arXiv subjects

J. Mazoyer

Publications and source records attributed to J. Mazoyer.

At least 19 recordsLinked to original sources

arXiv2026

Non-common path aberration compensation and a dark hole loop with a pyramid adaptive optics system: Application to SAXO+

In ground-based high-contrast instruments, non-common path aberrations (NCPAs) limit detection performance, as they are unseen by the adaptive optics (AO) wavefront sensor but impact the astrophysical image, creating quasi-static speckles. SAXO+, the upgrade of the SAXO (SPHERE AO system) includes a second loop of AO downstream of the SAXO loop that is equipped with a near-infrared pyramid wavefront sensor whose nonlinearities, usually described with modal optical gains, might be challenging for removing quasi-static speckles. We investigated two methods of quasi-static speckle removal : NCPA compensation and a dark hole loop, behind a pyramid AO system, measuring the interest of compensating for the pyramid optical gains. We performed end-to-end numerical simulations under various astrophysical conditions. We offset the pyramid wavefront sensor operating point to apply both the speckle suppression methods, with or without optical gain calibration. We evaluated the performance by measuring the residual starlight in the coronagraph image. A by-product of our study is an on-sky calibration method of measuring the pyramid optical gains. NCPA compensation reduces the residual starlight in the coronagraph image by a factor of 20 for seeing between 0.7" and 1" for a bright star and a factor of 2 at 0.7" for a faint star. Optical gains compensation enhances the performance at poor seeing and small pyramid modulation radius with a bright star, but shows a useless or even negative impact due to estimation inaccuracies at faint targets. On the other hand, the dark hole loop reduces the residual starlight by a factor of 200. The optical gain calibration enhances the dark hole performance behind a single pyramid AO system but is useless behind the SAXO+ system. Our parametric study gives baseline values for the efficient control of the dark hole loop for the SAXO+ system.

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arXiv2025

Optimising reference library selection for reference-star differential imaging of discs with SPHERE/IRDIS

The direct detection of circumstellar discs through high-contrast imaging provides key insights into the history and dynamics of planetary systems. Pole-on discs, especially faint debris discs, are difficult to detect and require careful consideration during post-processing to remove stellar residuals from the data while preserving the disc signal. Reference-star differential imaging (RDI) serves as one of the primary post-processing methods for disc observations. We aim to develop a method of reference frame selection that is optimised for the reduction of pole-on discs. Method: We performed principal component analysis based RDI on seven known disc targets and 20 disc-free targets with varying observational conditions, using reference libraries built from frames preselected to best match different observational, atmospheric, and stellar parameters of the science frames. The contrast of the disc-free reductions was measured, and forward modelling was used to estimate the signal loss from over-subtraction using synthetic pole-on discs with two different widths and four different radii. The signal-to-noise ratio (S/N) of the real disc targets was measured. Results: Diverse reference libraries built using subsets of frames that closely matched different parameters achieved the best disc S/N and smallest deviation from the best contrast of each target, outperforming libraries built using a single criterion as a selection metric. Libraries built using frame-to-frame Pearson correlation coefficient alone as a selection criterion achieved the best mean contrast overall. Both selection metrics performed consistently well for all disc radii and observational conditions. We also found that reference libraries built using frames observed close in time to the science frame performed well for discs at small separations, giving the best contrast for ~30% of the targets at a radius of 20px.

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arXiv2025

Dust populations from 30 to 1000 au in the debris disk of HD 120326

Context. To date, more than a hundred debris disks have been spatially resolved. Among them, the young system HD 120326 stands out, displaying different disk substructures on both intermediate (30-150 au) and large (150-1000 au) scales. Aims. We present new VLT/SPHERE (1.0-1.8 $\mu$m) and ALMA (1.3 mm) data of the debris disk around HD 120326. By combining them with archival HST/STIS (0.2-1.0 $\mu$m) and archival SPHERE data, we have been able to examine the morphology and photometry of the debris disk, along with its dust properties. Methods. We present the open-access code MoDiSc (Modeling Disks in Scattered light) to model the inner belt jointly using the SPHERE polarized and total intensity observations. Separately, we modeled the ALMA data and the spectral energy distribution (SED). We combined the results of both these analyses with the STIS data to determine the global architecture of HD 120326. Results. For the inner belt, identified as a planetesimal belt, we derived a semi-major axis of 43 au, fractional luminosity of 1.8 x 10-3 , and maximum degree of polarization of 45-57 % at 1.6 $\mu$m. The spectral slope of its reflectance spectrum is red between 1.0 and 1.3 $\mu$m and gray between 1.3 and 1.8 $\mu$m. Additionally, the SPHERE data show that there could be a halo of small particles or a second belt at distances <150 au. Using ALMA, we derived in the continuum (1.3 mm) an integrated flux of 541-581 $\mu$Jy. We did not detect any 12CO emission. At larger separations (>150 au), we highlight a spiral-like feature spanning hundreds of astronomical units in the STIS data. Conclusions. Further data are needed to confirm and better constrain the dust properties and global morphology of HD 120326.

