PHASE-RESOLVED HUBBLE-SPACE-TELESCOPE ULTRAVIOLET SPECTROSCOPY OF V795 HER

We present highly time-resolved HST FOS UV spectroscopy of the nova-li ke binary V795 Her. Several key results emerge. For the first time we find a strong 2.6-h signature in the variability of the UV lines. The HST data reveal no evidence of a 4.8-h 'period', in contrast to our pr evious IUE observations. This, and differences in the spectral line ch aracteristics, suggests that HST found the system in a different state from earlier IUE observations. The CIV line alone contains a fairly s table, asymmetric, extended blueward absorption trough which we associ ate with a wind outflow. The 2.6-h variations of the line profiles are largely confined to an interval of about 0.4 in phase and to the velo city regime - 1500 < v < 0 km s(-1), the changes being dominated by th e apparent decline and re-emergence of a blueshifted emission peak. Th e complex profiles permit many empirical interpretations, but the simp lest attributes the variability to a narrow (FWHM similar to 1000km s( -1)) emission component which is always blueshifted with a mean veloci ty of around -600 km s(-1) This interpretation, however, is not readil y related to any obvious source within the binary. An alternative pict ure, which attempts to relate the UV and (simultaneously observed) opt ical line behaviour, invokes a more stable, broad (FWHM similar to 200 0 km s(-1)) emission feature, the intrinsic morphology of which is dis guised by superposed constant and variable absorption components. One tentative physical explanation of such a decomposition involves an acc retion stream that overflows the accretion disc. However, several prob lems with this model remain to be resolved. We also draw attention to similarities between the velocity-restricted behaviour in the UV lines of V795 Her and that in the optical lines of T Tauri stars. This migh t indicate a connection between V795 Her and the magnetically influenc ed inflow/outflow characteristics associated with the central star in T Tauri systems. If such a connection were eventually demonstrated, it would reopen the question of whether the 2.6-h period in V795 Her is really the binary period and whether the system is in fact related to the intermediate polars.