2005A&A...433.1097V

We report observations of the planetary nebula nucleus Abell 43, obtained at the 2.5m Nordic Optical Telescope, which show that it is a pulsator. Abell 43, a ``hybrid-PG 1159'' type star, is the second pulsator of this class, after HS 2324+3944. From the limited data set acquired, we find that Abell 43 exhibits at least two periods of 2600s and 3035s, the longest ones observed up to now in PG 1159 and ``hybrid-PG 1159'' pulsators. This strongly suggests that the variations are due to non-radial g-mode pulsations and cannot be a consequence of binarity. This discovery raises puzzling questions regarding the excitation mechanism in this H rich, C and O poor ``hybrid-PG 1159'' since the C and O abundances are too low to trigger the instability through the κ-mechanism induced by the partial ionization of C and O, a mechanism invoked to explain the instability in the PG 1159 stars and in the previously known ``hybrid-PG 1159'' pulsator HS 2324+3944.