We present a new processing technique that significantly improves the angular differential imaging method (ADI). Its context of application is that of high-contrast imaging of faint objects nearby ...bright stars in observations obtained with extreme adaptive optics (EXAO) systems. This technique, named "SFADI" for "Speckle-Free ADI," improves the achievable contrast by means of speckles identification and suppression. This is possible in very high cadence data, which freeze the atmospheric evolution. Here we present simulations in which synthetic planets are injected into a real millisecond frame rate sequence, acquired at the LBT telescope at a visible wavelength, and show that this technique can deliver a low and uniform background, allowing for unambiguous detection of 10−5 contrast planets, from 100 to 300 mas separations, under poor and highly variable seeing conditions (0.8 to 1.5 arcsec FWHM) and in only 20 minutes of acquisition. A comparison with a standard ADI approach shows that the contrast limit is improved by a factor of 5. We extensively discuss the SFADI dependence on the various parameters like the speckle identification threshold, frame integration time, and number of frames, as well as its ability to provide high-contrast imaging for extended sources and also to work with fast acquisitions.
Abstract
In the context of extreme adaptive optics for large telescopes, we present the Kraken multi-frame blind deconvolution (MFBD) algorithm for processing high-cadence acquisitions, capable of ...providing a diffraction-limited estimation of the source brightness distribution. This is achieved by a data modeling of each frame in the sequence driven by the estimation of the instantaneous wave front at the entrance pupil. Under suitable physical constraints, numerical convergence is guaranteed by an iteration scheme starting from a compact MFBD, which provides a very robust initial guess that only employs a few frames. We describe the mathematics behind the process and report the high-resolution reconstruction of the spectroscopic binary
α
And (16.3 mas separation) acquired with the precursor of SHARK-VIS, the upcoming high-contrast camera in the visible for the Large Binocular Telescope.
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes on Io's surface have been monitored from both spacecraft and ground‐based telescopes. Here, we present the ...highest spatial resolution images of Io ever obtained from a ground‐based telescope. These images, acquired by the SHARK‐VIS instrument on the Large Binocular Telescope, show evidence of a major resurfacing event on Io's trailing hemisphere. When compared to the most recent spacecraft images, the SHARK‐VIS images show that a plume deposit from a powerful eruption at Pillan Patera has covered part of the long‐lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth‐based telescopes. The SHARK‐VIS instrument ushers in a new era of high resolution imaging of Io's surface using adaptive optics at visible wavelengths.
Plain Language Summary
A new instrument, called SHARK‐VIS, on the Large Binocular Telescope in Arizona, has obtained high spatial resolution, visible wavelength images of Io, the highly volcanic moon of Jupiter. Large multicolored plume deposits were imaged, revealing where the red deposit from a volcano named Pele was covered by another plume deposit from another volcano, named Pillan Patera, the site of a powerful eruption in 2021. SHARK‐VIS ushers in a new age in planetary imaging.
Key Points
High resolution images taken with SHARK‐VIS at LBT reveal low and high albedo features obscuring a portion of Pele's red ring on Io
This new eruption deposit likely originated from a powerful eruption in August 2021 located at Pillan Patera
Such images provide a new imaging capability that yields vital context to other observations of planetary surfaces
Although many exoplanets have been indirectly detected over the last years, direct imaging of them with ground-based telescopes remains challenging. In the presence of atmospheric fluctuations, it is ...ambitious to resolve the high brightness contrasts at the small angular separation between the star and its potential partners. Post-processing of telescope images has become an essential tool to improve the resolvable contrast ratios. This paper contributes a post-processing algorithm for fast-cadence imaging, which deconvolves sequences of telescope images. The algorithm infers a Bayesian estimate of the astronomical object as well as the atmospheric optical path length, including its spatial and temporal structures. For this, we utilize physics-inspired models for the object, the atmosphere, and the telescope. The algorithm is computationally expensive but allows to resolve high contrast ratios despite short observation times and no field rotation. We test the performance of the algorithm with point-like companions synthetically injected into a real data set acquired with the SHARK-VIS pathfinder instrument at the LBT telescope. Sources with brightness ratios down to \(6\cdot10^{-4}\) to the star are detected at \(185\) mas separation with a short observation time of \(0.6\,\text{s}\).
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