Development of Space Based Microlensing Exoplanet Mass Measurement Method

Gravitational microlensing is a popular technique used for detecting cold, gas giant exoplanets. When a background star is being lensed by a foreground star, it shows a single lens microlensing light curve. The background star being known as the source and the foreground star as the lens. If the lens star also has a planet orbiting it, the source is lensed due to the planet as well, causing a perturbation in the single lens light curve. The light curve modeling of these perturbations yield the discovery of the exoplanets. This dissertation work is divided into two parts: a. detection and the light curve modeling of the microlensing exoplanets using ground based data b. detection and the confirmation of the microlensing exoplanet from the high resolution follow-up images. With microlensing survey data from MOA (Microlensing Observations in Astrophysics) and OGLE (Optical Gravitational Lensing Experiment) and follow up ground based data of ROBONET telescopes, a planetary anomaly was noticed in microlensing event OGLE-2014-BLG-1760. Light curve analysis of the event led to the discovery of a gas giant planet around OGLE-2014-BLG-1760. We also analyzed the follow up high resolution HST (Hubble Space Telescope) and Keck images of events OGLE-2005-BLG-169, MOA-2008-BLG-310 and MOA-2008-BLG-379. The study of OGLE-2005-BLG-169 HST images led to the first confirmation of a microlensing planetary signal. It yielded a direct detection of the lens system and mass measurement of a Uranus mass exoplanet. These HST studies were done folloeing a modified version of Dr. Jay Anderson's astrometry codes. Studies on MOA-2008-BLG-310 and MOA-2008-BLG-379 involved modification of the astrometry code to include MCMC (Monte Carlo Markov Chain) algorithm and also taking account of the crowded field photometry. MOA-2008-BLG-379 exoplanet is also confirmed using both HST and Keck. For MOA-2008-BLG-310 event, an upper limit on the lens mass was derived. The technique developed in this project will serve as the primary method for WFIRST microlensing exoplanet mass measurement. The method developed in this dissertation can be used to build the WFIRST pipeline for microlensing exoplanet detection and mass measurement. In WFIRST era, it will help to measure the properties of the cold giant planets toward the galactic center with planet mass down to mars mass. We will be able to build the statistics of exoplanets with different mass and different host stars. With the demographics of exoplanets, we will be able to verify the existing planet formation theories. This will help us to understand the planet formation and their evolution with the progress of time better.