Using Atmospheric Cherenkov Telescope arrays as Intensity Interferometers

The Narrabri intensity interferometer was successfully used until 1974 to observe 32 stars [1], all brighter than B=+2.5, among which some were found to have an angular diameter as small as 0.41+/-0.03 milli-arcseconds (mas). The technique was then abandoned in favor of Michelson interferometry [2, 3]. Here we consider the technical feasibility and scientific potential of implementing intensity interferometry on Imaging Air Cherenkov Telescope arrays. The scientific motivations are varied, including stellar diameter measurements and investigations of the circumstellar environment. Long baselines and short wavelengths are easily accesible to this technique, making it uniquely suited for some applications.