# Phi2 Hydrae

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Star in the constellation Hydra

For other stars with this [Bayer designation](/source/Bayer_designation), see [φ Hydrae](/source/Phi_Hydrae)

Phi2 Hydrae A light curve for Phi2 Hydrae, plotted from Hipparcos data[1] Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) Constellation Hydra[2] Right ascension 10h 36m 16.65890s[3] Declination −16° 20′ 39.5764″[3] Apparent magnitude (V) 5.97 to 6.04[4] Characteristics Evolutionary stage AGB[5] Spectral type M1 III[6] U−B color index +1.95[7] B−V color index +1.64[7] Variable type SR[8] Astrometry Radial velocity (Rv) +15.7±2.9[9] km/s Proper motion (μ) RA: −30.651[3] mas/yr Dec.: +4.212[3] mas/yr Parallax (π) 2.929±0.1349 mas[3] Distance 1,110 ± 50 ly (340 ± 20 pc) Absolute magnitude (MV) −0.80[2] Details Mass 6.4[3] M☉ Radius 85[10] R☉ Luminosity 1,470[10] L☉ Surface gravity (log g) 1.25[3] cgs Temperature 3,873[10] K Other designations φ2 Hya, BD−15°3087, HD 91880, HIP 51905, HR 4156, SAO 156093[11] Database references SIMBAD data

**Phi2 Hydrae**, [Latinized](/source/Latinisation_of_names) from **φ2 Hydrae**, is a [star](/source/Star) in the [constellation](/source/Constellation) [Hydra](/source/Hydra_(constellation)). It originally received the [Flamsteed designation](/source/Flamsteed_designation) of **1 Crateris** before being placed in the Hydra constellation.[12] Based upon an annual [parallax shift](/source/Stellar_parallax) of 2.9 [mas](/source/Milliarcsecond) as seen from Earth, it is located roughly 1,110 [light years](/source/Light_year) from the [Sun](/source/Sun). The star is faintly visible to the [naked eye](/source/Naked_eye) with an [apparent visual magnitude](/source/Apparent_visual_magnitude) of about six. It forms a triangle with the fainter [φ1 Hydrae](/source/Phi1_Hydrae) and the brighter [φ3 Hydrae](/source/Phi3_Hydrae), between [μ Hydrae](/source/%CE%9C_Hydrae) and [ν Hydrae](/source/%CE%9D_Hydrae).

Pulsations[8] Period (days) Amplitude (magnitude) 11.0 0.008 110.3 0.012 153.6 0.015

This is an [evolved](/source/Stellar_evolution) [red giant](/source/Red_giant) star with a [stellar classification](/source/Stellar_classification) of M1 III.[5] It is currently on the [asymptotic giant branch](/source/Asymptotic_giant_branch),[5] and is a [semiregular variable](/source/Semiregular_variable) that undergoes changes in luminosity according to three pulsation periods,[8] although it is formally still only a suspected variable.[13] The star is radiating an estimated 1,470 times the [Sun's luminosity](/source/Solar_luminosity) from its [photosphere](/source/Photosphere) at an [effective temperature](/source/Effective_temperature) of 3,873 [K](/source/Kelvin).

Phi2 Hydrae has a faint visual companion: a magnitude 12.20 star at an [angular separation](/source/Angular_separation) of 3.50 [arc seconds](/source/Arc_second) along a [position angle](/source/Position_angle) of 280°, as of 1959.[14] The companion has a similar [Gaia Data Release 3](/source/Gaia_Data_Release_3) parallax to Phi2 Hydrae[15] and is at a distance of 329+5 −4 [pc](/source/Parsec).[16]

## References

1. **[^](#cite_ref-CDS_1-0)** EAS (1997), ["The HIPPARCOS and TYCHO catalogues"](https://cdsarc.cds.unistra.fr/viz-bin/ftp-index?/ftp/cats/more/HIP/cdroms/cats), *Astrometric and Photometric Star Catalogues Derived from the ESA Hipparcos Space Astrometry Mission*, ESA SP Series, **1200**, Noordwijk, Netherlands: ESA Publications Division, [Bibcode](/source/Bibcode_(identifier)):[1997HIP...C......0E](https://ui.adsabs.harvard.edu/abs/1997HIP...C......0E), [ISBN](/source/ISBN_(identifier)) [9290923997](https://en.wikipedia.org/wiki/Special:BookSources/9290923997), retrieved 14 December 2024.{{[citation](https://en.wikipedia.org/wiki/Template:Citation)}}: CS1 maint: work parameter with ISBN ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_work_parameter_with_ISBN))

1. ^ [***a***](#cite_ref-Anderson2012_2-0) [***b***](#cite_ref-Anderson2012_2-1) 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-dr3_3-0) [***b***](#cite_ref-dr3_3-1) [***c***](#cite_ref-dr3_3-2) [***d***](#cite_ref-dr3_3-3) [***e***](#cite_ref-dr3_3-4) [***f***](#cite_ref-dr3_3-5) [***g***](#cite_ref-dr3_3-6) 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%3D3748037918486129408%26-go+%25%23Sesame%23%25%26) at [VizieR](/source/VizieR).

1. **[^](#cite_ref-vsx_4-0)** ["phi 2 Hya"](https://vsx.aavso.org/index.php?view=detail.top&oid=56887). *International Variable Star Index*. [AAVSO](/source/AAVSO). Retrieved 2026-05-20.

