Doppler tomography and photometry of the cataclysmic variable 1RXS J064434.5+334451

We have obtained simultaneous photometric and spectroscopic observations of the cataclysmic variable 1RXS J064434.5+334451. We have calibrated the spectra for slit losses using simultaneous photometry, allowing us to construct reliable Doppler images from H? and He?ii 4686-A emission lines. We have improved the ephemeris of the object based on new photometric eclipse timings, obtaining HJD = 245?3403.759?533 + 0.269?374?46E. Some eclipses present a clear internal structure, which we attribute to a central He?ii emission region surrounding the white dwarf, a finding supported by Doppler tomography. This indicates that the system has a large inclination angle i = 78 ± 2°. We have also analysed the radial velocity curve from the emission lines to measure its semi-amplitude, K1, from H? and He?ii 4686 and derive the masses of the components M1 = 0.82 ± 0.06 M?, M2 = 0.78 ± 0.04 M? and their separation a = 2.01 ± 0.06 R?. The Doppler tomography and other observed features in this nova-like system strongly suggest that this is a SW Sex type system.