2004MNRAS.353..310R

This paper presents simultaneous Strömgren uvby observations carried out during the years 1998 and 1999 on the Algol-type eclipsing binary system AB Cas, where the primary component is a δ Sct-type pulsator. These observations include complete binary uvby light curves which have been analysed using the Wilson-Devinney code. The new results are compared with those from the literature. The residuals from the computed binary light curves were then analysed for their pulsational content. A single frequency was found to be sufficient to describe the out-of-eclipse pulsational behaviour. Nevertheless, some indications of the existence of secondary frequencies are also found. The main period was found to be constant during the last twenty years, making use of the classical O-C method, but an increase in its amplitude is detected during the year 1998 as compared with other epochs. Concerning the nature of the pulsations, methods based on the phase shifts and amplitude ratios between different filters were used for out-of-eclipse data and the Spatial Filtration method for observations during the primary eclipses. All methods lead to the same result: the dominant pulsation is radial, confirming previous results from earlier works. In fact, neither significant amplitude variations nor phase shifts, relative to the pulsational out-of-eclipse behaviour, are found when the primary component is hidden during primary eclipse. An iterative process was also carried out to improve both the binary and pulsation solutions, but the final results remained essentially the same.