We report on analysis of 308.3 hrs of high speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope (WET) during the 2008 international observing run XCOV26. The Fourier transform of the light curve contains 19 independent frequencies and numerous combination frequencies. The dominant peaks are 1633.907, 1887.404, and 2504.897 µHz. Our analysis of the combination amplitudes reveals that the parent frequencies are consistent with modes of spherical degree l=1. The combination amplitudes also provide m identifications for the largest amplitude parent frequencies. Our seismology analysis, which includes 2004-2007 archival data, confirms these identifications, provides constraints on additional frequencies, and finds an average period spacing of 41 s. Building on this foundation, we present nonlinear fits to high signal-to-noise light curves from the SOAR 4.1m, Mc-Donald 2.1m, and KPNO 2m telescopes. The fits indicate a time-averaged convective response timescale of τ 0 = 99.4 ± 17 s, a temperature exponent N = 85 ± 6.2 and an inclination angle of θ i = 32.9 ± 3.2 • . We present our current empirical map of the convective response timescale across the DA instability strip.

PG 1351+489 is one of the 20 DBVs -pulsating helium-atmosphere white dwarf stars -known and has the simplest power spectrum for this class of star, making it a good candidate to study cooling rates. We report accurate period determinations for the main peak at 489.334 48 s and two other normal modes using data from the Whole Earth Telescope (WET) observations of 1995 and 2009. In 2009, we detected a new pulsation mode and the main pulsation mode exhibited substantial change in its amplitude compared to all previous observations. We were able to estimate the star's rotation period, of 8.9 h, and discuss a possible determination of the rate of period change of (2.0 ± 0.9) × 10 −13 s s −1 , the first such estimate for a DBV.

We report on the analysis of 34 years of photometric observations of the pulsating helium atmosphere white dwarf GD358. The complete data set includes archival data from 1982-2006, and 1195.2 hours of new observations from [2007][2008][2009][2010][2011][2012][2013][2014][2015][2016]. From this data set, we extract 15 frequencies representing g-mode pulsation modes, adding 4 modes to the 11 modes known previously. We present evidence that these 15 modes are ℓ = 1 modes, 13 of which belong to a consecutive sequence in radial overtone k. We perform a detailed asteroseismic analysis using models that include parameterized, complex carbon and oxygen core composition profiles to fit the periods. Recent spectroscopic analyses place GD358 near the red edge of the DBV instability strip, at 24,000 ± 500 K and a log g of 7.8 ± 0.08 dex.The surface gravity translates to a mass range of 0.455 to 0.540 M ⊙ . Our best fit model has a temperature of 23,650 K and a mass of 0.5706 M ⊙ . That is slightly more massive than suggested by most the recent spectroscopy. We find a pure helium layer mass of 10 −5.50 , consistent with the result of previous studies and the outward diffusion of helium over time. Subject headings: Stars: oscillations -Stars: variables: general -white dwarfs spectroscopic temperature (T eff = 24000 ± 500 K) and log g = 7.8 places GD358 near the red edge of the instability strip. GD358's pulsation spectrum contains a series of independent radial overtones, and many have complex frequency structure. For one epoch of data taken during the Whole Earth Telescope (WET) run XCOV25, models involving magnetic fields and oblique rotation are proposed to explain such structure (Montgomery et al. 2010). Since the XCOV25 WET run reported in Provencal et al. (2009), we have maintained an active observing program of this complex star. These new observations have successfully identified additional periods in GD358's pulsation spectrum, bringing the total known independent radial overtones to 15. Thirteen of these modes belong to a consecutive ℓ = 1 sequence, the longest sequence observed in a DBV. Paradoxically, among the DBVs with enough detected periods to be fitted asteroseismically, GD358 is the only one that has not been analyzed using the complex C/O profiles adapted and parameterized from stellar evolution calculations (e.g. Salaris et al. (1997); Althaus et al. (2005)). The most recent fits of GD358 (Metcalfe et al. 2003b) wereperformed using 11 observed modes and simple models where the oxygen abundance drops linearly from its central value to zero. This study was plagued by a symmetric asteroseismic signature from the core and the envelopes in the models and was subsequently unable to derive a unique fit to the period spectrum. We present here a new detailed asteroseismic analysis employing more sophisticated interior chemical profiles.With these profiles, we are able to remove the degeneracy in the best fit parameters and better constrain the asteroseismic fits.The present analysis also allows us to place GD358 in...

We present results from a preliminary asteroseismological analysis of the hot DBV EC20058-5234 based on an extensive grid of models. EC20058 is the only known stable DBV and also the hottest and provides an ideal laboratory to constrain the emission rate of plasmon neutrinos. In a Whole Earth Telescope (WET) campaign in 1997, Sullivan et al. (2008) have found 11 independent modes. We use the results of their work to perform a 6 parameter fit of the observed period spectrum. We find a best fit model consistent with the spectroscopically determined effective temperature and surface gravity for EC20058. We find that the periods can be fit successfully without invoking an uneven split of the 281s mode due to a magnetic field. Based on our best fit model, we compute rates of change for the two stable modes observed in the star, which in turn can be used to place tight constraints on plasmon neutrino emission. Astrophysical ContextAbove a temperature of about 26000 K, more than half of the luminosity of an average white dwarf comes from neutrino emission (Figure 1). In that temperature range, the neutrinos are mainly produced by the decay of photons coupled to a plasma (plasmons). If we measure a neutrino luminosity in hot white dwarfs, we are measuring plasmon neutrino rates. One can use the change in the pulsation periods over time to measure the neutrino luminosity. As a white dwarf cools, the period of a given mode increases because the interior is becoming less and less compressible. The faster the cooling, the faster the period increases. Mestel theory (Mestel 1952) predictsṖ if the white dwarf is leaking energy exclusively through photons. A higherṖ than expected means

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