Exploring Free Floating Planets with Microlensing

Abstract

About one year ago, the MOA microlensing team announced the discovery of a free floating planet population with the method of gravitational microlensing (Sumi et al. 2011). In this thesis, we test the possibility of these planets being in reality bound but getting confused as free floating because of the shape of their light curve. Following a review of extrasolar planets and a description of the method of gravitational microlensing, we simulate binary lensing events produced by several combinations of parameters for the source star, the lens star and the planet, the light curves of which, afterwards, are fitted to the light curve of a single lensing event. After rejecting some of the simulated events because of their unclear light curve, we determine which of the simulated binary microlensing events produce a light curve that cannot be differentiated to that of a free floating planet, their fitting parameters, the parameters that produced them and their relative frequency. Our results indicate that, for Jupiter mass free-floating planets, we expect less than 0.1 out of the 1000 events analysed by MOA to look like free floating systems yet be caused by bound planets within 100 AU of their host star. As a result, the comparison of our results with the results of Sumi et al. (2011) reveals that the population of exoplanets that Sumi et al. (2011) detected consists either from actually unbound planets or from bound planets with sky-projected separations from their host, longer than 100 AU.

Date of Award	17 Oct 2012
Original language	English
Awarding Institution	The University of Manchester