The Discovery of Ellipsoidal Variations in the Kepler Light Curve of HAT-P-7

TL;DR

This paper reports the detection of ellipsoidal variations in the Kepler light curve of HAT-P-7, caused by the star's distortion due to the close-in planet, and emphasizes their importance in accurate planetary modeling.

Contribution

It introduces the first detection and modeling of ellipsoidal variations in HAT-P-7's light curve using Roche potential approximation, refining planetary parameters.

Findings

Ellipsoidal variations are present and detectable in the Kepler data.

Modeling these variations improves the accuracy of planetary and orbital parameters.

Ellipsoidal variations can affect interpretation of planetary phase curves.

Abstract

We present an analysis of the early Kepler observations of the previously discovered transiting planet HAT-P-7b. The light curve shows the transit of the star, the occultation of the planet, and the orbit phase-dependent light from the planet. In addition, phase-dependent light from the star is present, known as "ellipsoidal variations". The very nearby planet (only 4 stellar radii away) gravitationally distorts the star and results in a flux modulation twice per orbit. The ellipsoidal variations can confuse interpretation of the planetary phase curve if not self-consistently included in the modeling. We fit the light curve using the Roche potential approximation and derive improved planet and orbit parameters.