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PG 1159-035, a pre-white dwarf with T=140000 K, is the prototype of thePG1159 spectroscopic class and the DOV pulsating class. Changes in the starcause variations in its oscillation periods. The measurement of temporal changein the oscillation periods, dP/dt, allows us to estimate directly rates ofstellar evolutionary changes, such as the cooling rate and the envelopecontraction rate, providing a way to test and refine evolutionary models forpre-white dwarf pulsating stars.  We measured 27 pulsation modes period changes. The periods varied at rates ofbetween 1 and 100 ms/yr, and several can be directly measured with a relativestandard uncertainty below 10%. For the 516.0 s mode (the highest in amplitude)in particular, not only the value of dP/dt can be measured directly with arelative standard uncertainty of 2%, but the second order period change,d(dP/dt)/dt, can also be calculated reliably. By using the (O-C) method werefined the dP/dt and estimated the d(dP/dt)/dt for six other pulsationperiods. As a first application, we calculated the change in the PG 1559-035rotation period, dP_rot/dt = -2.13*10^{-6} s/s, the envelope contraction ratedR/dt = -2.2*10^{-13} solar radius/s, and the cooling rante dT/dt =-1.42*10^{-3} K/s.

The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035