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arXiv2025

Evidence for a sub-jovian planet in the young TWA7 disk

Planets are thought to form from dust and gas in protoplanetary disks, and debris disks are the remnants of planet formation. Aged a few Myr up to a few Gyr, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies. Tens of debris disks, with sizes of tens, sometimes hundreds of au, have been resolved with high spatial resolution, high contrast imagers at optical/near-IR or (sub)-millimeter interferometers. They commonly show cavities, ring-like structures, and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2-10 MJ) of high contrast imaging instruments prior to JWST. We have used the unprecedented sensitivity of JWST/MIRI in the thermal IR to search for such planets in the disk of the ~ 6.4 Myr old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arsec from the star, that is best interpreted as a cold, sub-Jupiter mass planet. Its estimated mass (~ 0.3 MJ) and position (~ 52 au, de-projected) can thoroughly account for the main disk structures.

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arXiv2025

The SPHERE infrared survey for exoplanets (SHINE). V. Complete observations, data reduction and analysis, detection performances, and final results

During the past decade, state-of-the-art planet-finder instruments like SPHERE@VLT, coupling coronagraphic devices and extreme adaptive optics systems, unveiled, thanks to large surveys, around 20 planetary mass companions at semi-major axis greater than 10 astronomical units. Direct imaging being the only detection technique to be able to probe this outer region of planetary systems, the SPHERE infrared survey for exoplanets (SHINE) was designed and conducted from 2015 to 2021 to study the demographics of such young gas giant planets around 400 young nearby solar-type stars. In this paper, we present the observing strategy, the data quality, and the point sources analysis of the full SHINE statistical sample as well as snapSHINE. Both surveys used the SPHERE@VLT instrument with the IRDIS dual band imager in conjunction with the integral field spectrograph IFS and the angular differential imaging observing technique. All SHINE data (650 datasets), corresponding to 400 stars, including the targets of the F150 survey, are processed in a uniform manner with an advanced post-processing algorithm called PACO ASDI. An emphasis is put on the classification and identification of the most promising candidate companions. Compared to the previous early analysis SHINE F150, the use of advanced post-processing techniques significantly improved by one or 2 magnitudes (x3-x6) the contrast detection limits, which will allow us to put even tighter constraints on the radial distribution of young gas giants. This increased sensitivity directly places SHINE as the largest and deepest direct imaging survey ever conducted. We detected and classified more than 3500 physical sources. One additional substellar companion has been confirmed during the second phase of the survey (HIP 74865 B), and several new promising candidate companions are awaiting second epoch confirmations.

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arXiv2025

Searching for substellar companion candidates with Gaia. III. Search for companions to members of young associations

Absolute astrometry with Gaia is expected to detect and characterize the orbits of thousands of exoplanets in the coming years. A tool, GaiaPMEX, was recently developed to characterize multiple systems based on Gaia-only data, and, when possible, the Gaia-Hipparcos proper motion anomaly. We compare the detection capabilities of absolute astrometry and spectroscopy (RV), and to detect and characterize planetary-mass companions, combining the astrometric data with direct imaging and RV data. For companion masses possibly in the planetary range, we use direct imaging and when possible, RV data as well, to further constrain their nature and orbital properties. For each target, a diagnosis on its binarity based on absolute astrometry is given. When no binary is detected, we provides detection limits in the (sma, mass) space. We identify several companions with possible masses down to the brown dwarfs (BD; 50+) or planetary masses (13). We detect a new giant planet at less than 1-2 au from the M-type star G80-21. For AB Pic and HD 14082 B, we confirm the presence of substellar companions, and provide robust solutions for their mass and orbital properties. We further identify 9 planetary mass companions candidates. Finally, a detailed treatment of noises in Gaia astrometric measurements shows that there are no evidence at a 2-sigma level of two exoplanet detections previously announced. Combining GaiaPMEX and RV data is therefore perfectly adaptIn the 0.5 to 5 au domain, GaiaPMEX has an excellent sensitivity to BDs, and a good sensitivity to planetary mass planets for this sample.

