Iron Kα linewidths in magnetic cataclysmic variables

Following a recent report that AO Pse has broad iron Ka! emission lines we have looked at the ASCA spectra of 15 magnetic cataclysmic variables. We find that half of the systems have Ka! lines broadened by similar to 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.