# Kappa Hydrae

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Star in the constellation Hydra

κ Hydrae Location of κ Hydrae (circled in red) Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) Constellation Hydra Right ascension 09h 40m 18.36319s[1] Declination −14° 19′ 56.2396″[1] Apparent magnitude (V) 5.06[2] Characteristics Evolutionary stage main sequence[1] Spectral type B4 IV/V[3] U−B color index −0.57[2] B−V color index −0.15[2] Variable type Suspected[4][5] Astrometry Radial velocity (Rv) 20.6±2.0[6] km/s Proper motion (μ) RA: −26.481[1] mas/yr Dec.: −20.240[1] mas/yr Parallax (π) 6.9952±0.1897 mas[1] Distance 470 ± 10 ly (143 ± 4 pc) Absolute magnitude (MV) −0.98[7] Details Mass 5.0±0.1[3] M☉ Radius 3.4[8] R☉ Luminosity 328[9] L☉ Temperature 16,150±920[10] K Rotational velocity (v sin i) 115.0[11] km/s Age 30.7±3.3[3] Myr Other designations κ Hya, 38 Hydrae, BD−13°2917, FK5 364, HD 83754, HIP 47452, HR 3849, SAO 155388.[12] Database references SIMBAD data

**κ Hydrae**, Latinised as **Kappa Hydrae**, is a solitary[13] [star](/source/Star) in the equatorial [constellation](/source/Constellation) of [Hydra](/source/Hydra_(constellation)). Its [apparent visual magnitude](/source/Apparent_visual_magnitude) is 5.06,[2] which is bright enough to be faintly visible to the naked eye. The distance to this star is around 470 ly (143 pc), based upon an annual [parallax shift](/source/Stellar_parallax) of 7.0 [mas](/source/Minute_and_second_of_arc).[1] It may be a [variable star](/source/Variable_star), meaning it undergoes repeated fluctuations in brightness by at least 0.1 magnitude.[5]

This is an [evolving](/source/Stellar_evolution) [B-type star](/source/B-type_star) with a [stellar classification](/source/Stellar_classification) of B4 IV/V,[3] having a [luminosity class](/source/Luminosity_class) intermediate between a [subgiant](/source/Subgiant) and a [giant star](/source/Giant_star). It has an estimated five[3] times the [mass of the Sun](/source/Mass_of_the_Sun) and 3.4 times the [Sun's radius](/source/Sun's_radius).[8] Kappa Hydrae has a high rate of spin with a [projected rotational velocity](/source/Projected_rotational_velocity) of 115.0 km/s,[11] and is only about 31 million years old.[3] The star radiates 328 times the [solar luminosity](/source/Solar_luminosity) from its [outer atmosphere](/source/Stellar_atmosphere)[9] at an [effective temperature](/source/Effective_temperature) of 16,150 K.[10]

## Name

This star was one of the set assigned by the 16th-century astronomer Al Tizini[14] to **Al Sharāsīf** (**ألشراسيف**), the Ribs (of Hydra), which included the stars from [β Crateris](/source/%CE%92_Crateris) westward through κ Hydrae.[15][16]

According to the catalogue of stars in the *Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars*, *Al Sharāsīf* were the title for two stars: β Crateris as *Al Sharasīf II* and κ Hydrae as *Al Sharasīf I*.[17]

In [Chinese](/source/Chinese_language), 張宿 (*Zhāng Xiù*), meaning *[Extended Net](/source/Extended_Net)*, refers to an [asterism](/source/Asterism_(astronomy)) consisting of Kappa Hydrae, [Upsilon1 Hydrae](/source/Upsilon1_Hydrae), [Lambda Hydrae](/source/Lambda_Hydrae), [Mu Hydrae](/source/Mu_Hydrae), [HD 87344](https://en.wikipedia.org/w/index.php?title=HD_87344&action=edit&redlink=1), and [Phi1 Hydrae](/source/Phi1_Hydrae).[18] Consequently, Kappa Hydrae itself is known as 張宿五 (*Zhāng Xiù wǔ*), "the Fifth Star of Extended Net".[19]

