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Astron. Astrophys. 342, 745-755 (1999)


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

R. Silvotti 1, S. Dreizler 2, G. Handler 3 and X.J. Jiang 4

1 Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131 Napoli, Italy
2 Institut für Astronomie und Astrophysik, Waldhäuser Strasse 64, D-72076 Tübingen, Germany
3 Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, A-1180 Wien, Austria
4 Beijing Astronomical Observatory and United Laboratory of Optical Astronomy, CAS, Beijing 100012, P.R. China

Received 6 August 1998 / Accepted 9 November 1998

Abstract

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 950 µHz 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 µHz. 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 µHz 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.

Key words: stars: individual: HS 2324+3944 – stars: oscillations – stars: AGB and post-AGB

* Based on observations obtained at the McDonald, Loiano and Beijing Observatories and at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy.

Send offprint requests to: R. Silvotti (silvotti@na.astro.it)

© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999

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