# Psi Hydrae

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Binary star system in the constellation Hydra

Psi Hydrae Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) Constellation Hydra Right ascension 13h 09m 03.27026s[1] Declination −23° 07′ 05.0501″[1] Apparent magnitude (V) 4.97[2] Characteristics Spectral type K0 III[3] U−B color index +0.95[2] B−V color index +1.05[2] Astrometry Radial velocity (Rv) −17.2±0.6[4] km/s Proper motion (μ) RA: −20.08[1] mas/yr Dec.: −39.81[1] mas/yr Parallax (π) 14.09±0.48 mas[1] Distance 231 ± 8 ly (71 ± 2 pc) Absolute magnitude (MV) +0.54[5] Details Radius 10.6[6] R☉ Luminosity 56[7] L☉ Surface gravity (log g) 2.72[5] cgs Temperature 4,680[5] K Metallicity [Fe/H] −0.19±0.04[5] dex Other designations ψ Hya, 45 Hydrae, BD−22°3515, HD 114149, HIP 64166, HR 4958, SAO 181410[8] Database references SIMBAD data

**Psi Hydrae** (**ψ Hydrae**) is a [star system](/source/Star_system) in the equatorial [constellation](/source/Constellation) of [Hydra](/source/Hydra_(constellation)). Based upon an annual [parallax shift](/source/Stellar_parallax) of 14.09 [mas](/source/Milliarcsecond) as seen from Earth, it is located around 231 [light years](/source/Light_year) away from the [Sun](/source/Sun). It is faintly visible to the naked eye with an [apparent magnitude](/source/Apparent_magnitude) of 4.97.[2]

## System

This is a probable [astrometric binary](/source/Astrometric_binary) system.[9] The primary, component A, is an [evolved](/source/Stellar_evolution) [giant star](/source/Giant_star) with a [stellar classification](/source/Stellar_classification) of K0 III.[3] It is a [red clump](/source/Red_clump) star that is generating energy through the fusion of helium at its core.[10] The measured [angular diameter](/source/Angular_diameter) is 1.39±0.02 [mas](/source/Milliarcsecond),[11] which, at the estimated distance of Psi Hydrae, yields a physical size of about 10.6 times the [radius of the Sun](/source/Solar_radius).[6] It is radiating 56[7] times the [solar luminosity](/source/Solar_luminosity) from its [photosphere](/source/Photosphere) at an [effective temperature](/source/Effective_temperature) of 4,680. K.[5]

## Cultural significance

The [Kalapalo people](/source/Kalapalo_people) of [Mato Grosso](/source/Mato_Grosso) state in Brazil called this star and [β Hya](/source/Beta_Hydrae) *Kafanifani*.[12]

## References

1. ^ [***a***](#cite_ref-vanLeeuwen2007_1-0) [***b***](#cite_ref-vanLeeuwen2007_1-1) [***c***](#cite_ref-vanLeeuwen2007_1-2) [***d***](#cite_ref-vanLeeuwen2007_1-3) [***e***](#cite_ref-vanLeeuwen2007_1-4) van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", *Astronomy and Astrophysics*, **474** (2): 653–664, [arXiv](/source/ArXiv_(identifier)):[0708.1752](https://arxiv.org/abs/0708.1752), [Bibcode](/source/Bibcode_(identifier)):[2007A&A...474..653V](https://ui.adsabs.harvard.edu/abs/2007A&A...474..653V), [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20078357](https://doi.org/10.1051%2F0004-6361%3A20078357), [S2CID](/source/S2CID_(identifier)) [18759600](https://api.semanticscholar.org/CorpusID:18759600).

1. ^ [***a***](#cite_ref-Mermilliod1986_2-0) [***b***](#cite_ref-Mermilliod1986_2-1) [***c***](#cite_ref-Mermilliod1986_2-2) [***d***](#cite_ref-Mermilliod1986_2-3) Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", *Catalogue of Eggen's UBV Data*, [SIMBAD](/source/SIMBAD), [Bibcode](/source/Bibcode_(identifier)):[1986EgUBV........0M](https://ui.adsabs.harvard.edu/abs/1986EgUBV........0M).

