Measuring Exoplanetary Radii Using Transit Photometry

(1) Fairview High School, Boulder, Colorado, (2) University of Colorado, Boulder, Colorado
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The goal of this study was to measure the radii and constrain the orbital periods of three hot Jupiter exoplanets: HAT-P-25b, HAT-P-9b, and HAT-P-30b. Raw images of the host stars were acquired from the Apache Point Observatory in New Mexico. A data processing pipeline utilizing the Python programming language was used to convert the raw data images into calibrated pixels and transit light curve graphs. The graphs of HAT-P-25b and HAT-P-30b were fit with multiple light curve models, which varied based on a given range of radius and time of mid-transit parameters within the code. The data of HAT-P-9b were not further analyzed due to a non-detection in the data. We hypothesized that the differences between the dates the exoplanets were discovered and the dates on which we observed them have no effect on the radii of the exoplanets and their times of mid-transit. Chi-square Goodness of Fit tests were performed on all light curve models to isolate the chi-square value closest to 1.0. Chi-square maps were used to estimate the 1σ error bars for all light curve calculations. A significant shift in mid-transit time (-0.41 ± 0.31 hours from expected value) was detected for HAT-P-25, and a significant difference (0.04 ± 0.0020) from the literature value was calculated for the normalized radius (Rp/R*) of HAT-P-30b. These findings stress the importance of updating exoplanetary measurements and will help scientists obtain more accurate knowledge about the characteristics of these exoplanets and their evolution over time.

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