  The main goal of this project is to search for p-mode oscillations in a
selected sample of DA white dwarfs near the blue edge of the DAV (g-mode)
instability strip, where the p-modes should be excited following theoretical
models. A set of high quality time-series data on nine targets has been
obtained in 3 photometric bands (Sloan u', g', r') using ULTRACAM at the VLT
with a typical time resolution of a few tens of ms. Such high resolution is
required because theory predicts very short periods, of the order of a second,
for the p-modes in white dwarfs. The data have been analyzed using Fourier
transform and correlation analysis methods. Results: P-modes have not been
detected in any of our targets. The upper limits obtained for the pulsation
amplitude, typically less than 0.1%, are the smallest limits reported in the
literature. The Nyquist frequencies are large enough to fully cover the
frequency range of interest for the p-modes. For the brightest target of our
sample, G 185-32, a p-mode oscillation with a relative amplitude of 5x10**(-4)
would have been easily detected, as shown by a simple simulation. For G 185-32
we note an excess of power below ~2 Hz in all the three nights of observation,
which might be due in principle to tens of low-amplitude close modes. However,
neither correlation analysis nor Fourier transform of the amplitude spectrum
show significant results. We also checked the possibility that the p-modes have
a very short lifetime, shorter than the observing runs, by dividing each run in
several subsets and analyzing these subsets independently. The amplitude
spectra show only a few peaks with S/N ratio higher than 4 sigma but the same
peaks are not detected in different subsets, as we would expect, and we do not
see any indication of frequency spacing. As a secondary result of this project,
... (see the paper)
