Master's Thesis Defense by Christian Eistrup – Niels Bohr Institute - University of Copenhagen

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Master's Thesis Defense by Christian Eistrup

On Detectable Microlensing Events in the Milky Way Bulge

The microlensing technique within exoplanetary science is unique because it is capable of probing low mass exoplanets as lenses. In this thesis, I present an analysis of 11 years of OGLE microlensing data. The analysis deals with characterizing the dependence of the number of events (# of events ) that are detected, on two microlensing event parameters. These parameters are the source star magnitude MI0 , and the maximum amplification Amax during an event. I find that the dependence of the # of events on MI0 fits well with a parameterized Milky Way bulge luminosity function. I also find that the dependence on Amax can be well approximated using a 1-parameter exponential relation, and even better approximated, using a 3-dimensional exponential relation. I
adopted the Milky Way luminosity function, and the exponential relations, and I have used them to construct models of microlensing events available for detection in a given MI0 and Amax parameter space. I have appropriately normalized the models to fit the OGLE data. Using my models, I have made predictions on how many times more events that will be detectable, when instrument sensitivity improves. I find that, for events with amplifications 1.34≤ Amax <50, a 10 times increase in instrument sensitivity will make at least 2.12+0.02 times more events available for detection, than what is presently −0.03 available for detection. Since these many new available events will primarily be caused by fainter source stars than the source star which are causing events at the present, I also find that an increase in sensitivity will enable detection of smaller exoplanets, than what is detected presently. Further, small exoplanets are in higher abundance than large exoplanets, so a sensitivity increase will likely lead to a burst in the amount of microlensed exoplanets, of which the majority will be smaller planets than those that have been detected so far.

In addition to these results, I have also normalized the # of events in a selected range of OGLE data with respect to the bulge luminosity function. Thereby I have determined the OGLE phase 4 microlensing event detection rate to be ΓOGLE = 1.08±0.1/year/star. This value is comparable in size to the detection rate in the bulge found by the MOA collaboration, although my rate is higher.

Supervisor: Uffe Gråe Jørgensen