Overcoming stellar activity in radial velocity planet searches
Radial velocity (RV) planet searches are a key exoplanet detection method, and one of the only ways to measure a planet's mass. The best RV instruments today reach precisions well below 1 m/s, something which would have seemed impossible 30 years ago. The key factor limiting the sensitivity of RV surveys now is stellar activity. Regions of enhanced magnetic flux on the stellar surface alter the shape of absorption lines in the stellar spectrum, and perturb the measured RVs. I have developed physically motivated but flexible, data-driven methods to disentangle planets from activity in RV data, which are critical to the success of future surveys. I now propose to apply these state-of-the-art techniques to the very large sample of multi-epoch spectra collected by HARPS and HARPS-N, the leading RV spectrographs of the past decade, and then to the forthcoming Terra Hunting Experiment (THE), which will use a copy of HARPS on a dedicated telescope to search for Earth-analogues around nearby stars. 

The combined HARPS(N) archives are a treasure trove of information on activity-induced perturbations to spectra and RVs, which is currently under-exploited. This project have a transformative effect on our understanding of different types of activity effects, their dependence on stellar properties, and their signatures in the spectra and RVs. It will reveal planets that were missed by previous analyses, particularly around active (young) stars. Finally, it sets out a clear route to the efficient mitigation of activity effects that the THE survey requires to achieve its goals. THE will discover some of the best exoplanet characterisation targets for the next 15-20 years, and my ERC-funded team will be central to its success.