# 51 Hydrae

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/51_Hydrae
> Markdown URL: https://mediated.wiki/source/51_Hydrae.md
> Source: https://en.wikipedia.org/wiki/51_Hydrae
> Source revision: 1333605436
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

Star in the constellation Hydra

This article is about k Hydrae; not to be confused with [κ (kappa) Hydrae](/source/Kappa_Hydrae).

51 Hydrae Location of 51 Hydrae (circled in red) Observation data Epoch J2000 Equinox J2000 Constellation Hydra Right ascension 14h 23m 05.77393s[1] Declination −27° 45′ 14.4609″[1] Apparent magnitude (V) 4.78[2] Characteristics Evolutionary stage giant Spectral type K4 III[3] B−V color index 1.300±0.040[2] Astrometry Radial velocity (Rv) 19.7±0.9[2] km/s Proper motion (μ) RA: −202.476[1] mas/yr Dec.: −117.186[1] mas/yr Parallax (π) 19.2042±0.2252 mas[1] Distance 170 ± 2 ly (52.1 ± 0.6 pc) Absolute magnitude (MV) 1.36[2] Details Mass 1.31[4] M☉ Radius 13.47+0.48 −1.26[1] R☉ Luminosity 54.9+0.8 −1.5[1] L☉ Surface gravity (log g) 2.25[5] cgs Temperature 4,255±31[4] K Metallicity [Fe/H] 0.08[5] dex Other designations k Hya, 51 Hya, NSV 6648, CD−27°9803, HD 125932, HIP 70306, HR 5381, SAO 182483[6] Database references SIMBAD data

**51 Hydrae** is a single[7] [star](/source/Star) in the [equatorial](/source/Celestial_equator) [constellation](/source/Constellation) of [Hydra](/source/Hydra_(constellation)),[6] located 170 [light years](/source/Light_year) away from the Sun.[1] It has the [Bayer designation](/source/Bayer_designation) **k Hydrae**; *51 Hydrae* is the [Flamsteed designation](/source/Flamsteed_designation).[6] This object is visible to the naked eye as a faint, orange-hued star with an [apparent visual magnitude](/source/Apparent_visual_magnitude) of 4.78. It is moving further from the Earth with a heliocentric [radial velocity](/source/Radial_velocity) of +20 km/s.[2] Eggen (1971) listed it as a member of the [η Cephei](/source/Eta_Cephei) group of [old-disk stars](/source/Old-disk_star).[8]

This is an [evolved](/source/Stellar_evolution) [giant star](/source/Giant_star) with a [stellar classification](/source/Stellar_classification) of K4 III,[3] which indicates it has exhausted the supply of hydrogen at its [core](/source/Stellar_core) and expanded off the [main sequence](/source/Main_sequence). It has 1.31[4] times the [mass of the Sun](/source/Mass_of_the_Sun) but has swollen to 13.5[1] times the [Sun's radius](/source/Sun's_radius). The star is radiating 55[1] times the [luminosity of the Sun](/source/Luminosity_of_the_Sun) from its enlarged [photosphere](/source/Photosphere) at an [effective temperature](/source/Effective_temperature) of 4,255 K.[4]

## References

1. ^ [***a***](#cite_ref-GaiaDR2_1-0) [***b***](#cite_ref-GaiaDR2_1-1) [***c***](#cite_ref-GaiaDR2_1-2) [***d***](#cite_ref-GaiaDR2_1-3) [***e***](#cite_ref-GaiaDR2_1-4) [***f***](#cite_ref-GaiaDR2_1-5) [***g***](#cite_ref-GaiaDR2_1-6) [***h***](#cite_ref-GaiaDR2_1-7) [***i***](#cite_ref-GaiaDR2_1-8) [***j***](#cite_ref-GaiaDR2_1-9) [Brown, A. G. A.](/source/Anthony_Brown_(scientist)); et al. ([Gaia collaboration](/source/Data_Processing_and_Analysis_Consortium)) (August 2018). ["*Gaia* Data Release 2: Summary of the contents and survey properties"](https://doi.org/10.1051%2F0004-6361%2F201833051). *[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics)*. **616**. A1. [arXiv](/source/ArXiv_(identifier)):[1804.09365](https://arxiv.org/abs/1804.09365). [Bibcode](/source/Bibcode_(identifier)):[2018A&A...616A...1G](https://ui.adsabs.harvard.edu/abs/2018A&A...616A...1G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/201833051](https://doi.org/10.1051%2F0004-6361%2F201833051). [Gaia DR2 record for this source](https://vizier.u-strasbg.fr/viz-bin/VizieR-S?Gaia%20DR2%206269720523431409536) at [VizieR](/source/VizieR).

