Demonstration of stellar intensity interferometry with the four VERITAS telescopes

TL;DR

This paper demonstrates the successful use of the VERITAS telescope array for stellar intensity interferometry, enabling precise measurements of stellar diameters and showcasing the potential for scaling to larger telescope arrays in future astrophysical observations.

Contribution

It introduces a novel implementation of stellar intensity interferometry using existing Cherenkov telescopes, proving its feasibility and scalability for high-resolution stellar measurements.

Findings

Measured stellar diameters with better than 5% precision

Validated the off-line correlation technique for intensity interferometry

Showed potential for scaling to larger telescope arrays

Abstract

High angular resolution observations at optical wavelengths provide valuable insights in stellar astrophysics, directly measuring fundamental stellar parameters, and probing stellar atmospheres, circumstellar disks, elongation of rapidly rotating stars, and pulsations of Cepheid variable stars. The angular size of most stars are of order one milli-arcsecond or less, and to spatially resolve stellar disks and features at this scale requires an optical interferometer using an array of telescopes with baselines on the order of hundreds of meters. We report on the successful implementation of a stellar intensity interferometry system developed for the four VERITAS imaging atmospheric-Cherenkov telescopes. The system was used to measure the angular diameter of the two sub-mas stars $\beta$ Canis Majoris and $\epsilon$ Orionis with a precision better than 5%. The system utilizes an off-line approach where starlight intensity fluctuations recorded at each telescope are correlated post-observation. The technique can be readily scaled onto tens to hundreds of telescopes, providing a capability that has proven technically challenging to current generation optical amplitude interferometry observatories. This work demonstrates the feasibility of performing astrophysical measurements with imaging atmospheric-Cherenkov telescope arrays as intensity interferometers and the promise for integrating an intensity interferometry system within future observatories such as the Cherenkov Telescope Array.