{{Short description|Cataclysmic binary star system in the constellation Hydra}} {{Starbox begin}} {{starbox image | image = [[Image:EXHyaLightCurve.png|250px]] | caption = A [[light curve]] for EX Hydrae. The top two panels show the variation when the star is in its quiescent state. Red arrows mark the times of maximum eclipse. The bottom panel shows the brightness change caused by a flare. Adapted from [[Brian Warner (astronomer)|Warner]] and McGraw (1981)<ref name="Warner1981"/> and Reinsch and Beuermann (1990).<ref name="Reinsch1990"/> }} {{starbox observe | epoch=J2000 | ra = {{RA|12|52|24.22}}<ref name=dr3/> | dec = {{DEC|-29|14|56.0}}<ref name=dr3/> | constell=[[Hydra (constellation)|Hydra]] | appmag_v = 9.6 to 14.0<ref name=gcvs>{{cite journal |bibcode=2017ARep...61...80S |title=General catalogue of variable stars: Version GCVS 5.1 |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. |journal=Astronomy Reports |date=2017 |volume=61 |issue=1 |page=80 |doi=10.1134/S1063772917010085 }}</ref> }} {{Starbox character | class= [[white dwarf]] + M4/M5: | variable=[[Eclipsing variable star|eclipsing]] [[intermediate polar]]<ref name=beuermann2024a>{{cite journal |bibcode=2024A&A...686A.304B |title=High-resolution spectroscopy of the intermediate polar EX Hydrae. II. The inner disk radius |last1=Beuermann |first1=K. |last2=Reinsch |first2=K. |journal=Astronomy and Astrophysics |date=2024 |volume=686 |pages=A304 |doi=10.1051/0004-6361/202244473 |arxiv=2402.13834 }}</ref> }} {{Starbox astrometry | radial_v=−21<ref>{{cite journal |bibcode=1995A&AS..114..269D |title=Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue |last1=Duflot |first1=M. |last2=Figon |first2=P. |last3=Meyssonnier |first3=N. |journal=Astronomy and Astrophysics Supplement Series |date=1995 |volume=114 |page=269 }}</ref> | prop_mo_ra=−119.473<ref name=dr3/> | prop_mo_dec=+30.330<ref name=dr3/> | parallax=17.5716 | p_error=0.0166 | parallax_footnote=<ref name=dr3>{{cite Gaia DR3|6185040879503491584}}</ref> | absmag_v= }} {{Starbox orbit | reference = <ref name=beuermann2024b>{{cite journal |bibcode=2024A&A...687A.273B |title=Current and secular accretion rates of EX Hydrae |last1=Beuermann |first1=K. |last2=Reinsch |first2=K. |journal=Astronomy and Astrophysics |date=2024 |volume=687 |pages=A273 |doi=10.1051/0004-6361/202450486 |arxiv=2412.13850 }}</ref> | period_unitless = 6,894.4 s | axis_unitless = {{solar radius|0.68}} | k1 = {{val|58.9|1.8}} | k2 = {{val|432.4|4.8}} | inclination = {{val|78.0|0.2}} }} {{Starbox detail | component1=White dwarf | mass = {{val|0.788|0.025}}<ref name=beuermann2024b/> | radius = 0.011<ref name=beuermann2024b/> | rotation=67 [[minute]]s | component2=Red dwarf | mass2={{val|0.1074|0.0047}}<ref name=beuermann2024b/> | radius2 = 0.1513<ref name=beuermann2024b/> }} {{Starbox catalog | names=[[1RXS]] J125224.7-291451, 2E 2876, RX J1252.4-2914, [[AAVSO]] 1247-28<ref name="SIMBAD">{{cite simbad|title=V* EX Hya}}</ref> }} {{Starbox reference | Simbad=EX+Hya }} {{Starbox end}}
'''EX Hydrae''' is an [[eclipsing binary star|eclipsing]] [[intermediate polar]] (DQ Herculis) -type [[cataclysmic variable star]] that also undergoes eclipses. The system varies in [[apparent magnitude]] from 9.6 to 14.0.<ref name="AAVSO chart">[http://www.aavso.org/vstar/vsots/ locator chart] at [[AAVSO]]</ref> The system consists of a [[white dwarf]] primary and an [[M-type star|M-type]] secondary, of masses of {{Solar mass|0.4–0.7}} and {{Solar mass|0.07–0.10}} respectively.<ref name="Beuermann">{{cite journal |doi=10.1051/0004-6361:20031498 |bibcode=2003A&A...412..821B |title=A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate |year=2003 |last1=Beuermann |first1=K. |last2=Harrison |first2=Th. E. |last3=McArthur |first3=B. E. |last4=Benedict |first4=G. F. |last5=Gänsicke |first5=B. T. |journal=Astronomy & Astrophysics |volume=412 |issue=3 |pages=821–827 |arxiv=astro-ph/0309530 |s2cid=3167825 |doi-access=free }}</ref> The orbital period is 98.25696 minutes (0.068233846 days).<ref name="AAVSO" /> The system is {{val|65|11|ul=parsecs}} distant, making EX Hya one of the closest cataclysmic variable stars.<ref name="Eisenbart">{{cite journal |doi=10.1051/0004-6361:20011655 |bibcode=2002A&A...382..984E |title=Multi-wavelength spectrophotometry of EX Hydrae |year=2002 |last1=Eisenbart |first1=S. |last2=Beuermann |first2=K. |last3=Reinsch |first3=K. |last4=Gänsicke |first4=B. T. |journal=Astronomy & Astrophysics |volume=382 |issue=3 |pages=984–998 |arxiv=astro-ph/0111459 |s2cid=12934377 |doi-access=free }}</ref> The cataclysmic outbursts appear to be caused by accretion of material from the M-star to the white dwarf.<ref name="AAVSO">{{Cite web |url=http://www.aavso.org/vstar/vsots/exhya.shtml |title=AAVSO |access-date=2009-04-24 |archive-date=2010-06-15 |archive-url=https://web.archive.org/web/20100615094552/http://aavso.org/vstar/vsots/exhya.shtml |url-status=dead }}</ref>
EX Hydrae also possess a 67-minute oscillation, believed to be caused by the spin period of the white dwarf component.<ref name="AAVSO" /> EX Hydrae's outbursts are unpredictable.
==References== <references> <ref name="Warner1981">{{cite journal |last1=Warner |first1=B. |author-link1=Brian Warner (astronomer) |last2=McGraw |first2=J. T. |title=EX Hyd : modulated mass transfer of intermediate polar? |journal=Monthly Notices of the Royal Astronomical Society |date=August 1981 |volume=196 |pages=59P–63P |doi=10.1093/mnras/196.1.59P |doi-access=free |bibcode=1981MNRAS.196P..59W }}</ref>
<ref name="Reinsch1990">{{cite journal |last1=Reinsch |first1=K. |last2=Beuermann |first2=K. |title=Photometric observations of the intermediate polar EX Hydrae in outburst |journal=Astronomy and Astrophysics |date=December 1990 |volume=240 |pages=360–364 |bibcode=1990A&A...240..360R }}</ref> </references>
==External links== * [http://www.aavso.org/vstar/vsots/exhya.shtml AAVSO Variable Star of the Month. EX Hydrae: April 2009] {{Webarchive|url=https://web.archive.org/web/20100615094552/http://aavso.org/vstar/vsots/exhya.shtml |date=2010-06-15 }}
{{Stars of Hydra}}
[[Category:Objects with variable star designations|Hydrae, EX]] [[Category:Hydra (constellation)]] [[Category:White dwarfs]] [[Category:Intermediate polars]]