Modeling variability and irregular transits from circumstellar disks and debris

Abstract

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2017.Circumstellar material can lead to fluctuations in observed stellar flux by either occulting the star or contributing with reradiated light. These changes in flux providers a new window into the inner regions of the circumstellar environment. In Chapter 2, we explore circumbinary disc temperature variations as a source of broad-band infrared light curve variability. Approximating the wall of a circumbinary disc edge as a wide optically thick cylinder with surface temperature dependent on its illumination, we find that a pre-main sequence binary with a ~15.5 day period, would exhibit the largest amplitude variations of ~9% in near infrared. The light curve variations are smooth and very red with a non-sinusoidal shape for most of the parameter space explored. In Chapter 3, we revisit the nature of large dips in flux from extinction by dusty circumstellar material that is observed by Kepler for many young stars in the Upper Sco and p Oph star formation regions. We find the material causing the dips in most of these light curves to be approximately corotating with the star and temperatures computed at the disk corotation radius are cool enough that dust should not sublimate. If material needs to cooler than the dust sublimation temperature, then dippers are preferentially associated with young, low mass stars which is consistent with the sample. Magnetospheric truncation models can explain why the dips are associated with material near corotation and how dusty material is lifted out of the midplane to obscure the star which would account for the large fraction of young low mass stars that are dippers. In Chapter 4, we investigate the plausibility of a cometary source of the unusual transits observed in the KIC 8462852 light curve. We find that a series of large comet swarms provides a good fit for the KIC 8462852 data during Quarters 16 and 17, but does not explain the large dip observed during Quarter 8. A single comet family from a tidally disrupted Ceres-sized progenitor or the start of a Late Heavy Bombardment period explains the last ~ 60 days of the unusual KIC 8462852 light curve