Optical Intensity Interferometry with the Cherenkov Telescope Array

TL;DR

The paper explores using the Cherenkov Telescope Array as a multi-element intensity interferometer to achieve ultra-high angular resolution imaging of stellar surfaces and circumstellar structures, leveraging its large light-collecting area.

Contribution

It proposes a novel application of CTA for optical stellar interferometry, enabling imaging with sub-milliarcsecond resolution through intensity interferometry techniques.

Findings

Potential to resolve stellar surfaces and circumstellar features.

Insensitive to atmospheric turbulence and optical imperfections.

Operable during bright-Moon periods due to brightness limitations.

Abstract

With its unprecedented light-collecting area for night-sky observations, the Cherenkov Telescope Array (CTA) holds great potential for also optical stellar astronomy, in particular as a multi-element intensity interferometer for realizing imaging with sub-milliarcsecond angular resolution. Such an order-of-magnitude increase of the spatial resolution achieved in optical astronomy will reveal the surfaces of rotationally flattened stars with structures in their circumstellar disks and winds, or the gas flows between close binaries. Image reconstruction is feasible from the second-order coherence of light, measured as the temporal correlations of arrival times between photons recorded in different telescopes. This technique (once pioneered by Hanbury Brown and Twiss) connects telescopes only with electronic signals and is practically insensitive to atmospheric turbulence and to imperfections in telescope optics. Detector and telescope requirements are very similar to those for imaging air Cherenkov observatories, the main difference being the signal processing (calculating cross correlations between single camera pixels in pairs of telescopes). Observations of brighter stars are not limited by sky brightness, permitting efficient CTA use during also bright-Moon periods. While other concepts have been proposed to realize kilometer-scale optical interferometers of conventional amplitude (phase-) type, both in space and on the ground, their complexity places them much further into the future than CTA, which thus could become the first kilometer-scale optical imager in astronomy.