SAXO+ is the upgrade of SAXO, the adaptive optics system used by the SPHERE instrument on ESO’s Very Large Telescope. SAXO+ consists of a second stage adaptive optics downstream of the first stage, SAXO, to improve wavefront correction, achieve deeper contrast in the coronagraphic images and observe fainter and redder stars. Using the COMPASS end-to-end simulation tool, we assess the SAXO+ improved correction compared to SAXO in multiple science cases and turbulence conditions. The adaptive optics performance criterion is the starlight residual intensity in the coronagraph image: the lower the better. We show that SAXO+ improves the performance of the adaptive optics system by a factor of 10 in all simulated observing conditions. We specifically study the impact of the second stage frequency and we conclude that a 2kHz second stage is a reasonable trade-off between performance and technical constraints on the real-time system.
The Spectro-Polarimetric High-contrast Exoplanet REsearch instrument 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 have motivated a large consortium to propose 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 proposed upgrade takes the form of a high-speed adaptive optics second stage, SAXO+, including a deformable mirror, a pyramid wavefront sensor, and a Real-Time Controller (RTC). Paving the way toward PCS, SAXO+ can be seen as a technical demonstrator for advanced AO control strategies, with a fast-track development aiming at the first light in 2027. In this context, the RTC is a core component that must be flexible enough to handle various control strategies, including AI, while ensuring high efficiency to be able to control the AO loop at high frame-rate. To achieve those goals, COSMIC has been selected to provide the required hard real-time capabilities, supplemented by the ESO RTC Toolkit for the implementation of soft real-time clustering. This paper will focus on the SAXO+ RTC preliminary design, including the main features of the RTC and preliminary benchmark results.
In order to address new science objectives in exoplanet imaging, the SAXO+ technical development project has been undertaken for the SPHERE instrument at ESO’s VLT. As a part of this, the AO system will be completed by adding a second, faster stage of correction. We present simulation results obtained by implementing an optimal predictive linear quadratic Gaussian controller for the 2nd stage. The prediction relies on a stochastic state-space disturbance model fully identified from closed-loop measurements. In addition, we also investigate a disentangled cascade AO (dCAO) mode whIn order to address new science objectives in exoplanet imaging, the SAXO+ technical development project has been undertaken for the SPHERE instrument at ESO’s VLT. As a part of this, the AO system will be completed by adding a second, faster stage of correction. We present simulation results obtained by implementing an optimal predictive linear quadratic Gaussian controller for the 2nd stage. The prediction relies on a stochastic state-space disturbance model fully identified from closed-loop measurements. In addition, we also investigate a disentangled cascade AO (dCAO) mode where the model represents the full incoming disturbance and is identified using in addition the 1st stage commands.ere the model represents the full incoming disturbance and is identified using in addition the 1st stage commands.
SAXO+ is a second-stage adaptive optics module for the SPHERE instrument at VLT. It has been proposed to increase the achievable contrast and improve the current performance of detecting and characterizing exoplanets and disks. It is developed by the SPHERE+ consortium as part of the roadmap activity for the planet finder instrument (PCS) of the Extremely Large Telescope (ELT). This paper describes the optical and mechanical design of SAXO+.
This study introduces a novel frequency-based data-driven controller for adaptive optics, using power spectral density for optimization while ensuring stability criteria. It addresses disturbance rejection, command amplitude constraints and system transfer functions through convex optimization to obtain an optimal control in an infinite input response filter form. Evaluated within the SAXO+ project, it demonstrates efficacy under diverse atmospheric conditions and operational scenarios. The proposed controller is tested in both standard and disentangled adaptive optics schemes, showcasing its adaptability and performance. Experimental validation is conducted using the COMPASS simulation tool, affirming the controller’s promise for enhancing adaptive optics systems in real-world applications.
SAXO+ is a planned enhancement of the existing SAXO, the VLT/ SPHERE adaptive optics system, deployed on ESO’s Very Large Telescope. This upgrade is designed to significantly enhance the instrument’s capacity to detect and analyze young Jupiter-like planets. The pivotal addition in SAXO+ is a second-stage adaptive optics system featuring a dedicated near-infrared pyramid wavefront sensor and a second deformable mirror. This secondary stage is strategically integrated to address any residual wavefront errors persisting after the initial correction performed by the current primary AO loop, SAXO. However, several recent studies clearly showed that in good conditions, even in the current system SAXO, non-common path aberrations (NCPAs) are the limiting factor of the final normalized intensity in focal plane, which is the final metric for ground-based high-contrast instruments. This is likely to be even more so the case with the new AO system, with which the AO residuals will be minimized. Several techniques have already been extensively tested on SPHERE in internal source and/or on-sky and will be presented in this paper. However, the use of a new type of sensor for the second stage, a pyramid wavefront sensor, will likely complicate the correction of these aberrations. Using an end-to-end AO simulation tool, we conducted simulations to gauge the effect of measured SPHERE NCPAs in the coronagraphic image on the second loop system and their correction using focal plane wavefront sensing systems. We finally analyzed how the chosen position of SAXO+ in the beam will impact the evolution of the NCPAs in the new instrument.
