.3[6] Gyr
χ1 Hya B
Mass1.93[8] M
Other designations
χ1 Hya, CD−26°8338, FK5 419, GJ 3642, HD 96202, HIP 54204, HR 4314, SAO 179514[9]
Database references

The two components of this system appear to have equal masses of 1.93 times the mass of the Sun.[7] The pair circle each other with an orbital period of 7.55 years with an eccentricity of 0.35.[7]


  1. ^ a b 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 d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J.
  3. ^ a b 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.
  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:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  5. ^ a b c d e f Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  6. ^ a b c Nordström, B.; et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics, 418: 989–1019, arXiv:astro-ph/0405198, Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959, S2CID 11027621.
  7. ^ a b c Mason, Brian D.; et al. (February 1999), "Binary Star Orbits from Speckle Interferometry. I. Improved Orbital Elements of 22 Visual Systems", The Astronomical Journal, 117 (2): 1023–1036, Bibcode:1999AJ....117.1023M, doi:10.1086/300748.
  8. ^ a b Jaime, Luisa G.; et al. (December 2012), "Regions of dynamical stability for discs and planets in binary stars of the solar neighbourhood", Monthly Notices of the Royal Astronomical Society, 427 (4): 2723–2733, arXiv:1208.2051, Bibcode:2012MNRAS.427.2723J, doi:10.1111/j.1365-2966.2012.21839.x, S2CID 118570249.
  9. ^ "chi01 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-17.{{cite web}}: CS1 maint: postscript (link)
  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.