arXiv subjects

K. Dohlen

Publications and source records attributed to K. Dohlen.

At least 19 recordsLinked to original sources

arXiv2026

Cascade adaptive optics with a second stage based on a Zernike wavefront sensor for exoplanet observations II. Validation in broadband light on the ESO/GHOST testbed

Current high-contrast facilities on the ground use extreme adaptive optics (XAO) systems to achieve contrasts down to $10^{-6}$ at 200\,mas for exoplanet observations. This performance is mainly limited by the XAO residuals due to the temporal errors in the XAO control loop. To overcome this issue, a promising solution consists in using cascade adaptive optics with a fast second stage. This approach was recently validated for a control loop based on a Zernike wavefront sensor (ZWFS) in monochromatic light. As wavefront sensors operate in broadband light to maximise photon sensitivity, this work aims to validate the ZWFS-based control loop in polychromatic light and assess its performance over a wide range of seeings, wind speeds, and stellar fluxes. Experiments were conducted on the ESO's GPU-based High-order adaptive OpticS Testbench (GHOST) testbed to probe our scheme in polychromatic light. Residual aberrations from a first-stage XAO system were simulated and our approach was evaluated in narrowband and broadband light through contrast in Lyot coronagraphic images. Closing the ZWFS-based control loop consistently improves contrast within its correction region in most tested conditions. After subtraction of quasi-static aberrations, our loop reaches a contrast gain up to one order of magnitude, independently of bandwidth and turbulence strength. The broadband and narrowband cases match in performance for bright sources, while narrowband remains slightly preferable for faint targets. These results demonstrate the feasibility of broadband ZWFS-based control loop and underline promising avenues with achromatic masks and an accurate calibration of quasi-static aberrations for future high-contrast imaging on Extremely Large Telescopes.

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arXiv2026

The SPHERE infrared survey for exoplanets (SHINE) V. Full sample characterization

Unbiased surveys of large stellar samples are the prime means through which the prevalence of exoplanets can be derived, and crucial constraints to planet formation models can be set. Direct imaging (DI) is ideally positioned to probe the outer regions (5-300au) of planetary systems, providing complementary information to techniques such as transits and radial velocities. We present the full sample of the SpHere INfrared survey for Exoplanets (SHINE), the second largest DI campaign to date. SHINE observed 460 stars between 2015 and 2023 thanks to the guaranteed time observations (GTO) allocated by ESO to the SPHERE consortium at VLT. The goal of this paper is to homogeneously derive the stellar properties of the targets and to define a subsample of young single hosts to be used as a starting point for the final statistical analysis of the survey. Stellar ages were determined based on kinematic indicators (such as the membership to young moving groups), age diagnostics (lithium abundance, rotation, activity), and isochrone fitting. A thorough vetting for binarity was undertaken combining astrometric, spectroscopic, and imaging data. A subsample of 333 stars, covering a large extent of stellar ages and masses, was constructed. Selection criteria, global features, as well as the properties of individual stars are reported and discussed.

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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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arXiv2024

Cascade adaptive optics with a second stage based on a Zernike wavefront sensor for exoplanet observations

Over the past decade, the high-contrast observation of disks and gas giant planets around nearby stars has been made possible on ground-based instruments using extreme adaptive optics (XAO). While these facilities produce images with a Strehl ratio larger than 90% in H-band in median observing conditions and high-flux regime, the correction leaves AO residuals which impede the study of fainter or less massive exoplanets. Cascade AO systems with a fast second stage based on a Pyramid wavefront sensor have recently emerged as an appealing solution to reduce the atmospheric wavefront errors. Since these aberrations are expected to be small, they can also be accurately measured by a Zernike wavefront sensor (ZWFS), a well-known concept for its high sensitivity and moderate linear capture range. We propose an alternative second stage that relies on the ZWFS to correct for the AO residuals. We implemented the cascade AO with a ZWFS-based control loop on the ESO's GHOST testbed to validate the scheme in monochromatic light. In median wind speed and seeing, our second-stage AO with a ZWFS and a basic integrator reduce the atmospheric residuals by a factor of 6 and increase the wavefront error stability with a gain of 2 from open to closed loop. In the presence of non common path aberrations, we also reach a contrast gain by a factor of 2 in the images with a Lyot coronagraph at short separations from the source, proving the ability of our scheme to work in cascade with an XAO loop. In addition, it may prove useful for imaging fainter or lighter close-in companions. In more challenging conditions, contrast improvements are also achieved by adjusting the control loop features. Our study validates the ZWFS-based second-stage AO loop as an effective solution to address small residuals left from a single-stage XAO system for the coronagraphic observations of circumstellar environments.

