{{Short description|Binary star system in the constellation Hydra}} {{hatnote|For other stars with this [[Bayer designation]], see [[Chi Hydrae|χ Hydrae]]}} {{DISPLAYTITLE:Chi<sup>2</sup> Hydrae}} {{Starbox begin | name = Chi<sup>2</sup> Hydrae }} {{Starbox image | image = {{Location mark |image=Crater constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=Chi2 Hydrae |x=658|y=930 }} | caption = Location of χ<sup>2</sup> Hydrae (circled in red) }} {{Starbox observe | epoch = [[J2000.0]] | equinox = [[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell = [[Hydra (constellation)|Hydra]] | ra = {{RA|11|05|57.57000}}<ref name=dr3/> | dec = {{DEC|-27|17|16.2727}}<ref name=dr3/> | appmag_v = 5.65 - 5.94<ref name=gcvs/> {{nowrap|(5.85 + 7.57)}}<ref name=Torres2010/> }} {{Starbox character | class = {{nowrap|B8 III-IVe + B8.5 V}}<ref name=Malkov2006/> | b-v = −0.06<ref name=Nicolet1978/> | u-b = −0.26<ref name=Nicolet1978/> | r-i = | variable = [[Algol variable|Algol (detached)]]<ref name=gcvs/> }} {{Starbox astrometry | radial_v = {{Val|+30.6|0.9}}<ref name=deBruijne2012/> | prop_mo_ra = +34.417<ref name=dr3/> | prop_mo_dec = −16.477<ref name=dr3/> | parallax = 4.7616 | p_error = 0.0652 | parallax_footnote = <ref name=dr3/> | absmag_v = }} {{Starbox orbit | reference = <ref name=Pourbaix2004/> | period_unitless = 2.2677&nbsp;d | axis = <!--Semimajor axis (in arcseconds)--> | axis_unitless = <!--Semimajor axis (no units provided by template)--> | eccentricity = 0.00 | inclination = <!--Inclination (in degrees)--> | node = <!--Longitude of node (in degrees)--> | periastron = 2439925.545&nbsp;JD | periarg = 0.00 | k1 = 123.3 | k2 = 168.9 }} {{Starbox detail | source = <ref name=Brown2010/> | component1 = χ Hya A | mass = {{Val|3.605|0.078}} | radius = {{Val|4.391|0.039}} | luminosity = 344<ref name=Eker2015/> | temperature = {{Val|11750|190|fmt=commas}} | gravity = 3.65<ref name=Jordi1997/> | metal_fe = | rotational_velocity = {{Val|112|10}}<ref name=Torres2010/> | age_myr = 158<ref name=Torres2010/> | component2 = χ Hya B | mass2 = {{Val|2.632|0.049}} | radius2 = {{Val|2.160|0.030}} | luminosity2 = 66<ref name=Eker2015/> | temperature2 = {{Val|11100|230|fmt=commas}} | gravity2 = 4.23<ref name=Torres2010/> | rotational_velocity2 = {{Val|60|6}}<ref name=Torres2010/> }} {{Starbox catalog | names = [[Bayer designation|χ Hya]], [[Durchmusterung|CD]]−26°8342, [[Henry Draper Catalogue|HD]]&nbsp;96314, [[Hipparcos Catalogue|HIP]]&nbsp;54255, [[Harvard Revised catalogue|HR]]&nbsp;4317, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;179522<ref name=SIMBAD/> }} {{Starbox reference | Simbad = chi02+Hya }} {{Starbox end}}

'''Chi<sup>2</sup> Hydrae''', Latinised from χ<sup>2</sup> Hydrae, is a [[binary star]] system in the equatorial [[constellation]] of [[Hydra (constellation)|Hydra]]. Based upon an annual [[stellar parallax|parallax shift]] of 4.6&nbsp;[[milliarcsecond|mas]] as seen from Earth, it is located roughly 685&nbsp;[[light year]]s from the [[Sun]]. It is visible to the naked eye with a combined [[apparent visual magnitude]] of about 5.7.

