δ Sct-type pulsations in eclipsing binary systems: AB Cas

Abstract

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.

A photometric study of the Algol-type binary AB Cas

“…9. For the sake of comparison, f = 17.1564 cycles day −1 A = 22.2 mmag were reported in previous works (Rodriguez et al 1998(Rodriguez et al , 2004Soydugan et al 2003a). …”

δ Scuti light variations as a test for choosing the mechanism of cyclic orbital period changes in Algols

“…Ando (1980) confirmed this discovery. These pulsations were then studied by Frolov et al (1982), Soydugan et al (2003b) and Rodriguez et al (1998, 2004). The primary component of AB Cas pulsates radially with a single period of P sct = 0.058 28 d and with a photometric amplitude of about 0.05 mag.…”

“…We computed the epochs of maximum light simultaneously with solving the light curve using the method developed by Khaliullin et al (private communication) for solving the light curves of eclipsing binaries with δ Scuti type components. We used unpublished observations of AB Cas obtained by Khaliullin and Mironov in 1980–81 at the Tian‐Shan Observatory of the Sternberg Astronomical Institute of Moscow State University, observations of Rodriguez et al (1998, 2004) and Soydugan et al (2003b), observations reported on the AAVSO website, and recent observations by Kuznetsov (private communication). Unfortunately, we could not obtain individual observations by Tempesti (1971) and had to determine the corresponding epochs of maxima from the light curves plotted in his paper.…”

“…For AB Cas, like for most of the Algols, no additional evidence is available that would suggest the presence of a third or more bodies as reported by many of the above‐mentioned authors based on cyclic period variations. In particular, all the light‐curve solutions for AB Cas yield zero values for the third light L 3 (Rodriguez et al 1998, 2004; Soydugan et al 2003b; Abedi & Riazi 2007; Khaliullin et al, private communication). However, AB Cas offers us yet another opportunity to test this hypothesis.…”

“…One of the components of AB Cas is a δ Scuti type pulsating star with a pulsation period of P sct = 0.058 28 d (Tempesti 1971). While a number of authors (Frolov, Pastukhova & Mironov 1982; Rodriguez et al 1998, 2004; Soydugan et al 2003b) have analysed the temporal behaviour of P sct in this system, no one has studied the relationship between the observed variations in orbital period P and pulsation period P sct . The aim of this paper is to try to resolve the problem of cyclic variations in orbital periods in Algol‐type binaries and, particularly, in AB Cas, by performing a joint analysis of the temporal behaviour of P and P sct .…”