2023JAVSO..51..148S

CCD images of transits by the exoplanet XO-1b over the years 2018 to 2021 are analyzed. The data were collected by a MicroObservatory telescope in Arizona. These are supplemented by analysis of TESS space telescope data along with transits observed by amateur astronomers, leading to an investigation of the mid-transit times and the orbital period of the exoplanet. No evidence is found to support transit timing variations, with a period of 3.9415049 ± 0.0000008 days being sufficient to explain mid-transit times over 2006 to 2021. Using TESS data, the orbital radius is estimated to be some 11.10 ± 0.15 times the radius of the host star, and the planetary radius 0.1300 ± 0.0016 times the stellar radius. A simple transit model is combined with Bayesian sampling to provide estimates for the orbital inclination, radii, and limb darkening, however these estimates are not internally consistent. This is likely due to the application of the "small planet approximation," which neglects a radial gradient in the stellar flux obscured by the planet (due to the limb darkening effect), together with the model not accounting for variation in the stellar flux.