[[File:Chi2HyaLightCurve.png|thumb|left|A [[light curve]] for Chi<sup>2</sup> Hydrae, plotted from ''[[Transiting Exoplanet Survey Satellite|TESS]]'' data<ref name=MAST/>]] This is a [[Detached binary|detached]] [[eclipsing binary]] star system with an [[orbital period]] of 2.27&nbsp;days and an essentially circular orbit having a measured [[orbital eccentricity|eccentricity]] of 0.00.<ref name=Pourbaix2004/> The eclipse of the primary by the secondary component reduces the visual magnitude of the system by 0.29, while the eclipse of the secondary diminishes the magnitude by 0.27.<ref name=Malkov2006/>

The primary, component A, is a magnitude 5.85 [[B-type star]] with a [[stellar classification]] of B8&nbsp;III-IVe,<ref name=Torres2010/> suggesting it may be part way along the path of [[stellar evolution|evolving]] into a [[giant star]] from a [[subgiant star|subgiant]]. It has about 3.6 times the [[solar mass|mass of the Sun]] and 4.4 times the [[solar radius|Sun's radius]],<ref name=Brown2010/> although it may be tidally deformed since its radius is 86%<ref name=Eker2015/> of the [[Roche radius]].<ref name=Pols1997/> With an estimated age of 158&nbsp;million years, it has a [[projected rotational velocity]] of 112&nbsp;km/s.<ref name=Torres2010/>

Component B is a magnitude 7.57<ref name=Torres2010/> [[B-type main sequence star]] with a class of B8.5&nbsp;V.<ref name=Malkov2006/> It has 2.6 times the Sun's mass and 2.16 times the radius of the Sun. The star is filling 60% of its Roche radius.<ref name=Eker2015/>

==References== <references> <ref name=gcvs>{{citation |postscript=. |last1=Samus’ |first1=N. N. |last2=Kazarovets |first2=E. V. |last3=Durlevich |first3=O. V. |last4=Kireeva |first4=N. N. |last5=Pastukhova |first5=E. N. |title=General catalogue of variable stars: Version GCVS 5.1 |journal=Astronomy Reports |date=January 2017 |volume=61 |issue=1 |pages=80–88 |doi=10.1134/S1063772917010085 |issn=1063-7729 |bibcode=2017ARep...61...80S|s2cid=255195566 }}</ref>

<ref name=Eker2015>{{citation | title=Main-Sequence Effective Temperatures from a Revised Mass-Luminosity Relation Based on Accurate Properties | display-authors=1 | last1=Eker | first1=Z. | last2=Soydugan | first2=F. | last3=Soydugan | first3=E. | last4=Bilir | first4=S. | last5=Yaz Gökçe | first5=E. | last6=Steer | first6=I. | last7=Tüysüz | first7=M. | last8=Şenyüz | first8=T. | last9=Demircan | first9=O. | journal=The Astronomical Journal | postscript=. | volume=149 | issue=4 | id=131 | pages=16 | date=April 2015 | doi=10.1088/0004-6256/149/4/131 | bibcode=2015AJ....149..131E |arxiv = 1501.06585 | s2cid=118740259 }}</ref>

<ref name=MAST>{{citation |postscript=. | title=MAST: Barbara A. Mikulski Archive for Space Telescopes | url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html | publisher=Space Telescope Science Institute |access-date=8 December 2021}}</ref>

<ref name=Pols1997>{{citation | title=Further critical tests of stellar evolution by means of double-lined eclipsing binaries | display-authors=1 | last1=Pols | first1=Onno R. | last2=Tout | first2=Christopher A. | last3=Schroder | first3=Klaus-Peter | last4=Eggleton | first4=Peter P. | last5=Manners | first5=James | journal=Monthly Notices of the Royal Astronomical Society | volume=289 | issue=4 | pages=869–881 | date=August 1997 | postscript=. | doi=10.1093/mnras/289.4.869 | bibcode=1997MNRAS.289..869P | doi-access=free }}</ref>

