Extreme Adaptive Optics

2018 ◽  
Vol 56 (1) ◽  
pp. 315-355 ◽  
Author(s):  
Olivier Guyon
Keyword(s):  
Adaptive Optics ◽  
Thermal Emission ◽  
Contrast Ratio ◽  
Angular Separation ◽  
Circumstellar Disks ◽  
Spectroscopic Characterization ◽  
Central Star ◽  
High Contrast ◽  
Direct Imaging ◽  
Segmented Mirror

Over the last two decades, several thousand exoplanets have been identified, and their study has become a high scientific priority. Direct imaging of nearby exoplanets and the circumstellar disks in which they form and evolve is challenging due to the high contrast ratio and small angular separation relative to the central star. Exoplanets are typically within 1 arcsec of, and between 4 and 10 orders of magnitude fainter than, the stars they orbit. To meet these challenges, ground-based telescopes must be equipped with extreme adaptive optics (ExAO) systems optimized to acquire high-contrast images of the immediate surrounding of nearby bright stars. Current ExAO systems have the sensitivity to image thermal emission from young massive planets in near-IR, while future systems deployed on Giant Segmented Mirror Telescopes will image starlight reflected by lower-mass rocky planets. Thanks to rapid progress in optical coronagraphy, wavefront control, and data analysis techniques, direct imaging and spectroscopic characterization of habitable exoplanets will be within reach of the next generation of large ground-based telescopes.

scholarly journals High-fidelity photometry and astrometry of high-contrast imaged companions using LOCI processing.

2013 ◽  
Vol 8 (S299) ◽  
pp. 44-45
Author(s):  
Jérôme Maire ◽  
Jonathan Gagné ◽  
David Lafrenière ◽  
James R. Graham ◽  
René Doyon
Keyword(s):  
Contrast Ratio ◽  
Angular Separation ◽  
Speckle Noise ◽  
High Contrast ◽  
Contrast Imaging ◽  
High Contrast Imaging ◽  
Suppression Technique ◽  
Imaging And Spectroscopy ◽  
And Migration ◽  
Imaging Performance

RésuméDirect imaging and spectroscopy of exoplanets is a key element for understanding planet formation and migration. Such direct detections and characterizations remains technologically challenging, since a very high contrast ratio and small angular separation are involved, and futhermore speckle noise limits the high-contrast imaging performance. We further discuss a speckle subtraction and suppression technique that fully takes advantage of spectral and time-domain information on quasi-static speckles to measure the highest-fidelity photometry as well as accurate astrometry of detected companions.

scholarly journals Strategic Exploration of Exoplanets and Disks with Subaru: SEEDS

2010 ◽  
Vol 6 (S276) ◽  
pp. 436-437
Author(s):  
Nobuhiko Kusakabe ◽  
Motohide Tamura ◽  
Ryo Kandori ◽  
Tomoyuki Kudo ◽  
Jun Hashimoto ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Young Stars ◽  
Giant Planets ◽  
Current Status ◽  
High Contrast ◽  
Direct Imaging ◽  
Instrument Performance ◽  
Early Results ◽  
Solar Type ◽  
Adaptive Optics System

AbstractThe purpose of the SEEDS project (PI: M. Tamura) is to conduct a direct imaging survey, searching for giant planets as well as protoplanetary/debris disks at a few to a few tens of AU regions around 500 nearby solar-type or more massive young stars with the combination of the Subaru 8.2m telescope, the new high-contrast instrument HiCIAO, and the adaptive optics system AO188. After instrument performance verification, the SEEDS survey successfully started in October 2009. We have already detected many companion candidates to be followed-up, and clear and much better detections of disks or details of known disks structures. In this contribution, we will outline our goal, current status, early results, and future instrumentation plans.

scholarly journals PACO ASDI: an algorithm for exoplanet detection and characterization in direct imaging with integral field spectrographs

2020 ◽  
Vol 637 ◽  
pp. A9
Author(s):  
Olivier Flasseur ◽  
Loïc Denis ◽  
Éric Thiébaut ◽  
Maud Langlois
Keyword(s):  
Confidence Intervals ◽  
Adaptive Optics ◽  
Statistical Significance ◽  
Detection Threshold ◽  
Estimation Method ◽  
Detection Algorithm ◽  
Source Spectrum ◽  
Spectrum Estimation ◽  
High Contrast ◽  
Direct Imaging