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arXiv2024

The COBREX archival survey: improved constraints on the occurrence rate of wide-orbit substellar companions. I. A uniform re-analysis of 400 stars from the GPIES survey

Direct imaging (DI) campaigns are uniquely suited to probing the outer regions around young stars and looking for giant exoplanet and brown dwarf companions, hence providing key complementary information to radial velocity (RV) and transit searches for the purpose of demographic studies. However, the critical 5-20 au region, where most giant planets are thought to form, remains poorly explored, lying in-between RV and DI capabilities. Significant gains in detection performances can be attained at no instrumental cost by means of advanced post-processing techniques. In the context of the COBREX project, we have assembled the largest collection of archival DI observations to date in order to undertake a large and uniform re-analysis. In particular, this paper details the re-analysis of 400 stars from the GPIES survey operated at GPI@Gemini South. Following the pre-reduction of raw frames, GPI data cubes were processed by means of the PACO algorithm. Candidates were identified and vetted based on multi-epoch proper motion analysis -- whenever possible -- and by means of a suitable color-magnitude diagram. The conversion of detection limits into detectability maps allowed for an estimate of unbiased occurrence frequencies of giant planets and brown dwarfs. Deeper detection limits were derived compared to the literature, with up to a twofold gain in minimum detectable mass compared to previous GPI-based publications. Although no new substellar companion was confirmed, we identified two interesting planet candidates awaiting follow-up observations. We derive an occurrence rate of $1.7_{-0.7}^{+0.9}\%$ for $5$~\mjup$ < m < 13$~\mjup planets in $10~\text{au}< a < 100~\text{au}$, that raises to $2.2_{-0.8}^{+1.0}\%$ when including substellar objects up to 80 \mjup.(abridged)

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arXiv2023

An inner warp discovered in the disk around HD 110058 using VLT/SPHERE and HST/STIS

An edge-on debris disk was detected in 2015 around the young, nearby A0V star HD 110058. The disk showed features resembling those seen in the disk of beta Pictoris that could indicate the presence of a perturbing planetary-mass companion in the system. We investigated new and archival scattered light images of the disk in order to characterise its morphology and spectrum. In particular, we analysed the disk's warp to constrain the properties of possible planetary perturbers. Our work uses data from two VLT/SPHERE observations and archival data from HST/STIS. We measured the morphology of the disk by analysing vertical profiles along the length of the disk to extract the centroid spine position and vertical height. We extracted the surface brightness and reflectance spectrum of the disk. We detect the disk between 20 au (with SPHERE) and 150 au (with STIS), at a position angle of 159.6$^\circ\pm$0.6$^\circ$. Analysis of the spine shows an asymmetry between the two sides of the disk, with a 3.4$^\circ\pm$0.9$^\circ$ warp between ~20 au and 60 au. The disk is marginally vertically resolved in scattered light, with a vertical aspect ratio of 9.3$\pm$0.7% at 45 au. The extracted reflectance spectrum is featureless, flat between 0.95 micron and 1.1 micron, and red from 1.1 micron to 1.65 micron. The outer parts of the disk are also asymmetric with a tilt between the two sides compatible with a disk made of forward-scattering particles and seen not perfectly edge-on, suggesting an inclination of <84$^\circ$. The presence of an undetected planetary-mass companion on an inclined orbit with respect to the disk could explain the warp. The misalignment of the inner parts of the disk with respect to the outer disk suggests a warp that has not yet propagated to the outer parts of the disk, favouring the scenario of an inner perturber as the origin of the warp.

