Validation of the Frequency Modulation technique applied to the pulsating delta Sct - gamma Dor eclipsing binary star KIC 8569819

TL;DR

This study validates the frequency modulation (FM) technique for analyzing pulsating eclipsing binary stars using Kepler data, demonstrating its effectiveness in determining orbital parameters and detecting potential third bodies without relying on transits or radial velocities.

Contribution

The paper introduces and validates the FM technique as a reliable method for studying pulsating binary stars and detecting additional companions in Kepler data, expanding the tools available for exoplanet and companion detection.

Findings

FM technique yields orbital parameters consistent with traditional modeling.

Detected FM signal suggests a potential third body, a low-mass M dwarf.

No eclipse timing variations observed, indicating intrinsic pulsation frequency changes.

Abstract

KIC 8569819 is an eclipsing binary star with an early F primary and G secondary in a 20.85-d eccentric orbit. The primary is a delta Sct - gamma Dor star pulsating in both p modes and g modes. Using 4 years of Kepler Mission photometric data we independently model the light curve using the traditional technique with the modelling code PHOEBE, and we study the orbital characteristics using the new frequency modulation (FM) technique. We show that both methods provide the equivalent orbital period, eccentricity and argument of periastron, thus illustrating and validating the FM technique. In the amplitude spectrum of the p-mode pulsations we also discovered an FM signal compatible with a third body in the system, a low mass M dwarf in an 861-d orbit around the primary pair. However, the eclipses show no timing variations, indicating that the FM signal is a consequence of the intrinsic change in pulsation frequency, thus providing a cautionary tale. Our analysis shows the potential of the FM technique using {\it Kepler} data, and we discuss the prospects to detect planets and brown dwarfs in Kepler data for A and F stars even in the absence of transits and with no spectroscopic radial velocity curves. This opens the possibility of finding planets orbiting hotter stars that cannot be found by traditional techniques.