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The pulsating DAV white dwarf G185-32 was observed with the Whole Earth Telescope in 1992, during XCov8. We briefly report on the weighted Fourier transform of the data obtained.

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. Based on observations that span 31 years, we conclude that the period 213.132605 s observed in ZZ Ceti drifts at a rate dP/dt≤(5.5±1.9)×10−15 s/s, after correcting for proper motion. Our results are consistent with previous Ṗ values for this mode and an improvement over them due to the larger time-base. The characteristic stability timescale implied for the pulsation period is |P/ Ṗ|≥1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.132605 s is only slightly less than the present measurement for G117-B15A for the period 215.2 s, another DAV, establishing this mode in ZZ Ceti as the second most stable optical clock known, more stable than atomic clocks and most pulsars.

HR1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of nonradial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 μHz and 34.6 μHz, with a sixth mode at a problematic spacing of 50.0 μHz (which equals 1.5 × 33.3 μHz) to the highfrequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 μHz, but hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha (2001) predicted that there should be a previously undetected mode 34 μHz higher than the main group, with a smaller spacing between it and the highest one. The 20th extended coverage campaign of the Whole Earth Telescope (XCov20) has discovered this frequency as predicted by Cunha (2001). Amplitude modulation of several of the pulsation modes between the 1986 and 2000 data sets has also been discovered, while important parameters for modelling the geometry of the pulsation modes have been shown to be unchanged. With stringent selection of the best data from the WET network the amplitude spectrum shows highest peaks at only 50 μmag and formal errors on the determined amplitudes are 14 μmag. Some lessons for future use of WET for the highest precision photometry on bright stars are discussed.

The Multi-site spectroscopic telescope is a virtual instrument and the name of a collaboration that opens up a new observational window by combining continuous observations of spectroscopic variations and simultaneous photometric monitoring. This constitutes an enormous observational effort, but in return promises to finally provide access to a mode identification for and an asteroseismological analysis of the pulsating sdB star PG 1605+072. Multi-Site Spectroscopic Telescope observations for this object have been secured during a large coordinated campaign in May and June of the year 2002. The frequency resolution and coverage of the photometric time series has been noticeably enhanced by a significant contribution from the Whole Earth Telescope, which was used to observe PG 1605+072 as an alternate target during the WET XCov22 campaign, also conducted in May 2002. This paper briefly outlines the motivation for the MSST project and tries to give a first assessment of the overall quality of the data obtained, with a focus on the Whole Earth Telescope observations.

We report on the 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23 to June 8, 2000. We acquired more than 232 000 independent measurements and detected the non-radial g-modes consistent with degree ℓ = 1 and radial order 8 to 20 and their linear combinations up to 6th order. We also detect, for the first time, a high amplitude ℓ = 2 mode, with a period of 796 s. In the 2000 WET data, the largest amplitude modes are similar to those detected with the WET observations of 1990 and 1994, but the highest combination order previously detected was 4th order.

Asteroseismology is a unique tool to explore the internal structure of stars through both observational and theoretical research. The internal structure of pulsating hydrogen shell white dwarfs (ZZ Ceti stars) detected by asteroseismology is regarded as the representative of all DA white dwarfs. Observations for KUV 08368+4026, which locates in the middle of the ZZ Ceti instability strip, have been carried out in 1999 and from 2009 to 2012 with either single-site runs or multisite campaigns. Time series photometric data of about 300 h were collected in total. Through data reduction and analysis, 30 frequencies were extracted, including four triplets, two doublets, one single mode and further signals. The independent modes are identified as either 1 = 1 or 1 = 2 modes. Hence, a rotation period of 5.52 ± 0.22 d was deduced from the period spacing in the multiplets. Theoretical static models were built and a best-fitting model for KUV 08368+4026 was obtained with 0.692 ± 0.002M☉, (2.92 ± 0.02) × 10-3 L☉ and the hydrogen mass fraction of 10-4 stellar mass. [ABSTRACT FROM AUTHOR]

Aims. This paper presents a detailed and precise study of the characteristics of the exoplanet host star and CoRoT main target HD 52265, derived from asteroseismic studies. We compare our results with previous estimates, and provide a comprehensive summary and discussion. Methods. Our basic method is similar to that previously used by the Toulouse group for solar-type stars. Models are computed with various initial chemical compositions and the computed p-mode frequencies are compared with the observed ones. All models include atomic diffusion and we discuss the importance of radiative accelerations. Several tests are used, including the usual frequency combinations and the fits to the échelle diagrams. Possible surface effects are introduced and discussed. Automatic codes are also used to identify the best-fit model for this star (SEEK and AMP) and their results are compared with those obtained with the detailed method. Results. We find precise results for the mass, radius, and age of this star, as well as its effective temperature and luminosity. We also estimate the initial helium abundance. These results are important for the characterization of the star-planet system. [ABSTRACT FROM AUTHOR]

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 JohnsonBdata 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 14μmag, 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 andHipparcosparallax, three other modes must be eitherormodes, either distorted by the magnetic field, or a mix ofm-modes of givenℓ where the mixture is the result of magnetic and rotational effects. A study of all high-speed photometric JohnsonBdata from 1981 to 2000 gives a rotation period, 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 theMOSTsatellite observations. [ABSTRACT FROM AUTHOR]

After the initial discoveries fifteen years ago, over 200 extrasolar planets have now been detected. Most of them orbit main-sequence stars similar to our Sun, although a few planets orbiting red giant stars have been recently found. When the hydrogen in their cores runs out, main-sequence stars undergo an expansion into red-giant stars. This expansion can modify the orbits of planets and can easily reach and engulf the inner planets. The same will happen to the planets of our Solar System in about five billion years and the fate of the Earth is matter of debate. Here we report the discovery of a planetary-mass body (Msini = 3.2MJupiter) orbiting the star V 391 Pegasi at a distance of about 1.7 astronomical units (au), with a period of 3.2 years. This star is on the extreme horizontal branch of the Hertzsprung–Russell diagram, burning helium in its core and pulsating. The maximum radius of the red-giant precursor of V 391 Pegasi may have reached 0.7 au, while the orbital distance of the planet during the stellar main-sequence phase is estimated to be about 1 au. This detection of a planet orbiting a post-red-giant star demonstrates that planets with orbital distances of less than 2 au can survive the red-giant expansion of their parent stars. [ABSTRACT FROM AUTHOR]