2013MNRAS.432..598P

We present the results of a comparative period search on different time-scales and modelling of the ZZ Ceti (DAV) star GD 154. We determined six frequencies as normal modes and four rotational doublets around the ones having the largest amplitude. Two normal modes at 807.62 and 861.56µHz have never been reported before. A rigorous test revealed remarkable intrinsic amplitude variability of frequencies at 839.14 and 861.56µHz over a 50 d time-scale. In addition, the multimode pulsation changed to monoperiodic pulsation with an 843.15µHz dominant frequency at the end of the observing run. The 2.76µHz average rotational split detected led to a determination of a 2.1 d rotational period for GD 154. We searched for model solutions with effective temperatures and logg close to the spectroscopically determined ones. The best-fitting models resulting from the grid search have MH between 6.3x10-5 and 6.3x10-7M*, which means thicker hydrogen layer than the previous studies suggested. Our investigations show that mode trapping does not necessarily operate in all of the observed modes and the best candidate for a trapped mode is at 2484µHz.