The photometric behaviour of the peculiar PG1159 star HS2324+3944 at high frequency resolution

Abstract

We present the results from 135 hours of nearly continuous time series photometry on the ``hybrid'' (H-rich) PG1159 variable star HS2324+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 950 microHz in decreasing amplitude order. Most (if not all) of the peaks in the latter region are linear combinations of the high-amplitude frequencies between 455 and 500 microHz. If we divide the data set into two equal parts, the power spectra are different. This is probably 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 500 microHz suggests the presence of both l=1 and l=2 high-overtone nonradial g-modes. The insufficient frequency 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 successive overtones, the period spacings would be equal to 18.8 (l=1) and 10.4 (l=2) s.