1998A&A...339..170H

We performed a search for periodic light variations among low-mass DAO white dwarfs. These objects have theoretically been predicted to exhibit low-order g-mode pulsations due to a potent ε mechanism in hydrogen-burning shells according to model calculations of Charpinet et al. (1997ApJ...489L.149C). No pulsations were detected in any of our nine candidate stars. This can be attributed to the very narrow instability strip predicted or to the fact that pulsationally unstable modes are not necessarily excited, a common phenomenon among pulsating stars. It may also be the case that hydrogen-burning shells in the stars are too small to drive pulsations or not present.