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arXiv2024

WST -- Widefield Spectroscopic Telescope: design of a new 12m class telescope dedicated to widefield Multi-object and Integral Field Spectroscopy

The Wide-Field Spectroscopic Telescope (WST) is a concept for a 12-m class seeing-limited telescope providing two concentric fields of view for simultaneous Multi-Object Spectroscopy and Integral Field Spectroscopy. The specified wavelength range is 0.35-1.6 microns. The baseline optical design relies on a corrected Cassegrain solution feeding Multi-Object spectrographs through fibres, while the central area of the field is propagated down to a gravity-stable Integral Field Station housing 144 spectrographs. The Cassegrain corrector also provides for atmospheric dispersion compensation. All optical components are within commercially available dimensions. With a view to minimizing risks and costs, to the maximum possible extent the telescope relies on proven subsystem solutions. An exception is the tip-tilt secondary mirror, which would likely have to provide some rejection of wind shake. An iteration of the optical design is ongoing, with a view to mitigating the weaknesses of the first baseline design. The telescope would be wavefront-controlled on-sky at the common-path MOS focus. Controls in the IFS path will need to compensate for the effect of subsequent differentials - wavefront and line of sight. There is no shortage of degrees of freedom and metrology solution to do so. The size of the dome is driven by the Nasmyth footprint and the height of the pier, which houses the IFS station. The baseline assumption is that a VLT-like enclosure would provide suitable shielding and ventilation.

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arXiv2024

SPHERE RefPlanets: Search for epsilon Eridani b and warm dust

We carried out very deep VLT/SPHERE imaging polarimetry of the nearby system Eps Eri based on 38.5 hours of integration time with a 600 - 900 nm broadband filter to search for polarized scattered light from a planet or from circumstellar dust using AO, coronagraphy, high precision differential polarimetry, and angular differential imaging. We have improved several data reduction and post-processing techniques and also developed new ones to further increase the sensitivity of SPHERE/ZIMPOL. The data provide unprecedented contrast limits, but no significant detection of a point source or an extended signal from circumstellar dust. For each observing epoch, we obtained a point source contrast for the polarized intensity between $2\cdot 10^{-8}$ and $4\cdot 10^{-8}$ at the expected separation of the planet Eps Eri b of 1'' near quadrature phase. The polarimetric contrast limits are about six to 50 times better than the intensity limits because polarimetric imaging is much more efficient in speckle suppression. Combining the entire 14-month data set to the search for a planet moving on a Keplerian orbit with the K-Stacker software further improves the contrast limits by a factor of about two, to about $8 \cdot 10^{-9}$ at 1''. This would allow the detection of a planet with a radius of about 2.5 Jupiter radii. The surface brightness contrast limits achieved for the polarized intensity from an extended scattering region are about 15 mag arcsec$^{-2}$ at 1'', or up to 3 mag arcsec$^{-2}$ deeper than previous limits. For Eps Eri, these limits exclude the presence of a narrow dust ring and they constrain the dust properties. This study shows that the polarimetric contrast limits for reflecting planets with SPHERE/ZIMPOL can be improved to a level $<10^{-8}$ simply by collecting more data over many nights and using the K-Stacker software.

