Pulsational Activity on Ik-Pegasi

Abstract

High-time-resolution photometry of millimagnitude precision using the Fine Error Sensor on board the International Ultraviolet Explorer is presented. A few hours of data, when subjected to an optimal (Bayesian) analysis, reveal two pulsational frequencies in the star 1K Peg A, one of which was not previously known. A fit to the empirical P-L-C relation identifies the modes (almost) unambiguously, and interpolation from stellar evolution models yields fundamental parameters for this star, which are used to refine the dynamic parameters of its binary companion, a massive white dwarf. A study of an archival Hβ spectrum using spectral synthesis techniques demonstrates that 1K Peg A is, in all probability, of normal abundances and should not, therefore, be cited as an example of a star exhibiting pulsation and metallism. This further reduces the overlap between the populations of δ Scuti and Am stars to a mere three objects, leading to tighter restrictions on the physics responsible for these phenomena.