FIESTA II. Disentangling stellar variability from exoplanets in the Fourier domain

In the radial velocity detection of exoplanets, the planetary signal, i.e., the Keplerian Doppler wobbling of stars can be mimicked by stellar activities that deform the spectral line profiles, which results in apparent radial velocity shifts. Traditionally, stellar activity indicators assist in ruling out false planet detections but lack robustness and consistency. 

We’ve been developing the FourIEr phase SpecTrum Analysis (FIESTA) to parametrise spectral line profile variability in Fourier space for this challenge. The cross-correlation function (CCF) of each stellar spectrum is decomposed into Fourier basis functions and parametrised by their amplitudes and phases. We show such a parametrisation preserves all the information of the line profile and robustly traces the line variability, with examples of the SOAP solar simulations and the 3 years of HARPS-N solar observations.