Simultaneous Two Colour Intensity Interferometry with H.E.S.S

TL;DR

This paper reports the first successful simultaneous dual-wavelength intensity interferometry measurements of stars using the H.E.S.S. telescopes, enabling new insights into stellar sizes at different wavelengths.

Contribution

It introduces a novel setup for simultaneous two-colour intensity interferometry with H.E.S.S., expanding observational capabilities beyond previous single-wavelength measurements.

Findings

Measured angular diameters of four stars including limb darkening effects

Demonstrated feasibility of dual-wavelength interferometry with Cherenkov telescopes

Enhanced understanding of stellar physical sizes at different wavelengths

Abstract

In recent years, intensity interferometry has been successfully applied to the Imaging Atmospheric Cherenkov Telescopes H.E.S.S. , MAGIC, and VERITAS. All three telescope systems have proven the feasibility and capability of this method. After our first campaign in 2022, when two of the H.E.S.S. telescopes in Namibia were equipped with our external setup and the angular diameter of two stars was measured, our setup was upgraded for a second campaign in 2023, where the goal is to perform simultaneous two colour measurements. The second campaign not only involves a third equipped telescope, but also each mechanical setup now includes two interference filters at two different wavelengths (375 nm and 470 nm) with a broader bandwidth of 10 nm. This enables having simultaneous two colour measurements, which yields information about the star's physical size at different wavelengths. This is the first time that simultaneous dual-waveband intensity interferometry measurements are performed. The angular diameter results of the 4 stars, Mimosa (beta Cru), Eta Centauri (eta Cen), Nunki (sigma Sgr) and Dschubba (delta Sco), are reported, where the effects of limb darkening are also taken into account.