Context. PG 1159-035, a pre-white dwarf with T eff 140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M = 0.59 ± 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r c /R = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period P rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for = 1 modes and less than 50% for = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.Key words. stars: oscillations -stars: individual: PG 1159-035 -stars: interiors -stars: white dwarfs IntroductionThe star PG 1159-035 was identified by Green in 1977 in a survey for objects with ultraviolet excess, known as the PalomarGreen Survey (Green et al. 1986). The presence of lines of He II in the PG 1159-035 spectrum suggested a high superficial temperate (McGraw et al. 1979). The analysis of the far ultraviolet flux distribution -from ∼1200 Å to the Lyman limit at 912 Å -obtained with the Voyager 2 ultraviolet spectrophotometer indicated an effective temperature above 100 000 K (Wegner et al. 1982). Later analysis with the IUE and EXOSAT show that PG 1159-035 is one of the hottest stars known (Sion et al. 1985;Barstow et al. 1986); the current estimated temperature for PG 1159-035 is 140 000 ± 5000 K (Werner et al. 1991;Dreizler et al. 1998;and Jahn et al. 2007) and log g(cgs) = 7.0 ± 0.5 Tables 12-17 a...

Context. The variable pre-white dwarf PG 1159 stars (GW Vir) are g-mode non-radial pulsators. Asteroseismology puts strong constraints on their global parameters and internal structure. PG 0122+200 defines the red edge of the instability strip and its evolutionary timescale is predicted to be dominated by neutrino emission. Its study offers the opportunity to better understand the instability mechanism and to validate the physics of the neutrino production in dense plasma. Aims. To achieve such a goal requires determining precisely its fundamental parameters. This is the goal of this paper. Methods. We present new multi-site photometric observations obtained in 2001 and 2002. Together with previous data, they allow us to detect 23 frequencies, composed of 7 triplets and 2 single frequencies, which are used to constrain its internal structure and derive its fundamental parameters. Results. All the observed frequencies correspond to = 1 g-modes. The period distribution shows a signature of mode trapping from which we constrain the He-rich envelope mass fraction to be -6.0 ≤ log(q y ) ≤ −5.3. The comparison of the mode trapping amplitudes among GW Vir stars suggests that the mass-loss efficiency must decrease significantly below T eff ≤ 140 kK. We measure an average period spacing of 22.9 s from which we derive a mass of 0.59 ± 0.02 M . From the triplets we measure a mean rotational splitting of 3.74 µHz and a rotational period of 1.55 days. We derive an upper limit to the magnetic field of B ≤ 4 × 10 3 G. The luminosity (log L/L = 1.3 ± 0.5) and the distance (D = 0.7 +1.0 −0.4 kpc) are only weakly constrained due to the large uncertainty on the spectroscopically derived surface gravity and the absence of a measured parallax. Conclusions. From the asteroseismic mass, the ratio of the neutrino luminosity on the photon luminosity is 1.6 ± 0.2 confirming that the PG 0122+200 evolutionary time scale should be dominated by neutrino cooling. A measurement ofṖ for the largest amplitude untrapped modes should verify this prediction.

Abstract. We report the discovery of a new eclipsing system less than one arcminute south of the pulsating DB white dwarf KUV 05134+2605. The object could be identified with the point source 2MASS J0516288+260738 published by the Two Micron All Sky Survey. We present and discuss the first light curves as well as some additional colour and spectral information. The eclipse period of the system is 1.29 d, and, assuming this to be identical to the orbital period, the best light curve solution yields a mass ratio of m 2 /m 1 = 0.11, a radius ratio of r 2 /r 1 ≈ 1 and an inclination of 74• . The spectral anaylsis results in a T eff = 4200 K for the primary. On this basis, we suggest that the new system probably consists of a late K + Brown dwarf (which would imply a system considerably younger than ≈0.01 Gyr to have r 2 /r 1 ≈ 1), and outline possible future observations.

Abstract. Stability of both the fundamental and first overtone oscillations of RV Ari was investigated by different methods which led to concordant results. The fundamental period of RV Ari has been decreasing very slowly with a rate of (1/P 0 )(dP 0 /dt) = −0.6 × 10 −8 y −1 while the first overtone period has been increasing a little faster with a rate of (1/P 1 )(dP 1 /dt) = +0.9 × 10 −8 y −1 , if we assume linear period changes over the past 65 years. Although the very slow change in the periods is consistent with the evolutionary theories, the fact that the signs of the period changes for the two modes are opposite indicates that the dominating part of the period variation may be the result of non-evolutionary effects. The amplitudes of the fundamental and overtone oscillations have undergone small changes (several mmag) on a time scale of years, and a slight increase in the amplitude of the first overtone pulsation is suspected. An additional frequency at f 2 = 13.6116 cd −1 is found.