Multimode pulsation of the ZZ Ceti star GD 154

Paparó, Margit and Sódorné Bognár, Zsófia and Plachy, Emese and Molnár, László and Bradley, P. A. (2013) Multimode pulsation of the ZZ Ceti star GD 154. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 432 (1). pp. 598-608. ISSN 0035-8711

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Abstract

We present the results of a comparative period search on different timescales and modeling 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 861.56 μHz have never been reported before. A rigorous test revealed remarkable intrinsic amplitude variability of frequencies at 839.14 and 861.56 μHz over a 50-day timescale. In addition, the multi-mode pulsation changed to monoperiodic pulsation with an 843.15 μHz dominant frequency at the end of the observing run. The 2.76 μHz average rotational split detected led to a determination of a 2.1-day rotational period for GD 154. We searched for model solutions with effective temperatures and log g close to the spectroscopically determined ones. The best-fitting models resulting from the grid search have MH between 6.3 ∗ 10−5 and 6.3∗10−7M∗, 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 2484 μHz.

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