1999MNRAS.305..437H

We observed the intermediate polar RX J0558+53 with the 4.2-m William Herschel Telescope (WHT) and find a `corkscrew' pattern in the pulsed emission lines, which indicates a two-pole white dwarf accretion. The `corkscrew' pattern consists of two emission-line pulses, separated by half the white dwarf spin period, and moving from red to blue velocities. The detected emission-line pulsations have an amplitude of 1.1–2.7 per cent in the He II and Balmer emission lines at the 545-s spin period of the white dwarf compared with 3.5–4.8 per cent for the continuum double-peak pulsations. We image the emission-line pulse pattern and it is shown to lag the continuum pulse by 0.12 spin cycles. We interpret the pattern by invoking an accretion curtain from the disrupted, inner disc to the two poles of the magnetic white dwarf. The semi-amplitude of the He II pulse of 408±35 km.s^–1 can be used to constrain the size of the magnetosphere, R ∼ 4.1x10⁴ km, and the magnetic moment of the white dwarf (∼ 2.4x10³² G cm³). Power spectra show dominant frequencies at 2 ο and 2(ο - Ο) which suggest reprocessing of the illuminating beams of the white dwarf in the accretion disc. Finally, the steady He II emission line shows a strong sinusoidal component moving from red to blue at binary phase 0.5, with a width similar to that expected from irradiation of the secondary star. Imaging of the emission lines indicates illuminated locations at the inner side of the red star and the back side of the accretion disc.