Stellar intensity interferometry: Optimizing air Cherenkov telescope array layouts

TL;DR

This paper explores how to optimize the layout of air Cherenkov telescope arrays for stellar intensity interferometry, aiming to improve imaging capabilities by analyzing different array geometries and their Fourier coverage.

Contribution

It provides a numerical simulation study of various array configurations, identifying optimal layouts for enhanced interferometric performance and image reconstruction.

Findings

Dense array sampling of the $(u,v)$-plane is achievable with many telescopes.

Avoiding exact east-west grids improves coverage for smaller telescopes.

Baselines should span 30--2000 m for effective stellar imaging.

Abstract

Kilometric-scale optical imagers seem feasible to realize by intensity interferometry, using telescopes primarily erected for measuring Cherenkov light induced by gamma rays. Planned arrays envision 50--100 telescopes, distributed over some 1--4 km$^2$. Although array layouts and telescope sizes will primarily be chosen for gamma-ray observations, also their interferometric performance may be optimized. Observations of stellar objects were numerically simulated for different array geometries, yielding signal-to-noise ratios for different Fourier components of the source images in the interferometric $(u,v)$-plane. Simulations were made for layouts actually proposed for future Cherenkov telescope arrays, and for subsets with only a fraction of the telescopes. All large arrays provide dense sampling of the $(u,v)$-plane due to the sheer number of telescopes, irrespective of their geographic orientation or stellar coordinates. However, for improved coverage of the $(u,v)$-plane and a wider variety of baselines (enabling better image reconstruction), an exact east-west grid should be avoided for the numerous smaller telescopes, and repetitive geometric patterns avoided for the few large ones. Sparse arrays become severely limited by a lack of short baselines, and to cover astrophysically relevant dimensions between 0.1--3 milliarcseconds in visible wavelengths, baselines between pairs of telescopes should cover the whole interval 30--2000 m.