SPHERE+ is a proposed upgrade of the SPHERE instrument at VLT, which will boost the current performances of detection and characterization of exoplanets and disks, and will serve as a demonstrator for the future planet finder (PCS) of the European ELT. The performance gain will be delivered by a second-stage AO module (SAXO+), including a dedicated wavefront sensor and deformable mirror to remove the residual wavefront errors left by the primary AO loop. This paper is focused on the optical and mechanical implementation of SAXO+ and describes the baseline design concept, selected from trade-off analysis of different options.
A key challenge of high contrast imaging (HCI) is to differentiate a speckle from an exoplanet signal. The sources of speckles are a combination of atmospheric residuals and aberrations in the non-common path. Those non-common path aberrations (NCPA) are particularly challenging to compensate for as they are not directly measured, and because they include static, quasi-static and dynamic components. The proposed method directly addresses the challenge of compensating the NCPA. The algorithm DrWHO - Direct Reinforcement Wavefront Heuristic Optimisation - is a quasi-real-time compensation of static and dynamic NCPA for boosting image contrast. It is an image-based lucky imaging approach, aimed at finding and continuously updating the ideal reference of the wavefront sensor (WFS) that includes the NCPA, and updating this new reference to the WFS. Doing so changes the point of convergence of the AO loop. We introduce here the upgrade concept of the algorithm. DrWHO does not rely on any model nor requires accurate wavefront sensor calibration, and is applicable to non-linear wavefront sensing situations. We present on-sky performances using a pyramid WFS sensor with the Subaru coronagraph extreme AO (SCExAO) instrument.
SPHERE+ is a proposed upgrade of the SPHERE instrument on the ESO’s Very Large Telescope which aims at improving detection and characterization capabilities of young giant planets by means of a second-stage AO system, including dedicated wavefront sensor and deformable mirror to remove the residual wavefront errors left by the primary AO loop. This paper is focused on the numerical simulations of the second stage (SAXO+) and conclude on the impact of the main AO parameters used to build the design strategy.
KEYWORDS: Optical spheres, Sensors, Planets, Spectrographs, Iterated function systems, Stars, Spectral resolution, Coronagraphy, Adaptive optics, Signal to noise ratio
MedRes is a proposed MEDium RESolution integral field spectrograph for upgrading SPHERE, the high contrast instrument for the ESO VLT telescope. MedRes is actually thought of as a potential Visitor Instrument with the scope to provide high contrast diffraction limited medium-high resolution spectra (R ≥ 1000) over a reasonably large field of view (a square with a side of at least 0.4) and across the spectral region 1.2-1.65 microns. Two main science objectives are driving the proposition for such an instrument on SPHERE. First of all, MedRes shall improve the detection of previously unknown giant planets (contrast 10−5 , goal 10−6 ), in particular accreting planets, at small separation from the star (< 0.2”, goal, 0.1”). And second, MedRes will boost the characterisation of known (faint) planets at a spectral resolution substantially higher than currently possible with SPHERE IFS (R ~ 35 − 50) and for contrasts much better than achievable with IRDIS Long Slit Spectroscopy (LSS) at small separations. The design will be optimised for SPHERE, fully exploiting the capabilities offered by a second stage Adaptive Optics (SAXO+) and complementing the niches of IRDIS, IFS and HiRise in the near IR channel. A preliminary optomechanical design and simulations of performance will be presented.
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 ~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 tradeoff that were done for SPHERE+ to reach the final selected baseline concept.
