Time-series Spectroscopy of the Oscillating Algol-type Binary AB Cas

Abstract

This study presents the high-resolution spectra of the eclipsing binary AB Cas with a δ Sct-type pulsating component, which were obtained using the Bohyunsan Optical Echelle Spectrograph in Korea. In this paper, the radial velocities for the primary and secondary stars were measured from a total of 27 spectra made during two nights in 2015 October. We derived accurate physical properties of the system for the first time by simultaneously analyzing our radial velocity curves together with previously published uvby light curves. Individual masses, radii, and effective temperatures of both components were determined to be {M}₁=2.01+/- 0.02 M _⊙ and {M}₂=0.37+/- 0.02 M _⊙, {R}₁=1.84+/- 0.02 R _⊙ and {R}₂=1.69+/- 0.03 R _⊙, and {T}_{eff,1}=8080+/- 170 K and {T}_{eff,2}=4925+/- 150 K, respectively. The results should be more accurate than previous photometric studies. We investigated the evolutionary history of AB Cas by comparing its physical parameters with stellar evolutionary models. The primary component is not a classical δ Sct pulsator but is the result of mass accretion transferred from the initial more massive star, which is the present secondary. This indicates that AB Cas is an oscillating Algol-type eclipsing binary with a low-mass and oversized secondary component filling its inner Roche lobe.