## References

1. ^ [***a***](#cite_ref-dr3_1-0) [***b***](#cite_ref-dr3_1-1) [***c***](#cite_ref-dr3_1-2) [***d***](#cite_ref-dr3_1-3) [***e***](#cite_ref-dr3_1-4) [***f***](#cite_ref-dr3_1-5) [***g***](#cite_ref-dr3_1-6) Vallenari, A.; et al. (Gaia collaboration) (2023). ["*Gaia* Data Release 3. Summary of the content and survey properties"](https://doi.org/10.1051%2F0004-6361%2F202243940). *Astronomy and Astrophysics*. **674**: A1. [arXiv](/source/ArXiv_(identifier)):[2208.00211](https://arxiv.org/abs/2208.00211). [Bibcode](/source/Bibcode_(identifier)):[2023A&A...674A...1G](https://ui.adsabs.harvard.edu/abs/2023A&A...674A...1G). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202243940](https://doi.org/10.1051%2F0004-6361%2F202243940). [S2CID](/source/S2CID_(identifier)) [244398875](https://api.semanticscholar.org/CorpusID:244398875). [Gaia DR3 record for this source](https://vizier.cds.unistra.fr/viz-bin/VizieR-4?-source=+I%2F355&-from=nav&-nav=cat%3AI%2F355%26tab%3A%7BI%2F355%2Fgaiadr3%7D%26key%3Asource%3D1355%2Fgaiadr3%26HTTPPRM%3A%26-out.add%3D.%26Source%3D%3D%3D5688852413126934912%26-go+%25%23Sesame%23%25%26) at [VizieR](/source/VizieR).

1. ^ [***a***](#cite_ref-Nicolet1978_2-0) [***b***](#cite_ref-Nicolet1978_2-1) [***c***](#cite_ref-Nicolet1978_2-2) [***d***](#cite_ref-Nicolet1978_2-3) Nicolet, B. (October 1978), "Catalogue of homogeneous data in the UBV photoelectric photometric system", *Astronomy and Astrophysics Supplement Series*, **34**: 1–49, [Bibcode](/source/Bibcode_(identifier)):[1978A&AS...34....1N](https://ui.adsabs.harvard.edu/abs/1978A&AS...34....1N).

1. ^ [***a***](#cite_ref-Tetzlaff2011_3-0) [***b***](#cite_ref-Tetzlaff2011_3-1) [***c***](#cite_ref-Tetzlaff2011_3-2) [***d***](#cite_ref-Tetzlaff2011_3-3) [***e***](#cite_ref-Tetzlaff2011_3-4) [***f***](#cite_ref-Tetzlaff2011_3-5) Tetzlaff, N.; et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*, **410** (1): 190–200, [arXiv](/source/ArXiv_(identifier)):[1007.4883](https://arxiv.org/abs/1007.4883), [Bibcode](/source/Bibcode_(identifier)):[2011MNRAS.410..190T](https://ui.adsabs.harvard.edu/abs/2011MNRAS.410..190T), [doi](/source/Doi_(identifier)):[10.1111/j.1365-2966.2010.17434.x](https://doi.org/10.1111%2Fj.1365-2966.2010.17434.x), [S2CID](/source/S2CID_(identifier)) [118629873](https://api.semanticscholar.org/CorpusID:118629873).

1. **[^](#cite_ref-gcvs2009_4-0)** Samus, N. N.; Durlevich, O. V.; et al. (2009), "General Catalogue of Variable Stars", *VizieR Online Data Catalog*, **1**, [Bibcode](/source/Bibcode_(identifier)):[2009yCat....102025S](https://ui.adsabs.harvard.edu/abs/2009yCat....102025S).

1. ^ [***a***](#cite_ref-Rufener1982_5-0) [***b***](#cite_ref-Rufener1982_5-1) Rufener, F.; Bartholdi, P. (June 1982), "List of 333 variable, microvariable or suspected variable stars detected in the Geneva photometry", *Astronomy and Astrophysics Supplement Series*, **48**: 503–511, [Bibcode](/source/Bibcode_(identifier)):[1982A&AS...48..503R](https://ui.adsabs.harvard.edu/abs/1982A&AS...48..503R).

1. **[^](#cite_ref-deBruijne2012_6-0)** 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](/source/ArXiv_(identifier)):[1208.3048](https://arxiv.org/abs/1208.3048), [Bibcode](/source/Bibcode_(identifier)):[2012A&A...546A..61D](https://ui.adsabs.harvard.edu/abs/2012A&A...546A..61D), [doi](/source/Doi_(identifier)):[10.1051/0004-6361/201219219](https://doi.org/10.1051%2F0004-6361%2F201219219), [S2CID](/source/S2CID_(identifier)) [59451347](https://api.semanticscholar.org/CorpusID:59451347), A61.

1. **[^](#cite_ref-Zorec1991_7-0)** Zorec, J.; Briot, D. (May 1991), "Absolute magnitudes of B emission line stars - Correlation between the luminosity excess and the effective temperature", *Astronomy and Astrophysics*, **245** (1): 150–170, [Bibcode](/source/Bibcode_(identifier)):[1991A&A...245..150Z](https://ui.adsabs.harvard.edu/abs/1991A&A...245..150Z).