Context. Exoplanet detection and characterization by direct imaging both rely on sophisticated instruments (adaptive optics and coronagraph) and adequate data processing methods. Angular and spectral differential imaging (ASDI) combines observations at different times and a range of wavelengths in order to separate the residual signal from the host star and the signal of interest corresponding to off-axis sources. Aims. Very high contrast detection is only possible with an accurate modeling of those two components, in particular of the background due to stellar leakages of the host star masked out by the coronagraph. Beyond the detection of point-like sources in the field of view, it is also essential to characterize the detection in terms of statistical significance and astrometry and to estimate the source spectrum. Methods. We extend our recent method PACO, based on local learning of patch covariances, in order to capture the spectral and temporal fluctuations of background structures. From this statistical modeling, we build a detection algorithm and a spectrum estimation method: PACO ASDI. The modeling of spectral correlations proves useful both in reducing detection artifacts and obtaining accurate statistical guarantees (detection thresholds and photometry confidence intervals). Results. An analysis of several ASDI datasets from the VLT/SPHERE-IFS instrument shows that PACO ASDI produces very clean detection maps, for which setting a detection threshold is statistically reliable. Compared to other algorithms used routinely to exploit the scientific results of SPHERE-IFS, sensitivity is improved and many false detections can be avoided. Spectrally smoothed spectra are also produced by PACO ASDI. The analysis of datasets with injected fake planets validates the recovered spectra and the computed confidence intervals. Conclusions. PACO ASDI is a high-contrast processing algorithm accounting for the spatio-spectral correlations of the data to produce statistically-grounded detection maps and reliable spectral estimations. Point source detections, photometric and astrometric characterizations are fully automatized.

scholarly journals Constraints on observing brightness asymmetries in protoplanetary disks at solar system scale

2018 ◽  
Vol 611 ◽  
pp. A90 ◽  
Author(s):  
Robert Brunngräber ◽  
Sebastian Wolf
Keyword(s):  
Solar System ◽  
Flux Ratio ◽  
Angular Separation ◽  
Circumstellar Disks ◽  
Theoretical Models ◽  
Central Star ◽  
Resolving Power ◽  
Nearby Star ◽  
Significance Level ◽  
Infrared Wavelength

We have quantified the potential capabilities of detecting local brightness asymmetries in circumstellar disks with the Very Large Telescope Interferometer (VLTI) in the mid-infrared wavelength range. The study is motivated by the need to evaluate theoretical models of planet formation by direct observations of protoplanets at early evolutionary stages, when they are still embedded in their host disk. Up to now, only a few embedded candidate protoplanets have been detected with semi-major axes of 20–50 au. Due to the small angular separation from their central star, only long-baseline interferometry provides the angular resolving power to detect disk asymmetries associated to protoplanets at solar system scales in nearby star-forming regions. In particular, infrared observations are crucial to observe scattered stellar radiation and thermal re-emission in the vicinity of embedded companions directly. For this purpose we performed radiative transfer simulations to calculate the thermal re-emission and scattered stellar flux from a protoplanetary disk hosting an embedded companion. Based on that, visibilities and closure phases are calculated to simulate observations with the future beam combiner MATISSE, operating at the L, M and N bands at the VLTI. We find that the flux ratio of the embedded source to the central star can be as low as 0.5 to 0.6% for a detection at a feasible significance level due to the heated dust in the vicinity of the embedded source. Furthermore, we find that the likelihood for detection is highest for sources at intermediate distances r ≈ 2–5 au and disk masses not higher than ≈10−4 M⊙.

scholarly journals Polarimetric imaging of circumstellar disks

2019 ◽  
Vol 627 ◽  
pp. A156
Author(s):  
S. Heikamp ◽  
C. U. Keller
Keyword(s):  
Adaptive Optics ◽  
Angular Resolution ◽  
Rotational Symmetry ◽  
Polarized Light ◽  
Circumstellar Disks ◽  
Central Star ◽  
Finite Point ◽  
Optical Images ◽  
Intensity Images ◽  
Circumstellar Environments

Context. Polarimetric images of circumstellar environments, even when corrected with adaptive optics, have a limited angular resolution. Finite resolution greatly affects polarimetric images because of the canceling of adjacent polarization signals with opposite signs. In radio astronomy this effect is called beam depolarization and is well known. However, radio techniques to mitigate beam depolarization are not directly applicable to optical images as a consequence of the inherent lack of phase information at optical wavelengths. Aims. We explore the effects of a finite point-spread function (PSF) on polarimetric images and the application of Richardson-Lucy deconvolution to polarimetric images. Methods. We simulated polarimetric images of highly simplified, circumstellar disk models and convolved these with simulated and actual SPHERE/ZIMPOL PSFs. We attempted to deconvolve simulated images in orthogonal linear polarizations and polarized intensity images. Results. The most significant effect of finite angular resolution is the loss of polarimetric signal close to the central star where large polarization signals of opposite signs average out. The finite angular resolution can also introduce polarized light in areas beyond the original, polarized signal such as outside of disks. These effects are particularly severe for disks that are not rotationally symmetric. The deconvolution of polarimetric images is far from trivial. Richardson-Lucy deconvolution applied to images in opposite linear polarization states, which are subsequently subtracted from each other, cannot recover the signal close to the star. Sources that lack rotational symmetry cannot be recovered with this deconvolution approach.

scholarly journals Adaptive Optics Imaging of Circumstellar Environments

2004 ◽  
Vol 221 ◽  
pp. 307-312
Author(s):  
Dániel Apai ◽  
Ilaria Pascucci ◽  
Hongchi Wang ◽  
Wolfgang Brandner ◽  
Thomas Henning ◽  
...  
Keyword(s):  
High Resolution ◽  
Adaptive Optics ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Circumstellar Disks ◽  
Circumstellar Envelope ◽  
High Contrast ◽  
Contrast Imaging ◽  
High Contrast Imaging ◽  
Circumstellar Environments

