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We report the results of 143.2 hours of time-series photometry over a 12 day period for AM CVn (= HZ 29) as part of the Whole Earth Telescope (WET) project.ˡ This star is believed to be an ultra-short period cataclysmic binary. In the temporal spectrum of the light curve we find a series of 5 harmonically related frequency mo dulations, some with sidebands with a constant frequency spacing of 20.8 μHz always on the high-frequency side. The set of harmonics has a fundamental frequency of 951 μHz. No modulation is detected at this frequency in the light curve. In addition, modulations with frequencies 972.5 and 988.9 μHz are detected with low amplitudes. The structure of the dominant 1903 Hz modulation explains part of the “phase jitter” observed earlier. The amplitude of this peak is modulated with a period of 13.32 ± 0.05 hrs.

This paper presents the results of high speed photometric observations of the cool variable DA white dwarf (DAV) GD 154 obtained with the Whole Earth Telescope. GD 154 is one of the coolest pulsating DA white dwarfs and its study is important for understanding the red edge of the ZZ Ceti instability strip. Its power spectrum is dominated by three independent modes (P₁ = 1186.5s, P₂ = 1088.6s and P₃ = 402.6s), and their harmonics and linear combinations. None of the half-integer harmonics reported in previous observations were present during the WET campaign. We propose that the observed modes are trapped in the thin outer hydrogen layers. From the resulting identification of the pulsation modes, one derives an estimate of the rotation period (2.3 days) and of the mass ofthe outer hydrogen layer (2 x 10ˉ¹° M*).

We report a frequency analysis of the δ Scuti star CD-24°7599 and the discovery that it pulsates nonradially with at least 7 frequencies between 27.01 and 38.11 cycles per day (312 to 441 μHz). These results are based on 116.7 hours of photometric data obtained with the Whole Earth Telescope network. New uvbyβ photometry implies that the star is unevolved and located near the observed hot border of the classical instability strip. We give arguments for interpreting the pulsation periods in terms of low-order low-degree nonradial p-modes. Rotational m-mode splitting is likely. Few radial modes could also be present. The rich modal content and unevolved state of CD-24°7599 emphasize its importance for δ Scuti star asteroseismology. We detect linear combination frequencies of the pulsation modes with the highest photometric amplitudes and suggest they are not normal modes excited by resonance.

We observed G226-29 for 121 hr in 1992 February and confirm the presence of the three previously identified frequencies close to 109 s. We find no evidence of other pulsation periods down to our noise level of about 0.35 millimodulation amplitudes. The presence of only one triplet pulsation mode in G226-29 and its effective temperature near the blue edge of the instability strip identify the observed triplet of modes near 109 s as rotationally split components of the k = 1, l = 1 mode. With the mode identification, we derived a rotation period of 8.9 hr and an inclination of the pulsation axis of 70°-75° to our line of sight.

We report on the analysis of 154 hours of early continuous high-speed photometry on the pulsating DB white dwarf (DBV) GD 358, obtained during the Whole Earth Telescope (WET) run of 1990 May. The power spectrum of the light curve is dominated by power in the range from 1000 to 2400 μHz, with more than 180 significant peaks in the total spectrum. We identify ali of the triplet frequencies as degree l = 1, and from the details of their spacings we derive the total stellar mass as 0.61 ± 0.03 Mʘ , the mass of the outer helium envelope as 2.0 ± 1.0 x 10-6 M*, the absolute luminosity as 0.050 ± 0.012 Lʘ and the distance as 42 ± 3 pc. We find strong evidence for differential rotation in the radial direction−the outer envelope is rotating at least 1.8 times faster than the core−and we detect the presence of a weak magnetic field with a strength of 1300 ± 300 G. We also find a significant power at the sums and differences of the dominant frequencies, indi­ cating nonlinear processes are significant, but they have a richness and complexity that rules out resonant mode coupling as a major cause.