SIMBAD references

A new technique for analysing phase-resolved spectral lines from the Roche-lobe filling secondary star in cataclysmic variables (CVs) and related 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 both Doppler shifts and line intensity variations through the binary orbit. It may be used to analyse emission lines as well as absorption lines. The intrinsic shape of the spectral line may be taken into account, and the effects of limb darkening, instrumental resolution and phase resolution may be incorporated. The maximum-entropy criterion is used to optimize the fit to the data, yielding the smoothest possible intensity distribution on the star. The technique can be used to constrain the mass ratio and inclination of the binary system, and to study the effects of irradiation, or other surface inhomogeneities. Experiments on computer generated data are presented in conjunction with an analysis of Balmer emission line observations from the secondary star in the nova-like variable DW Ursae Majoris. DW UMa shows strongly enhanced emissivity in the Balmer lines close to the L1 point, suggesting irradiation from the central part of the accretion disk or the bright spot.