WHOLE EARTH TELESCOPE OBSERVATIONS AND SEISMOLOGICAL ANALYSIS OF THE PRE-WHITE DWARF PG-2131+066

As transition objects between the asymptotic giant branch (AGE) and co oling white dwarfs, the PG 1159 stars are key objects for understandin g the late stages of stellar evolution. The pulsations exhibited by ma ny members of the PG 1159 spectral class provide a mechanism for ferre ting out this information, We present an analysis of the pulsation spe ctrum of the naked PG 1159 star PG 2131+066, which we completely resol ve using data from the Whole Earth Telescope (WET). The pulsation spec trum shows patterns that are expected from pulsation theory; compariso n of these patterns with theoretical models indicate that PG 2131 has a mass of 0.61 +/- 0.02 M., a luminosity of log (L/L.) = 1.0 +/- 0.2, and it lies at a distance of 470(-130)(+180) pc. It rotates with a per iod of 5.1 hr and shows evidence of a discontinuity in composition app roximately 6 x 10(-31)M below the surface. Certain modes show complex structure in the power spectrum, while others show measurable frequen cy changes in 8 years. Fine structure in the prograde (m = -1) modes s uggests the presence of nonlinear effects.