Judith L. Provencal

2006 WHOLE EARTH TELESCOPE OBSERVATIONS OF GD358: A NEW LOOK AT THE PROTOTYPE DBV

We report on the analysis of 436.1 hr of nearly continuous high-speed photometry on the pulsating DB white dwarf GD358 acquired with the Whole Earth Telescope (WET) during the 2006 international observing run, designated XCOV25. The Fourier transform (FT) of the light curve contains power between 1000 and 4000 μHz, with the dominant peak at 1234 μHz. We find 27 independent frequencies distributed in 10 modes, as well as numerous combination frequencies. Our discussion focuses on a new asteroseismological analysis of GD358, incorporating the 2006 data set and drawing on 24 years of archival observations. Our results reveal that, while the general frequency locations of the identified modes are consistent throughout the years, the multiplet structure is complex and cannot be interpreted simply as l = 1 modes in the limit of slow rotation. The high-k multiplets exhibit significant variability in structure, amplitude and frequency. Any identification of the m components for the high-k multiplets is highly suspect. The k = 9 and 8 modes typically do show triplet structure more consistent with theoretical expectations. The frequencies and amplitudes exhibit some variability, but much less than the high-k modes. Analysis of the k = 9 and 8 multiplet splittings from 1990 to 2008 reveal a long-term change in multiplet splittings coinciding with the 1996 sforzando event, where GD358 dramatically altered its pulsation characteristics on a timescale of hours. We explore potential implications, including the possible connections between convection and/or magnetic fields and pulsations. We suggest future investigations, including theoretical investigations of the relationship between magnetic fields, pulsation, growth rates, and convection.

Observations of the Pulsating White Dwarf G 185-32

We observed the pulsating hydrogen atmosphere white dwarf G 185-32 with the Whole Earth Telescope in 1992. We report on a weighted Fourier transform of the data detecting 18 periodicities in its light curve. Using the Hubble Space Telescope Faint Object Spectrograph time resolved spectroscopy, and the wavelength dependence of the relative amplitudes, we identify the spherical harmonic degree (� ) for 14 pulsation signals. We also compare the determinations of effective temperature and surface gravity using the excited modes and atmospheric methods, obtaining Teff = 11 960 ± 80 K, log g = 8.02 ± 0.04 and M = 0.617 ± 0.024 M� .

Discovery of a New AM CVn System with the Kepler Satellite

We report the discovery of a new AM CVn system on the basis of broadband photometry obtained with the Kepler satellite supplemented by ground-based optical spectroscopy. Initially retained on Kepler target lists as a potential compact pulsator, the blue object SDSS J190817.07+394036.4 (KIC 004547333) has turned out to be a high-state AM CVn star showing the He-dominated spectrum of its accretion disk significantly reddened by interstellar absorption. We constructed new grids of NLTE synthetic spectra for accretion disks in order to analyze our spectroscopic observations. From this analysis, we infer preliminary estimates of the rate of mass transfer, the inclination angle of the disk, and the distance to the system. The AM CVn nature of the system is also evident in the Kepler light curve, from which we extracted 11 secure periodicities. The luminosity variations are dominated by a basic periodicity of 938.507 s, likely to correspond to a superhump modulation. The light curve folded on the period of 938.507 s exhibits a pulse shape that is very similar to the superhump wavefront seen in AM CVn itself, which is a high-state system and the prototype of the class. Our Fourier analysis also suggests the likely presence of a quasi-periodic oscillation similar to those already observed in some high-state AM CVn systems. Furthermore, some very low-frequency, low-amplitude aperiodic photometric activity is likely present, which is in line with what is expected in accreting binary systems. Inspired by previous work, we further looked for and found some intriguing numerical relationships between the 11 secure detected frequencies, in the sense that we can account for all of them in terms of only three basic clocks. This is further evidence in favor of the AM CVn nature of the system.

Whole Earth Telescope observations of the pulsating hot white dwarf PG 1707+427

We report on the analysis of multisite time-series photometry of the pulsating pre-white dwarf (GW Vir star) PG 1707+427, obtained by the Whole Earth Telescope collaboration. This is the last of the known GW Vir stars without surrounding nebulae to be resolved by multisite data. Successful resolution of the pulsation spectrum resulted from the com- bination of high signal-to-noise observations with a large telescope and wide coverage in longitude with smaller telescopes. We find a series of 8 pulsation frequencies (along with two nonlinear combination frequencies), and identify 7 of them as part of a sequence of � = 1 modes, with a common period spacing of 23.0 s. This spacing implies that the mass of PG 1707+427 is 0.57 M� . Preliminary model fits suggest that the mass determined via asteroseismology is consistent with the mass determined from spectroscopy combined with evolutionary tracks.

Seven-period asteroseismic fit of the Kepler DBV

We present a new, better-constrained asteroseismic analysis of the helium-atmosphere (DB) white dwarf discovered in the field of view of the original Kepler mission. Observations obtained over the course of two years yield at least seven independent modes, two more than were found in the discovery paper for the object. With several triplets and doublets, we are able to fix the

Whole Earth Telescope Observations of the Pulsating Subdwarf B Star PG 0014+067

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PULSATIONAL MAPPING OF CALCIUM ACROSS THE SURFACE OF A WHITE DWARF

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Whole Earth Telescope discovery of a strongly distorted quadrupole pulsation in the largest amplitude rapidly oscillating Ap star

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The O‐C Diagram of EC20058‐5234: Detection of Neutrino Emission?

identification of several modes before performing the fitting, greatly reducing the number of assumptions we must make about mode identification. We find a very thin helium layer for this relatively hot DB, which adds evidence to the hypothesis that helium diffuses outward during DB cooling. At least a few of the modes appear to be stable on evolutionary timescales and could allow us to obtain a measurement of the rate of cooling with monitoring of the star over the course of the next few years with ground-based follow-up.

Searching for Planets with White Dwarf Pulsations: Spurious Detections

PG 0014+067 is one of the most promising pulsating subdwarf B stars for seismic analysis, as it has a rich pulsation spectrum. The richness of its pulsations, however, poses a fundamental challenge to understanding the pulsations of these stars, as the mode density is too complex to be explained only with radial and nonradial low-degree (l < 3) p-modes without rotational splittings. One proposed solution, suggested by Brassard et al. in 2001 for the case of PG 0014+067 in particular, assigns some modes with high degree (l = 3). On the other hand, theoretical models of sdB stars suggest that they may retain rapidly rotating cores, and so the high mode density may result from the presence of a few rotationally split triplet (l = 1) and quintuplet (l = 2) modes, along with radial (l = 0) p-modes. To examine alternative theoretical models for these stars, we need better frequency resolution and denser longitude coverage. Therefore, we observed this star with the Whole Earth Telescope for two weeks in 2004 October. In this paper we report the results of Whole Earth Telescope observations of the pulsating subdwarf B star PG 0014+067. We find that the frequencies seen in PG 0014+067 do not appear to fit any theoretical model currently available; however, we find a simple empirical relation that is able to match all of the well-determined frequencies in this star.