Direct imaging of exoplanets is usually limited by quasi-static speckles. These uncorrected aberrations in a star's point spread function (PSF) obscure faint companions and limit the sensitivity of high-contrast imaging instruments. Most current approaches to processing differential imaging sequences like angular differential imaging (ADI) and spectral differential imaging (SDI) produce a self-calibrating dataset that are combined in a linear least squares solution to minimize the noise. Due to temporal and chromatic evolution of a telescope's PSF, the best correlated reference images are usually the most contaminated by the planet, leading to self-subtraction and reducing the planet throughput. In this paper, we present an algorithm that directly optimizes the non-linear equation for planet signal to noise ratio (SNR). This new algorithm does not require us to reject adjacent reference images and optimally balances noise reduction with self-subtraction. We then show how this algorithm can be applied to multiple images simultaneously for a further reduction in correlated noise, directly maximizing the SNR of the final combined image. Finally, we demonstrate the technique on an illustrative sequence of HR8799 using the new Julia-based Signal to Noise Analysis Pipeline (SNAP). We show that SNR optimization can provide up to a $5\times$ improvement in contrast close to the star. Applicable to both new and archival data, this technique will allow for the detection of lower mass, and closer in companions, or achieve the same sensitivity with less telescope time.
The Large Interferometer For Exoplanets (LIFE) initiative is developing the science and a technology roadmap for an ambitious space mission featuring a space-based mid-infrared (MIR) nulling interferometer in order to detect the thermal emission of hundreds of exoplanets and characterize their atmospheres. In order to quantify the science potential of such a mission, in particular in the context of technical trade-offs, an instrument simulator is required. In addition, signal extraction algorithms are needed to verify that exoplanet properties (e.g., angular separation, spectral flux) containe…
Direct imaging of exoplanets is a challenging task due to the small angular distance and high contrast relative to their host star, and the presence of quasi-static noise. We propose a new statistical method for direct imaging of exoplanets based on a likelihood ratio detection map, which assumes that the noise after the background subtraction step obeys a Laplacian distribution. We compare the method with two detection approaches based on signal-to-noise ratio (SNR) map after performing the background subtraction by the widely used Annular Principal Component Analysis (AnnPCA). The experiment…
We set out a simulation to explore the follow-up of exoplanet candidates. We look at comparing photometric (transit method) and spectroscopic (Doppler shift method) techniques using three instruments: NGTS, HARPS and CORALIE. We take into account precision of follow-up and required observing time in attempt to rank each method for a given set of planetary system parameters. The methods are assessed on two criteria, SNR of the detection and follow-up time before characterisation. We find that different follow-up techniques are preferred for different regions of parameter space. For SNR we find …
Space-borne nulling interferometers have long been considered as the best option for searching and characterizing extra-solar planets located in the habitable zone of their parent stars. Solutions for achieving deep starlight extinction are now numerous and well demonstrated. However they essentially aim at realizing an achromatic central null in order to extinguish the star. In this communication is described a major improvement of the technique, where the achromatization process is extended to the entire fringe pattern. Therefore higher Signal-to-noise ratios (SNR) and appreciable simplifica…
Further advances in exoplanet detection and characterisation require sampling a diverse population of extrasolar planets. One technique to detect these distant worlds is through the direct detection of their thermal emission. The so-called direct imaging technique, is suitable for observing young planets far from their star. These are very low signal-to-noise-ratio (SNR) measurements and limited ground truth hinders the use of supervised learning approaches. In this paper, we combine deep generative and discriminative models to bypass the issues arising when directly training on real data. We …
One of the key science goals for extremely large telescopes (ELTs) is the detailed characterization of already known directly imaged exoplanets. The typical adaptive optics (AO) Nyquist control region for ELTs is ~0.4 arcseconds, placing many already known directly imaged planets outside the DM control region and not allowing any standard wavefront control scheme to remove speckles that would allow higher SNR images/spectra to be acquired. This can be fixed with super-Nyquist wavefront control (SNWFC), using a sine wave phase plate to allow for wavefront control outside the central DM Nyquist …
