# 27 Hydrae

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Triple star system in the constellation Hydra

27 Hydrae Location of 27 Hydrae (circled in red) Observation data Epoch J2000 Equinox J2000 Constellation Hydra Right ascension 09h 20m 29.01857s[1] Declination −09° 33′ 20.5054″[1] Apparent magnitude (V) 4.818[2] (4.91 + 7.03 + 10.99)[3] Characteristics Evolutionary stage red clump[4] Spectral type K0III[5] + F4V + K2V[6] Astrometry Radial velocity (Rv) +25.60±0.13[7] km/s Proper motion (μ) RA: −12.48[1] mas/yr Dec.: −27.37[1] mas/yr Parallax (π) 14.66±0.31 mas[1] Distance 222 ± 5 ly (68 ± 1 pc) Details A Mass 2.17[2] M☉ Radius 11[7] R☉ Luminosity 57.5[2] L☉ Surface gravity (log g) 2.9[7] cgs Temperature 4,965±26[2] K Metallicity [Fe/H] −0.07[7] dex Rotational velocity (v sin i) 3.3[7] km/s Age 1.91[2] Gyr B Radius 1.82[8] R☉ Luminosity 5.885[8] L☉ Temperature 6,664[8] K C Radius 0.72[9] R☉ Luminosity 0.227[9] L☉ Temperature 4,685[9] K Other designations CCDM J09204-0934, WDS J09204-0934[10] A: 27 Hya, BD−08°2643, HD 80586, HIP 45811, HR 3709, SAO 136768 B: BD−09°2801, HD 80550, HIP 45802, SAO 136767 C: TYC 5463-1518-1 Database references SIMBAD data B C

**27 Hydrae** is a [triple star system](/source/Triple_star_system)[6] in the [equatorial](/source/Celestial_equator) [constellation](/source/Constellation) of [Hydra](/source/Hydra_(constellation)),[10] located 222 [light years](/source/Light_year) away from the Sun.[1] It is visible to the naked eye as a faint, orange-hued star with a combined [apparent visual magnitude](/source/Apparent_visual_magnitude) of 4.82.[2] The system is moving further from the Earth with a heliocentric [radial velocity](/source/Radial_velocity) of +25.6 km/s.[7]

The magnitude 4.91[6] primary, component A, is an aging [giant star](/source/Giant_star) with a [stellar classification](/source/Stellar_classification) of K0 III.[5] It is a [red clump](/source/Red_clump) giant,[4] which indicates it is on the [horizontal branch](/source/Horizontal_branch) and is generating energy through [helium fusion](/source/Helium_fusion) at its [core](/source/Stellar_core). The star is 1.9[2] billion years old with 2.17[2] times the [mass of the Sun](/source/Mass_of_the_Sun). It has swelled to 11[7] times the [Sun's radius](/source/Sun's_radius) and is radiating 57.5[2] times the [Sun's luminosity](/source/Sun's_luminosity) from its enlarged [photosphere](/source/Photosphere) at an [effective temperature](/source/Effective_temperature) of 4,965 K.[2] The star is suspected to host a [low-mass](/source/Planemo) companion.[11]

The stellar companions to this star, designated components B and C, lie at an [angular separation](/source/Angular_separation) of 229.10[″](/source/Second_of_arc) from the primary, and form a binary pair with a separation of 9.20″ as of 2015.[3] The brighter member of the pair, component B, is a seventh magnitude [F-type main-sequence star](/source/F-type_main-sequence_star) with a class of F4 V, while its companion is an eleventh magnitude [K-type main-sequence star](/source/K-type_main-sequence_star) with a class of K2 V.[6]

## Substellar companion candidate

The [Okayama Planet Search](/source/Okayama_Planet_Search_Program) team published a paper in late 2008 reporting investigations into radial velocity variations observed for a set of evolved stars, showing hints of a [substellar](/source/Substellar) companion orbiting the primary member of the wide [binary system](/source/Binary_system) 27 Hydrae (ADS 7311).[11] A later study revised the [minimum mass](/source/Minimum_mass) of this candidate companion to 28 [Jupiter masses](/source/Jupiter_mass), indicating that if it exists, it is a [brown dwarf](/source/Brown_dwarf) rather than a planet.[12]

The 27 Hydrae A planetary system Companion (in order from star) Mass Semimajor axis (AU) Orbital period (days) Eccentricity Inclination (°) Radius (unconfirmed) ≥28 MJ ≈5.9 3,400 — — —

