KIC 4544587: an eccentric, short-period binary system with δ Sct pulsations and tidally excited modes

Abstract

We present Kepler photometry and ground based spectroscopy of KIC 4544587, a\nshort-period eccentric eclipsing binary system with self-excited pressure and\ngravity modes, tidally excited modes, tidally influenced p modes, and rapid\napsidal motion of 182 y per cycle. The primary and secondary components of KIC\n4544587 reside within the delta Scuti and gamma Dor instability region of the\nHurtzsprung-Russell diagram, respectively. By applying the binary modelling\nsoftware PHOEBE to prewhitened Kepler photometric data and radial velocity data\nobtained using the William Herschel Telescope and 4-m Mayall telescope at KPNO,\nthe fundamental parameters of this important system have been determined,\nincluding the stellar masses, 1.98+/-0.07 MSun and 1.60+/-0.06 MSun, and radii,\n1.76+/-0.03 RSun and 1.42+/-0.02 RSun, for the primary and secondary\ncomponents, respectively. Frequency analysis of the residual data revealed 31\nmodes, 14 in the gravity mode region and 17 in the pressure mode region. Of the\n14 gravity modes 8 are orbital harmonics: a signature of tidal resonance. While\nthe measured amplitude of these modes may be partially attributed to residual\nsignal from binary model subtraction, we demonstrate through consideration of\nthe folded light curve that these frequencies do in fact correspond to tidally\nexcited pulsations. Furthermore, we present an echelle diagram of the pressure\nmode frequency region (modulo the orbital frequency) and demonstrate that the\ntides are also influencing the p modes. A first look at asteroseismology hints\nthat the secondary component is responsible for the p modes, which is contrary\nto our expectation that the hotter star should pulsate in higher radial\novertone, higher frequency p modes.\n