High-resolution spectroscopy of the intermediate polar EX Hydrae: II. The inner disk radius

EX Hya is one of the best studied, but still enigmatic intermediate polars. We present phase-resolved blue VLT/UVES high-resolution (/ 16. 000) spectra of EX Hya taken in January 2004. Our analysis involves a unique decomposition of the Balmer line profiles into the spin-modulated line wings that represent streaming motions in the magnetosphere and the orbital-phase modulated line core that represents the accretion disk. Spectral analysis and tomography show that the division line between the two is solidly located at ₑ₀₃1200 km s^-1, defining the inner edge of the accretion disk at r₈₍7 10^9 cm or 10 R₁ (WD radii). This large central hole allows an unimpeded view of the tall accretion curtain at the lower pole with a shock height up to hₒ₇1 R₁ that is required by X-ray and optical observations. Our results contradict models that advocate a small magnetosphere and a small inner disk hole. Equating r₈₍ with the magnetospheric radius in the orbital plane allows us to derive a magnetic moment of the WD of ₁1. 3 10^32 G cm^3 and a surface field strength B₁0. 35 MG. Given a polar field strength B₏ 1. 0 MG, optical circular polarization is not expected. With an accretion rate M = 3. 910^-11 M_yr^-1, the accretion torque is G₀₂₂ 2. 2 10^33 g cm^2s^-2. The magnetostatic torque is of similar magnitude, suggesting that EX Hya is not far from being synchronized. We measured the orbital radial-velocity amplitude of the WD, K₁=58. 73. 9 km s^-1, and found a spin-dependent velocity modulation as well. The former is in perfect agreement with the mean velocity amplitude obtained by other researchers, confirming the published component masses M₁0. 79 M_ and M₂0. 11 M_.