{{Short description|Star in the constellation Hydra}} {{hatnote|For other stars with this [[Bayer designation]], see [[Phi Hydrae|φ Hydrae]]}} {{DISPLAYTITLE:Phi<sup>2</sup> Hydrae}} {{Starbox begin | name = Phi<sup>2</sup> Hydrae }} {{Starbox image | image = [[Image:Phi2HyaLightCurve.png|250px]] | caption = A [[light curve]] for Phi<sup>2</sup> Hydrae, plotted from ''[[Hipparcos]]'' data<ref name=CDS/> }} {{Starbox observe | epoch = [[J2000.0]] | equinox = [[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell = [[Hydra (constellation)|Hydra]]<ref name=Anderson2012/> | ra = {{RA|10|36|16.65890}}<ref name=dr3/> | dec = {{DEC|-16|20|39.5764}}<ref name=dr3/> | appmag_v = 5.97 to 6.04<ref name=vsx/> }} {{Starbox character | type = [[asymptotic giant branch|AGB]]<ref name=Eggen1992/> | class = M1 III<ref name=houk1978/> | b-v = +1.64<ref name=Mermilliod1986/> | u-b = +1.95<ref name=Mermilliod1986/> | r-i = | variable = [[Semiregular variable star|SR]]<ref name=tabur2009/> }} {{Starbox astrometry | radial_v = {{Val|+15.7|2.9}}<ref name=deBruijne2012/> | prop_mo_ra = −30.651<ref name=dr3/> | prop_mo_dec = +4.212<ref name=dr3/> | parallax = 2.929 | p_error = 0.1349 | parallax_footnote = <ref name=dr3/> | absmag_v = −0.80<ref name=Anderson2012/> }} {{Starbox detail | source = | component1 = | mass = 6.4<ref name=dr3/> | radius = 85<ref name=fetherolf2023/> | luminosity = 1,470<ref name=fetherolf2023/> | temperature = 3,873<ref name=fetherolf2023/> | gravity = 1.25<ref name=dr3/> | metal_fe = | rotational_velocity = | age_gyr = }} {{Starbox catalog | names = [[Bayer designation|φ<sup>2</sup> Hya]], [[Durchmusterung|BD]]−15°3087, [[Henry Draper Catalogue|HD]] 91880, [[Hipparcos Catalogue|HIP]] 51905, [[Harvard Revised catalogue|HR]] 4156, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 156093<ref name=SIMBAD/> }} {{Starbox reference | Simbad = phi02+Hya }} {{Starbox end}} '''Phi<sup>2</sup> Hydrae''', [[Latinisation of names|Latinized]] from '''φ<sup>2</sup> Hydrae''', is a [[star]] in the [[constellation]] [[Hydra (constellation)|Hydra]]. It originally received the [[Flamsteed designation]] of '''1 Crateris''' before being placed in the Hydra constellation.<ref name=Wagman1987/> Based upon an annual [[stellar parallax|parallax shift]] of {{val|2.9|ul=mas}} as seen from Earth, it is located roughly 1,110 [[light year]]s from the [[Sun]]. The star is faintly visible to the [[naked eye]] with an [[apparent visual magnitude]] of about six. It forms a triangle with the fainter [[phi1 Hydrae|φ<sup>1</sup> Hydrae]] and the brighter [[phi3 Hydrae|φ<sup>3</sup> Hydrae]], between [[μ Hydrae]] and [[ν Hydrae]].
{| class="wikitable" style="text-align: center; float: left; margin-right: 0.5em;" |+Pulsations<ref name=tabur2009/> ! Period<br/>(days) ! Amplitude<br/>(magnitude) |- | 11.0 || 0.008 |- | 110.3 || 0.012 |- | 153.6 || 0.015 |}
This is an [[stellar evolution|evolved]] [[red giant]] star with a [[stellar classification]] of M1 III.<ref name=Eggen1992/> It is currently on the [[asymptotic giant branch]],<ref name=Eggen1992/> and is a [[semiregular variable]] that undergoes changes in luminosity according to three pulsation periods,<ref name=tabur2009/> although it is formally still only a suspected variable.<ref name=gcvs/> The star is radiating an estimated 1,470 times the [[solar luminosity|Sun's luminosity]] from its [[photosphere]] at an [[effective temperature]] of {{val|fmt=commas|3,873|ul=K}}.
