First indications of a non-round star with stellar intensity interferometry

Gamma Cassiopeia is a rapid rotator (believed to be spinning at 99% of its break-up velocity), as evidenced from spectroscopy and the extended decretion disk imaged at infrared frequencies. However, measuring the photosphere at optical wavelengths with stellar intensity interferometry has so far yielded only a measure of the average angular size of the star. VERITAS-SII uses four 12-meter telescopes to simultaneously sample 6 baseline vectors at various angles in the u-v plane. Between Jan 2023 and May 2024, more than 20 hours of SII data were accumulated on gam Cas. We will present the measurement details, the extracted correlations, and evidence for an anisotropic photosphere bulging at the equator, perpendicular to its angular momentum. The results are largely consistent with expectations based on infrared measurements and stellar models. This measurement is the first time that optical stellar intensity interferometry has extracted the size, shape, and orientation of a non-round star.