A key challenge of high contrast imaging (HCI) is to differentiate a speckle from an exoplanet signal. The sources of speckles are a combination of atmospheric residuals and aberrations in the non-common path. Those non-common path aberrations (NCPA) are particularly challenging to compensate for as they are not directly measured, and because they include static, quasi-static and dynamic components. The proposed method directly addresses the challenge of compensating the NCPA. The algorithm DrWHO - Direct Reinforcement Wavefront Heuristic Optimisation - is a quasi-real-time compensation of static and dynamic NCPA for boosting image contrast. It is an image-based lucky imaging approach, aimed at finding and continuously updating the ideal reference of the wavefront sensor (WFS) that includes the NCPA, and updating this new reference to the WFS. Doing so changes the point of convergence of the AO loop. We show here the first results of a post-coronagraphic application of DrWHO. DrWHO does not rely on any model nor requires accurate wavefront sensor calibration, and is applicable to non-linear wavefront sensing situations. We present on-sky performances using a pyramid WFS sensor with the Subaru coronagraph extreme AO (SCExAO) instrument.
Measuring the orbits of directly imaged exoplanets requires precise astrometry at the milliarcsec level over long periods of time due to their wide separation to the stars (≳10 au) and long orbital period (≳20 yr). To reach this challenging goal, a specific strategy was implemented for the instrument Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE), the first dedicated exoplanet imaging instrument at the Very Large Telescope of the European Southern Observatory (ESO). A key part of this strategy relies on the astrometric stability of the instrument over time. We monitored for five years the evolution of the optical distortion, pixel scale, and orientation to the True North of SPHERE images using the near-infrared instrument IRDIS. We show that the instrument calibration achieves a positional stability of ∼1 mas over 2″ field of views. We also discuss the SPHERE astrometric strategy, issues encountered in the course of the on-sky operations, and lessons learned for the next generation of exoplanet imaging instruments on the Extremely Large Telescope being built by ESO.
Combining adaptive optics and interferometric observations results in a considerable contrast gain compared to single-telescope, extreme AO systems. Taking advantage of this, the ExoGRAVITY project is a survey of known young giant exoplanets located in the range of 0.1” to 2” from their stars. The observations provide astrometric data of unprecedented accuracy, being crucial for refining the orbital parameters of planets and illuminating their dynamical histories. Furthermore, GRAVITY will measure non-Keplerian perturbations due to planet-planet interactions in multi-planet systems and measure dynamical masses. Over time, repetitive observations of the exoplanets at medium resolution (R = 500) will provide a catalogue of K-band spectra of unprecedented quality, for a number of exoplanets. The K-band has the unique properties that it contains many molecular signatures (CO, H2O, CH4, CO2). This allows constraining precisely surface gravity, metallicity, and temperature, if used in conjunction with self-consistent models like Exo-REM. Further, we will use the parameter-retrieval algorithm petitRADTRANS to constrain the C/O ratio of the planets. Ultimately, we plan to produce the first C/O survey of exoplanets, kick-starting the difficult process of linking planetary formation with measured atomic abundances.
The aim of the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument is to detect extremely faint astronomical sources (i.e., giant extra-solar planets, disks etc …) in the vicinity of bright stars. The detection capabilities of an exoplanet hunter are largely controlled by its adaptive optics (AO) system. Better AO correction provides improved coronagraph extinction and fewer starlight residuals. The challenging SPHERE science goals require a very high performance AO system to feed a quasi-perfect flat wave front, corrected for atmospheric turbulence and internal defects, to the scientific instruments.
In May 2014 SPHERE was installed on the third unit telescope (Melipal) of the Very Large Telescope (VLT) in Chile. The results obtained over 3 years of operations essentially nicely confirm the AO predictions made at the time of the design phase and the corresponding performance budget analysis to cover various operation conditions in terms of target brightness and turbulence conditions. This is a strong basis to propose a realistic SPHERE AO upgrade.
The SPHERE upgrade project intends to push the ultimate performance of SPHERE in terms of both final contrast and sensitivity (especially towards redder and fainter stars), thus allowing to address new science cases and to offer new detection or characterisation modes such as the coupling with high spectral resolution spectrographs, either in the infrared or in the visible.
To do so, we have to address several tasks:
• The main AO loop has to be accelerated (up to 3 kHz) and efficient predictive control laws have to be implemented in order to significantly reduce the temporal effects;
• The main wave front sensor scheme has to be revisited in order to make the system more sensitive and make possible to work on very red stars. It will be achieved by adding to the current Visible Spatially Filtered Shack-Hartman an IR-Pyramid counterpart;
• The NCPA correction and the system ability to create and stabilize dark-hole during an entire observation block has to be developed in order to get rid of the residual quasi-static speckles and residual diffraction patterns. This will be done thanks to the combination of very accurate coronagraphic wave front sensors (COFFEE and ZELDA).
