Exploring the effects of limb darkening on multi-wavelength photometric and spectroscopic studies of extrasolar planets

• Applicant: Professor Dr. Jürgen H.M.M. Schmitt
• Subject Area: Astrophysics and Astronomy
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 402218555

Limb darkening, i.e., the brightness change on the visible stellar disk in radial direction, is an important physical parameter in the research area of stellar and planetary systems. Unfortunately, a direct measurement of limb darkening is only possible for the Sun, while limb darkening for stars is usually inferred from atmosphere models. Due to the discovery of many planets around solar-like stars especially with the transit method, the study of the limb darkening has undergone some kind of renaissance. Limb darkening does show strong correlations with most other transit parameters, therefore most exoplanet observers treat stellar limb darkening as a ``nuisance'' parameter in their transit modeling.However, limb darkening can directly be measured during a planetary eclipse, if the data quality is sufficiently high. Furthermore and less well known, limb darkening is also very important for the area of transmission spectroscopy and consequently for all studies of the exoplanetary atmospheres and their chemical composition. The time has therefore come to take a fresh look at stellar limb darkening with a specific focus on its influence on the study of extrasolar planets using the transit method, which is the central theme of the here proposed research project. We specifically propose to carry out transit light curve simulations as realistically as possible using most recent stellar model atmospheres and develop analysis methods that allow to derive the transit parameters in a fashion as independently from limb darkening as possible. These analysis methods shall be applied to existing archival data, and at the same time, we plan to study the potential of JWST for transit studies of extrasolar planets. A further major issue is that of differential limb darkening, a good knowledge of which is absolutely essential to disentangle planetary and stellar signals in high resolution transmission spectroscopy aimed at revealing spectroscopic signatures of exoplanetary atmospheres. To complete our research project we plan to investigate the influence of oblateness of both the host star and the planet caused by fast rotation.

• DFG Programme: Research Grants