WHOLE EARTH TELESCOPE OBSERVATIONS OF THE DBV WHITE-DWARF GD-358

We report on the analysis of 154 hours of early continuous high-speed photometry on the pulsating DB white dwarf (DBV) GD 358, obtained duri ng the Whole Earth Telescope (WET) run of 1990 May. The power spectrum of the light curve is dominated by power in the range from 1000 to 24 00 muHz, with more than 180 significant peaks in the total spectrum. W e identify all of the triplet frequencies as degree l = 1, and from th e details of their spacings we derive the total stellar mass as 0.61 /- 0.03 M., the mass of the outer helium envelope as 2.0 +/- 1.0 x 10( -6) M, the absolute luminosity as 0.050 +/- 0.012 L. and the distance as 42 +/- 3 pc. We find strong evidence for differential rotation in the radial direction-the outer envelope is rotating at least 1.8 times faster than the core-and we detect the presence of a weak magnetic fi eld with a strength of 1300 +/- 300 G. We also find a significant powe r at the sums and differences of the dominant frequencies, indicating nonlinear processes are significant, but they have a richness and comp lexity that rules out resonant mode coupling as a major cause.