Investigating spatial variation in the surface and atmosphere of Pluto through stellar occultations and PSF photometry

Abstract

Stellar occultations provide a high-resolution view of a single chord through Pluto's atmosphere. This thesis presents three projects related to stellar occultation observations of Pluto. The first project concerns the ground testing of the High-speed Imaging Photometer for Occultations (HIPO), a camera aboard the Stratospheric Observatory For Infrared Astronomy (SOFIA). Differential photometry was found to be reliable to one part in 104. The second project is a modern determination of the light ratio of Charon and Pluto, essential for predicting future occultations. The final project considers twenty years worth of Pluto stellar occultation results, including new measurements using HIPO, and determines whether temperature asymmetries can be seen in fits for the upper atmosphere. These measurements allow the first Earth-based assessment of Pluto's geographic temperature distribution. Included is a description of the extensive test modeling to determine the boundary selection methods for the upper atmosphere for each differently-shaped light curve. The temperature asymmetries or lack thereof, are considered in the context of time of day, average insolation and surface features in the vicinity of the area near the occultation half-light radius. No clear correlation was found for any of the three metrics, suggesting that Pluto's atmosphere is spatially isothermal.