Calibration of VERITAS Stellar Intensity Interferometry with Vega

The VERITAS-SII (Very Energetic Radiation Imaging Telescope Array System with Stellar Intensity Interferometry, or VSII) collaboration aims to measure the properties of stars, such as the angular diameter, using optical interferometric observations. In this project, the angular diameter of the star Vega and the zero-baseline normalization factor associated with the VSII instrument are estimated. Vega's angular diameter is found to be 2.40 milliarcseconds with 1-sigma errors of 0.49 mas (lower) and 0.55 mas (upper). At the 3 sigma level, the maximum angular diameter is unconstrained. Though the uncertainty is large, this estimate (specific to VERITAS' observational wavelength) is consistent with measurements at longer wavelengths. In addition, these observations are a useful test of the largest angular diameter that VERITAS can measure. Measurements of the instrumental normalization factor came from the stars alp Lyr (Vega), gam Cas, and gam Ori. The measured normalization is within the uncertainty of previously published values but itself has a large associated uncertainty, which can be decreased with observations made under good weather and further improvements to the VERITAS telescopes' hardware.