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doi: 10.32023/0001-5237/69.3.1

Vol. 69 (2019), No. 3

pp. 205-226

CoRoT-18 b: Analysis of High-Precision Transit Light Curves with Starspot Features

St. Raetz^1,2,3, A.M. Heras³, P. Gondoin⁴, M. Fernández⁵, V. Casanova⁵, T.O.B. Schmidt⁶ and G. Maciejewski^7
1Institute for Astronomy and Astrophysics Tübingen (IAAT), University of Tübingen, Sand 1, D-72076 Tübingen, Germany
e-mail:raetz@astro.uni-tuebingen.de
²Freiburg Institute of Advanced Studies (FRIAS), University of Freiburg, Albertstraße 19, D-79104 Freiburg, Germany
³Science Support Office, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁴Future Missions Department, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁵Instituto de Astrofísica de Andalucía, CSIC, Apdo. 3004, 18080 Granada, Spain
⁶Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany
⁷Centre for Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Toru�, Poland


Received: April 12, 2019


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 analyzed 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 of a spot over several transits enabled us to measure the stellar rotation period and the spin-orbit alignment. Our derived values of P_rot=5.19±0.03 d and λ=6±13° 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.
Key words: Planets and satellites: individual: CoRoT-18b - Stars: individual: CoRoT-18 - planetary systems

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