Master's Thesis Defense by Stefano Bellotti

Supervisor: Heidi Korhonen
External examiner:  Frank Grundahl

Title:  Stellar activity induced detection limits for habitable zone planets around a representative sample of known planet hosts

Abstract: Starspots are one of the main hindering factors when searching for extra-solar planets. They represent a practical problem which is connected to the magnetic activity of the star and that is known to contribute to radial velocity measurements. Indeed, starspots alter the shapes of spectral line profiles, leading to an apparent radial velocity variation (known as ``jitter'') which might both drown the signal from the planetary companion and result in the erroneous determination of planetary parameters.
I simulate radial velocity curves that an Earth-mass planet in the habitable zone would produce, while taking into account the magnetic activity of the host star. The simulations are performed generating synthetic stellar spectra for a sample of known host stars ranging from F to M type and spanning different activity levels. The datasets are then investigated by means of the Lomb-Scargle period search with the aim to assess whether the detection of a habitable Earth-mass planet would be feasible or not. I find that M dwarfs are more suitable targets for observational surveys with this objective, in agreement with current and prospective missions. In case the planetary signature is completely overpowered by the stellar activity, I further extend the period analysis to a wider range of planetary masses in order to determine the lower limit of mass at which the detection would be successful. I finally apply the harmonic decomposition filtering technique on the datasets to present how a priori knowledge on the stellar parameters is a determining factor in improving the detection towards low-mass planets.