1. ^ [***a***](#cite_ref-Anderson2012_2-0) [***b***](#cite_ref-Anderson2012_2-1) [***c***](#cite_ref-Anderson2012_2-2) [***d***](#cite_ref-Anderson2012_2-3) [***e***](#cite_ref-Anderson2012_2-4) Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", *Astronomy Letters*, **38** (5): 331, [arXiv](/source/ArXiv_(identifier)):[1108.4971](https://arxiv.org/abs/1108.4971), [Bibcode](/source/Bibcode_(identifier)):[2012AstL...38..331A](https://ui.adsabs.harvard.edu/abs/2012AstL...38..331A), [doi](/source/Doi_(identifier)):[10.1134/S1063773712050015](https://doi.org/10.1134%2FS1063773712050015), [S2CID](/source/S2CID_(identifier)) [119257644](https://api.semanticscholar.org/CorpusID:119257644).

1. ^ [***a***](#cite_ref-Keenan1989_3-0) [***b***](#cite_ref-Keenan1989_3-1) Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins Catalog of Revised MK Types for the Cooler Stars", *The Astrophysical Journal Supplement Series*, **71**: 245, [Bibcode](/source/Bibcode_(identifier)):[1989ApJS...71..245K](https://ui.adsabs.harvard.edu/abs/1989ApJS...71..245K), [doi](/source/Doi_(identifier)):[10.1086/191373](https://doi.org/10.1086%2F191373).

1. ^ [***a***](#cite_ref-Luck2015_4-0) [***b***](#cite_ref-Luck2015_4-1) [***c***](#cite_ref-Luck2015_4-2) [***d***](#cite_ref-Luck2015_4-3) Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", *Astronomical Journal*, **150** (3), 88, [arXiv](/source/ArXiv_(identifier)):[1507.01466](https://arxiv.org/abs/1507.01466), [Bibcode](/source/Bibcode_(identifier)):[2015AJ....150...88L](https://ui.adsabs.harvard.edu/abs/2015AJ....150...88L), [doi](/source/Doi_(identifier)):[10.1088/0004-6256/150/3/88](https://doi.org/10.1088%2F0004-6256%2F150%2F3%2F88), [S2CID](/source/S2CID_(identifier)) [118505114](https://api.semanticscholar.org/CorpusID:118505114)

1. ^ [***a***](#cite_ref-McWilliam1990_5-0) [***b***](#cite_ref-McWilliam1990_5-1) 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](/source/Bibcode_(identifier)):[1990ApJS...74.1075M](https://ui.adsabs.harvard.edu/abs/1990ApJS...74.1075M), [doi](/source/Doi_(identifier)):[10.1086/191527](https://doi.org/10.1086%2F191527).

1. ^ [***a***](#cite_ref-SIMBAD_6-0) [***b***](#cite_ref-SIMBAD_6-1) [***c***](#cite_ref-SIMBAD_6-2) ["k Hya"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=k+Hya). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved May 3, 2019.

