CoRoT-18 b: Analysis of high-precision transit light curves with starspot features

TL;DR

This study analyzes high-precision transit light curves of CoRoT-18 b, focusing on starspot features, to refine system parameters, measure stellar rotation, and assess star age, contributing to understanding planet formation and migration.

Contribution

It provides a detailed analysis of starspot crossings in CoRoT-18 b transits, refining system parameters and measuring stellar rotation and spin-orbit alignment.

Findings

Derived stellar rotation period Prot=5.19 days

Measured spin-orbit angle Lambda=6 degrees

Supports a young star hypothesis for CoRoT-18

Abstract

When a planet occults a spotty area on a stellar surface, the flux increases and a characteristic feature in a light curve - a bump - is observed. Among the planets detected by the CoRoT-mission CoRoT-18 is especially interesting as it exhibited spot crossings that we have analysed in detail. We used four ground-based observations obtained at a 1.5-m telescope in Spain and the 13 available CoRoT-transits to refine and constrain stellar, planetary and geometrical parameters of the system. We found that the derived physical properties slightly deviate from the previously published values, most likely due to the different treatment of the stellar activity. Following a spot over several transits enabled us to measure the stellar rotation period and the spin-orbit alignment. Our derived values of Prot=5.19 +/- 0.03 d and Lambda=6 +/- 13 deg are in agreement with the literature values that were obtained with other methods. Although we cannot exclude a very old age for CoRoT-18, our observations support the young star hypothesis and, hence, yield constraints on the time-scale of planet formation and migration.