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We present a comprehensive study of Far Ultraviolet Spectroscopic Explorer(FUSE) spectra (912-1190 A) of two members of the PG1159 spectral class, whichconsists of hydrogen-deficient (pre-) white dwarfs with effective temperaturesin the range Teff = 75,000-200,000 K. As two representatives of the coolerobjects, we have selected PG1707+427 (Teff = 85,000 K) and PG1424+535 (Teff =110,000 K), complementing a previous study of the hotter prototype PG1159-035(Teff = 140,000 K). The helium-dominated atmospheres are strongly enriched incarbon and oxygen, therefore, their spectra are dominated by lines from CIII-IV and O III-VI, many of which were never observed before in hot stars. Inaddition, lines of many other metals (N, F, Ne, Si, P, S, Ar, Fe) aredetectable, demonstrating that observations in this spectral region are mostrewarding when compared to the near-ultraviolet and optical wavelength bands.We perform abundance analyses of these species and derive upper limits forseveral undetected light and heavy metals including iron-group and trans-ironelements. The results are compared to predictions of stellar evolution modelsfor neutron-capture nucleosynthesis and good agreement is found.

The far-ultraviolet spectra of "cool" PG1159 stars