# EX Hydrae

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Cataclysmic binary star system in the constellation Hydra

EX Hydrae 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 Warner and McGraw (1981)[1] and Reinsch and Beuermann (1990).[2] Observation data Epoch J2000 Equinox J2000 Constellation Hydra Right ascension 12h 52m 24.22s[3] Declination −29° 14′ 56.0″[3] Apparent magnitude (V) 9.6 to 14.0[4] Characteristics Spectral type white dwarf + M4/M5: Variable type eclipsing intermediate polar[5] Astrometry Radial velocity (Rv) −21[6] km/s Proper motion (μ) RA: −119.473[3] mas/yr Dec.: +30.330[3] mas/yr Parallax (π) 17.5716±0.0166 mas[3] Distance 185.6 ± 0.2 ly (56.91 ± 0.05 pc) Orbit[7] Period (P) 6,894.4 s Semi-major axis (a) 0.68 R☉ Inclination (i) 78.0±0.2° Semi-amplitude (K1) (primary) 58.9±1.8 km/s Semi-amplitude (K2) (secondary) 432.4±4.8 km/s Details White dwarf Mass 0.788±0.025[7] M☉ Radius 0.011[7] R☉ Rotation 67 minutes Red dwarf Mass 0.1074±0.0047[7] M☉ Radius 0.1513[7] R☉ Other designations 1RXS J125224.7-291451, 2E 2876, RX J1252.4-2914, AAVSO 1247-28[8] Database references SIMBAD data

**EX Hydrae** is an [eclipsing](/source/Eclipsing_binary_star) [intermediate polar](/source/Intermediate_polar) (DQ Herculis) -type [cataclysmic variable star](/source/Cataclysmic_variable_star) that also undergoes eclipses. The system varies in [apparent magnitude](/source/Apparent_magnitude) from 9.6 to 14.0.[9] The system consists of a [white dwarf](/source/White_dwarf) primary and an [M-type](/source/M-type_star) secondary, of masses of 0.4–0.7 M☉ and 0.07–0.10 M☉ respectively.[10] The orbital period is 98.25696 minutes (0.068233846 days).[11] The system is 65±11 [parsecs](/source/Parsecs) distant, making EX Hya one of the closest cataclysmic variable stars.[12] The cataclysmic outbursts appear to be caused by accretion of material from the M-star to the white dwarf.[11]

EX Hydrae also possess a 67-minute oscillation, believed to be caused by the spin period of the white dwarf component.[11] EX Hydrae's outbursts are unpredictable.

## References

1. **[^](#cite_ref-Warner1981_1-0)** [Warner, B.](/source/Brian_Warner_(astronomer)); McGraw, J. T. (August 1981). ["EX Hyd : modulated mass transfer of intermediate polar?"](https://doi.org/10.1093%2Fmnras%2F196.1.59P). *Monthly Notices of the Royal Astronomical Society*. **196**: 59P–63P. [Bibcode](/source/Bibcode_(identifier)):[1981MNRAS.196P..59W](https://ui.adsabs.harvard.edu/abs/1981MNRAS.196P..59W). [doi](/source/Doi_(identifier)):[10.1093/mnras/196.1.59P](https://doi.org/10.1093%2Fmnras%2F196.1.59P).

1. **[^](#cite_ref-Reinsch1990_2-0)** Reinsch, K.; Beuermann, K. (December 1990). "Photometric observations of the intermediate polar EX Hydrae in outburst". *Astronomy and Astrophysics*. **240**: 360–364. [Bibcode](/source/Bibcode_(identifier)):[1990A&A...240..360R](https://ui.adsabs.harvard.edu/abs/1990A&A...240..360R).

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) 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%3D6185040879503491584%26-go+%25%23Sesame%23%25%26) at [VizieR](/source/VizieR).

1. **[^](#cite_ref-gcvs_4-0)** Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". *Astronomy Reports*. **61** (1): 80. [Bibcode](/source/Bibcode_(identifier)):[2017ARep...61...80S](https://ui.adsabs.harvard.edu/abs/2017ARep...61...80S). [doi](/source/Doi_(identifier)):[10.1134/S1063772917010085](https://doi.org/10.1134%2FS1063772917010085).

1. **[^](#cite_ref-beuermann2024a_5-0)** Beuermann, K.; Reinsch, K. (2024). "High-resolution spectroscopy of the intermediate polar EX Hydrae. II. The inner disk radius". *Astronomy and Astrophysics*. **686**: A304. [arXiv](/source/ArXiv_(identifier)):[2402.13834](https://arxiv.org/abs/2402.13834). [Bibcode](/source/Bibcode_(identifier)):[2024A&A...686A.304B](https://ui.adsabs.harvard.edu/abs/2024A&A...686A.304B). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202244473](https://doi.org/10.1051%2F0004-6361%2F202244473).

