Performance of the upgraded VERITAS Stellar Intensity Interferometer (VSII)

TL;DR

The upgraded VERITAS Stellar Intensity Interferometer (VSII) enhances high-resolution stellar measurements during bright moon periods, demonstrating improved sensitivity and resolution in measuring stellar diameters with short exposures.

Contribution

This paper introduces the upgraded VSII instrumentation and reports on its improved sensitivity and angular resolution capabilities for stellar diameter measurements.

Findings

Successful measurement of two B star diameters with < 5% accuracy

Enhanced instrumentation increases sensitivity and efficiency

Progress in measuring dimmer stars and achieving better than 1% angular resolution

Abstract

The VERITAS Imaging Atmospheric Cherenkov Telescope array (IACT) was augmented in 2019 with high-speed focal plane electronics to create a new Stellar Intensity Interferometry (SII) observational capability (VERITAS-SII, or VSII). VSII operates during bright moon periods, providing high angular resolution observations ( < 1 mas) in the B photometric band using idle telescope time. VSII has already demonstrated the ability to measure the diameters of two B stars at 416 nm (Bet CMa and Eps Ori) with < 5% accuracy using relatively short (5 hours) exposures. The VSII instrumentation was recently improved to increase instrumental sensitivity and observational efficiency. This paper describes the upgraded VSII instrumentation and documents the ongoing improvements in VSII sensitivity. The report describes VSII's progress in extending SII measurements to dimmer magnitude stars and improving the VSII angular diameter measurement resolution to better than 1%.