Context. High-contrast exoplanet imaging is a rapidly growing field as can be seen through the significant resources invested. In fact, the detection and characterization of exoplanets through direct imaging is featured at all major ground-based observatories. Aims. We aim to improve the signal-to-noise ratio (SNR) achievable for ground-based, adaptive-optics assisted exoplanet imaging by applying sophisticated post-processing algorithms. In particular, we investigate the benefits of including time domain information. Methods. We introduce a new speckle-suppression technique in data post-proce…
We present a new algorithm designed to improve the signal to noise ratio (SNR) of point and extended source detections in direct imaging data. The novel part of our method is that it finds the linear combination of the science images that best match counterpart images with signal removed from suspected source regions. The algorithm, based on the Locally Optimized Combination of Images (LOCI) method, is called Matched LOCI or MLOCI. We show using data obtained with the Gemini Planet Imager (GPI) and Near-Infrared Coronagraphic Imager (NICI) that the new algorithm can improve the SNR of point so…
Polarimetry is one of the keys to enhanced direct imaging of exoplanets. Not only does it deliver a differential observable providing extra contrast, but when coupled with spectroscopy, it also reveals valuable information on the exoplanetary atmospheric composition. Nevertheless, angular separation and contrast ratio to the host-star make for extremely challenging observation. Producing detailed predictions for exactly how the expected signals should appear is of critical importance for the designs and observational strategies of tomorrow's telescopes. We aim at accurately determining the mag…
Jointly Modeling Roman Coronagraph Astrometry and Photometry Improves Orbital Parameter Estimates
Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University（西北大学跨学科天体物理探索与研究中心）；Department of Physics and Engineering, University of St. Thomas（圣托马斯大学物理与工程系）；Department of Astronomy and Astrophysics, University of California, Santa Cruz（加州大学圣克鲁斯分校天文与天体物理系）
We discuss the feasibility of direct multipixel imaging of exoplanets with the solar gravitational lens (SGL) in the context of a realistic deep space mission. For this, we consider an optical telescope, placed in the image plane that forms in the strong interference region of the SGL. We consider an Earth-like exoplanet located in our immediate stellar neighborhood and model its characteristics using our own Earth. We estimate photon fluxes from such a compact, extended, resolved exoplanet. This light appears in the form of an Einstein ring around the Sun, seen through the solar corona. The s…
National Tsing-Hua University（国立清华大学）；National Astronomical Observatory of Japan（日本国立天文台）；Oita University（大分大学）
The method of direct imaging has detected many exoplanets and made important contribution to the field of planet formation. The standard method employs angular differential imaging (ADI) technique, and more ADI image frames could lead to the results with larger signal-to-noise-ratio (SNR). However, it would need precious observational time from large telescopes, which are always over-subscribed. We thus explore the possibility to generate a converter which can increase the SNR derived from a smaller number of ADI frames. The machine learning technique with two-dimension convolutional neural ne…
Combining high-contrast imaging with medium-resolution spectroscopy has been shown to significantly boost the direct detection of exoplanets. HARMONI, one of the first-light instruments to be mounted on ESO's ELT, will be equipped with a single-conjugated adaptive optics system to reach the diffraction limit of the ELT in H and K bands, a high-contrast module dedicated to exoplanet imaging, and a medium-resolution (up to R = 17 000) optical and near-infrared integral field spectrograph. Combined together, these systems will provide unprecedented contrast limits at separations between 50 and 40…
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its $\sim$130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescope's overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L' (3.8 $μ$m), as opposed to the shorter wavelength …
We present a new matched filter algorithm for direct detection of point sources in the immediate vicinity of bright stars. The stellar Point Spread Function (PSF) is first subtracted using a Karhunen-Loéve Image Processing (KLIP) algorithm with Angular and Spectral Differential Imaging (ADI and SDI). The KLIP-induced distortion of the astrophysical signal is included in the matched filter template by computing a forward model of the PSF at every position in the image. To optimize the performance of the algorithm, we conduct extensive planet injection and recovery tests and tune the exoplanet s…
This year, a second generation of coronagraphs dedicated to high-contrast direct imaging of exoplanets is starting operations. Among them, SPHERE, installed at the focus of the UT3 Very Large Telescope, reaches unprecedented contrast ratios up to $10^{-6}$ -$ 10^{-7}$, using eXtreme Adaptive Optics and the Angular Differential Imaging (ADI) techniques. In this paper, we present a new method called Keplerian-Stacker that improves the detection limit of high contrast instruments like SPHERE, by up to a factor of 10. It consists of observing a star on a long enough period to let a hypothetical pl…