1. ^ [***a***](#cite_ref-Eggen1992_5-0) [***b***](#cite_ref-Eggen1992_5-1) [***c***](#cite_ref-Eggen1992_5-2) Eggen, Olin J. (July 1992), "Asymptotic giant branch stars near the sun", *Astronomical Journal*, **104** (1): 275–313, [Bibcode](/source/Bibcode_(identifier)):[1992AJ....104..275E](https://ui.adsabs.harvard.edu/abs/1992AJ....104..275E), [doi](/source/Doi_(identifier)):[10.1086/116239](https://doi.org/10.1086%2F116239).

1. **[^](#cite_ref-houk1978_6-0)** 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. ^ [***a***](#cite_ref-Mermilliod1986_7-0) [***b***](#cite_ref-Mermilliod1986_7-1) 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-tabur2009_8-0) [***b***](#cite_ref-tabur2009_8-1) [***c***](#cite_ref-tabur2009_8-2) Tabur, V.; et al. (2009), "Long-term photometry and periods for 261 nearby pulsating M giants", *[Monthly Notices of the Royal Astronomical Society](/source/Monthly_Notices_of_the_Royal_Astronomical_Society)*, **400** (4): 1945–61, [arXiv](/source/ArXiv_(identifier)):[0908.3228](https://arxiv.org/abs/0908.3228), [Bibcode](/source/Bibcode_(identifier)):[2009MNRAS.400.1945T](https://ui.adsabs.harvard.edu/abs/2009MNRAS.400.1945T), [doi](/source/Doi_(identifier)):[10.1111/j.1365-2966.2009.15588.x](https://doi.org/10.1111%2Fj.1365-2966.2009.15588.x), [S2CID](/source/S2CID_(identifier)) [15358380](https://api.semanticscholar.org/CorpusID:15358380).

1. **[^](#cite_ref-deBruijne2012_9-0)** 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-fetherolf2023_10-0) [***b***](#cite_ref-fetherolf2023_10-1) [***c***](#cite_ref-fetherolf2023_10-2) Fetherolf, Tara; Pepper, Joshua; Simpson, Emilie; Kane, Stephen R.; Močnik, Teo; English, John Edward; Antoci, Victoria; Huber, Daniel; Jenkins, Jon M.; Stassun, Keivan; Twicken, Joseph D.; Vanderspek, Roland; Winn, Joshua N. (2023), "Variability Catalog of Stars Observed during the TESS Prime Mission", *The Astrophysical Journal Supplement Series*, **268** (1): 4, [arXiv](/source/ArXiv_(identifier)):[2208.11721](https://arxiv.org/abs/2208.11721), [Bibcode](/source/Bibcode_(identifier)):[2023ApJS..268....4F](https://ui.adsabs.harvard.edu/abs/2023ApJS..268....4F), [doi](/source/Doi_(identifier)):[10.3847/1538-4365/acdee5](https://doi.org/10.3847%2F1538-4365%2Facdee5).

1. **[^](#cite_ref-SIMBAD_11-0)** ["* phi02 Hya"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+phi02+Hya), *[SIMBAD](/source/SIMBAD)*, [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg), retrieved 2017-03-17.

1. **[^](#cite_ref-Wagman1987_12-0)** Wagman, M. (August 1987), "Flamsteed's Missing Stars", *Journal for the History of Astronomy*, **18** (3): 216, [Bibcode](/source/Bibcode_(identifier)):[1987JHA....18..209W](https://ui.adsabs.harvard.edu/abs/1987JHA....18..209W), [doi](/source/Doi_(identifier)):[10.1177/002182868701800305](https://doi.org/10.1177%2F002182868701800305), [S2CID](/source/S2CID_(identifier)) [118445625](https://api.semanticscholar.org/CorpusID:118445625).

1. **[^](#cite_ref-gcvs_13-0)** Samus, N. N.; Durlevich, O. V.; et al. (2009), "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)", *VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S*, **1**: B/GCVS, [Bibcode](/source/Bibcode_(identifier)):[2009yCat....102025S](https://ui.adsabs.harvard.edu/abs/2009yCat....102025S).

1. **[^](#cite_ref-WDSC2014_14-0)** Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", *The Astronomical Journal*, **122** (6): 3466–3471, [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).

1. **[^](#cite_ref-dr3b_15-0)** 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%3D3748037918485238016%26-go+%25%23Sesame%23%25%26) at [VizieR](/source/VizieR).

1. **[^](#cite_ref-bj2021_16-0)** Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Demleitner, M.; Andrae, R. (2021), "Estimating Distances from Parallaxes. V. Geometric and Photogeometric Distances to 1.47 Billion Stars in Gaia Early Data Release 3", *The Astronomical Journal*, **161** (3): 147, [arXiv](/source/ArXiv_(identifier)):[2012.05220](https://arxiv.org/abs/2012.05220), [Bibcode](/source/Bibcode_(identifier)):[2021AJ....161..147B](https://ui.adsabs.harvard.edu/abs/2021AJ....161..147B), [doi](/source/Doi_(identifier)):[10.3847/1538-3881/abd806](https://doi.org/10.3847%2F1538-3881%2Fabd806).

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 [Phi2 Hydrae](https://en.wikipedia.org/wiki/Phi2_Hydrae) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Phi2_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.