An overview of the VERITAS stellar intensity interferometer

Abstract

Imaging air Cherenkov telescope (IACT) arrays have long been viewed as potential observatories for performing stellar intensity interferometry (SII). We present results and the current status of an ongoing SII campaign using the four 12 m diameter VERITAS telescopes located at the Fred Lawrence Whipple Observatory. Each of the telescopes have been equipped with SII instrumentation, consisting of a removable SII camera and a continuous high speed data acquisition system. The correlation of digitized starlight intensities is performed off-line using FPGA hardware to calculate the squared visibilities. The system enables high angular resolution measurements with baselines ranging from approximately 81.5 to 173 m in the B photometric band. Stellar angular diameter measurements were successfully performed using all four VERITAS telescopes. These results show that IACTs can operate as SII observatories, demonstrating a technological pathway for a similar system with future IACT observatories with a hundred fold increase in the number of simultaneous baselines.