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arXiv2023

First light of VLT/HiRISE: High-resolution spectroscopy of young giant exoplanets

A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT), which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The goal of HiRISE is to enable the characterization of known companions in the $H$ band, at a spectral resolution of the order of $R = \lambda/\Delta\lambda = 100\,000$, in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak value of $\sim$3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to illustrate its potential.

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arXiv2023

Low-order wavefront control using a Zernike sensor through Lyot coronagraphs for exoplanet imaging: II. Concurrent operation with stroke minimization

Wavefront sensing and control (WFSC) will play a key role in improving the stability of future large segmented space telescopes while relaxing the thermo-mechanical constraints on the observatory structure. Coupled with a coronagraph to reject the light of an observed bright star, WFSC enables the generation and stabilisation of a dark hole (DH) in the star image to perform planet observations. While WFSC traditionally relies on a single wavefront sensor (WFS) input to measure wavefront errors, the next generation of instruments will require several WFSs to address aberrations with different sets of spatial and temporal frequency contents. The multiple measurements produced in such a way will then have to be combined and converted to commands for deformable mirrors (DMs) to modify the wavefront subsequently. We asynchronously operate a loop controlling the high-order modes digging a DH and a control loop that uses the rejected light by a Lyot coronagraph with a Zernike wavefront sensor to stabilize the low-order aberrations. Using the HiCAT testbed with a segmented telescope aperture, we implement concurrent operations and quantify the expected cross-talk between the two controllers. We then present experiments that alternate high-order and low-order control loops to identify and estimate their respective contributions. We show an efficient combination of the high-order and low-order control loops, keeping a DH contrast better than 5 x 10-8 over a 30 min experiment and stability improvement by a factor of 1.5. In particular, we show a contrast gain of 1.5 at separations close to the DH inner working angle, thanks to the low-order controller contribution. Concurrently digging a DH and using the light rejected by a Lyot coronagraph to stabilize the wavefront is a promising path towards exoplanet imaging and spectroscopy with future large space observatories.

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arXiv2022

Connecting SPHERE and CRIRES+ for the characterisation of young exoplanets at high spectral resolution: status update of VLT/HiRISE

New generation exoplanet imagers on large ground-based telescopes are highly optimised for the detection of young giant exoplanets in the near-infrared, but they are intrinsically limited for their characterisation by the low spectral resolution of their integral field spectrographs ($R<100$). High-dispersion spectroscopy at $R \gg 10^4$ would be a powerful tool for the characterisation of these planets, but there is currently no high-resolution spectrograph with extreme adaptive optics and coronagraphy that would enable such characterisation. With project HiRISE we propose to use fiber coupling to combine the capabilities of two flagship instruments at the Very Large Telescope in Chile: the exoplanet imager SPHERE and the high-resolution spectrograph CRIRES+. The coupling will be implemented at the telescope in early 2023. We provide a general overview of the implementation of HiRISE, of its assembly, integration and testing (AIT) phase in Europe, and a brief assessment of its expected performance based on the final hardware.

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arXiv2022

Validation of strategies for coupling exoplanet PSFs into single-mode fibres for high-dispersion coronagraphy

On large ground-based telescopes, the combination of extreme adaptive optics (ExAO) and coronagraphy with high-dispersion spectroscopy (HDS), sometimes referred to as high-dispersion coronagraphy (HDC), is starting to emerge as a powerful technique for the direct characterisation of giant exoplanets. The high spectral resolution not only brings a major gain in terms of accessible spectral features but also enables a better separation of the stellar and planetary signals. Ongoing projects such as Keck/KPIC, Subaru/REACH, and VLT/HiRISE base their observing strategy on the use of a few science fibres, one of which is dedicated to sampling the planet's signal, while the others sample the residual starlight in the speckle field. The main challenge in this approach is to blindly centre the planet's point spread function (PSF) accurately on the science fibre, with an accuracy of less than 0.1 $\lambda/D$ to maximise the coupling efficiency. In the context of the HiRISE project, three possible centring strategies are foreseen, either based on retro-injecting calibration fibres to localise the position of the science fibre or based on a dedicated centring fibre. We implemented these three approaches, and we compared their centring accuracy using an upgraded setup of the MITHiC high-contrast imaging testbed, which is similar to the setup that will be adopted in HiRISE. Our results demonstrate that reaching a specification accuracy of 0.1 $\lambda/D$ is extremely challenging regardless of the chosen centring strategy. It requires a high level of accuracy at every step of the centring procedure, which can be reached with very stable instruments. We studied the contributors to the centring error in the case of MITHiC and we propose a quantification for some of the most impacting terms.

