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

William F. Welsh, Jerome A. Orosz, Sara Seager, Jonathan J. Fortney, Jon Jenkins, Jason F. Rowe, David Koch, William J. Borucki

Published 2010-01-03, updated 2010-02-05Version 2

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.