The Milky Way and its Exoplanets

Sammanfattning: The detections of over 4000 exoplanets as of today has shown that they exist in a wide range of different configurations, otherwise known as architectures. Recently, studies have been made trying to link the environment of host stars to the architectures of their planetary systems and have found that the architectures of planetary systems may not necessarily be uniform in the Milky Way. Since effects such as photoevaporation may truncate or dissipate protoplanetary discs and thus affect the formation and evolution of planetary systems, we aim to investigate how planetary system architectures are affected by the galactocentric radius at which their host stars were formed. By determining the ages of stars using a precise Bayesian fitting algorithm and combining these with their metallicities and models of the evolution of the radial metallicity gradient in the Milky Way, the \textit{formation radii} of stars are determined. By binning the stars in formation radius and estimating the occurrence rates in each bin through Markov Chain Monte Carlo simulations of a Poisson process likelihood model which separates different orders of detection, individual multiplicities of planetary systems can be linked with the birth environment of their stars. \\ \\ Six-planet systems were found to be the most common multiplicity for all formation radii and was also the highest multiplicity considered although due to very large uncertainties and the expectation that high multiplicities are common, these results will need to be further investigated. No statistically significant trend between the occurrence rate of planetary systems and the formation radius of their host stars was found for any of the multiplicities considered but the large uncertainties make the results still inconclusive. \\ \\ KS tests were performed on the orbital period and planet radii distributions of planets around host stars formed inside and outside a given Galactocentric radius. After debiasing for stellar ages, the null hypothesis that the two subsamples of orbital periods and planet radii were drawn from the same, underlying distribution, could not be rejected for any formation radius. These results hints towards the formation process and evolution of planetary systems being independent of the galactocentric radius at which the system was formed although further investigations are needed.