58 Hydrae

58 Hydrae is a single[6] star in the equatorial constellation of Hydra, located around 290 light years away from the Sun based on parallax.[1] It has the Bayer designation E Hydrae; 58 Hydrae is the Flamsteed designation − a later designation of 6 Librae.[7] It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.42.[2] This object is moving closer to the Earth with a heliocentric radial velocity of −9 km/s.[2]

58 Hydrae
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension  14h 50m 17.30146s[1]
Declination −27° 57′ 37.3385″[1]
Apparent magnitude (V) 4.42[2]
Characteristics
Evolutionary stage giant
Spectral type K2.5 IIIb Fe-1:[3]
B−V color index 1.366±0.050[2]
Astrometry
Radial velocity (Rv)−8.7±1.5[2] km/s
Proper motion (μ) RA: −232.696[1] mas/yr
Dec.: −60.118[1] mas/yr
Parallax (π)11.4440 ± 0.5105[1] mas
Distance290 ± 10 ly
(87 ± 4 pc)
Absolute magnitude (MV)−0.60[2]
Details[4]
Mass0.88 M☉
Radius33.40+0.41
−1.13[1] R☉
Luminosity310.19 L☉
Surface gravity (log g)1.35 cgs
Temperature4,210 K
Metallicity [Fe/H]−0.43±0.04[2] dex
Age8.1 Gyr
Other designations
E Hya, 58 Hya, CD−27°10073, HD 130694, HIP 72571, HR 5526, SAO 182911, LTT 5887[5]
Database references
SIMBADdata

This is an aging giant star with a stellar classification of K2.5 IIIb Fe-1:,[3] most likely (98% chance) on the red giant branch.[4] The suffix notation indicates an underabundance of iron in the spectrum, and some uncertainty about the classification. It is around 8.1 billion years old with 0.88 times the mass of the Sun.[4] As a consequence of exhausting the hydrogen at its core, the star has expanded to 33.4[1] times the Sun's radius. It is radiating 310 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,210 K.[4]

References
  1. 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. 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. Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  4. Stock, S.; et al. (August 2018), "Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search", Astronomy & Astrophysics, 616: 15, arXiv:1805.04094, Bibcode:2018A&A...616A..33S, doi:10.1051/0004-6361/201833111, A33.
  5. "E Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 4, 2019.
  6. 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.
  7. Wagman, M. (August 1987), "Flamsteed's Missing Stars", Journal for the History of Astronomy, 18: 218, Bibcode:1987JHA....18..209W, doi:10.1177/002182868701800305
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