Transit light curve and inner structure of close-in planets

TL;DR

This paper introduces a method to account for tidal bulges in transit light curves of close-in planets, enabling better estimates of their internal structure and density.

Contribution

It presents an easy approach to incorporate tidal deformation effects into transit observations and derives formulas to estimate internal properties and correct density measurements.

Findings

Differences in light curves due to tidal bulges are larger than previously thought.

Detectable differences allow estimation of the fluid Love number, revealing internal structure.

Corrected densities can be up to 20% smaller than spherical assumptions.

Abstract

Planets orbiting very close to their host stars have been found, some of them on the verge of tidal disruption. The ellipsoidal shape of these planets can significantly differ from a sphere, which modifies the transit light curves. Here we present an easy method for taking the effect of the tidal bulge into account in the transit photometric observations. We show that the differences in the light curve are greater than previously thought. When detectable, these differences provide us an estimation of the fluid Love number, which is invaluable information on the internal structure of close-in planets. We also derive a simple analytical expression to correct the bulk density of these bodies, that can be 20% smaller than current estimates obtained assuming a spherical radius.