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...

Aims. We present the results of contemporaneous spectroscopic and photometric monitoring of the young solar-type star HD 171488 (P rot 1.337 days) aimed at studying surface inhomogeneities at both photospheric and chromospheric levels. Methods. Echelle FOCES spectra (R 40 000) and Johnson BV photometry have been performed in August 2006, with a good coverage of rotational phases. Spectral type, rotational velocity, metalicity, and gravity were determined with a code developed by us (Rotfit) and a library of high-resolution spectra of slowly-rotating reference stars. The metalicity was measured from the analysis of iron lines with the Moog code. The spectral subtraction technique was applied to the most relevant chromospheric diagnostics included in the FOCES spectral range, namely Ca ii IRT, Hα, He i D 3 , Hβ, and Ca ii H&K lines.Results. A simple model with two large high-latitude spots is sufficient to reproduce the B and V light curves as well as the radial velocity modulation if a temperature difference between photosphere and spots of about 1500 K is used. A Doppler-imaging analysis of photospheric lines basically confirms a similar spot distribution. With the help of an analogous geometric two-spot model, we are able to reproduce the observed modulations in the residual chromospheric emissions adopting different values of ratios between the flux of plages and the quiet chromosphere (about 5 for Hα and 3 for Ca ii diagnostics). Facular regions of solar type appear to be the main responsible features for the modulations of chromospheric diagnostics. Both the spot/plage model and the cross-correlation between the light curve and the chromospheric line fluxes display a significant lead effect of plages with respect to spots (from 20 • to 40 • in longitude), as already observed in some active solar-type stars and RS CVn systems. Conclusions. The contemporaneous monitoring of photospheric and chromospheric diagnostics in the young and rapidly rotating solar-type star HD 171488 allowed us to detect active regions which have nearly the same location at both atmospheric layers, with plages slightly leading spots in longitudes. These active regions are similar to the solar ones in some respects, because the spot temperature is close to that of sunspot umbrae and the plage flux-contrast is consistent with the average solar values. The main differences with respect to the Sun are larger sizes and higher latitudes.

The post‐common envelope and pre‐cataclysmic binary V471 Tau has been observed by the authors since 1973. At least a complete light curve in B and V bands and more than two eclipse timings were obtained in each year. All the available data published so far (including the authors') have been collected and analysed for the brightness and orbital period changes. The system brightened about 0.22 mag in both B and V bands more or less regularly up to 1997 and started to decrease afterwards. A search for periodicity of this variation yields a period longer than 85 yr. In addition to this long‐period variation, a small amplitude of about 0.08 mag and short time‐interval fluctuations on the mean brightness have been detected. The variations of the mean brightness have been discussed and plausible causes suggested. The changes of the apparent period have been attributed to a third body. Analysis of all the ‘observed−calculated’ (O−C) data yields a period of 32.4 yr, with a semi‐amplitude of 151 s and an eccentricity of 0.30 for the third‐body orbit. For orbital inclinations greater than 34° the mass of the third body would possibly match to a brown dwarf. One of the most interesting features in the light curve of V471 Tau is the decrement of the eclipse depth with time. The depth of the eclipse in the B band has been decreased from 0.082 to 0.057 mag over 34 yr. Subtracting the variation of the depth due to the brightening of the red dwarf star, the actual variation in depth, originated from from the white dwarf, was found to be about 0.012 mag. This change in the brightness of the compact object has been attributed to the mass accretion from its primary component via thermally driven wind and/or flare‐like events.

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We present spectroscopic observations of the massive multiple system HD 167971, located in the open cluster NGC 6604. The brighter component of the triple system is the overcontact eclipsing binary MY Ser with an orbital period of 3.32 days. The radial velocities and the previously published UBV data obtained by Mayer et al. (2010) and the UBVRI light curves by Davidge & Forbes (1988) are analysed for the physical properties of the components. We determine the following absolute parameters: for the primary star M p =32.23±0.54 M ⊙ , R p =14.23±0.75 R ⊙ ; and for the secondary star M s =30.59±0.53 M ⊙ , R s =13.89±0.75 R ⊙ . Photoelectric times of minimum light are analyzed under the consideration of the light-time orbit. The center-ofmass of the eclipsing binary is orbiting around the common center-of-gravity of the triple system with a period of 21.2±0.7 yr and with a projected semi-major axis of 5.5±0.7 AU. The mass function for the third star was calculated as 0.370±0.036 M ⊙ . The light contributions of the third star to the triple system in the UBV pass-bands were derived and the intrinsic magnitudes and colors were calculated individually for the three stars. The components of the eclipsing pair were classified as O7.5 III and O9.5 III. The intrinsic color indices for the third star yield a spectral type of (O9.5-B0) III-I. This classification leads to constrain the inclination of the thirdbody orbit, which should be about 30 o , and therefore its mass should be about 29 M ⊙ . MY Ser is one of the rare massive O-type triple system at a distance of 1.65±0.13 kpc, the same as for the NGC 6604 embedded in the Ser OB2 association.