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arXiv2022

Low-order wavefront control using a Zernike sensor through Lyot coronagraphs for exoplanet imaging

Combining large segmented space telescopes, coronagraphy and wavefront control methods is a promising solution to produce a dark hole (DH) region in the coronagraphic image of an observed star and study planetary companions. The thermal and mechanical evolution of such a high-contrast facility leads to wavefront drifts that degrade the DH contrast during the observing time, thus limiting the ability to retrieve planetary signals. Lyot-style coronagraphs are starlight suppression systems that remove the central part of the image for an unresolved observed star, the point spread function, with an opaque focal plane mask (FPM). When implemented with a flat mirror containing an etched pinhole, the mask rejects part of the starlight through the pinhole which can be used to retrieve information about low-order aberrations. We propose an active control scheme using a Zernike wavefront sensor (ZWFS) to analyze the light rejected by the FPM, control low-order aberrations, and stabilize the DH contrast. The concept formalism is first presented before characterizing the sensor behavior in simulations and in laboratory. We then perform experimental tests to validate a wavefront control loop using a ZWFS on the HiCAT testbed. By controlling the first 11 Zernike modes, we show a decrease in wavefront error standard deviation by a factor of up to 9 between open- and closed-loop operations using the ZWFS. In the presence of wavefront perturbations, we show the ability of this control loop to stabilize a DH contrast around 7x10^-8 with a standard deviation of 7x10^-9. Active control with a ZWFS proves a promising solution in Lyot coronagraphs with an FPM-filtered beam to control and stabilize low-order wavefront aberrations and DH contrast for exoplanet imaging with future space missions.

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arXiv2022

Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. IV. Temporal stability of non-common path aberrations in VLT/SPHERE

Coronagraphic imaging of exoplanets using ground-based instruments on large telescopes is intrinsically limited by speckles induced by uncorrected aberrations. These aberrations originate from the imperfect correction of the atmosphere by an extreme adaptive optics system; from static optical defects; or from small opto-mechanical variations due to changes in temperature, pressure, or gravity vector. More than the speckles themselves, the performance of high-contrast imagers is ultimately limited by their temporal stability, since most post-processing techniques rely on difference of images acquired at different points in time. Identifying the origin of the aberrations and the timescales involved is therefore crucial to understanding the fundamental limits of dedicated high-contrast instruments. We previously demonstrated the use of a Zernike wavefront sensor called ZELDA for sensing non-common path aberrations (NCPA) in VLT/SPHERE. We now use ZELDA to investigate the stability of the instrumental aberrations using 5 long sequences of measurements obtained at high cadence on the internal source. Our study reveals two regimes of decorrelation of the NCPA. The first, with a characteristic timescale of a few seconds and an amplitude of a few nanometers, is induced by a fast internal turbulence within the enclosure. The second is a slow quasi-linear decorrelation on the order of a few $10^{-3}$ nm rms/s that acts on timescales from minutes to hours. We use coronagraphic image reconstruction to demonstrate that these two NCPA contributions have a measurable impact on differences of images, and that the fast internal turbulence is a dominating term over to the slow linear decorrelation. We also use dedicated sequences where the derotator and atmospheric dispersion compensators emulate a real observation to demonstrate the importance of performing observations symmetric around the meridian.

