The Frequency of Extrasolar Planet Detections with Microlensing Simulations

Abstract

To date, over 500 extrasolar planets have been discovered. The microlensing planets, although relatively few in number, probe a region of the planet mass versus semi-major axis plane that is currently out of reach of the other methods, with the sensitivity peaking just beyond $\sim 1$ AU. Microlensing planets are therefore very useful for placing constraints on planet formation models.We simulate light curves for 1000 extrasolar planet systems around host stars of mass $0.25\,\,{\textrm{M}}_{\odot}$, drawn from the Ida \& Lin core accretion models of planet formation, to determine the frequency of single and multiple planet perturbations. The simulated data is first fitted with a single-lens model. If the fit is poor, combinations of the planets most likely to be causing perturbations are placed around the star and new light curves are generated to attempt to reproduce the original light curve. It was found that the majority of the light curves were well-fitted by single-lens models, corresponding to the absence of planetary signals. However, 26 were determined to contain pertubations due to at least one planet. Of the 26 interesting light curves, it was found that 16 could be explained by the presence of a single planet. A greater number of planets were necessary to explain the remaining 10 cases. The fraction of planetary events to all microlensing events was found to be $0.026^{+0.006}_{-0.005}$, while the fraction of multiple-planet events to planetary events was $0.38^{+0.10}_{-0.09}$, increasing to $0.50^{+0.17}_{-0.17}$ when only the relatively high-magnification events (those with impact parameter $

Date of Award	1 Aug 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Shude Mao (Supervisor)