NirvanaVIS at LBT: AO-assisted speckle holography for wide-field visible imaging

Abstract

High-angular-resolution image reconstruction from ground-based telescopes remains limited by atmospheric tur bulence and by the rapid temporal decorrelation of the speckle pattern. Speckle holography and bispectrum phase retrieval provide efficient post-processing approaches that complement adaptive optics (AO) correction and extend diffraction-limited imaging toward wider fields and fainter targets. NirvanaVIS, is a visible-band imaging camera planned for the Large Binocular Telescope, operating in conjunction with the ground-layer correction delivered by LINC-NIRVANA instrument. Equipped with a fast large-format CMOS detector, the instrument is designed to provide a stable and spatially uniform point spread function across a field of view of approximately 52′′ × 52′′ in the 600–1000nm spectral range, extending the LINC-NIRVANA capability into the visible regime. In this paper, we review the main Fourier-based speckle reconstruction techniques relevant to AO-assisted visible imaging, including classical speckle interferometry, Knox–Thompson phase retrieval, bispectrum analysis, and speckle holography, and discuss their respective operational regimes and limitations. We then present end-to end simulations of the GLAO-corrected point spread function cubes expected for NirvanaVIS, based on the Mt. Graham astroclimatic parameters and on the LINC-NIRVANA Ground-layer Wavefront Sensor configuration. Two representative science fields are considered: the planetary system around GJ15b and the open cluster NGC7914. The GJ 15 field was selected as a representative sparse stellar field centred on the nearby M2V dwarf GJ 15 A (d=3.56 pc, R≃8.4), one of the nearest exoplanet-host stars. Its brightness provides an ideal reference source for evaluating the performance of AO-assisted speckle holography. The simulations indicate that GLAO assisted speckle holography can recover diffraction-limited visible imaging at angular resolutions of approximately 20–40mas across the full NirvanaVIS field of view, with sensitivity to companions several magnitudes fainter than the reference sources. Based on these results, a modular Python reconstruction pipeline is currently under development, building on the existing IDL simulation framework. Validation is planned both on short-exposure stellar datasets acquired with the Copernico 1.82m telescope at the Asiago Observatory and on the Ekarus adaptive-optics test bench, in preparation for the future on-sky deployment of NirvanaVIS at LBT.