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arXiv2022

Exoplanet Imaging Data Challenge, phase II: Characterization of exoplanet signals in high-contrast images

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 therefore challenging, and new post-processing algorithms are striving to achieve more accurate astrophysical results. The Exoplanet Imaging Data Challenge is a community-wide effort to develop, compare and evaluate algorithms using a set of benchmark high-contrast imaging datasets. After a first phase ran in 2020 and focused on the detection capabilities of existing algorithms, the focus of this ongoing second phase is to compare the characterisation capabilities of state-of-the-art techniques. The characterisation of planetary companions is two-fold: the astrometry (estimated position with respect to the host star) and spectrophotometry (estimated contrast with respect to the host star, as a function of wavelength). The goal of this second phase is to offer a platform for the community to benchmark techniques in a fair, homogeneous and robust way, and to foster collaborations.

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arXiv2022

Upgrading the high contrast imaging facility SPHERE: science drivers and instrument choices

SPHERE+ is a proposed upgrade of the SPHERE instrument at the VLT, which is intended to boost the current performances of detection and characterization for exoplanets and disks. SPHERE+ will also serve as a demonstrator for the future planet finder (PCS) of the European ELT. The main science drivers for SPHERE+ are 1/ to access the bulk of the young giant planet population down to the snow line ($3-10$ au), to bridge the gap with complementary techniques (radial velocity, astrometry); 2/ to observe fainter and redder targets in the youngest ($1-10$\,Myr) associations compared to those observed with SPHERE to directly study the formation of giant planets in their birth environment; 3/ to improve the level of characterization of exoplanetary atmospheres by increasing the spectral resolution in order to break degeneracies in giant planet atmosphere models. Achieving these objectives requires to increase the bandwidth of the xAO system (from $\sim$1 to 3\,kHz) as well as the sensitivity in the infrared (2 to 3\,mag). These features will be brought by a second stage AO system optimized in the infrared with a pyramid wavefront sensor. As a new science instrument, a medium resolution integral field spectrograph will provide a spectral resolution from 1000 to 5000 in the J and H bands. This paper gives an overview of the science drivers, requirements and key instrumental trade-off that were done for SPHERE+ to reach the final selected baseline concept.

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arXiv2022

Detection of Near-Infrared Water Ice at the Surface of the (pre)Transitional Disk of AB Aur: Informing Icy Grain Abundance, Composition, and Size

We present near-infrared Large Binocular Telescope Interferometer LMIRCam imagery of the disk around the Herbig Ae/Be star AB Aurigae. A comparison of surface brightness at Ks (2.16 $μ$m), H2O narrowband (3.08 $μ$m), and L' (3.7 $μ$m) allows us to probe the presence of icy grains in this (pre)transitional disk environment. By applying Reference Differential Imaging PSF subtraction, we detect the disk at high signal to noise in all three bands. We find strong morphological differences between bands, including asymmetries consistent with observed spiral arms within 100 AU in L'. An apparent deficit of scattered light at 3.08 $μ$m relative to bracketing wavelengths (Ks and L') is evocative of ice absorption at the disk surface layer. However, the $Δ$(Ks-H2O) color is consistent with grains with little to no ice (0-5% by mass). The $Δ$(H2O-L') color, conversely, suggests grains with a much higher ice mass fraction (~0.68), and the two colors cannot be reconciled under a single grain population model. Additionally, we find the extremely red $Δ$(Ks-L') disk color cannot be reproduced under conventional scattered light modeling with any combination of grain parameters or reasonable local extinction values. We hypothesize that the scattering surfaces at the three wavelengths are not co-located, and optical depth effects result in each wavelength probing the grain population at different disk surface depths. The morphological similarity between Ks and H2O suggests their scattering surfaces are near one another, lending credence to the $Δ$(Ks-H2O) disk color constraint of < 5% ice mass fraction for the outermost scattering disk layer.

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arXiv2020

SPHERE+: Imaging young Jupiters down to the snowline

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. The achievements obtained thus far with SPHERE (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. The SPHERE+ project capitalizes on the expertise and lessons learned from SPHERE to push high contrast imaging performance to its limits on the VLT 8m-telescope. The scientific program of SPHERE+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and WFIRST). While SPHERE has sampled the outer parts of planetary systems beyond a few tens of AU, SPHERE+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. Building on SPHERE's scientific heritage and resounding success, SPHERE+ will be a dedicated survey instrument which will strengthen the leadership of ESO and the European community in the very competitive field of direct imaging of exoplanetary systems. With enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei.

