High-speed spectroscopy and photometry of the interacting binary white dwarf V803 Cen (AE-1)

High-speed spectroscopy and photometry are presented for the interacting binary white dwarf candidate V803 Cen. The low-state spectrum shows a blue, almost featureless continuum; some weak emission lines may be present. The mean high-state spectrum contains no hydrogen lines and, with the exception of some weak lines possibly due to O II or N II, is dominated by He I lines. The lines are slightly and variably asymmetric, and exhibit peculiar relative strengths. The depths and widths of these lines are shallower and narrower than in the DB white dwarfs but deeper and narrower than in AM CVn and PG 1346 + 082. The widths do not appear to be consistent with rotational Doppler broadening, but are qualitatively explained by Stark broadening in an environment in which log g ∼ 6; the strength of some of the gravity-sensitive lines supports this view. It is argued that this suggests that the lines are formed in an accretion disc of low inclination; a similar suggestion is made for the spectral features of AM CVn and PG 1346 + 082, except that their inclination must be higher to explain their relatively broader lines by rotational Doppler broadening. A search for rapid variability in radial velocity or line profile shape using three different techniques, failed to detect any periodic variability with a limit on K₁ of 16 km s⁻¹ in the 0.1–2.5-mHz frequency interval which, together with a similarly low limit for AM CVn, demonstrates that the secondary is of very low mass ($$\sim0.02\enspace M_\odot$$). The asymmetry in the line profiles appears to vary on a time-scale of several hours or longer. It is argued that the asymmetry is not due to filling-in of the absorption lines by an ‘s-wave’, but rather indicates the presence of a non-circular, perhaps elliptical, outer edge to the accretion disc. Similar evidence for the same phenomenon in the hydrogen-rich cataclysmic variables is discussed. The high-speed photometry shows up to seven harmonics of the fundamental 1611-s oscillation. Its mean pulse shape can vary significantly within a few hours and, during four consecutive days, was very similar to the pulse shapes found during four consecutive days in the previous year, suggesting that the pulse shape evolution is periodic. Although both the 1611- and 175-s oscillations can be phased over a week with a single, unique period, phase jitter of up to 0.2 cycles is present from one day to the next. A possible model for the 1611-s oscillation involving tidal interactions between the secondary and the outer edge of the accretion disc is discussed, and theoretical work in this direction is urged.