High-speed photometric observations have been obtained for 15 stars sharing some of the properties of the class of hot, hydrogen-deficient pulsators represented by PG 1159-035 and the nucleus of the planetary nebula K1-16. With the exception of PG 0122+200, the stars showed no evidence of periodic variability on time scales of 60 s up to as long as 1 - 2 hr; typical amplitude limits are a few millimagnitudes. Also presented are UBV photometry and optical spectroscopy for several of the stars. The authors discuss what is known about the temperatures, gravities, luminosities, and compositions of the program stars and assess what has been learned about the location of the instability strip in the HR diagram.
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Grauer et al. (1987) studied this question.