KIC 3749404: A heartbeat Star with Rapid Apsidal Advance Indicative of a Tertiary Component

TL;DR

This paper models the heartbeat star KIC 3749404, revealing a rapid apsidal advance likely caused by a tertiary component, with implications for understanding complex stellar interactions.

Contribution

It introduces a modified binary star model including tidally induced pulsations and Doppler boosting, and identifies a third body as the likely cause of rapid apsidal motion.

Findings

Observed apsidal advance is two orders of magnitude greater than theoretical predictions.

Including pulsations significantly alters model parameters.

Evidence suggests a third body influences the system's dynamics.

Abstract

Heartbeat stars are eccentric (e > 0.2) ellipsoidal variables whose light curves resemble a cardiogram. We present the observations and corresponding model of KIC 3749404, a highly eccentric (e = 0.66), short period (P = 20.3 d) heartbeat star with tidally induced pulsations. A binary star model was created using PHOEBE, which we modified to include tidally induced pulsations and Doppler boosting. The morphology of the photometric periastron variation (heartbeat) depends strongly on the eccentricity, inclination and argument of periastron. We show that the inclusion of tidally induced pulsations in the model significantly changes the parameter values, specifically the inclination and those parameters dependent on it. Furthermore, we determine the rate of apsidal advance by modelling the periastron variation at the beginning and end of the 4-yr Kepler data set and dividing by the elapsed time. We compare the model with the theoretical expectations for classical and general relativistic apsidal motion and find the observed rate to be two orders of magnitude greater than the theoretical rate. We find that the observed rate cannot be explained by tidally induced pulsations alone and consequently hypothesise the presence of a third body in the system.