Algol-Type Eclipsing Binaries with δ Scuti-Type Pulsating Components: IV Cas

Abstract

We present the results of photometric and spectroscopic observations of the Algol-type eclipsing binary with a δ Scuti-type pulsating component IV Cas. This is the first comprehensive study of the absolute properties of the binary system and also of the pulsation characteristics of the primary component. The high-resolution spectroscopic data have enabled us to estimate the atmospheric parameters of the primary component. Our BV light-curve analysis has revealed that the binary system is in a semidetached configuration, consisting of a detached main-sequence primary of spectral type A3 and an evolved secondary of early-K spectral type, which fills its inner Roche lobe completely. We found that the two components are too close to each other to form an accretion disk. Spectroscopic results without an emission feature supported the nonexistence of noticeable disk. The rotation of the primary turned out to be nearly synchronized with the revolution, giving a hint that IV Cas is in the middle or late stage of the slow mass transfer phase. This coincides well with a slow mass transfer rate deduced from the fact that there was no secular parabolic change of the orbital period for the past ∼100 yr. Using residuals subtracted from synthetic eclipsing curves of photometric data, we examined the pulsation properties of the primary component. A multiple-frequency analysis was applied to the residuals in the out-of-primary eclipsing phases and this resulted in the detection of four frequencies: f1 = 32.69236 cycles day-1, f2 = 36.65999 cycles day-1, f3 = 20.71649 cycles day-1, and f4 = 30.66072 cycles day-1. We tentatively identified their pulsation modes on the basis of pulsation constants, frequency spacing, mode visibility in eclipsing binaries, phase differences, and amplitude ratios; f1 and f4 (or f1 and f2) appeared to be rotational splitting frequencies. The observational properties of IV Cas well matched the empirical relations for Algol-type eclipsing binaries with δ Scuti-type pulsating components.