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arXiv2019

Imaging the 44 AU Kuiper Belt-analogue debris ring around HD 141569A with GPI polarimetry

We present the first polarimetric detection of the inner disk component around the pre-main sequence B9.5 star HD 141569A. Gemini Planet Imager H-band (1.65 micron) polarimetric differential imaging reveals the highest signal-to-noise ratio detection of this ring yet attained and traces structure inwards to 0.25" (28 AU at a distance of 111 pc). The radial polarized intensity image shows the east side of the disk, peaking in intensity at 0.40" (44 AU) and extending out to 0.9" (100 AU). There is a spiral arm-like enhancement to the south, reminiscent of the known spiral structures on the outer rings of the disk. The location of the spiral arm is coincident with 12CO J=3-2 emission detected by ALMA, and hints at a dynamically active inner circumstellar region. Our observations also show a portion of the middle dusty ring at ~220 AU known from previous observations of this system. We fit the polarized H-band emission with a continuum radiative transfer Mie model. Our best-fit model favors an optically thin disk with a minimum dust grain size close to the blow-out size for this system: evidence of on-going dust production in the inner reaches of the disk. The thermal emission from this model accounts for virtually all of the far-infrared and millimeter flux from the entire HD 141569A disk, in agreement with the lack of ALMA continuum and CO emission beyond ~100 AU. A remaining 8-30 micron thermal excess a factor of ~2 above our model argues for a yet-unresolved warm innermost 5-15 AU component of the disk.

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arXiv2019

Spatially resolved spectroscopy of the debris disk HD 32297: Further evidence of small dust grains

Spectro-photometry of debris disks in total intensity and polarimetry can provide new insight into the properties of the dust grains therein (size distribution and optical properties). We aim to constrain the morphology of the highly inclined debris disk HD 32297. We also intend to obtain spectroscopic and polarimetric measurements to retrieve information on the particle size distribution within the disk for certain grain compositions. We observed HD 32297 with SPHERE in Y, J, and H bands in total intensity and in J band in polarimetry. The observations are compared to synthetic models of debris disks and we developed methods to extract the photometry in total intensity overcoming the data-reduction artifacts, namely the self-subtraction. The spectro-photometric measurements averaged along the disk mid-plane are then compared to model spectra of various grain compositions. These new images reveal the very inner part of the system as close as 0.15". The disk image is mostly dominated by the forward scattering making one side (half-ellipse) of the disk more visible, but observations in total intensity are deep enough to also detect the back side for the very first time. The images as well as the surface brightness profiles of the disk rule out the presence of a gap as previously proposed. We do not detect any significant asymmetry between the northeast and southwest sides of the disk. The spectral reflectance features a "gray to blue" color which is interpreted as the presence of grains far below the blowout size. The presence of sub-micron grains in the disk is suspected to be the result of gas drag and/or "avalanche mechanisms". The blue color of the disk could be further investigated with additional total intensity and polarimetric observations in K and H bands respectively to confirm the spectral slope and the fraction of polarization.

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arXiv2019

Investigating the presence of two belts in the HD 15115 system

We present new observations of the edge-on debris disk around HD 15115 (F star at 48.2 pc) obtained in the near-IR. We search for observational evidence for a second inner planetesimal ring in the system. We obtained total intensity and polarimetric data in the broad bands J and H and processed the data with differential imaging techniques achieving an angular resolution of about 40 mas. We observe an axisymmetric planetesimal belt with a radius of $\sim$2$''$, an inclination of $85.8^{\circ} \pm 0.7^{\circ}$ and position angle of 278.9$^{\circ} \pm 0.1^{\circ}$. A grid of models describing the spatial distribution of the grains in the disk is generated to constrain the geometric parameters of the disk and to explore the presence of a second belt. We perform a photometric analysis of the data and compare disk brightness in two bands in scattered and in polarized light. The analysis shows that the west side is $\sim$2.5 times brighter in total intensity than the east side in both bands, while for polarized light in the J band this ratio is only 1.25. The maximum polarization fraction is 15--20% at $r\sim$2.5$''$. We also find that the J - H color of the disk appears to be red for the radial separations $r\lesssim2''$ and is getting bluer for the larger separations. This apparent change of disk color from red to blue with an increasing radial separation could be explained by the decreasing average grain size with distance. The presence of an additional inner belt slightly inclined with respect to the main planetesimal belt is suspected from the polarized intensity image but the analysis and modeling presented here cannot establish a firm conclusion due to the faintness of the disk and its high inclination.

