The photometric behaviour of the peculiar PG 1159 star HS 2324+3944 at high frequency resolution

We present the results from 135 hours of nearly continuous time series photometry on the "hybrid" (H-rich) PG 1159 variable star HS 2324+3944, obtained in August- September 1997. The power spectrum of the data shows several frequencies (about 20 or more), concentrated in three narrow and very crowded regions near 475, 390 and 950Hz in de- creasing amplitude order. Most (if not all) of the peaks in the latter region are linear combinations of the high-amplitude fre- quencies between 455 and 500Hz. If we divide the data set into two equal parts, the power spectra are different. This is proba- bly due to a not sufficiently long (and therefore not completely resolved) light curve; nevertheless an alternative hypothesis of a single damped oscillator may not be completely ruled out. If we adopt the first hypothesis, the high concentration of peaks between 455 and 500Hz suggests the presence of both l=1 and l=2 high-overtone nonradial g-modes. The insufficient fre- quency resolution of our data does not allow to obtain definite precision asteroseismology results. Nevertheless a spacing of the signals is observed, probably due to stellar rotation with a period of 2.3 days. If the signal spacing was due to the succes- sive overtones, the period spacings would be equal to 18.8 (l=1) and 10.4 (l=2) s.