Abstract
We present phase-resolved infrared and optical spectrophotometry of the intermediate polar EX Hya supplemented by archival ultraviolet data. The spin-modulated emission from the accretion funnel and the emission from the accretion disk or ring contain substantial optically thin components. The white dwarf dominates the unmodulated flux in the ultraviolet and is identied by numerous absorption lines. Metal absorption in the accretion curtain may add to the observed spectral features. The secondary star is of spectral type M4 1 and is detected by its ellipsoidal modulation. We derive a distance of 65 11 pc which makes EX Hydrae one of the closest cataclysmic variables with a known distance. The luminosity derived from the integrated overall spectral energy distribution is 3 10 32 erg s 1 . The accretion rate of 3 10 15 gs 1 (for an 0.6M white dwarf) is in reasonable agreement with the rates expected from angular momentum loss by gravitational radiation and from the observed spin-up of the white dwarf.
Highlights
EX Hya was discovered by Kraft (1962) and quickly recognised as an eclipsing system with an orbital period Porb = 98 min
We present phase-resolved infrared and optical spectrophotometry of the intermediate polar EX Hya supplemented by archival ultraviolet data
We have identified the secondary star in the infrared and use its K-band flux to determine the distance to EX Hya, a key parameter for the discussion of its luminosity and accretion rate
Summary
Combining our data with archival IUE and HST spectrophotometry, we determine the contributions to the overall flux distribution from the rotating funnel, the accretion disk or ring, and the white dwarf. The shortwavelength ultraviolet spectrum contains metal absorption lines which are a clear signature of the white dwarf and/or absorption in the accretion funnel which surrounds the white dwarf. Based on these findings, we discuss the overall energy balance and present an internally consistent description of EX Hya as an intermediate polar
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