Investigating the structure of the accretion disc in WZ Sge from multiwaveband time-resolved spectroscopic observations - I

We present the first of two papers describing an in-depth study of multiwav eband phase-resolved spectroscopy of the unusual dwarf nova WZ Sge. In this paper we present an extensive set of Doppler maps of WZ Sge covering optic al and infrared emission lines, and describe a new technique for studying t he accretion discs of cataclysmic variables using ratioed Doppler maps. App lying the ratioed Doppler map technique to our WZ Sge data shows that the r adial temperature profile of the disc is unlike that predicted for a steady state a disc, Time-averaged spectra of the accretion disc line flux (with the bright spot contribution removed) show evidence in the shapes of the li ne profiles for the presence of shear broadening in a quiescent non-turbule nt accretion disc. From the positions of the bright spots in the Doppler ma ps of different lines, we conclude that the bright spot region is elongated along the ballistic stream, and that the density of the outer disc is low, The velocity of the outer edge of the accretion disc measured from the H a lpha line is found to be 723 +/- 23 km s(-1). Assuming that the accretion d isc reaches to the 3:1 tidal resonance radius, we derive a value for the pr imary star mass of 0.82 M-.. We discuss the implications of our results on the present theories of WZ Sge type dwarf nova outbursts.