6 Hydrae

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6 Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hydra
Right ascension  08h 40m 01.47182s[1]
Declination −12° 28′ 31.3433″[1]
Apparent magnitude (V) 4.98[2]
Evolutionary stage giant
Spectral type K3 III[3]
B−V color index 1.415±0.001[2]
Radial velocity (Rv)−7.8±0.6[4] km/s
Proper motion (μ) RA: −81.619[1] mas/yr
Dec.: −1.646[1] mas/yr
Parallax (π)8.7394 ± 0.1769[1] mas
Distance373 ± 8 ly
(114 ± 2 pc)
Absolute magnitude (MV)−0.40[2]
[1] R
Luminosity267±6[1] L
Surface gravity (log g)1.91[5] cgs
[1] K
Metallicity [Fe/H]−0.21[5] dex
Other designations
a Hya, 6 Hya, BD−11°2420, HD 73840, HIP 42509, HR 3431, SAO 154515[6]
Database references

6 Hydrae is a single[7] star in the equatorial constellation of Hydra,[6] located 373 light years away from the Sun.[1] It has the Bayer designation a Hydrae; 6 Hydrae is the Flamsteed designation. This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.98.[2] It is moving closer to the Earth with a heliocentric radial velocity of −8 km/s.[4] Eggen (1995) listed it as a proper motion candidate for membership in the IC 2391 supercluster.[8]

This is an aging giant star with a stellar classification of K3 III,[3] which indicates it has exhausted the hydrogen at its core and evolved away from the main sequence. As a consequence, it has expanded to 33[1] times the radius of the Sun. The star is radiating 267[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,080 K.[1]


  1. ^ a b c d e f g h i j k l 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.
  2. ^ a b c d 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.
  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, Bibcode:1988mcts.book.....H.
  4. ^ a b 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, A61.
  5. ^ a b McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527.
  6. ^ a b "6 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-04-23.
  7. ^ Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  8. ^ Eggen, Olin J. (December 1995), "Reality Tests of Superclusters in the Young Disk Population", Astronomical Journal, 110: 2862, Bibcode:1995AJ....110.2862E, doi:10.1086/117734.