Resolving Stellar Angular Diameters with Asteroid Occultations

Occultations have been used for measuring stellar angular diameters since 1936 when French astronomy M. A. Arnulf measured the radius of Regulus during a lunar occultation. Since then, astronomers have used lunar occultations to measure the angular diameters of hundreds of bright stars m≤5. The technique of measuring an angular diameter using lunar occultations is based on the diffraction of light around the limb of the moon. With this technique, stars down to 1 milliarcsecond could be resolved. In 2018, the ground-based gamma-ray observatory VERITAS detected two asteroid occultations. By imaging the diffraction pattern produced during the ingress and egress of the occultation, VERITAS measured at that time the smallest stellar angular diameter ever recorded of the G IV star TYC 278-748-1 (0.094+0.009 −0.010 mas). Currently, several other stars have also had angular diameters measured. This presentation details the technique, current analysis, and some preliminary results for stellar angular diameters