## 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) [***f***](#cite_ref-vanLeeuwen2007_1-5) 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-Luck2015_2-0) [***b***](#cite_ref-Luck2015_2-1) [***c***](#cite_ref-Luck2015_2-2) [***d***](#cite_ref-Luck2015_2-3) [***e***](#cite_ref-Luck2015_2-4) [***f***](#cite_ref-Luck2015_2-5) [***g***](#cite_ref-Luck2015_2-6) [***h***](#cite_ref-Luck2015_2-7) [***i***](#cite_ref-Luck2015_2-8) [***j***](#cite_ref-Luck2015_2-9) 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-WDSC2014_3-0) [***b***](#cite_ref-WDSC2014_3-1) Mason, B. D.; et al. (2014), ["The Washington Visual Double Star Catalog"](http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/wds), *The Astronomical Journal*, **122** (6): 3466, [Bibcode](/source/Bibcode_(identifier)):[2001AJ....122.3466M](https://ui.adsabs.harvard.edu/abs/2001AJ....122.3466M), [doi](/source/Doi_(identifier)):[10.1086/323920](https://doi.org/10.1086%2F323920), retrieved 2015-07-22

1. ^ [***a***](#cite_ref-Alves2000_4-0) [***b***](#cite_ref-Alves2000_4-1) 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. ^ [***a***](#cite_ref-Houk1999_5-0) [***b***](#cite_ref-Houk1999_5-1) Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". *Michigan Spectral Survey*. **5**. [Bibcode](/source/Bibcode_(identifier)):[1999MSS...C05....0H](https://ui.adsabs.harvard.edu/abs/1999MSS...C05....0H).

1. ^ [***a***](#cite_ref-Eggleton2008_6-0) [***b***](#cite_ref-Eggleton2008_6-1) [***c***](#cite_ref-Eggleton2008_6-2) [***d***](#cite_ref-Eggleton2008_6-3) Eggleton, P. P.; Tokovinin, A. A. (September 2008). ["A catalogue of multiplicity among bright stellar systems"](https://doi.org/10.1111%2Fj.1365-2966.2008.13596.x). *[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. ^ [***a***](#cite_ref-Massarotti2008_7-0) [***b***](#cite_ref-Massarotti2008_7-1) [***c***](#cite_ref-Massarotti2008_7-2) [***d***](#cite_ref-Massarotti2008_7-3) [***e***](#cite_ref-Massarotti2008_7-4) [***f***](#cite_ref-Massarotti2008_7-5) [***g***](#cite_ref-Massarotti2008_7-6) Massarotti, Alessandro; et al. (January 2008). ["Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity"](https://doi.org/10.1088%2F0004-6256%2F135%2F1%2F209). *The Astronomical Journal*. **135** (1): 209–231. [Bibcode](/source/Bibcode_(identifier)):[2008AJ....135..209M](https://ui.adsabs.harvard.edu/abs/2008AJ....135..209M). [doi](/source/Doi_(identifier)):[10.1088/0004-6256/135/1/209](https://doi.org/10.1088%2F0004-6256%2F135%2F1%2F209). [S2CID](/source/S2CID_(identifier)) [121883397](https://api.semanticscholar.org/CorpusID:121883397).

1. ^ [***a***](#cite_ref-dr2b_8-0) [***b***](#cite_ref-dr2b_8-1) [***c***](#cite_ref-dr2b_8-2) [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%205742848123496954112) at [VizieR](/source/VizieR).

1. ^ [***a***](#cite_ref-dr2c_9-0) [***b***](#cite_ref-dr2c_9-1) [***c***](#cite_ref-dr2c_9-2) [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%205742848123496954496) at [VizieR](/source/VizieR).

1. ^ [***a***](#cite_ref-SIMBAD_10-0) [***b***](#cite_ref-SIMBAD_10-1) ["27 Hya"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=27+Hya). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg). Retrieved May 3, 2019.

1. ^ [***a***](#cite_ref-Toyota2009_11-0) [***b***](#cite_ref-Toyota2009_11-1) Toyota, Eri; et al. (2008). ["Radial Velocity Search for Extrasolar Planets in Visual Binary Systems"](https://doi.org/10.1093%2Fpasj%2F61.1.19). *[Publications of the Astronomical Society of Japan](/source/Publications_of_the_Astronomical_Society_of_Japan)*. **61** (1): 19–28. [Bibcode](/source/Bibcode_(identifier)):[2009PASJ...61...19T](https://ui.adsabs.harvard.edu/abs/2009PASJ...61...19T). [doi](/source/Doi_(identifier)):[10.1093/pasj/61.1.19](https://doi.org/10.1093%2Fpasj%2F61.1.19). [hdl](/source/Hdl_(identifier)):[20.500.14094/90001422](https://hdl.handle.net/20.500.14094%2F90001422).

1. **[^](#cite_ref-Katoh2018_12-0)** Katoh, Noriyuki; Itoh, Yoichi; Sato, Bun’ei (August 1, 2018). ["Search for companions in visual binary systems using precise radial-velocity measurements"](https://academic.oup.com/pasj/article/doi/10.1093/pasj/psy054/5025942). *Publications of the Astronomical Society of Japan*. **70** (4). [doi](/source/Doi_(identifier)):[10.1093/pasj/psy054](https://doi.org/10.1093%2Fpasj%2Fpsy054). [ISSN](/source/ISSN_(identifier)) [0004-6264](https://search.worldcat.org/issn/0004-6264).

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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