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arXiv2018

Review of high-contrast imaging systems for current and future ground- and space-based telescopes I. Coronagraph design methods and optical performance metrics

The Optimal Optical Coronagraph (OOC) Workshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 25 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. In this first installment of a series of three papers summarizing the outcomes of the OOC workshop, we present an overview of design methods and optical performance metrics developed for coronagraph instruments. The design and optimization of coronagraphs for future telescopes has progressed rapidly over the past several years in the context of space mission studies for Exo-C, WFIRST, HabEx, and LUVOIR as well as ground-based telescopes. Design tools have been developed at several institutions to optimize a variety of coronagraph mask types. We aim to give a broad overview of the approaches used, examples of their utility, and provide the optimization tools to the community. Though it is clear that the basic function of coronagraphs is to suppress starlight while maintaining light from off-axis sources, our community lacks a general set of standard performance metrics that apply to both detecting and characterizing exoplanets. The attendees of the OOC workshop agreed that it would benefit our community to clearly define quantities for comparing the performance of coronagraph designs and systems. Therefore, we also present a set of metrics that may be applied to theoretical designs, testbeds, and deployed instruments. We show how these quantities may be used to easily relate the basic properties of the optical instrument to the detection significance of the given point source in the presence of realistic noise.

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arXiv2017

Active correction of aperture discontinuities - optimized stroke minimization I: a new adaptive interaction matrix algorithm

Future searches for biomarkers on habitable exoplanets will rely on telescope instruments that achieve extremely high contrast at small planet-to-star angular separations. Coronagraphy is a promising starlight suppression technique, providing excellent contrast and throughput for off-axis sources on clear apertures. However, the complexity of space- and ground-based telescope apertures goes on increasing over time, owing to the combination of primary mirror segmentation, secondary mirror, and support structures. These discontinuities in the telescope aperture limit the coronagraph performance. In this paper, we present ACAD-OSM, a novel active method to correct for the diffractive effects of aperture discontinuities in the final image plane of a coronagraph. Active methods use one or several deformable mirrors that are controlled with an interaction matrix to correct for the aberrations in the pupil. However, they are often limited by the amount of aberrations introduced by aperture discontinuities. This algorithm relies on the recalibration of the interaction matrix during the correction process to overcome this limitation. We first describe the ACAD-OSM technique and compare it to the previous active methods for the correction of aperture discontinuities. We then show its performance in terms of contrast and off-axis throughput for static aperture discontinuities (segmentation, struts) and for some aberrations evolving over the life of the instrument (residual phase aberrations, artifacts in the aperture, misalignments in the coronagraph design). This technique can now obtain the earth-like planet detection threshold of 10^(-10) contrast on any given aperture over at least a 10% spectral bandwidth, with several coronagraph designs.

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arXiv2016

Discovery of concentric broken rings at sub-arcsec separations in the HD 141569A gas-rich, debris disk with VLT/SPHERE

Transition disks correspond to a short stage between the young protoplanetary phase and older debris phase. Along this evolutionary sequence, the gas component disappears leaving room for a dust-dominated environment where already-formed planets signpost their gravitational perturbations. We endeavor to study the very inner region of the well-known and complex debris, but still gas-rich disk, around HD 141569A using the exquisite high-contrast capability of SPHERE at the VLT. Recent near-infrared (IR) images suggest a relatively depleted cavity within ~200 au, while former mid-IR data indicate the presence of dust at separations shorter than ~100 au. We obtained multi-wavelength images in the near-IR in J, H2, H3 and Ks bands with the IRDIS camera and a 0.95-1.35 micrometers spectral data cube with the IFS. Data were acquired in pupil-tracking mode, thus allowing for angular differential imaging. We discovered several new structures inside 1", of which the most prominent is a bright ring with sharp edges (semi-major axis: 0.4") featuring a strong north-south brightness asymmetry. Other faint structures are also detected from 0.4" to 1" in the form of concentric ringlets and at least one spiral arm. Finally, the VISIR data at 8.6 micrometers suggests the presence of an additional dust population closer in. Besides, we do not detect companions more massive than 1-3 mass of Jupiter. The performance of SPHERE allows us to resolve the extended dust component, which was previously detected at thermal and visible wavelengths, into very complex patterns with strong asymmetries ; the nature of these asymmetries remains to be understood. Scenarios involving shepherding by planets or dust-gas interactions will have to be tested against these observations.

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