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Provencal J.L.,University of Delaware | Provencal J.L.,Delaware Asteroseismic Research Center | Montgomery M.H.,Delaware Asteroseismic Research Center | Montgomery M.H.,University of Texas at Austin | And 64 more authors.
Astrophysical Journal | Year: 2012

We report on an analysis of 308.3hr of high-speed photometry targeting the pulsating DA white dwarf EC14012-1446. The data were acquired with the Whole Earth Telescope 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 41s. Building on this foundation, we present nonlinear fits to high signal-to-noise light curves from the SOAR 4.1m, McDonald 2.1m, and KPNO 2m telescopes. The fits indicate a time-averaged convective response timescale of τ0 = 99.4 ± 17s, a temperature exponent N = 85 ± 6.2, and an inclination angle of θi = 32°.9 ± 3°.2. We present our current empirical map of the convective response timescale across the DA instability strip. © 2012. The American Astronomical Society. All rights reserved. Source

Redaelli M.,Federal University of Rio Grande do Sul | Kepler S.O.,Federal University of Rio Grande do Sul | Costa J.E.S.,Federal University of Rio Grande do Sul | Winget D.E.,University of Texas at Austin | And 79 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

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 489.33448s 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 8.9h, and discuss a possible determination of the rate of period change of (2.0 ± 0.9) × 10-13ss -1, the first such estimate for a DBV. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

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