# Astrophysical measurements with the VERITAS Stellar Intensity Interferometer

## TL;DR

This paper demonstrates the use of the VERITAS Cherenkov telescopes for optical intensity interferometry, enabling high-resolution stellar measurements at short wavelengths and complementing existing optical interferometry methods.

## Contribution

It introduces a dedicated intensity interferometry system for VERITAS and reports the first observational results with two telescopes, extending to four.

## Key findings

- Successful implementation of intensity interferometry with VERITAS
- First observational results obtained since 2018
- System extended to all four telescopes for enhanced observations

## Abstract

Imaging Atmospheric Cherenkov Telescopes have long been viewed as potential light collectors to be used for long baseline optical intensity interferometry observations. Intensity interferometry, as implemented with Cherenkov telescopes, is well suited for studying the spatial structure of stars of O/B/A stellar types at short optical wavelengths. Such observations complement those with the current generation of optical amplitude interferometers, which are typically restricted to longer wavelengths. Dedicated intensity interferometry instrumentation has been developed for the VERITAS observatory with engineering tests and observations occurring since October 2018. Here, the first results using two of the VERITAS telescopes are reported. The system has already been extended to the two additional telescopes, enabling SII observations with all four VERITAS telescopes.