The project "Stellar GRAnulation in Photometric Data: Properties, Predictions and an Analysis Tool for CHEOPS (GRAPPA)" is funded by the Austrian Research Promotion Agency (FFG) under the ASAP13 scheme and as part of the Austrian contribution to the CHEOPS mission.


Project summary

Extrasolar planets that transit their host stars are key objects for the study of planets and planetary systems. As the planet passes in front of its host star, the observed flux drop reveals the planetary radius and bulk density. High-precision transit light curves (time sequence flux measurements) allow us to obtain a wealth of information on the planet, its interior structure, atmospheric composition, and the planetary system's dynamics.

The CHEOPS satellite (launch 2018) is the first ESA mission dedicated fully to the study of extrasolar planets and will obtain highest-precision transit light curves for many bright planetary systems. It will be followed by PLATO 2.0 (launch 2024), which will use the transit method to create an inventory of small transiting planets orbiting bright stars. At the precision level reached by CHEOPS, the mission is designed to be capable of detecting the minuscule signatures of planets the size of Earth, transiting Solar analogues.

However, granulation processes on the host star contribute substantial correlated noise ("Flicker"), largely limiting the attainable precision. From an exploratory project, we measure a flicker amplitude of 40 parts-per-million on the Sun, which amounts to roughly 50% of the transit depth of an Earth transiting a Solar analogue. For other stars, amplitudes of up to 350 parts-per-million have been measured.

Within GRAPPA, we aim to characterize flicker noise at high temporal resolution for a wide range of stellar types. We investigate the properties of flicker at their full resolution, and develop strategies for its modelization. To do so, we use currently existing observations of the sun and other stars and compare these to theoretical simulations to create a predictive set of theoretical model flicker light curves. Based on this understanding, we obtain realistic predictions for CHEOPS, and use these to find the optimal data analysis approach for modelling flicker-induced correlated noise. Within GRAPPA, we will create a dedicated software tool to be included in the CHEOPS data analysis toolbox. Finally, we will estimate the effects of flicker on the performance of CHEOPS, and make recommendations for an efficient observing strategy.



Project participants

Monika Lendl (PI)
Sophia Sulis (main project postdoc/engineer)
Luca Fossati
Patricio Cubillos



Resources

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