Today, there exists a wide variety of algorithms dedicated to high-contrast imaging, especially for the detection and characterisation of exoplanet signals. These algorithms are tailored to address the very high contrast between the exoplanet signal(s), which can be more than two orders of magnitude fainter than the bright starlight residuals in coronagraphic images. The starlight residuals are inhomogeneously distributed and follow various timescales that depend on the observing conditions and on the target star brightness. Disentangling the exoplanet signals within the starlight residuals is…
Differential imaging is a postprocessing method to obtain high contrast, often used for exoplanet searches. The coherent differential imaging on speckle area nulling (CDI-SAN) method was developed to detect a faint exoplanet lying beneath residual speckles of a host star. It utilizes image acquisitions faster than the stellar speckle variation synchronized with five shapes of a deformable mirror repeatedly. By using the only the integrated values of each of the five images and square differences for a long interval of observations, the light of the exoplanet could be separated from the stellar…
To directly image exoplanets and faint circumstellar disks, the noisy stellar halo must be suppressed to a high level. To achieve this feat, the angular differential imaging observing technique and the least-squares Locally Optimized Combination of Images (LOCI) algorithm have now become the standard in single band direct imaging observations and data reduction. With the development and commissioning of new high-order high-contrast adaptive optics equipped with integral field units, the image subtraction algorithm needs to be modified to allow the optimal use of polychromatic images, field-rot…
The high-contrast coronagraph for direct imaging earth-like exoplanet at the visible needs a contrast of 10^(-10) at a small angular separation of 4 lambda/D or less. Here we report our recent laboratory experiment that is close to the limits. The test of the high-contrast imaging coronagraph is based on our step-transmission apodized filter. To achieve the goal, we use a liquid crystal array (LCA) as a phase corrector to create a dark hole based on our dedicated focal dark algorithm. We have suppressed the diffracted and speckle noise near the star point image to a level of 1.68 x 10^(-9) at …
Understanding the atmospheres of exoplanets is a milestone to decipher their formation history and potential habitability. High-contrast imaging and spectroscopy of exoplanets is the major pathway towards the goal. Directly imaging of an exoplanet requires high spatial resolution. Interferometry has proven to be an effective way of improving spatial resolution. However, means of combining interferometry, high-contrast imaging, and high-resolution spectroscopy have been rarely explored. To fill in the gap, we present the dual-aperture fiber nuller (FN) for current-generation 8-10 meter telescop…
Time-resolved photometry is an important new probe of the physics of condensate clouds in extrasolar planets and brown dwarfs. Extreme adaptive optics systems can directly image planets, but precise brightness measurements are challenging. We present VLT/SPHERE high-contrast, time-resolved broad H-band near-infrared photometry for four exoplanets in the HR 8799 system, sampling changes from night to night over five nights with relatively short integrations. The photospheres of these four planets are often modeled by patchy clouds and may show large-amplitude rotational brightness modulations. …
The Exoplanet Imaging Data Challenge is a community-wide effort meant to offer a platform for a fair and common comparison of image processing methods designed for exoplanet direct detection. For this purpose, it gathers on a dedicated repository (Zenodo), data from several high-contrast ground-based instruments worldwide in which we injected synthetic planetary signals. The data challenge is hosted on the CodaLab competition platform, where participants can upload their results. The specifications of the data challenge are published on our website. The first phase, launched on the 1st of Sept…
Instrumentation techniques in the field of direct imaging of exoplanets have greatly advanced over the last two decades. Two of the four NASA-commissioned large concept studies involve a high-contrast instrument for the imaging and spectral characterization of exo-Earths from space: LUVOIR and HabEx. This whitepaper describes the status of 8 optical testbeds in the US and France currently in operation to experimentally validate the necessary technologies to image exo-Earths from space. They explore two complementary axes of research: (i) coronagraph designs and manufacturing and (ii) active wa…
The recovery of an exoplanet's atmospheric parameters from its spectrum requires accurate knowledge of the spectral errors and covariances. Unfortunately, the complex image processing used in high-contrast integral-field spectrograph (IFS) observations generally produces spectral covariances that are poorly understood and often ignored. In this work, we show how to measure the spectral errors and covariances and include them self-consistently in parameter retrievals. By combining model exoplanet spectra with a realistic noise model generated from GPI early science data, we show that ignoring s…
Deep learning for exoplanet detection and characterization by direct imaging at high contrast