We present results from our high-resolution, high-contrast imaging campaign targeting the circumstellar environments of young, nearby stars of different masses. The observations have been conducted using the ALFA/CA 3.5m and NACO UT4/VLT adaptive optics systems. In order to enhance the contrast we applied the methods PSF-subtraction and polarimetric differential imaging (PDI). The observations of young stars yielded the identification of numerous new companion candidates, the most interesting one being ∼ 0.5″ from FU Ori. We also obtained high-resolution near-infrared imaging of the circumstellar envelope of SU Aur and AB Aur. Our PDI of the TW Hya circumstellar disk traced back the disk emission as close as 0.1″ ≃ 6 AU from the star, the closest yet. Our results demonstrate the potential of the adaptive optics systems in achieving high-resolution and high-contrast imaging and thus in the study of circumstellar disks, envelopes and companions.

scholarly journals Adaptive Optics Observations of Exoplanets, Brown Dwarfs, and Binary Stars

2011 ◽  
Vol 7 (S282) ◽  
pp. 181-188
Author(s):  
Sasha Hinkley
Keyword(s):  
Adaptive Optics ◽  
Binary Stars ◽  
Imaging Techniques ◽  
Contrast Ratio ◽  
Brown Dwarfs ◽  
Formation Mechanisms ◽  
High Contrast ◽  
Contrast Imaging ◽  
High Contrast Imaging ◽  
Low Mass

AbstractThe current direct observations of brown dwarfs and exoplanets have been obtained using instruments not specifically designed for overcoming the large contrast ratio between the host star and any wide-separation faint companions. However, we are about to witness the birth of several new dedicated observing platforms specifically geared towards high contrast imaging of these objects. The Gemini Planet Imager, VLT-SPHERE, Subaru HiCIAO, and Project 1640 at the Palomar 5m telescope will return images of numerous exoplanets and brown dwarfs over hundreds of observing nights in the next five years. Along with diffraction-limited coronagraphs and high-order adaptive optics, these instruments also will return spectral and polarimetric information on any discovered targets, giving clues to their atmospheric compositions and characteristics. Such spectral characterization will be key to forming a detailed theory of comparative exoplanetary science which will be widely applicable to both exoplanets and brown dwarfs. Further, the prevalence of aperture masking interferometry in the field of high contrast imaging is also allowing observers to sense massive, young planets at solar system scales (~3–30 AU)— separations out of reach to conventional direct imaging techniques. Such observations can provide snapshots at the earliest phases of planet formation—information essential for constraining formation mechanisms as well as evolutionary models of planetary mass companions. As a demonstration of the power of this technique, I briefly review recent aperture masking observations of the HR 8799 system. Moreover, all of the aforementioned techniques are already extremely adept at detecting low-mass stellar companions to their target stars, and I present some recent highlights.

scholarly journals Patterned waveguide liquid crystal displays

RSC Advances ◽  
2020 ◽  
Vol 10 (68) ◽  
pp. 41693-41702
Author(s):  
Yunho Shin ◽  
Jinghua Jiang ◽  
Guangkui Qin ◽  
Qian Wang ◽  
Ziyuan Zhou ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Switching Time ◽  
Contrast Ratio ◽  
Liquid Crystal Displays ◽  
High Contrast ◽  
High Brightness ◽  
Photo Polymerization ◽  
Ultrafast Switching ◽  
Light Waveguide ◽  
Polymer Stabilized

A polymer stabilized LC based light waveguide display is reported. Performance is improved by patterned photo-polymerization or electrode. It has high brightness, ultrafast switching time, high contrast ratio, and high transmittance for transparent and augmented displays.

scholarly journals Full-frame and high-contrast smart windows from halide-exchanged perovskites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
You Liu ◽  
Jungan Wang ◽  
Fangfang Wang ◽  
Zhengchun Cheng ◽  
Yinyu Fang ◽  
...  
Keyword(s):  
Contrast Ratio ◽  
High Contrast ◽  
Smart Window ◽  
Frame Size ◽  
Smart Windows ◽  
Ideal Solutions ◽  
Ion Gel ◽  
And Control ◽  
Colour Rendering ◽  
Perovskite Photovoltaic

AbstractWindow glazing plays an essential role to modulate indoor light and heat transmission, which is a prospect to save the energy cost in buildings. The latest photovoltachromic technology has been regarded as one of the most ideal solutions, however, to achieve full-frame size (100% active area) and high-contrast ratio (>30% variable in visible wavelength) for smart window applicability is still a challenge. Here we report a photovoltachromic device combining full-transparent perovskite photovoltaic and ion-gel based electrochromic components in a vertical tandem architecture without any intermediated electrode. Most importantly, by accurately adjusting the halide-exchanging period, this photovoltachromic module can realize a high pristine transmittance up to 76%. Moreover, it possesses excellent colour-rendering index to 96, wide contrast ratio (>30%) on average visible transmittance (400-780 nm), and a self-adaptable transmittance adjustment and control indoor brightness and temperature automatically depending on different solar irradiances.

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