Presentation description

The angular diameter of a star can be used for probing models of stellar structure and evolution. Star angular diameters are challenging to get through direct observation, as it is difficult for any telescope to resolve the image of a distant star. Asteroid occultation provides an alternative way to measure the angular diameter of a star. This work continues the original work found in W. Benbow et al. (Nature, 2019), using data from Imaging Atmospheric Cherenkov Telescopes (IACTs) VERITAS (Very Energetic Radiation Imaging Telescope Array System). Located in Southern Arizona, VERITAS is designed to study sources of astrophysical gamma-rays due to larger mirror areas (>100 m^2), and very fast camera electronics (500 MHz bandwidth). Using several updates to observe optical targets, VERITAS now has the capability for asteroid occultation observation. When an asteroid passes in front of the star, it blocks some of the light emitted by the star, causing not only a drop in the intensity observed, but also diffraction pattern. Monochromatic diffraction patterns can be simulated by using wavelength, distance to the asteroid, and the speed of the asteroid. Using the spectrum profile of the TYC 2924-02100-1 from the Gaia archive, the final Fresnel diffraction pattern can be obtained by adding a monochromatic diffraction pattern. The stellar angular diameter can then be estimated by fitting the final polychromatic diffraction pattern to the occultation event from VERITAS, using python library lmfit. The Grid Search method, Least Chi-Square method, and Markov Chain Monte Carlo method will be applied to determine the final stellar angular diameter and standard deviation. An observed asymmetry between diffraction pattern at the beginning and at the end of occultation could also provide a hint to the geometrical profile of the asteroid or the effects of limb darkening. The resulting angular diameter will be part of the angular diameter catalog from VERITAS and will also be utilized for further stellar analysis and asteroid analysis.