Planetary eclipse mapping of CoRoT-2a. Evolution, differential rotation, and spot migration

TL;DR

This study models the lightcurve of CoRoT-2 to analyze starspot distribution, evolution, and differential rotation, revealing significant spot coverage, rotation period variations, and preferred longitudes on the star's surface.

Contribution

It provides a comprehensive modeling approach combining transit and rotational data to map starspots and measure differential rotation on CoRoT-2a, which is novel in its detailed surface analysis.

Findings

Spot coverage up to 40% on eclipsed surface

Differential rotation with ΔΩ > 0.1 detected

Preferred longitudes separated by 180 degrees identified

Abstract

The lightcurve of CoRoT-2 shows substantial rotational modulation and deformations of the planet's transit profiles caused by starspots. We consistently model the entire lightcurve, including both rotational modulation and transits, stretching over approximately 30 stellar rotations and 79 transits. The spot distribution and its evolution on the noneclipsed and eclipsed surface sections are presented and analyzed, making use of the high resolution achievable under the transit path. We measure the average surface brightness on the eclipsed section to be (5\pm1) % lower than on the noneclipsed section. Adopting a solar spot contrast, the spot coverage on the entire surface reaches up to 19 % and a maximum of almost 40 % on the eclipsed section. Features under the transit path, i.e. close to the equator, rotate with a period close to 4.55 days. Significantly higher rotation periods are found for features on the noneclipsed section indicating a differential rotation of $\Delta \Omega > 0.1$. Spotted and unspotted regions in both surface sections concentrate on preferred longitudes separated by roughly 180 deg.