1. ^ [***a***](#cite_ref-PasinettiFracassini2001_8-0) [***b***](#cite_ref-PasinettiFracassini2001_8-1) Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", *Astronomy and Astrophysics*, **367** (3rd ed.): 521–524, [arXiv](/source/ArXiv_(identifier)):[astro-ph/0012289](https://arxiv.org/abs/astro-ph/0012289), [Bibcode](/source/Bibcode_(identifier)):[2001A&A...367..521P](https://ui.adsabs.harvard.edu/abs/2001A&A...367..521P), [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20000451](https://doi.org/10.1051%2F0004-6361%3A20000451), [S2CID](/source/S2CID_(identifier)) [425754](https://api.semanticscholar.org/CorpusID:425754).

1. ^ [***a***](#cite_ref-Mcdonald2012_9-0) [***b***](#cite_ref-Mcdonald2012_9-1) 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](/source/ArXiv_(identifier)):[1208.2037](https://arxiv.org/abs/1208.2037), [Bibcode](/source/Bibcode_(identifier)):[2012MNRAS.427..343M](https://ui.adsabs.harvard.edu/abs/2012MNRAS.427..343M), [doi](/source/Doi_(identifier)):[10.1111/j.1365-2966.2012.21873.x](https://doi.org/10.1111%2Fj.1365-2966.2012.21873.x), [S2CID](/source/S2CID_(identifier)) [118665352](https://api.semanticscholar.org/CorpusID:118665352).

1. ^ [***a***](#cite_ref-Soubiran2010_10-0) [***b***](#cite_ref-Soubiran2010_10-1) Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", *Astronomy and Astrophysics*, **515**: A111, [arXiv](/source/ArXiv_(identifier)):[1004.1069](https://arxiv.org/abs/1004.1069), [Bibcode](/source/Bibcode_(identifier)):[2010A&A...515A.111S](https://ui.adsabs.harvard.edu/abs/2010A&A...515A.111S), [doi](/source/Doi_(identifier)):[10.1051/0004-6361/201014247](https://doi.org/10.1051%2F0004-6361%2F201014247), [S2CID](/source/S2CID_(identifier)) [118362423](https://api.semanticscholar.org/CorpusID:118362423).

1. ^ [***a***](#cite_ref-Abt2002_11-0) [***b***](#cite_ref-Abt2002_11-1) Abt, Helmut A.; et al. (July 2002), "Rotational Velocities of B Stars", *The Astrophysical Journal*, **573** (1): 359–365, [Bibcode](/source/Bibcode_(identifier)):[2002ApJ...573..359A](https://ui.adsabs.harvard.edu/abs/2002ApJ...573..359A), [doi](/source/Doi_(identifier)):[10.1086/340590](https://doi.org/10.1086%2F340590).

1. **[^](#cite_ref-SIMBAD_12-0)** ["kap Hya"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=kap+Hya). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 2017-01-05.

1. **[^](#cite_ref-Eggleton2008_13-0)** 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-14)** Turkmani, Rim (7 July 2011). ["Arabic Roots of the Scientific Revolution"](http://www.muslimheritage.com/article/arabic-roots-scientific-revolution). *Muslim Heritage*. Retrieved 1 July 2016.

1. **[^](#cite_ref-15)** [Star Names - R.H.Allen p. 182](https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Crater*.html)

1. **[^](#cite_ref-16)** [Star Names - R.H.Allen p. 246](https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Hydra*.html)

1. **[^](#cite_ref-rhoads1971_17-0)** Rhoads, Jack W. (November 15, 1971), [*Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars*](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720005197_1972005197.pdf) (PDF), Jet Propulsion Laboratory, California Institute of Technology.

1. **[^](#cite_ref-18)** (in Chinese) *中國星座神話*, written by 陳久金. Published by 台灣書房出版有限公司, 2005, [ISBN](/source/ISBN_(identifier)) [978-986-7332-25-7](https://en.wikipedia.org/wiki/Special:BookSources/978-986-7332-25-7).

1. **[^](#cite_ref-19)** (in Chinese) [香港太空館 - 研究資源 - 亮星中英對照表](http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm) [Archived](https://web.archive.org/web/20081025110153/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm) 2008-10-25 at the [Wayback Machine](/source/Wayback_Machine), Hong Kong Space Museum. Accessed on line November 23, 2010.

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

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Adapted from the Wikipedia article [Kappa Hydrae](https://en.wikipedia.org/wiki/Kappa_Hydrae) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Kappa_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.