Gravitational microlensing as a diagnostic tool for stellar astrophysics
Chapter One introduces the theory of galactic microlensing and develops the necessary formulae needed to discuss extended source events in the subsequent Chapters. Some of the complications encountered by groups observing such events are discussed, as are a few of the more notable events themselves. In Chapter Two an extended source model for microlensing is presented and applied to different atmosphere models, with different surface brightness profiles including simple one and two parameter limb darkening models and the more sophisticated and recently developed "Next Generation" stellar atmosphere models. It is shown that microlensing can distinguish between these different surfaces brightness profiles and thus, the underlying stellar atmosphere models, for realistic observational strategies. In Chapter Three a second stellar atmosphere models is introduced. This model includes the effects of a non-radial surface brightness profile, i.e. starspots. Such effects are interesting for several reasons. Firstly, the existence or otherwise of starspots is an important indicator of stellar surface activity and would provide valuable information for the testing and development of more sophisticated stellar atmosphere models. Additionally, there has been concern that starspots could mimic planetary microlensing lightcurves making it important to consider how their observational signatures could be distinguished from those of planets. The microlensing signatures of starspots are considered for point mass lens in Chapter Three and for fold caustic crossings in Chapter Four. In Chapter Five the extended source model used previously is applied to a source model with a small level of radial and temperature variability, to allow examination of how such events, if observed, would compare to standard microlensing events. In Chapter Six an investigation is made of the spectroscopic signatures of microlensing from circumstellar envelopes and the opportunities of using microlensing to diagnose bulk motion in these envelopes during caustic crossing events is examined.