Phi<sup>2</sup> Hydrae has a faint visual companion: a magnitude 12.20 star at an [[angular separation]] of 3.50 [[arc second]]s along a [[position angle]] of 280°, as of 1959.<ref name=WDSC2014/> The companion has a similar [[Gaia Data Release 3]] parallax to Phi<sup>2</sup> Hydrae<ref name=dr3b/> and is at a distance of {{val|329|5|4|ul=pc}}.<ref name=bj2021/> {{clear left}}
==References== <references> <ref name=dr3>{{cite Gaia DR3|3748037918486129408}}</ref>
<ref name=dr3b>{{cite Gaia DR3|3748037918485238016}}</ref>
<ref name=fetherolf2023>{{citation |postscript=. |bibcode=2023ApJS..268....4F |title=Variability Catalog of Stars Observed during the TESS Prime Mission |last1=Fetherolf |first1=Tara |last2=Pepper |first2=Joshua |last3=Simpson |first3=Emilie |last4=Kane |first4=Stephen R. |last5=Močnik |first5=Teo |last6=English |first6=John Edward |last7=Antoci |first7=Victoria |last8=Huber |first8=Daniel |last9=Jenkins |first9=Jon M. |last10=Stassun |first10=Keivan |last11=Twicken |first11=Joseph D. |last12=Vanderspek |first12=Roland |last13=Winn |first13=Joshua N. |journal=The Astrophysical Journal Supplement Series |date=2023 |volume=268 |issue=1 |page=4 |doi=10.3847/1538-4365/acdee5 |doi-access=free |arxiv=2208.11721 }}</ref>
<ref name=gcvs>{{citation|postscript=.|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|pages=B/GCVS|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>
<ref name=bj2021>{{citation |postscript=. |bibcode=2021AJ....161..147B |title=Estimating Distances from Parallaxes. V. Geometric and Photogeometric Distances to 1.47 Billion Stars in Gaia Early Data Release 3 |last1=Bailer-Jones |first1=C. A. L. |last2=Rybizki |first2=J. |last3=Fouesneau |first3=M. |last4=Demleitner |first4=M. |last5=Andrae |first5=R. |journal=The Astronomical Journal |date=2021 |volume=161 |issue=3 |page=147 |doi=10.3847/1538-3881/abd806 |doi-access=free |arxiv=2012.05220 }}</ref>
<ref name=CDS>{{citation | postscript=. | title=The HIPPARCOS and TYCHO catalogues | author=EAS | journal=Astrometric and Photometric Star Catalogues Derived from the ESA Hipparcos Space Astrometry Mission | publication-place=Noordwijk, Netherlands | publisher=ESA Publications Division | year=1997 | series=ESA SP Series | volume=1200 | isbn=9290923997 | bibcode=1997HIP...C......0E | url=https://cdsarc.cds.unistra.fr/viz-bin/ftp-index?/ftp/cats/more/HIP/cdroms/cats | access-date=14 December 2024}}</ref>
<ref name=Anderson2012>{{citation | title=XHIP: An extended hipparcos compilation | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | arxiv=1108.4971 | s2cid=119257644 | postscript=. }}</ref>
<ref name=WDSC2014>{{citation | display-authors=1 | last1=Mason | first1=B. D. | last2=Wycoff | first2=G. L. | last3=Hartkopf | first3=W. I. | last4=Douglass | first4=G. G. | last5=Worley | first5=C. E. | title=The Washington Visual Double Star Catalog | year=2014 | bibcode=2001AJ....122.3466M | doi=10.1086/323920 | postscript=. | volume=122 | journal=The Astronomical Journal | issue=6 | pages=3466–3471| doi-access=free }}</ref>
<ref name=Eggen1992>{{citation | title=Asymptotic giant branch stars near the sun | last1=Eggen | first1=Olin J. | journal=Astronomical Journal | postscript=. | volume=104 | issue=1 | pages=275–313 | date=July 1992 | doi=10.1086/116239 | bibcode=1992AJ....104..275E }}</ref>
<ref name=tabur2009>{{citation | title=Long-term photometry and periods for 261 nearby pulsating M giants | last1=Tabur |first1 =V. | last2=Bedding | first2=T. R. | first3=L. L. | last3=Kiss | first4=T. T. | last4=Moon | first5=B. | last5=Szeidl | first6=H. | last6=Kjeldsen | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=400 | issue=4 | pages=1945–61 | year=2009 | display-authors=1 | doi=10.1111/j.1365-2966.2009.15588.x | doi-access=free | arxiv=0908.3228 | bibcode=2009MNRAS.400.1945T | s2cid=15358380 | postscript=. }}</ref>
<ref name=houk1978>{{citation | last1=Houk | first1=Nancy | last2=Smith-Moore | first2=M. | title=Michigan catalogue of two-dimensional spectral types for the HD stars | volume=4 | location=Ann Arbor | year=1978 | publisher=Dept. of Astronomy, University of Michigan | bibcode=1988mcts.book.....H | postscript=. }}</ref>
<ref name=deBruijne2012>{{citation | last1=de Bruijne | first1=J. H. J. | last2=Eilers | first2=A.-C. | title=Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project | journal=Astronomy & Astrophysics | volume=546 | id=A61 | pages=14 | date=October 2012 | doi=10.1051/0004-6361/201219219 | bibcode=2012A&A...546A..61D | arxiv=1208.3048 | s2cid=59451347 | postscript=. }}</ref>
<ref name=Wagman1987>{{citation | last=Wagman | first=M. | postscript=. | title=Flamsteed's Missing Stars | journal=Journal for the History of Astronomy | volume=18 | page=216 |date=August 1987 | issue=3 | bibcode=1987JHA....18..209W | doi=10.1177/002182868701800305| s2cid=118445625 }}</ref>
<ref name=Mermilliod1986>{{citation | last1=Mermilliod | first1=J.-C. | title=Compilation of Eggen's UBV data, transformed to UBV (unpublished) | journal=Catalogue of Eggen's UBV Data | year=1986 | publisher=[[SIMBAD]] | bibcode=1986EgUBV........0M | postscript=. }}</ref>
<ref name=SIMBAD>{{cite simbad | mode=cs2 | title=* phi02 Hya | access-date=2017-03-17 | postscript=. }}</ref>
<ref name=vsx>{{cite web |url=https://vsx.aavso.org/index.php?view=detail.top&oid=56887 |title=phi 2 Hya |website=International Variable Star Index |publisher=[[AAVSO]] |access-date=2026-05-20 }}</ref>
</references>
{{Stars of Hydra|state=collapsed}}
[[Category:M-type giants]] [[Category:Semiregular variable stars]] [[Category:Double stars]] [[Category:Hydra (constellation)]] [[Category:Bayer objects|Hydrae, Phi2]] [[Category:Henry Draper Catalogue objects|091880]] [[Category:Hipparcos objects|051905]] [[Category:Bright Star Catalogue objects|4156]] [[Category:Flamsteed objects|Crateris, 01]] [[Category:Durchmusterung objects]]