Département d'Informatique de l' \'E cole normale supérieure (ENS-PSL, CNRS, Inria)；Universite Claude Bernard Lyon 1, Centre de Recherche Astrophysique de Lyon UMR 5574, ENS de Lyon, CNRS, Villeurbanne, France；Université Grenoble Alpes, Inria, CNRS, Grenoble INP, LJK；Courant Institute；Center for Data Science, New York University；LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CNRS, Meudon, France
Here we review the current conceptual optical mechanical design of GMagAO-X --the extreme AO (ExAO) system for the Giant Magellan Telescope (GMT). The GMagAO-X tweeter deformable mirror (DM) design is novel in that it uses an optically distributed set of pupils that allows seven commercially available 3000 actuator BMC DMs to work "in parallel" to effectively create an ELT-scale ExAO tweeter DM --with all parts commercially available today. The GMagAO-X "parallel DM" tweeter will have 21,000 actuators to be used at ~2kHz update speeds enabling high-contrast science at ~5 mas separations in the…
ANDES, the high-resolution spectrograph of the ELT: simulated performance of the CORO module and overview of the high-contrast capabilities for exoplanet observations
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台，法国国家科学研究中心，拉格朗日实验室）；Lund Observatory, Division of Astrophysics, Department of Physics, Lund University（隆德大学，物理系，天体物理学部，隆德天文台）；INAF - Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所，阿切特里天文台）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Instituto de Astronomía, Univ. Nacional Autónoma de México（墨西哥国立自治大学，天文研究所）；LUPM, Université de Montpellier, CNRS（蒙彼利埃大学，法国国家科学研究中心，LUPM实验室）；Université Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，IPAG实验室）；INAF - Osservatorio Astrofisico di Brera（意大利国家天体物理研究所，布雷拉天文台）；Aix Marseille Université, CNRS, CNES, LAM（艾克斯马赛大学，法国国家科学研究中心，法国国家空间研究中心，LAM实验室）；INAF - Osservatorio Astronomico di Trieste（意大利国家天体物理研究所，的里雅斯特天文台）
介绍了 ANDES 高分辨率光谱仪日冕仪模块，其能结合高对比度成像与高色散光谱学研究系外行星特性，详细阐述设计、特征及模拟性能，展示初步模拟结果并讨论表征操作，以评估其对系外行星大气特征的探测能力。
High-dispersion coronagraphy (HDC) optimally combines high contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a critical pathway towards fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we …
Future space-based direct imaging missions will perform low-resolution (R$<$100) optical (0.3-1~$μ$m) spectroscopy of planets, thus enabling reflected spectroscopy of cool giants. Reflected light spectroscopy is encoded with rich information about the scattering and absorbing properties of planet atmospheres. Given the diversity of clouds and hazes expected in exoplanets, it is imperative we solidify the methodology to accurately and precisely retrieve these scattering and absorbing properties that are agnostic to cloud species. In particular, we focus on determining how different cloud parame…
Modeling the Impact of Starspot Inhomogeneity on Spectroscopic Retrievals of Directly-Imaged Planets
The Catholic University of America（美国天主教大学）；NASA Goddard Space Flight Center（NASA戈达德太空飞行中心）；Center for Research and Exploration in Space Science and Technology（空间科学与工程研究中心）；Sellers Exoplanets Environment Collaboration（塞勒斯系外行星环境合作组织）；SETI Institute（SETI研究所）
The Solar Gravitational Lens (SGL) allows for major brightness amplification ($\sim 10^{11}$ at wavelength of $1~μ$m) and extreme angular resolution ($\sim10^{-10}$ arcsec) within a narrow field of view. A meter-class telescope, with a modest coronagraph to block solar light with 1e-6 suppression placed in the focal area of the SGL, can image an exoplanet at a distance of 30 parsec with few kilometer-scale resolution on its surface. Notably, spectroscopic broadband SNR is $\sim 10^{-6}$ in two weeks of integration time, providing this instrument with incredible remote sensing capabilities. A m…
Interferometric techniques such as aperture masking have the potential to enhance spatial resolution capabilities when imaging moderate-contrast sources with small angular size, such as close-in exoplanets and circumstellar disks around distant young stars. The Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) instrument, currently under development, is a lenslet integral field spectrograph that will enable the W. M. Keck Observatory to carry out high-contrast direct imaging of exoplanets between 2 and 5 microns. We explore the potential benefit of aperture masking …
This Final Report (FR) presents the results of the Enhanced direct imaging exoplanet detection with astrometry mass determination project, which was executed in support of NASA's Exoplanet Exploration Program and the ROSES Technology Development for Exoplanet Missions (TDEM). The first milestone is concerned with a demonstration of medium fidelity astrometry accuracy and the second milestone demonstrates high-contrast imaging utilizing the same astrometry-capable optics. We have met milestone #1 with a comfortable margin. The average accuracy obtained over the three datasets is 5.75e-5 L/D, wh…
Direct imaging of exoplanets requires establishing and maintaining a high contrast dark field (DF) within the science image to a high degree of precision (10^-10). Current approaches aimed at establishing the DF, such as electric field conjugation (EFC), have been demonstrated in the lab and have proven capable of high contrast DF generation. The same approaches have been considered for the maintenance of the DF as well. However, these methods rely on phase diversity measurements which require field modulation; this interrupts the DF and consequently competes with the science acquisition. In t…
Use the 4S (Signal-Safe Speckle Subtraction): Explainable Machine Learning reveals the Giant Exoplanet AF Lep b in High-Contrast Imaging Data from 2011
