KIC 4544587: an Eccentric, Short Period Binary System with delta Sct Pulsations and Tidally Excited Modes

TL;DR

This study combines Kepler photometry and ground spectroscopy to analyze the eccentric binary system KIC 4544587, revealing tidally excited pulsations, rapid apsidal motion, and detailed stellar parameters, advancing understanding of pulsation-tide interactions.

Contribution

It provides the first detailed binary model of KIC 4544587, identifying tidally excited pulsations and their influence on both gravity and pressure modes, with new insights into stellar oscillations in eccentric binaries.

Findings

Identification of 31 pulsation modes, including tidally excited ones.

Detection of rapid apsidal motion of 182 years per cycle.

Determination of stellar masses and radii with high precision.

Abstract

We present Kepler photometry and ground based spectroscopy of KIC 4544587, a short-period eccentric eclipsing binary system with self-excited pressure and gravity modes, tidally excited modes, tidally influenced p modes, and rapid apsidal motion of 182 y per cycle. The primary and secondary components of KIC 4544587 reside within the delta Scuti and gamma Dor instability region of the Hurtzsprung-Russell diagram, respectively. By applying the binary modelling software PHOEBE to prewhitened Kepler photometric data and radial velocity data obtained using the William Herschel Telescope and 4-m Mayall telescope at KPNO, the fundamental parameters of this important system have been determined, including the stellar masses, 1.98+/-0.07 MSun and 1.60+/-0.06 MSun, and radii, 1.76+/-0.03 RSun and 1.42+/-0.02 RSun, for the primary and secondary components, respectively. Frequency analysis of the residual data revealed 31 modes, 14 in the gravity mode region and 17 in the pressure mode region. Of the 14 gravity modes 8 are orbital harmonics: a signature of tidal resonance. While the measured amplitude of these modes may be partially attributed to residual signal from binary model subtraction, we demonstrate through consideration of the folded light curve that these frequencies do in fact correspond to tidally excited pulsations. Furthermore, we present an echelle diagram of the pressure mode frequency region (modulo the orbital frequency) and demonstrate that the tides are also influencing the p modes. A first look at asteroseismology hints that the secondary component is responsible for the p modes, which is contrary to our expectation that the hotter star should pulsate in higher radial overtone, higher frequency p modes.