1. **[^](#cite_ref-6)** Duflot, M.; Figon, P.; Meyssonnier, N. (1995). "Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue". *Astronomy and Astrophysics Supplement Series*. **114**: 269. [Bibcode](/source/Bibcode_(identifier)):[1995A&AS..114..269D](https://ui.adsabs.harvard.edu/abs/1995A&AS..114..269D).

1. ^ [***a***](#cite_ref-beuermann2024b_7-0) [***b***](#cite_ref-beuermann2024b_7-1) [***c***](#cite_ref-beuermann2024b_7-2) [***d***](#cite_ref-beuermann2024b_7-3) [***e***](#cite_ref-beuermann2024b_7-4) Beuermann, K.; Reinsch, K. (2024). "Current and secular accretion rates of EX Hydrae". *Astronomy and Astrophysics*. **687**: A273. [arXiv](/source/ArXiv_(identifier)):[2412.13850](https://arxiv.org/abs/2412.13850). [Bibcode](/source/Bibcode_(identifier)):[2024A&A...687A.273B](https://ui.adsabs.harvard.edu/abs/2024A&A...687A.273B). [doi](/source/Doi_(identifier)):[10.1051/0004-6361/202450486](https://doi.org/10.1051%2F0004-6361%2F202450486).

1. **[^](#cite_ref-SIMBAD_8-0)** ["V* EX Hya"](http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=V%2A+EX+Hya). *[SIMBAD](/source/SIMBAD)*. [Centre de données astronomiques de Strasbourg](/source/Centre_de_donn%C3%A9es_astronomiques_de_Strasbourg).

1. **[^](#cite_ref-AAVSO_chart_9-0)** [locator chart](http://www.aavso.org/vstar/vsots/) at [AAVSO](/source/AAVSO)

1. **[^](#cite_ref-Beuermann_10-0)** Beuermann, K.; Harrison, Th. E.; McArthur, B. E.; Benedict, G. F.; Gänsicke, B. T. (2003). ["A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate"](https://doi.org/10.1051%2F0004-6361%3A20031498). *Astronomy & Astrophysics*. **412** (3): 821–827. [arXiv](/source/ArXiv_(identifier)):[astro-ph/0309530](https://arxiv.org/abs/astro-ph/0309530). [Bibcode](/source/Bibcode_(identifier)):[2003A&A...412..821B](https://ui.adsabs.harvard.edu/abs/2003A&A...412..821B). [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20031498](https://doi.org/10.1051%2F0004-6361%3A20031498). [S2CID](/source/S2CID_(identifier)) [3167825](https://api.semanticscholar.org/CorpusID:3167825).

1. ^ [***a***](#cite_ref-AAVSO_11-0) [***b***](#cite_ref-AAVSO_11-1) [***c***](#cite_ref-AAVSO_11-2) ["AAVSO"](https://web.archive.org/web/20100615094552/http://aavso.org/vstar/vsots/exhya.shtml). Archived from [the original](http://www.aavso.org/vstar/vsots/exhya.shtml) on 2010-06-15. Retrieved 2009-04-24.

1. **[^](#cite_ref-Eisenbart_12-0)** Eisenbart, S.; Beuermann, K.; Reinsch, K.; Gänsicke, B. T. (2002). ["Multi-wavelength spectrophotometry of EX Hydrae"](https://doi.org/10.1051%2F0004-6361%3A20011655). *Astronomy & Astrophysics*. **382** (3): 984–998. [arXiv](/source/ArXiv_(identifier)):[astro-ph/0111459](https://arxiv.org/abs/astro-ph/0111459). [Bibcode](/source/Bibcode_(identifier)):[2002A&A...382..984E](https://ui.adsabs.harvard.edu/abs/2002A&A...382..984E). [doi](/source/Doi_(identifier)):[10.1051/0004-6361:20011655](https://doi.org/10.1051%2F0004-6361%3A20011655). [S2CID](/source/S2CID_(identifier)) [12934377](https://api.semanticscholar.org/CorpusID:12934377).

## External links

- [AAVSO Variable Star of the Month. EX Hydrae: April 2009](http://www.aavso.org/vstar/vsots/exhya.shtml) [Archived](https://web.archive.org/web/20100615094552/http://aavso.org/vstar/vsots/exhya.shtml) 2010-06-15 at the [Wayback Machine](/source/Wayback_Machine)

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 [EX Hydrae](https://en.wikipedia.org/wiki/EX_Hydrae) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/EX_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.