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Wednesday 22 Nov 2023 Modelling stellar activity to detect and characterise exoplanets

Baptiste Klein - University of Oxford

Physics building, 4th floor 14:00-15:00

The detection of an Earth twin is one of the most exciting prospects for future astrophysics. New-generation high-resolution spectrographs, have now the sensitivity to detect Earth-mass planets in the habitable zone of stars with masses comparable to or less than that of the Sun. Yet, radial velocity (RV) planet searches are largely hampered by signals induced by the host star's intrinsic variability. In particular, magnetically-active photospheric regions distort the stellar absorption lines, resulting in apparent RV signals that mask planet signatures. As if that wasn't enough, stellar magnetic activity is also affecting the characterisation of planetary atmospheres at low and high resolutions.

Over the past few years, the accurate modelling of stellar activity signals has become an extremely active area of research with promising state-of-the-art methods being released every year. In this seminar, I will give a review some of these new approaches, and illustrate their performances on our own Sun, observed, as a star, with the high-precision spectrograph HARPS-N. I will demonstrate that modelling activity not only in the time domain, as traditionally done, but also in the wavelength domain (i.e. from the spectrum itself) has the potential to separate, in a robust way, planet and stellar contributions, to the point where the RV measurement could actually be bypassed. I will conclude by discussing how these methods fit in the context of forthcoming missions of planet detection and atmosphere characterisation.

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