1. **[^](#cite_ref-Eggleton2008_7-0)** Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*, **389** (2): 869–879, [arXiv](/source/ArXiv_(identifier)):[0806.2878](https://arxiv.org/abs/0806.2878), [Bibcode](/source/Bibcode_(identifier)):[2008MNRAS.389..869E](https://ui.adsabs.harvard.edu/abs/2008MNRAS.389..869E), [doi](/source/Doi_(identifier)):[10.1111/j.1365-2966.2008.13596.x](https://doi.org/10.1111%2Fj.1365-2966.2008.13596.x), [S2CID](/source/S2CID_(identifier)) [14878976](https://api.semanticscholar.org/CorpusID:14878976).

1. **[^](#cite_ref-Eggen1971_8-0)** Eggen, O. J. (June 1971), "The ζ Herculis, σ Puppis, ∈ Indi, and η Cephei Groups of Old Disk Population Stars", *Publications of the Astronomical Society of the Pacific*, **83** (493): 251, [Bibcode](/source/Bibcode_(identifier)):[1971PASP...83..251E](https://ui.adsabs.harvard.edu/abs/1971PASP...83..251E), [doi](/source/Doi_(identifier)):[10.1086/129119](https://doi.org/10.1086%2F129119).

v t e Constellation of Hydra List of stars in Hydra Hydra in Chinese astronomy Stars Bayer α (Alphard) β γ (Naga) δ ε (Ashlesha) ζ η θ ι (Ukdah) κ λ μ ν ξ ο π ρ σ (Minchir) τ1 τ2 υ1 (Zhang) υ2 φ1 φ2 φ3 χ1 χ2 ψ ω b1 b3 C F Flamsteed 1 2 3 6 (a) 9 10 12 (D) 14 15 17 19 20 21 23 24 25 26 27 (P) 28 29 33 (A) 34 37 44 47 48 50 51 (k) 52 (l) 54 (m) 55 56 57 58 (Solitaire) 59 60 10 Crt 17 Crt 20 Crt 2 Sex Variable R U V W TW EX HS KU LQ V361 V419 V421 V478 V484 HR 3378 3538 3749 (G) 3750 3858 (I) 3862 3919 3923 (Felis) 4162 4328 4339 (β Ant) 4445 5265 HD 72659 74156 82943 86226 86264 90156 (γ Ant) Other 2MASS 1114−2618 ESO 439-26 Gliese 328 Gliese 357 Gliese 433 Gliese 453 GJ 3634 HAT-P-30 HE 1256−2738 HE 1327−2326 LHS 2065 LHS 3003 LTT 3780 SDSS J090745.0+024507 WASP-25 WASP-36 WASP-84 WASP-166 (Filetdor) WISE 0855−0714 WISEA J1141−3326 Exoplanets Gliese 357 d HD 72659 b HD 74156 b c HD 82943 b c HD 86226 b HD 86264 b TW Hydrae b (unconfirmed) WASP-193b Star clusters Messier 48 Messier 68 NGC 5694 Price-Whelan 1 Nebulae Abell 33 Abell 35 NGC 3242 Southern Owl Nebula Galaxies Messier 83 NGC 2617 2642 2697 2708 2758 2835 2848 2865 2890 2935 2936 2937 2960 2962 2986 2992 3030 3052 3054 3081 3109 3124 3200 3285 3285B 3290 3305 3307 3308 3309 3311 3312 3313 3314 3315 3316 3336 3369 3383 3393 3402 3463 3464 3585 3621 3673 3717 3904 3923 3936 4980 4993 5042 5061 5078 5085 5101 5135 5260 5264 5495 5626 Other 3C 196.1 AM 1316−241 Arp 7 CTQ 327 ESO 510-G13 GAMA202627 GLEAM J0917−0012 Hydra A IC 535 MRC 1138−262 Peekaboo Galaxy PKS 1151−348 RX J0911.4+0551 SDSS J0841+0101 TN J0924−2201 Tololo 1247−232 ZwCl 1693 BCG Galaxy clusters Abell 754 Abell 3411 Abell 3412 Bullet Group Hickson 40 Astronomical events GW170817 Category

---
Adapted from the Wikipedia article [51 Hydrae](https://en.wikipedia.org/wiki/51_Hydrae) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/51_Hydrae?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.