Abstract
We have analyzed 96 hours of high-speed photometry the pulsating variable star PG 1159-035, obtained from 1979 through 1984. We find that the pulsation period with the larqest amplitude at 516 s, is changing at a rate dP/dt = (-1.2 ± O.1) x 10^-11 s/s, corresponding to an evolutionary timescale of τ ∼ (1.4 ± 0.1) x 10^6 yrs. This period change is consistent with theoretical descriptionsof a gravitationally contracting pre-white-dwarf object undergoing nonradial g-mode pulsations. The analysis of the light curve is materially complicated by the presence of at least seven additional periodicities, ranging from 350 s to 842 s, and by the inevitable presence of 24 hour aliases for all of them. We describe in detail the methods used to measure dP/dt and to eliminate all possible alternative values for it.
