ROCHE TOMOGRAPHY - IMAGING THE STARS IN INTERACTING BINARIES

A new technique for analysing phase-resolved spectral lines from the R oche-lobe filling secondary star in cataclysmic variables (CVs) and re lated objects is presented. This technique, Roche tomography, enables mapping of the line intensity distribution on the surface of the Roche -lobe filling star by employing the shape of the Roche lobe to model b oth Doppler shifts and line intensity variations through the binary or bit. It may be used to analyse emission lines as well as absorption li nes. The intrinsic shape of the spectral line may be taken into accoun t, and the effects of limb darkening, instrumental resolution and phas e resolution may be incorporated. The maximum-entropy criterion is use d to optimize the fit to the data, yielding the smoothest possible int ensity distribution on the star. The technique can be used to constrai n the mass ratio and inclination of the binary system, and to study th e effects of irradiation, or other surface inhomogeneities. Experiment s on computer generated data are presented in conjunction with an anal ysis of Balmer emission line observations from the secondary star in t he nova-like variable DW Ursae Majoris. DW UMa shows strongly enhanced emissivity in the Balmer lines close to the L1 point, suggesting irra diation from the central part of the accretion disk or the bright spot .