Abell 43, a second pulsating “hybrid-PG 1159” star

¹ Université Paul-Sabatier, Observatoire Midi-Pyrénées, CNRS/UMR5572, 14 Av. E. Belin, 31400 Toulouse, France e-mail: gerardv@obs-mip.fr
² Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, 0315, Blindern, Oslo, Norway
³ Isaac Newton Group, Apartado de correos 321, 38700, Santa Cruz de la Palma, Spain

Received: 13 September 2004
Accepted: 22 November 2004

Abstract

We report observations of the planetary nebula nucleus Abell 43, obtained at the 2.5 m 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 2600 s and 3035 s, 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.