  Following a recent report that AO Psc has broad iron Kalpha emission lines we
have looked at the ASCA spectra of 15 magnetic cataclysmic variables. We find
that half of the systems have Kalpha lines broadened by ~200 eV, while the
remainder have narrow lines. We argue that the Doppler effect is insufficient
to explain the finding and propose that the lines originate in accretion
columns on the verge of optical thickness, where Compton scattering of
resonantly-trapped line photons broadens the profile. We suggest that the
broadening is a valuable diagnostic of conditions in the accretion column.
