  We present high quality optical spectroscopy of the SU UMa-subtype dwarf
nova, VW Hyi taken while the system was in quiescence. An S-wave is executed by
the emission cores of the Hydrogen Balmer lines and by the emission lines of He
I, Ca II, Fe II and He II. Using Doppler tomography we show it originates in
the accretion stream-disc impact region. The He II emission is strongly
phase-dependent, suggesting it originates exclusively within a hot cavity at
the initial impact. We map the ionization structure of the stream-disc
interaction region. One possible interpretation of this is that the Balmer
hotspot lies downstream of the He II hotspot in the outer accretion disc, with
the He I and Ca II hotspots at intermediate locations between the two. This
suggests that Balmer emission is suppressed until material has cooled somewhat
downstream of the impact site and is able to recombine. We favour a phase
offset of 0.15+/-0.04 between the photometric ephemeris and inferior
conjunction of the mass donor. The white dwarf contributes significantly to the
optical continuum, with broad Balmer absorption and narrow Mg II 4481
absorption clearly apparent. This latter feature yields the gravitational
redshift: v_grav=38+/-21 km s^-1, so M_1=0.71+0.18-0.26 M_sun. This implies
M_2=0.11 +/- 0.03 M_sun and hence the donor is not a brown dwarf. A prominent
Balmer jump is also observed. We note that the previously accepted system
parameters for both VW Hyi and WX Hyi incoporate an algebraic error, and we
provide a recalculated M_1(q) plane for WX Hyi.

Astrophysics