STREAM-FED AND DISC-FED ACCRETION IN TX COLUMBAE

We report on two recent X-ray observations of the intermediate polar T X Col made with ASCA and ROSAT, From a consideration of the power spec tra of their light curves, we show that the system was accreting predo minantly via a disc in 1994 October, but had reverted to a discover fl ow mode of accretion by 1995 October, at which time a substantial amou nt of the accretion was directly via a stream. We discuss possible rea sons for this change, By considering the relative phases of the spin a nd beat pulsations seen in the ROSAT data, as well as their orbital ha rmonics, we demonstrate that the stream-fed accretion regions on the w hite dwarf surface remain fixed at about orbital phase 0.7, and thus m igrate around the white dwarf, We suggest that the observed orbital mo dulation results from a combination of two effects: first, attenuation of emission sites by material located at the stream-disc boundary at orbital phase 0.8, and, secondly, the changing visibility of the strea m-fed accretion sites which are always on the side of the white dwarf facing the stream.