A $5/4$ commensurability of KIC 5773205, the smallest eclipsing red dwarf detected by the Kepler mission

TL;DR

This paper reports the discovery of a unique eclipsing M dwarf star with a 5/4 commensurability between its pulsation and orbital periods, suggesting possible tidal interactions or resonances.

Contribution

It introduces the first observation of a star possibly exhibiting tidally excited pulsations in a heartbeat binary system.

Findings

Detected a 4:5 commensurability between pulsation and orbital periods.

Discussed three potential explanations for the observed periodic variation.

Favors the tidally driven pulsation scenario as the most plausible explanation.

Abstract

KIC 5773205 is the least luminous eclipsing M dwarf found in the Villanova catalog of eclipsing binaries detected by the {\it Kepler} mission. We processed and analyzed the three available quarters of mission data for this star and discovered a persistent periodic variation of the light curve with a period, which is in exact 4:5 commensurability to the orbital period. Three routes of interpretation are considered: 1) non-radial pulsations excited by the tidal interaction at a specific eigenfrequency; 2) a high-order spin-orbit resonance caused by the tides; 3) an ellipsoidal deformation caused by an outer orbiting companion in a mean motion resonance. All three explanations meet considerable difficulties, but the available facts seem to favor the tidally driven pulsation scenario. The star may represent a new type of heartbeat binary with tidally excited pulsations that are close to the orbital motion in frequency.