A measurement of secular evolution in the pre-white dwarf star

Abstract

Green (1977) has identified the star PG 1159-035 as a faint blue object of magnitude 14.5 on the Palomar Green survey, while McGraw et al. (1979) found that the star is a multiperiodic variable. The present paper is concerned with an analysis of PG 1159-035 on the basis of observations of the star extending back to 1979 December. The star was selected for the analysis because it is the brightest known member of its class. Light curves of PG 1159-035 totaling 96 hours in length and spanning 4.4 yr were obtained. Attention is given to the stability of the pulsation periods, the 516 second pulsation period, and the rate of period change for the 516.0 second period. The decreasing period of the star is interpreted as indicating that contraction is more important, in this stage of the star's evolution, than cooling. The resulting increase in density causes the period to decrease, while cooling tends to make it increase.