Band 12, Heft 1

The Council of the Wise is the governing body for the Whole Earth Telescope, and its main function is to decide on scientific issues concerning WET

I have collected all the WET archival data on the pulsating DB white dwarf stars (DBVs) and re-reduced them. In addition, the WET has recently observed three DBVs. Preliminary results on PG 1115+158, PG 1351+489, KUV 05134+2605, PG 1654+160 and PG 1456+103 are presented, and the future use of the data is outlined.

PG 1159-035 has been observed with the Whole Earth Telescope on XCov3, 9, 19 and 22. In this work we present a brief summary of the campaigns.

We briefly report on the April 1995 XCov12 campaign on the DBV PG 1351+489.

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 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.

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 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. Constraining the cooling rate of ZZ Ceti aids theoretical evolutionary models and white dwarf cosmochronology. The drift rate of this clock is small enough that reflex motion caused by any orbital planets is detectable within limits; our Ṗ constraint places limits on the mass and/or distance of any orbital companions.

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.

We present time series observations of the Herbig Ae star V351 Ori. This star presents light variations on short time scale (a few hours), typical of the δ Scuti pulsation. The new data are briefly described and the possibility to observe V351 Ori with the WET is discussed.

We present a study over three single-site campaigns to investigate the photometric behaviour of the PNN NGC 246. We observed this object in 2000 and 2001. The analysis of the light curves indicates complex and variable temporal spectra. Using wavelet analysis we have found evidences for changes on time scales of hours in the 2000 dataset. The temporal spectra obtained during 2001 are quite different from the results of the previous year. The modulations in the light curve are more noticeable and the temporal spectra present a higher number of modulation frequencies. One peculiar characteristic is the presence of a variable harmonic structure related to one of these modulation frequencies. This complex photometric behaviour may be explained by a more complicated unresolved combination of modulation frequencies, but more likely due to a combination of pulsations of the star plus modulations related to interaction with a close companion, maybe indicating a disc. However, these characteristics cannot be confirmed from single site observations. The complex and variable behaviour of NGC 246 needs the WET co-operation in order to completely resolve its light curve.

KPD 1930+2752 is a pulsating subdwarf B star with a particularly rich period spectrum, likely due to significant rotational splitting. It is also a short period (~ 2h17m), close binary system (as revealed by the presence of an ellipsoidal variation in the light curve) containing an unseen companion - almost certainly a white dwarf. Radial velocity measurements indicate that the total binary mass exceeds the Chandrasekhar limit. KPD 1930+2752 is therefore the first known (non-X-ray source) candidate for a Type Ia supernova (SNe Ia) progenitor that should explode within an astrophysically interesting timescale (~ 200 Myr) after the two stars merge due to gravitational wave radiation. Additionally, the tidal distortions are indicative of the strong tidal force incurred on the pulsating star by its companion. This will allow us to test the effects such strong tidal forces have on pulsations. Hence, this object presents an outstanding astrophysical interest, and deserves to be observed with the WET network to fully resolve the complex pulsation pattern of the pulsating sdB star, as well as the details of the ellipsoidal modulation. The asteroseismological analysis of the pulsation data obtained with the WET, along with a detailed analysis of the folded, high S/N ellipsoidal variation will lead to strong physical constraints on this particularly interesting stellar object.

Using high-speed photometry techniques, three transits of the extrasolar planet across the disk of the star HD 209458 have been observed. The combination of a WET-style 3-channel photometer and an excellent site yielded millimagnitude photometric precision. The various techniques used to reduce the raw data obtained under different observing conditions are presented along with modelling of the transit light curves. Finally, a summary of what we have learned about this unique extrasolar planet is provided.