1. ^ [***a***](#cite_ref-houk1978_3-0) [***b***](#cite_ref-houk1978_3-1) Houk, Nancy; Smith-Moore, M. (1978), *Michigan catalogue of two-dimensional spectral types for the HD stars*, vol. 4, Ann Arbor: Dept. of Astronomy, University of Michigan, [Bibcode](/source/Bibcode_(identifier)):[1988mcts.book.....H](https://ui.adsabs.harvard.edu/abs/1988mcts.book.....H).

1. **[^](#cite_ref-deBruijne2012_4-0)** 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. ^ [***a***](#cite_ref-McWilliam1990_5-0) [***b***](#cite_ref-McWilliam1990_5-1) [***c***](#cite_ref-McWilliam1990_5-2) [***d***](#cite_ref-McWilliam1990_5-3) [***e***](#cite_ref-McWilliam1990_5-4) McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants", *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-lang2006_6-0) [***b***](#cite_ref-lang2006_6-1) Lang, Kenneth R. (2006), [*Astrophysical formulae*](https://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41), Astronomy and astrophysics library, vol. 1 (3rd ed.), [Birkhäuser](/source/Birkh%C3%A4user), [ISBN](/source/ISBN_(identifier)) [3-540-29692-1](https://en.wikipedia.org/wiki/Special:BookSources/3-540-29692-1). The radius (R*) is given by: 1. 2 ⋅ R ∗ = ( 71.0 ⋅ 1.39 ⋅ 10 − 3 ) AU 0.0046491 AU / R ⨀ ≈ 21.2 ⋅ R ⨀ {\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(71.0\cdot 1.39\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 21.2\cdot R_{\bigodot }\end{aligned}}}

1. ^ [***a***](#cite_ref-Mcdonald2012_7-0) [***b***](#cite_ref-Mcdonald2012_7-1) 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. **[^](#cite_ref-SIMBAD_8-0)** ["* psi Hya"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+psi+Hya). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved 2017-03-17.{{[cite web](https://en.wikipedia.org/wiki/Template:Cite_web)}}: CS1 maint: postscript ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_postscript))

1. **[^](#cite_ref-Makarov2005_9-0)** Makarov, V. V.; Kaplan, G. H. (May 2005), "Statistical Constraints for Astrometric Binaries with Nonlinear Motion", *The Astronomical Journal*, **129** (5): 2420–2427, [Bibcode](/source/Bibcode_(identifier)):[2005AJ....129.2420M](https://ui.adsabs.harvard.edu/abs/2005AJ....129.2420M), [doi](/source/Doi_(identifier)):[10.1086/429590](https://doi.org/10.1086%2F429590).

1. **[^](#cite_ref-Alves2000_10-0)** Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", *The Astrophysical Journal*, **539** (2): 732–741, [arXiv](/source/ArXiv_(identifier)):[astro-ph/0003329](https://arxiv.org/abs/astro-ph/0003329), [Bibcode](/source/Bibcode_(identifier)):[2000ApJ...539..732A](https://ui.adsabs.harvard.edu/abs/2000ApJ...539..732A), [doi](/source/Doi_(identifier)):[10.1086/309278](https://doi.org/10.1086%2F309278), [S2CID](/source/S2CID_(identifier)) [16673121](https://api.semanticscholar.org/CorpusID:16673121).

1. **[^](#cite_ref-Richichi2005_11-0)** Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", *Astronomy and Astrophysics*, **431** (2): 773–777, [Bibcode](/source/Bibcode_(identifier)):[2005A&A...431..773R](https://ui.adsabs.harvard.edu/abs/2005A&A...431..773R), [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20042039](https://doi.org/10.1051%2F0004-6361%3A20042039).

1. **[^](#cite_ref-basso87_12-0)** Basso, Ellen B. (1987). [*In Favor of Deceit: A Study of Tricksters in an Amazonian Society*](https://archive.org/details/infavorofdeceits0000bass). Tucson, Arizona: University of Arizona Press. p. [360](https://archive.org/details/infavorofdeceits0000bass/page/360). [ISBN](/source/ISBN_(identifier)) [0-8165-1022-9](https://en.wikipedia.org/wiki/Special:BookSources/0-8165-1022-9).

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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