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Planet Analysis and Small Transit Investigation Software

Final Report Summary - PASTIS (Planet Analysis and Small Transit Investigation Software)

Small planets orbiting other stars are difficult to find. Their astrophysical signature might be mimicked by different other sources, biasing their interpretation. The PASTIS (Planet Analysis and Small Transit Investigation Software) is a unique European code that aims at determining if a planetary signal, detected by state-of-the-art space missions or ground-based instruments, is actually a planet or not. This validation procedure is however limited by the lack of knowledge on the host star or by its intrinsic variability. To improve the validation capabilities of the PASTIS tool, in particular towards small planets in the habitable zone of their star, this MSCA project aims at:
(1) implementing new constraints about the host star, in particular the result from asteroseismology (stellar density)
(2) implementing new models to account for stellar variability (such as spots, plages, granulation, magnetic cycles)
The upgrade of PASTIS is needed to be ready to validate small planets that will be detected by the next-generation instruments like the ESPRESSO (ESO / VLT) and the PLATO space mission (ESA).

At the end of this MSCA project, the new developments have been implemented and tested. Using the asteroseismic constraints on the host star substantially improves the validation efficiency. This has already been used for a design study of the PLATO mission. A model for stellar activity (SOAP) has been fully implemented. However, during the test phase, it turns out that the complexity added by this new model substantially increased the computing time, as such as the code could not be used anymore within a reasonable amount of time (a week). Hence, another approach has been explored: such as Gaussian Process. This new approach allows to model stellar activity "noise" as long as this noise is coherent (hence producing a correlated noise). It has been applied to the test case of CoRoT-7.

The PASTIS software was used to validate about a dozen of planets, down to the size of the Earth, from the Kepler, K2, and Super-WASP surveys.

During the two years of this project, the fellow published 35 papers as first author or co-author and gave talks or invited review in 14 international conferences and seminars.