2013MNRAS.431..520C

We present the analysis of 71 h of high-quality time series CCD photometry of the helium atmosphere pulsating white dwarf (DBV) EC 04207-4748 obtained using the facilities at Mt John University Observatory in New Zealand. The photometric data set consists of four week-long observing sessions covering the period 2011 March to November. A Fourier analysis of the light curves yielded clear evidence of four independent eigenmodes in the star with the dominant mode having a period of 447 s. The light-curve variations exhibit distinct non-sinusoidal shapes, which result in significant harmonics of the dominant frequency appearing in the Fourier transforms. These observed variations are interpreted in terms of non-linear contributions from the energy flux transmission through the sub-surface convection zone in the star. Our modelling of this mechanism, using the methods first introduced by Montgomery, yields a time-averaged convective response time of τ0 ∼ 150 s for the star, and this is shown to be broadly consistent with an MLT/α parameter value between 0.8 and 1.2. It is argued that for the DBV pulsators the measured value of τ0 is a better estimate of the relative stellar surface temperatures than those obtained via spectroscopic techniques.