The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and compositions, critical to understanding post main sequence evolution, along with their cooling rates, allowing us to calibrate their ages directly. The most important set of white dwarf variables to measure are the oldest of the pulsators, the cool DAVs, which have not previously been explored through asteroseismology due to their complexity and instability. Through a time-series photometry data set spanning ten years, we explore the pulsation spectrum of the cool DAV, G29-38 and find an underlying structure of 19 (not including multiplet components) normal-mode, probably ℓ = 1 pulsations amidst an abundance of time variability and linear combination modes. Modelling results are incomplete, but we suggest possible starting directions and discuss probable values for the stellar mass and hydrogen layer size. For the first time, we have made sense out of the complicated power spectra of a large-amplitude DA pulsator. We have shown its seemingly erratic set of observed frequencies can be understood in terms of a recurring set of normal-mode pulsations and their linear combinations. With this result, we have opened the interior secrets of the DAVs to future asteroseismological modelling, thereby joining the rest of the known white dwarf pulsators.

Abstract. We report the discovery of an eclipsing binary -HS 0705+6700 -being an sdB star with a faint companion. From its light curve the orbital period of 8263.87 s, the mass ratio of the system q = 0.28, the inclination of 84.• 4 and other system parameters are derived. The companion does not contribute to the optical light of the system except through a strong reflection effect. The semi-amplitude of the radial velocity curve K1 = 85.8 km s −1 and a mass function of f (m) = 0.00626 M are determined. A spectroscopic analysis of the blue spectra results in T eff = 28 800 K, log g = 5.40, and log(nHe/nH) = −2.68. These characteristics are typical for sdB stars, as is its mass of 0.48 M . According to its mass (0.13 M ) and radius (0.19 R ), the companion is an M dwarf. The primary is in a core helium burning phase of evolution, and the system must have gone through a common envelope stage when the primary was near the tip of the red giant branch.

HR 1217 is one of the best‐studied rapidly oscillating Ap (roAp) stars, with a frequency spectrum of alternating even‐ and odd‐ℓ modes that are distorted by the presence of a strong, global magnetic field. Several recent theoretical studies have found that within the observable atmospheres of roAp stars the pulsation modes are magneto‐acoustic with significant frequency perturbations that are cyclic with increasing frequency. To test these theories a Whole Earth Telescope extended coverage campaign obtained 342 h of Johnson B data at 10‐s time resolution for the roAp star HR 1217 over 35 d with a 36 per cent duty cycle in 2000 November–December. The precision of the derived amplitudes is 14 μmag, making this one of the highest precision ground‐based photometric studies ever undertaken. Substantial support has been found for the new theories of the interaction of pulsation with the strong magnetic field. In particular, the frequency jump expected as the magnetic and acoustic components cycle through 2π rad in phase has been found. Additionally, comparison of the new 2000 data with an earlier 1986 multisite study shows clear amplitude modulation for some modes between 1986 and 2000. The unique geometry of the roAp stars allows their pulsation modes to be viewed from varying aspect with rotation, yielding mode identification information in the rotational sidelobes that is available for no other type of pulsating star. Those rotational sidelobes in HR 1217 confirm that two of the modes are dipolar, or close to dipolar; based on the frequency spacings and Hipparcos parallax, three other modes must be either ℓ= 0 or 2 modes, either distorted by the magnetic field, or a mix of m‐modes of given ℓ where the mixture is the result of magnetic and rotational effects. A study of all high‐speed photometric Johnson B data from 1981 to 2000 gives a rotation period Prot= 12.4572 d, as found in previous pulsation and photometric studies, but inconsistent with a different rotation period found in magnetic studies. We suggest that this rotation period is correct and that zero‐point shifts between magnetic data sets determined from different spectral lines are the probable cause of the controversy over the rotation period. This WET data set is likely to stand as the definitive ground‐based study of HR 1217. It will be the baseline for comparison for future space studies of HR 1217, particularly the MOST satellite observations.

Abstract. We have discovered periodic light variations (P = 0.1718023 d) in the sdB star HS 2333+3927 in the BVR bands with amplitudes of 0.21, 0.28 and 0.33 mag, respectively. Sinusoidal radial velocity variations at the same period were detected with a semi-amplitude of K 1 = 89.6 km s −1 , indicating that it is binary system and that the light variations are caused by the reflection effect with no eclipses. A mass function of f (m) = 0.0128 M has been determined. The analysis of the light curve did not yield a unique solution, mainly because the albedo of the secondary is poorly constrained. Two solutions of equal quality with a high (A 2 = 1.0) and a low (A 2 = 0.39) albedo were considered further. Variability of the Balmer line profiles, most notably for Hα, was discovered, probably also caused by the reflection effect. A spectroscopic analysis results in T eff = 36 500 K, log g = 5.70, and log (n He /n H ) = −2.15. These characteristics are typical for sdB stars. Mass-radius relations are derived from the results of the analysis of light and radial-velocity curves. Comparison with the observed mass-radius relation of the sdB star and with that of lower main sequence stars for the companion allows us to discard the high albedo solution, because the resulting mass of the primary and the radius of the secondary would be unreasonably low. From a discussion of evolutionary models we constrain the plausible mass of the sdB to the range between 0.29 M and 0.47 M . Accordingly, the mass of the secondary is between 0.24 M and 0.32 M , indicating a spectral type of M3 to M4. HS 2333+3927 is only the sixth sdB+dM system discovered so far. An improved measurement of the gravity and the projected rotational velocity of the sdB star is required to further constrain the masses and to identify the evolutionary state of the sdB star uniquely.

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