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arXiv2021

A metrological characterization of the SPEED test-bed PIAACMC components

The segmented pupil experiment for exoplanet detection (SPEED) facility aims to improve knowledge and insight into various areas required for gearing up high-contrast imaging instruments adapted to the unprecedented high angular resolution and complexity of the forthcoming extremely large telescopes (ELTs). SPEED combines an ELT simulator, cophasing optics, wavefront control and shaping with a multi-deformable mirror (DM) system, and optimized small inner-working angle (IWA) coronagraphy. The fundamental objective of the SPEED setup is to demonstrate deep contrast into a dark hole optimized for small field of view and very small IWA, adapted to the hunt of exoplanets in the habitable zone around late-type stars. SPEED is designed to implement an optimized small IWA coronagraph: the phase-induced amplitude apodization complex mask coronagraph (PIAACMC). The PIAACMC consists in a multi-zone phase-shifting focal plane mask (FPM) and two apodization mirrors (PIAA-M1 and PIAA-M2), with strong manufacturing specifications. Recently, a first-generation prototype of a PIAACMC optimized for the SPEED facility has been designed and manufactured. The manufacturing components exhibit high optical quality that meets specifications. In this paper, we present how these components have been characterized by a metrological instrument, an interferential microscope, and then we show what is yielded from this characterization for the FPM and the mirrors. Eventually, we discuss the results and the perspectives of the implementation of the PIAACMC components on the SPEED setup.

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arXiv2021

HD142527: Quantitative disk polarimetry with SPHERE

We present high-precision photometry and polarimetry for the protoplanetary disk around HD142527, with a focus on determining the light scattering parameters of the dust. We re-reduced polarimetric differential imaging data of HD142527 in the VBB (735 nm) and H-band (1625 nm) from the ZIMPOL and IRDIS subinstruments of SPHERE/VLT. With polarimetry and photometry based on reference star differential imaging, we were able to measure the linearly polarized intensity and the total intensity of the light scattered by the circumstellar disk with high precision. We used simple Monte Carlo simulations of multiple light scattering by the disk surface to derive constraints for three scattering parameters of the dust: the maximum polarization of $P_{\rm max}$, the asymmetry parameter $g$, and the single-scattering albedo $\omega$. We measure a reflected total intensity of $51.4\pm1.5$ mJy and $206\pm12$ mJy and a polarized intensity of $11.3\pm0.3$ mJy and $55.1\pm3.3$ mJy in the VBB and H-band, respectively. We also find in the visual range a degree of polarization that varies between $28\%$ on the far side of the disk and $17\%$ on the near side. The disk shows a red color for the scattered light intensity and the polarized intensity, which are about twice as high in the near-infrared when compared to the visual. We determine with model calculations the scattering properties of the dust particles and find evidence for strong forward scattering ($g\approx 0.5-0.75$), relatively low single-scattering albedo ($\omega \approx 0.2-0.5$), and high maximum polarization ($P_{\rm max} \approx 0.5-0.75$) at the surface on the far side of the disk for both observed wavelengths. The optical parameters indicate the presence of large aggregate dust particles, which are necessary to explain the high maximum polarization, the strong forward-scattering nature of the dust, and the observed red disk color.

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arXiv2021

The SPHERE infrared survey for exoplanets (SHINE)- I Sample definition and target characterization

