Speckle Imaging with Hypertelescopes

TL;DR

This paper explores speckle imaging techniques with hypertelescopes, demonstrating high-quality image reconstruction of star clusters and extended objects despite phase errors, and estimating photon requirements for effective imaging.

Contribution

It introduces the application of speckle imaging to hypertelescope systems with changing apertures, showing its effectiveness in reconstructing complex astronomical images.

Findings

Reconstructed images of star clusters are of high quality.

Speckle imaging remains effective despite phase errors caused by turbulence.

Photon level estimates for good signal-to-noise ratios are provided.

Abstract

Optical stellar interferometers have demonstrated milli-arcsecond resolution with few apertures spaced hundreds of meters apart. To obtain rich direct images, many apertures will be needed, for a better sampling of the incoming wavefront. The coherent imaging thus achievable improves the sensitivity with respect to the incoherent combination of successive fringed exposures. Efficient use of highly diluted apertures for coherent imaging can be done with pupil densification, a technique also called 'hypertelescope imaging'. Although best done with adaptive phasing, concentrating most energy in a dominant interference peak for a rich direct image of a complex source, such imaging is also possible with random phase errors such as caused by turbulent 'seeing', using methods such as speckle imaging which uses several short exposure images to reconstruct the true image. We have simulated such observations using an aperture which changes through the night, as naturally happens on Earth with fixed grounded mirror elements, and find that reconstructed images of star clusters and extended objects are of high quality. As part of the study we also estimated the required photon levels for achieving a good signal to noise ratio using such a technique.