J. L. Provencal

Whole earth telescope observations of the DBV white dwarf GD 358

We report on the analysis of 154 hours of early continuous high-speed photometry on the pulsating DB white dwarf (DBV) GD 358, obtained during the Whole Earth Telescope (WET) run of 1990 May. The power spectrum of the light curve is dominated by power in the range from 1000 to 2400 microHz with more than 180 significant peaks in the total spectrum. We identify all of the triplet frequencies as degree l = 1, and from the details of their spacings we derive the total stellar mass as 0.61 + or - 0.03 solar mass, the mass of the outer helium envelope as 2.0 + or - 1.0 x 10(exp -6) M(sub *), the absolute luminosity as 0.050 + or - 0.012 solar luminosity and the distance as 42 + or - 3 pc. We find strong evidence for differential rotation in the radial direction -- the outer envelope is rotating at least 1.8 times faster than the core -- and we detect the presence of a weak magnetic field with a strength of 1300 + or - 300 G. We also find a significant power at the sums and differences of the dominant frequencies, indicating nonlinear processes are significant, but they have a richness and complexity that rules out resonant mode coupling as a major cause.

Whole earth telescope observations of the helium interacting binary PG 1346+082 (CR Bootis)

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670 ± 0.004 μHz and 669.887 ± 0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. We also uncover an unexpected dependence of the high-frequency powers amplitude and frequency structure on overall system magnitude. We discuss these findings in light of the general AM CVn system model, particularly the implications of the high-order harmonics on future studies of disk structure, mass transfer, and disk viscosity.

Whole Earth Telescope Observations of the Interacting White Dwarf Binary System AM CVn: First Results

We report the first results of the Whole Earth Telescope observations of AM CVn in March/April 1990. The Fourier Spectrum of the light curve shows harmonically related peaks. High frequency sidebands with the fine-splitting of 21 µHz are observed for the fundamental period of 1051 s and its 4 lowest harmonics. These have not been observed before. The fundamental period itself is not detected.

A Measurement of the Evolutionary Timescale of the Cool White Dwarf G117-B15A with Wet

We have measured the cooling rate of the 13,000K DA white dwarf G117-B15A by measuring the rate of period change with time for the main pulsation of this ZZ Ceti star, using the Whole Earth Telescope. The observed rate of period change is larger than the predictions of g-mode pulsation theory applied to C/O core white dwarf models.

The time dependence of the phases of the harmonics relative to the 1490 sec fundamental in PG1346+082

On the basis of our preliminary analysis of the harmonic structure, we suggest that the 1493 s oscillation is either the orbital period of the system or the rotation period of a magnetized, accreting white dwarf. The 1471 s is most probably a nonradial oscillation of the primary white dwarf since its character mimics that of oscillations seen in single DB variables.

Preliminary Results from XCOV 17: PG 1336-018

We present a preliminary analysis of the data collected during the 1999/1 (XCOV17) Whole Earth Telescope (WET) campaign to observe the pulsating subdwarf B star PG 1336-018. Since PG 1336-018 is an HW Vir type eclipsing binary, our hope is to use the known orbital period, assume a tidally locked system, and search for rotationally split modes. To this end, we can already report some success.

Whole Earth Telescope Observations of the DBV White Dwarf PG1115+158: Preliminary Results

We present preliminary results from Whole Earth Telescope (WET) data on the DBV star PG1115+158. In the Fourier Transform of this data, we have tentatively identified peaks arranged in multiplets with common frequency splitting. The average period spacing between these multiplets is ~ 40s, very similar to the multiplet spacing found in the DBV GD358. Theoretical models show l = 1 modes with ~ 40s period spacing between modes of consecutive k for white dwarfs with niasses near 0.6M ⊙. If we assume the identified multiplets are l = 1 modes, then the rotation rate of the star is 0.45 days. Furthermore, the deviations of the period spacing between modes from the mean period spacing indicates that, like GD358, the surface Helium layer is thin, less than 10-4 M *.

Whole Earth Telescope Observations of PG1346+082

We report the latest results of continuing analysis of Whole Earth Telescope data of PG1346+082, acquired in March 1988. We present the light curve of the data set and its Fourier Transform. Examination of the dominant short-term photometric variation at 1490 seconds has revealed a band of power consisting of fifteen separate frequencies. We present the list of frequencies and discuss the status of our investigation of their nature.

Constraining the physics of carbon crystallization through pulsations of a massive DAV BPM37093

We are trying to reduce the largest uncertainties in using white dwarf stars as Galactic chronometers by understanding the details of carbon crystalliazation that currently result in a 1–2 Gyr uncertainty in the ages of the oldest white dwarf stars. We expect the coolest white dwarf stars to have crystallized interiors, but theory also predicts hotter white dwarf stars, if they are massive enough, will also have some core crystallization. BPM 37093 is the first discovered of only a handful of known massive white dwarf stars that are also pulsating DAV, or ZZ Ceti, variables. Our approach is to use the pulsations to constrain the core composition and amount of crystallization. Here we report our analysis of 4 hours of continuous time series spectroscopy of BPM 37093 with Gemini South combined with simultaneous time-series photometry from Mt. John (New Zealand), SAAO, PROMPT, and Complejo Astronomico El Leoncito (CASLEO, Argentina).

PG 1605+072 in WET XCoV22: Support for the multi site spectroscopic telescope

Abstract 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.