The eclipsing binary systems with $\delta$ Scuti component -- II. AB Cas

TL;DR

This study of AB Cas combines light curve analysis, period change measurement, and binary evolution modeling to understand its pulsations, mass transfer history, and current evolutionary state, revealing insights into binary and stellar evolution.

Contribution

It provides the first detailed demonstration of how binary evolution influences radial pulsations and constrains key stellar parameters for AB Cas.

Findings

Detected 112 significant frequencies, with 17 independent signals.

Confirmed ongoing mass transfer causing orbital period change at 0.03 s/year.

Estimated system parameters, including age, overshooting, and mixing-length, through combined modeling.

Abstract

We present a complex study of the eclipsing binary system, AB Cas. The analysis of the whole TESS light curve, corrected for the binary effects, reveals 112 significant frequency peaks with 17 independent signals. The dominant frequency $f_1 = $17.1564 d$^{-1}$ is a radial fundamental mode. The $O-C$ analysis of the times of light minima from over 92 years leads to a conclusion that due to the ongoing mass transfer the system exhibits a change of the orbital period at a rate of 0.03 s per year. In order to find evolutionary models describing the current stage of AB Cas, we perform binary evolution computations. Our results show the AB Cas system as a product of the rapid non-conservative mass transfer with about 5-26 % of transferred mass lost from the system. This process heavily affected the orbital characteristics of this binary and its components in the past. In fact, this system closely resembles the formation scenarios of EL CVn type binaries. For the first time, we demonstrate the effect of binary evolution on radial pulsations and determine the lines of constant frequency on the HR diagram. From the binary and seismic modelling, we obtain constraints on various parameters. In particular, we constrain the overshooting parameter, $f_{\rm ov}\in [0.010,~0.018]$, the mixing-length parameter, $\alpha_{\rm MLT}\in[1.2,~1.5]$ and the age, $t \in [2.3,~3.4]$ Gyr.