The direct detection of exoplanets has been the subject of intensive research in the recent years. Data obtained with future high-contrast imaging instruments optimized for giant planets direct detection are strongly limited by the speckle noise. Specific observing strategies and data analysis methods, such as angular and spectral differential imaging, are required to attenuate the noise level and possibly detect the faint planet flux. Even though these methods are very efficient at suppressing the speckles, the photometry of the faint planets is dominated by the speckle residuals. The determi…
Measurements of the frequency with which short-period planets occur around main sequence stars allows a direct prediction of the number and types of such planets that will be amenable to characterization by high-contrast instruments on future giant segmented- mirror telescopes (GSMTs). Adopting conservative assumptions, I predict of order 10 planets with radii R_P=1-8 R_Earth and equilibrium temperatures <400 K should be accessible around stars within 8 pc of the Sun. These numbers are roughly the same for both near-infrared observations of scattered starlight and mid-infrared observations of …
Max Planck Institute for Intelligent Systems（马克斯·普朗克智能系统研究所）；ETH Zurich（苏黎世联邦理工学院）
The detection of exoplanets in high-contrast imaging (HCI) data hinges on post-processing methods to remove spurious light from the host star. So far, existing methods for this task hardly utilize any of the available domain knowledge about the problem explicitly. We propose a new approach to HCI post-processing based on a modified half-sibling regression scheme, and show how we use this framework to combine machine learning with existing scientific domain knowledge. On three real data sets, we demonstrate that the resulting system performs clearly better (both visually and in terms of the SNR…
Impact of segmented deformable mirrors on high-contrast testbeds for exoplanet imaging with future large space telescopes: contrast stability assessment on the HiCAT bench
Université Côte d’Azur（蔚蓝海岸大学）；Observatoire de la Côte d’Azur（蔚蓝海岸天文台）；CNRS（法国国家科学研究中心）；Laboratoire Lagrange（拉格朗日实验室）；Space Telescope Science Institute（太空望远镜科学研究所）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；University of California, Santa Cruz（加州大学圣克鲁兹分校）；LIRA, Observatoire de Paris（巴黎天文台LIRA）；Thales Alenia Space（泰雷兹阿莱尼亚太空公司）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Johns Hopkins University（约翰斯·霍普金斯大学）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；California Institute of Technology（加州理工学院）
Mock Observations for the CSST Mission: CPI-C -- Targets for High Contrast Imaging
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）；Center of CSST in the great bay area, Sun Yat-sen University（中山大学粤港澳大湾区CSST中心）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；CAS Key Laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台FAST国家重点实验室）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
We propose a coronagraphic system with fourth-order null for off-axis segmented telescopes, which is sufficiently insensitive to the telescope pointing errors and finite angular diameter of the host star to enable high-contrast imaging of potentially habitable planets. The inner working angle of the coronagraphic system is close to $1λ/D$, and there is no outer limit. The proposed coronagraphic system is made up of a new focal plane mask and an optimized Lyot stop with the second-order null. The new focal plane mask is an extension of the band-limited masks with a phase modulation. We construc…
High-contrast imaging surveys for exoplanet detection have shown giant planets at large separations to be rare. It is important to push towards detections at smaller separations, the part of the parameter space containing most planets. The performance of traditional methods for post-processing of pupil-stabilized observations decreases at smaller separations, due to the larger field-rotation required to displace a source on the detector in addition to the intrinsic difficulty of higher stellar contamination. We developed a method of extracting exoplanet signals that improves performance at sma…
The next generation of ground-based instruments aims to break through the knowledge we have on exoplanets by imaging circumstellar environments always closer to the stars. However, direct imaging requires an AO system and high-contrast techniques like a coronagraph to reject the diffracted light of an observed star and an additional wavefront sensor to control quasi-static aberrations, including the non common path aberrations. To observe faint objects, a focal plane wavefront sensor with a sub-nanometric wavefront control capability is required. In the past few years, we developed the THD2 be…
Current post-processing techniques in high contrast imaging depend on some source of diversity between the exoplanet signal and the residual star light at that location. The two main techniques are angular differential imaging (ADI), which makes use of parallactic sky rotation to separate planet from star light, and spectral differential imaging (SDI), which makes use of differences in the spectrum of planet and star light and the wavelength dependence of the point spread function (PSF). Here we introduce our technique for exploiting another source of diversity: orbital motion. Given repeated …
