MULTICOLOR OBSERVATIONS OF RAPID OSCILLATIONS IN WZ SAGITTAE

We present an analysis of high-speed multicolour photometry of the dwa rf nova WZ Sagittae (WZ Sge). We have updated the orbital ephemeris an d found that P lies within the limits - 4.53 x 10(-13) s s(-1) and 1.5 3 x 10(-13) s s(-1) (3 sigma limits). We have detected rapid coherent oscillations at three different epochs with periods of 28.95, 29.33 an d 28.13 s, respectively. The detection of the oscillation with period 29.33 s is marginal. The amplitude and phase of the oscillations have been found to vary over time-scales of a few tens of minutes. The colo urs of the oscillations can be represented by a power-law spectrum (f, proportional to nu(alpha)) with alpha similar or equal to 1.8, a blac kbody spectrum of temperature T similar or equal to 120 000 K or a hyd rogen white dwarf spectrum with log g = 8 and T similar or equal to 10 0 000 K. The colours of the oscillation amplitudes are not consistent with those expected from a ZZ Ceti type white dwarf (with a temperatur e of 15 000 K). We conclude that the oscillations in WZ Sge do not ari se from direct viewing of the surface of a pulsating white dwarf.