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We present the analysis of 71 hours of high quality time-series CCDphotometry of the helium atmosphere pulsating white dwarf (DBV) EC 04207-4748obtained using the facilities at Mt John University Observatory in New Zealand.The photometric data set consists of four week-long observing sessions coveringthe period March to November 2011. A Fourier analysis of the lightcurvesyielded clear evidence of four independent eigenmodes in the star with thedominant mode having a period of 447 s. The lightcurve variations exhibitdistinct nonsinusoidal shapes, which results in significant harmonics of thedominant frequency appearing in the Fourier transforms. These observedvariations are interpreted in terms of nonlinear contributions from the energyflux transmission through the subsurface convection zone in the star. Ourmodelling of this mechanism, using the methods first introduced by Montgomery(2005), yields a time-averaged convective response time of tau_0 ~ 150 s forthe star, and this is shown to be broadly consistent with a MLT/alpha parametervalue between 0.8 and 1.2. It is argued that for the DBV pulsators the measuredvalue of tau_0 is a better estimate of the relative stellar surfacetemperatures than those obtained via spectroscopic techniques.

Time series photometry of the helium atmosphere pulsating white dwarf EC 04207-474