EX Hydrae
Cataclysmic binary star system in the constellation Hydra
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EX Hydrae is an 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.[9] The system consists of a white dwarf primary and an M-type 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 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]
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 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.