Outbursts of EX Hydrae Revisited

Abstract

We present optical spectroscopy of EX Hya during its 1991 outburst. This outburst is characterised by strong irradiation of the front face of the secondary star by the white dwarf, an overflowing stream which is seen strongly in HeII and by a dip in the light curves, which extends from 0.1-0.6 in the binary and spin phases. Strong irradiation of the accretion curtain and that of the inner regions of the disc led to strong emission of HeII and to the suppression of the Hg and Hb emission. Disc overflow was observed in quiescence in earlier studies, where the overflow stream material was modulated at high velocities close to 1000 km/s. In outburst, the overflowing material is modulated at even higher velocities (~1500 km/s). These are streaming velocities down the field lines close to the white dwarf. Evidence for material collecting near the outer edge of the disc and corotating with the accretion curtain was observed. In decline, this material and the accretion curtain obscured almost all the emission near binary phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse minimum. This has provided additional evidence for an extended accretion curtain, and for the corotation of material with the accretion curtain at the outer edge of the disc. From these observations we suggest that a mechanism similar to that of Spruit & Taam, where outbursts result due to the storage and release of matter outside the magnetosphere, triggers the outbursts of EX Hya. This is followed by the irradiation of the secondary star due to accretion induced radiation.

12 pages, 14 figures, 1 table. Figures 6, 7, 8 and 11 at low resolution. Paper accepted by the Monthly Notices of the Royal Astronomical Society

References in corpus (13)

• The spin periods and magnetic moments of white dwarfs in magnetic cataclysmic variables
• The Spin Period of EX Hydrae
• A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate
• An outburst of the magnetic cataclysmic variable XY Arietis observed with RXTE
• Outbursts of EX Hydrae: mass-transfer events or disc instabilities?
• HST/STIS Spectroscopy of the Intermediate Polar EX Hydrae
• A spectroscopic search for faint secondaries in cataclysmic variables
• Multi-wavelength spectrophotometry of EX Hydrae
• ORFEUS II and IUE Spectroscopy of EX Hydrae
• Spectroscopic Observations of the Intermediate Polar EX Hydrae in Quiescence
• Mapping quasi-periodic oscillations from the outbursting intermediate polar GK Persei
• An EUV Study of the Intermediate Polar EX Hydrae
• X-ray Light Curves and Accretion Disk Structure of EX Hydrae

Cited by in corpus (5)

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• Discovery of spin modulated circular polarization from IGR J17014-4306, the remnant of Nova Scorpii 1437 A.D
• Rapid bursts of magnetically gated accretion in the intermediate polar V1025 Cen
• Magnetically-gated accretion model: application to short bursts in the intermediate polar V1223 Sgr
• Variability of the Spin Period of the White Dwarf in the Magnetic Cataclysmic Binary System EX Hya