<ref name=Jordi1997>{{citation | title=Photometric versus empirical surface gravities of eclipsing binaries. | last1=Jordi | first1=C. | last2=Ribas | first2=I. | last3=Torra | first3=J. | last4=Gimenez | first4=A. | journal=Astronomy and Astrophysics | volume=326 | pages=1044–1054 | date=October 1997 | bibcode=1997A&A...326.1044J | postscript=. }}</ref>

<ref name=Malkov2006>{{citation | last1=Malkov | first1=O. Yu. | last2=Oblak | first2=E. | last3=Snegireva | first3=E. A. | last4=Torra | first4=J. | title=A catalogue of eclipsing variables | postscript=. | journal=Astronomy and Astrophysics | display-authors=1 | volume=446 | issue=2 | pages=785–789 |date=February 2006 | doi=10.1051/0004-6361:20053137 | bibcode=2006A&A...446..785M | doi-access=free | hdl=10995/73280 | hdl-access=free }}</ref>

<ref name=Brown2010>{{citation | title=Radii of Rapidly Rotating Stars, with Application to Transiting-Planet Hosts | last1=Brown | first1=Timothy M. | postscript=. | journal=The Astrophysical Journal | volume=709 | issue=1 | pages=535–545 | date=January 2010 | doi=10.1088/0004-637X/709/1/535 | bibcode=2010ApJ...709..535B |arxiv = 0912.1639 | s2cid=119253009 }}</ref>

<ref name=Pourbaix2004>{{citation | title=S<sub>B<sup>9</sup></sub>: The ninth catalogue of spectroscopic binary orbits | journal=Astronomy & Astrophysics |display-authors=5 | last1=Pourbaix | first1=D. | last2=Tokovinin | first2=A. A. | last3=Batten | first3=A. H. | last4=Fekel | first4=F. C. | last5=Hartkopf | first5=W. I. | last6=Levato | first6=H. | last7=Morrell | first7=N. I. | last8=Torres | first8=G. | last9=Udry | first9=S. | volume=424 | issue=2 | pages=727–732 | date=2004 | doi=10.1051/0004-6361:20041213 | bibcode=2004A&A...424..727P | arxiv=astro-ph/0406573 | s2cid=119387088 | 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=Torres2010>{{citation | display-authors=1 | last1=Torres | first1=G. | last2=Andersen | first2=J. | last3=Giménez | first3=A. | title=Accurate masses and radii of normal stars: modern results and applications | journal=The Astronomy and Astrophysics Review | volume=18 | issue=1–2 | pages=67–126 | date=February 2010 | doi=10.1007/s00159-009-0025-1 | bibcode=2010A&ARv..18...67T | arxiv=0908.2624 | s2cid=14006009 | postscript=. }}</ref>

<ref name=Nicolet1978>{{citation | last1=Nicolet | first1=B. | year=1978 | postscript=. | title=Photoelectric photometric Catalogue of homogeneous measurements in the UBV System | journal=Astronomy and Astrophysics Supplement Series | volume=34 | pages=1–49 | bibcode=1978A&AS...34....1N }}</ref>

<ref name=SIMBAD>{{cite simbad | title=chi02 Hya | accessdate=2017-03-17 | postscript=. |mode=cs2 }}</ref>

<ref name=dr3>{{cite Gaia DR3|3532312225289255040}}</ref> </references>

{{Stars of Hydra|state=collapsed}}

[[Category:B-type giants]] [[Category:B-type subgiants]] [[Category:B-type main-sequence stars]] [[Category:Eclipsing binaries]] [[Category:Hydra (constellation)]] [[Category:Bayer objects|Hydrae, Chi2]] [[Category:Henry Draper Catalogue objects|096314]] [[Category:Hipparcos objects|054255]] [[Category:Bright Star Catalogue objects|4317]] [[Category:Durchmusterung objects|CD-26 08342]]