Optical intensity interferometry with the H.E.S.S. gamma-ray telescopes
Final Report Abstract
The goal of this project was to develop and implement a system for stellar intensity interferometry to perform high-angular resolution (sub-mili-arcsecond) measurements of stars with the H.E.S.S. gamma-ray telescopes in Namibia. While the idea for intensity interferometry was coined in the 1960s by Hanbury Brown and Twiss, only recently large Imaging Atmospheric Cherenkov Telescopes (IACTs) coupled with fast electronics spawned a revival of the technique in which photons arriving from a distant source are correlated between two telescopes and the decoherence as a function of the distance between the telescopes serves as a measure of the extension of the object. The project was divided into three modules for each of which the central goals were achieved. First a light-detection and electronics chain for intensity interferometry was established in the lab and tested with an LED as artificial light source. Second, we developed the mechanical and optical system to be mounted on the H.E.S.S. telescopes during times of bright moonlight to not interfere with standard gamma-ray observations. Third, we implemented data analysis and simulation tools. The project led to two measurement campaigns at H.E.S.S. , in April 2022 and April/May 2023. In the first campaign two stellar angular diameters were successfully measured for the bright stars λ Sco (Shaula) and σ Sgr (Nunki). For the second campaign the mechanical and optical setup was extended to measure stellar diameters in two different colors. In this second campaign four stellar angular diameters were successfully determined in two wavebands for the stars β Cru (Mimosa), η Cen, δ(Dschubba) and σ Sgr. The measured extension of the stars was at the scale of half a mili-arcsecond with a precision of a few percent. Such an angular resolution corresponds to the size of a basketball on the surface of the moon.
Publications
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LED as laboratory test source for astronomical intensity interferometry. Optics Express, 28(4), 5248.
Zmija, Andreas; Deiml, Peter; Malyshev, Dmitry; Zink, Adrian; Anton, Gisela; Michel, Thilo & Funk, Stefan
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Optical intensity interferometry lab tests in preparation of stellar diameter measurements at IACTs at GHz photon rates. Monthly Notices of the Royal Astronomical Society, 509(3), 3113-3118.
Zmija, Andreas; Vogel, Naomi; Anton, Gisela; Malyshev, Dmitry; Michel, Thilo; Zink, Adrian & Funk, Stefan
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Comparing different approaches for stellar intensity interferometry. Monthly Notices of the Royal Astronomical Society, 512(2), 1722-1729.
Karl, Sebastian; Zmija, Andreas; Richter, Stefan; Vogel, Naomi; Malyshev, Dmitry; Zink, Adrian; Michel, Thilo; Anton, Gisela; von Zanthier, Joachim & Funk, Stefan
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First intensity interferometry measurements with the H.E.S.S. telescopes. Monthly Notices of the Royal Astronomical Society, 527(4), 12243-12252.
Zmija, Andreas; Vogel, Naomi; Wohlleben, Frederik; Anton, Gisela; Zink, Adrian & Funk, Stefan
