All the aberrations not corrected by Adaptive Optics (AO) systems are important limitations for high contrast imaging at large telescopes. Among them, the most relevant ones are called Non-Common Path Aberrations (NCPA): these are present downstream of the separation of the optical paths to Wavefront Sensor and scientific focal plane. The typical approach to mitigate them is to set an offset on the AO system with the opposite sign of this NCPA. It can be obtained with a trial-and-error approach or with sophisticated focal plane Wavefront sensing. There is a need for a fast procedure to measure NCPA in order to limit the telescope downtime and to repeat, if needed, the correction procedure to cope with any temporal variation. Different methods exists to measure and compensate it introducing the correction as offset in the AO control loop. New approaches based on Neural Networks (NNs) have also been proposed. In this work, using simulated images, we test and describe the application of a supervised Multi-layer Perceptron (MLP) NN for the mitigation of NCPA in high contrast imaging at visible wavelengths. As shown in our previous work, we already tested the method on simulated images and showed that this method is robust even in the presence of turbulence-induced dynamic aberrations that are not labelled in the training phase of the NN corresponding to the typical AO residual of the daytime calibration. We tested the method on the GHOST optical test bench at ESO laboratories and preliminary results show the method is very promising, recovering almost completely the SR in an iterative correction process.
SHARK-VIS the Large Binocular Telescope (LBT) forthcoming optical high-contrast imager is completed and will soon see its first light. Thanks to the high performances of SOUL, the new LBT adaptive optics (AO) system, SHARK-VIS will extend the capabilities of one arm of the binocular telescope down to 400 nm, delivering spatial resolutions (≈ 15 mas) that in the infrared bands will be achieved only by future extremely large telescopes (ELTs). This document describes the instrument and its final laboratory test that assessed the expected performances. End to End test, done on a dedicated test-bench resembling on sky conditions, showed the capability to detect faint target with contrast lower than 10−4 at only 50mas away from a magR 12 point like source.
Recurrence Quantification Analysis (RQA) is a non-linear time series analysis technique widely employed in many different research fields. Among the many applications of this method, it has been shown that it can be successfully employed in the detection of small signals embedded into noise. In this work we explore the possibility of using the RQA in astronomical high contrast imaging, for the detection of faint objects nearby bright sources in very high frame rate (1 KHz) data series. For this purpose, we used a real 1 kHz image sequence of a bright star, acquired with the SHARK-VIS forerunner at LBT. Our results show excellent performances in terms of detection contrasts even with a very short data sequence (a few seconds). The use of RQA in astronomical high contrast imaging is discussed in light of the possible science applications and with respect to other techniques like, for example, the angular differential imaging (ADI) or the Speckle-Free ADI (SFADI).
We present the R and D status of the Speckle-Free Angular Differential Imaging method (SFADI), that we developed for the SHARK-VIS high-contrast imager for the LBT telescope. The technique bases on the acquisition of kHz frame-rate image sequences, which we combine in post-processing after speckle identification and suppression in each frame. With respect to the standard angular differential imaging, this method reaches a much smoother residual background and hence higher detection contrast at a given signal-to-noise ratio. Furthermore, it can reveal faint extended sources around bright central stars, and can use de-rotated images as well as quick second-lasting sequences. We reached a contrast of around 10-5 for integration times of the order of tens of minutes at 100 mas for a 5.7th magnitude star, as we demonstrated on both a real-sky acquisition and at the SHARK-VIS laboratory test bench. Such long sequences though produces a large amount of data (around a million frames every 15 minutes) that we manage to processed in a reasonable computation time with the described implementation scheme.
SHARK-VIS, the LBT forthcoming high-contrast imager, is undergoing its fabrication phase and will see its first light in Q4-2019. By exploiting the outstanding performance of the LBT SOUL adaptive optics in the range of wavelength from 400 to 1000 nm, the instrument is expected to provide breakthrough science results in different fields, from exoplanets detection and characterization, to star formation with resolutions around 15mas and a contrast larger than 1e-5 at 100mas of separation. This will be possible thanks to the unprecedented performances of the LBT extreme AO system and the instrument fast-frame-rate acquisition as already demonstrated by preliminary tests on-sky. In this contribution, we will review the main technical aspects of the instrument and present the current project status.
The possibility to open a near-IR window at stratospheric altitude is crucial for a large variety of astronomical issues,
from cosmology to the star formation processes. Up to now, one of the main issue is the role of the OH and thermal sky
emission that are rising the sky background level when such observations are performed through ground based
telescopes. We present the results of our technological activity aimed at affording some critical aspects typical of balloon
flights. In particular, the obtained performances of prototype systems for rough and fine tracking will be illustrated. Both
these systems constitute a high precision device (≤ 1 arcsec) for pointing and tracking light telescopes on board
stratospheric balloons. We give the details concerning the optical and mechanical layout, as well as the detector and the
control system. We demonstrate how such devices, when used at the focal plane of enough large telescopes(2-4m, F/10),
may be capable to provide diffraction limited images in the near infrared bands. We have also developed a prototypal
single channel photometer NISBA (Near Infrared Sky Background at Arctic pole), working in the H band (1.65 μm), able
to evaluate, during a high-latitude balloon flight, how OH emission affects the sky background during the arctic night.
The laboratory tests and performance on sky are presented and analyzed.
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