Large surveys with new-generation high-contrast imaging instruments are needed to derive the frequency and properties of exoplanet populations with separations from $\sim$5 to 300 AU. A careful assessment of the stellar properties is crucial for a proper understanding of when, where, and how frequently planets form, and how they evolve. The sensitivity of detection limits to stellar age makes this a key parameter for direct imaging surveys. We describe the SpHere INfrared survey for Exoplanets (SHINE), the largest direct imaging planet-search campaign initiated at the VLT in 2015 in the context of the SPHERE Guaranteed Time Observations of the SPHERE consortium. In this first paper we present the selection and the properties of the complete sample of stars surveyed with SHINE, focusing on the targets observed during the first phase of the survey (from February 2015 to February 2017). This early sample composed of 150 stars is used to perform a preliminary statistical analysis of the SHINE data, deferred to two companion papers presenting the survey performance, main discoveries, and the preliminary statistical constraints set by SHINE. Based on a large database collecting the stellar properties of all young nearby stars in the solar vicinity (including kinematics, membership to moving groups, isochrones, lithium abundance, rotation, and activity), we selected the original sample of 800 stars that were ranked in order of priority according to their sensitivity for planet detection in direct imaging with SPHERE. The properties of the stars that are part of the early statistical sample were revisited, including for instance measurements from the GAIA Data Release 2.

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arXiv2021

The SPHERE infrared survey for exoplanets (SHINE) -- II. Observations, Data reduction and analysis Detection performances and early-results

Over the past decades, direct imaging has confirmed the existence of substellar companions (exoplanets or brown dwarfs) on wide orbits (>10 au) from their host stars. To understand their formation and evolution mechanisms, we have initiated in 2015 the SPHERE infrared survey for exoplanets (SHINE), a systematic direct imaging survey of young, nearby stars to explore their demographics.} {We aim to detect and characterize the population of giant planets and brown dwarfs beyond the snow line around young, nearby stars. Combined with the survey completeness, our observations offer the opportunity to constrain the statistical properties (occurrence, mass and orbital distributions, dependency on the stellar mass) of these young giant planets.} {In this study, we present the observing and data analysis strategy, the ranking process of the detected candidates, and the survey performances for a subsample of 150 stars, which are representative of the full SHINE sample. The observations were conducted in an homogeneous way from February 2015 to February 2017 with the dedicated ground-based VLT/SPHERE instrument equipped with the IFS integral field spectrograph and the IRDIS dual-band imager covering a spectral range between 0.9 and 2.3 $\mu$m. We used coronographic, angular and spectral differential imaging techniques to reach the best detection performances for this study down to the planetary mass regime.}

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arXiv2021

Imaging low-mass planets within the habitable zone of {\alpha} Centauri

Giant exoplanets on wide orbits have been directly imaged around young stars. If the thermal background in the mid-infrared can be mitigated, then exoplanets with lower masses can also be imaged. Here we present a ground-based mid-infrared observing approach that enables imaging low-mass temperate exoplanets around nearby stars, and in particular within the closest stellar system, Alpha Centauri. Based on 75-80% of the best quality images from 100 hours of cumulative observations, we demonstrate sensitivity to warm sub-Neptune-sized planets throughout much of the habitable zone of Alpha Centauri A. This is an order of magnitude more sensitive than state-of-the-art exoplanet imaging mass detection limits. We also discuss a possible exoplanet or exozodiacal disk detection around Alpha Centauri A. However, an instrumental artifact of unknown origin cannot be ruled out. These results demonstrate the feasibility of imaging rocky habitable-zone exoplanets with current and upcoming telescopes.

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arXiv2020

Characterisation of a turbulent module for the MITHIC high-contrast imaging testbed

Future high-contrast imagers on ground-based extremely large telescopes will have to deal with the segmentation of the primary mirrors. Residual phase errors coming from the phase steps at the edges of the segments will have to be minimized in order to reach the highest possible wavefront correction and thus the best contrast performance. To study these effects, we have developed the MITHIC high-contrast testbed, which is designed to test various strategies for wavefront sensing, including the Zernike sensor for Extremely accurate measurements of Low-level Differential Aberrations (ZELDA) and COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection (COFFEE). We recently equipped the bench with a new atmospheric turbulence simulation module that offers both static phase patterns representing segmented primary mirrors and continuous phase strips representing atmospheric turbulence filtered by an AO or an XAO system. We present a characterisation of the module using different instruments and wavefront sensors, and the first coronagraphic measurements obtained on MITHIC.

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