44 research outputs found
SFADI: the Speckle-Free Angular Differential Imaging method
We present a new processing technique aimed at significantly improving the
angular differential imaging method (ADI) in the context 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", allows to improve 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 visible wavelength, and show that
this technique can deliver low and uniform background, allowing unambiguous
detection of contrast planets, from to mas separations,
under poor and highly variable seeing conditions ( to arcsec FWHM)
and in only min of acquisition. A comparison with a standard ADI approach
shows that the contrast limit is improved by a factor of . We extensively
discuss the SFADI dependence on the various parameters like 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.Comment: Accepted for publication in Ap
Speckle statistics in adaptive optics images at visible wavelengths
Residual speckles in adaptive optics (AO) images represent a well-known
limitation on the achievement of the contrast needed for faint source
detection. Speckles in AO imagery can be the result of either residual
atmospheric aberrations, not corrected by the AO, or slowly evolving
aberrations induced by the optical system. We take advantage of the high
temporal cadence (1 ms) of the data acquired by the System for Coronagraphy
with High-order Adaptive Optics from R to K bands-VIS forerunner experiment at
the Large Binocular Telescope to characterize the AO residual speckles at
visible wavelengths. An accurate knowledge of the speckle pattern and its
dynamics is of paramount importance for the application of methods aimed at
their mitigation. By means of both an automatic identification software and
information theory, we study the main statistical properties of AO residuals
and their dynamics. We therefore provide a speckle characterization that can be
incorporated into numerical simulations to increase their realism and to
optimize the performances of both real-time and postprocessing techniques aimed
at the reduction of the speckle noise
On-sky single-mode fiber coupling measurements at the Large Binocular Telescope
The demonstration of efficient single-mode fiber (SMF) coupling is a key
requirement for the development of a compact, ultra-precise radial velocity
(RV) spectrograph. iLocater is a next generation instrument for the Large
Binocular Telescope (LBT) that uses adaptive optics (AO) to inject starlight
into a SMF. In preparation for commissioning iLocater, a prototype SMF
injection system was installed and tested at the LBT in the Y-band (0.970-1.065
m). This system was designed to verify the capability of the LBT AO system
as well as characterize on-sky SMF coupling efficiencies. SMF coupling was
measured on stars with variable airmasses, apparent magnitudes, and seeing
conditions for six half-nights using the Large Binocular Telescope
Interferometer. We present the overall optical and mechanical performance of
the SMF injection system, including details of the installation and alignment
procedure. A particular emphasis is placed on analyzing the instrument's
performance as a function of telescope elevation to inform the final design of
the fiber injection system for iLocater.Comment: 11 pages, 7 figure
IBIS-TRE-01: Conceptual design of the IBIS 2.0 polarimetric unit
This document describes the polarimetric and optical design of the IBIS 2.0 polarimetric unit. Designed for the German Vacuum Tower Telescope, it will allow to acquire high resolution spectro-polarimetric data of the solar photosphere and chromosphere
Fast cadence speckle-free high-contrast imaging: SFADI and SFI
We present the research and developement 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 1e-5 for integration times of the order of tens of minutes at 100 mas for a 5.7 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
Asteroid Distributions in the Ecliptic
We present analysis of the asteroid surface density distribution of main belt
asteroids (mean perihelion AU) in five ecliptic latitude
fields, -17 \gtsimeq \beta(\degr) \ltsimeq +15, derived from deep
\textit{Large Binocular Telescope} (LBT) band (85% completeness limit mag) and \textit{Spitzer Space Telescope} IRAC 8.0 \micron (80%
completeness limit Jy) fields enabling us to probe the 0.5--1.0
km diameter asteroid population. We discovered 58 new asteroids in the optical
survey as well as 41 new bodies in the \textit{Spitzer} fields. The derived
power law slopes of the number of asteroids per square degree are similar
within each \degr{} ecliptic latitude bin with a mean value of . For the 23 known asteroids detected in all four IRAC channels mean
albedos range from to . No low albedo asteroids
( \ltsimeq 0.1) were detected in the \textit{Spitzer} FLS fields,
whereas in the SWIRE fields they are frequent. The SWIRE data clearly samples
asteroids in the middle and outer belts providing the first estimates of these
km-sized asteroids' albedos. Our observed asteroid number densities at optical
wavelengths are generally consistent with those derived from the Standard
Asteroid Model within the ecliptic plane. However, we find an over density at
\beta \gtsimeq 5\degr{} in our optical fields, while the infrared number
densities are under dense by factors of 2 to 3 at all ecliptic latitudes.Comment: 35 pages including 5 figures, accepted to The Astronomical Journa
BRUTE, PSF Reconstruction for the SOUL pyramid-based Single Conjugate Adaptive Optics facility of the LBT
The astronomical applications greatly benefit from the knowledge of the
instrument PSF. We describe the PSF Reconstruction algorithm developed for the
LBT LUCI instrument assisted by the SOUL SCAO module. The reconstruction
procedure considers only synchronous wavefront sensor telemetry data and a few
asynchronous calibrations. We do not compute the Optical Transfer Function and
corresponding filters. We compute instead a temporal series of wavefront maps
and for each of these the corresponding instantaneous PSF. We tested the
algorithm both in laboratory arrangement and in the nighttime for different
SOUL configurations, adapting it to the guide star magnitudes and seeing
conditions. We nick-named it "BRUTE", Blind Reconstruction Using TElemetry,
also recalling the one-to-one approach, one slope-to one instantaneous PSF the
algorithm applies.Comment: 11 pages, 7 figures, Proceeding of the SPIE Conference 12185,
Adaptive Optics Systems VIII, 1218540 (29 August 2022
LBT SOUL data as a science test bench for MICADO PSF-R tool
Current state-of-the-art adaptive optics (AO) provides ground-based,
diffraction-limited observations with high Strehl ratios (SR). However, a
detailed knowledge of the point spread function (PSF) is required to fully
exploit the scientific potential of these data. This is even more crucial for
the next generation AO instruments that will equip 30-meter class telescopes,
as the characterization of the PSF will be mandatory to fulfill the planned
scientific requirements. For this reason, there is a growing interest in
developing tools that accurately reconstruct the observed PSF of AO systems,
the so-called PSF reconstruction. In this context, a PSF-R service is a planned
deliverable for the MICADO@ELT instrument and our group is in charge of its
development. In the case of MICADO, a blind PSF-R approach is being pursued to
have the widest applicability to science cases. This means that the PSF is
reconstructed without extracting information from the science data, relying
only on telemetry and calibrations. While our PSF-R algorithm is currently
being developed, its implementation is mature enough to test performances with
actual observations. In this presentation we will discuss the reliability of
our reconstructed PSFs and the uncertainties introduced in the measurements of
scientific quantities for bright, on-axis observations taken with the SOUL+LUCI
instrument of the LBT. This is the first application of our algorithm to real
data. It demonstrates its readiness level and paves the way to further testing.
Our PSF-R algorithm is able to reconstruct the SR and full-width at half
maximum of the observed PSFs with errors smaller than 2% and 4.5%,
respectively. We carried out the scientific evaluation of the obtained
reconstructed PSFs thanks to a dedicated set of simulated observations of an
ideal science case.Comment: 10 pages, 3 figures. Proceeding of the SPIE conference Adaptive
Optics Systems VIII, SPIE Astronomical Telescopes + Instrumentation 2022
(paper 12185-12). arXiv admin note: substantial text overlap with
arXiv:2209.0156