This presentation will detail the various system studies and trade-off choices which have led to the new concept of the SPHERE upgrade. A preliminary design of the new AO loop and its main components (IR pyramid, RTC, post-coronographic WFS) will be presented. We will show that the proposed SPHERE upgrade development can be achieved in a timely manner without affecting the current SPHERE configuration and for a reasonable cost. Finally, an AIT concept minimizing the down-time of the instrument will be described. At each stage of the project, special attention will be paid to ensure that the initial capabilities and performance of SPHERE are not be jeopardized by the proposed SPHERE upgrade developments.
The SPHERE instrument, dedicated to high contrast imaging on VLT, has been routinely operated for more than 3 years, over a large range of conditions and producing observations from visible to NIR. A central part of the instrument is the high order adaptive optics system, named SAXO, designed to deliver high Strehl image quality with a balanced performance budget for bright stars up to magnitude R=9.
We take benefit now from the very large set of observations to revisit the assumptions and analysis made at the time of the design phase: we compare the actual AO behavior as a function of expectations. The data set consists of the science detector data, for both coronagraphic images and non-coronagraphic PSF calibrations, but also of AO internal data from the high frequency sensors and statistics computations from the real-time computer which are systematically archived, and finally of environmental data, monitored at VLT level. This work is supported and made possible by the SPHERE « Data Center » infrastructure hosted at Grenoble which provides an efficient access and the capability for the homogeneous analysis of this large and statistically-relevant data set.
We review in a statistical manner the actual AO performance as a function of external conditions for different regimes and we discuss the possible performance metrics, either derived from AO internal data or directly from the high contrast images. We quantify the dependency of the actual performance on the most relevant environmental parameters. By comparison to earlier expectations, we conclude on the reliability of the usual AO modeling. We propose some practical criteria to optimize the queue scheduling and the expression of observer requirements ; finally, we revisit what could be the most important AO specifications for future high contrast imagers as a function of the primary science goals, the targets and the turbulence properties.
MIRI, the mid-IR instrument of JWST (JamesWebb Space Telescope), will include a coronagraphic device for which the ultimate goal is the detection and caracterization of extrasolar planets around nearby stars. In this paper, we describe the optical concept of MIRI and the instrumental choices that were made in phase A and B regarding the coronagraphic system. Finally, we will present numerical simulations that we carried out to evaluate the capability for detecting extrasolar giant gazeous planets.
The VLT second generation instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanets Research) was commissioned in the Summer of 2014, and offered to the community in the Spring of 2015. SPHERE is a high contrast imager that exploits its three scientific channels in order to observe and discover young warm exoplanets in the glare of their host stars. The three scientific instrument are: ZIMPOL, a polarization analyzer and imager that works in the visible range of wavelength, IRDIS a dual band imager and spectro polarimetric Camera that works in the NIR range up to K band, and IFS, an integral field spectrograph working in the YJH band. Very important is the complementarity between IRDIS and IFS. The former has a larger Field of view (about 12 arcseconds) while the IFS push its examination very close to the central star (FoV ~ 1.7 arcsec). In one year of operational time a lot of very interesting scientific cases were investigated and very nice results were gathered. In this paper we would like to focus the attention on the high quality results and performances obtained with the IFS.
MICADO will equip the E-ELT with a first light capability for diffraction limited imaging at near-infrared wavelengths. The instrument’s observing modes focus on various flavours of imaging, including astrometric, high contrast, and time resolved. There is also a single object spectroscopic mode optimised for wavelength coverage at moderately high resolution. This contribution provides an overview of the key functionality of the instrument, outlining the scientific rationale for its observing modes. The interface between MICADO and the adaptive optics system MAORY that feeds it is summarised. The design of the instrument is discussed, focusing on the optics and mechanisms inside the cryostat, together with a brief overview of the other key sub-systems.
The major source of noise in high-contrast imaging is the presence of slowly evolving speckles that do not average with time. The temporal stability of the point-spread-function (PSF) is therefore critical to reach a high contrast with extreme adaptive optics (XAO) instruments. Understanding on which timescales the PSF evolves and what are the critical parameters driving the speckle variability allow to design an optimal observing strategy and data reduction technique to calibrate instrumental aberrations and reveal faint astrophysical sources. We have obtained a series of 52 min, AO-corrected, coronagraphically occulted, high-cadence (1.6Hz), H-band images of the star HR 3484 with the SPHERE (Spectro-Polarimeter High-contrast Exoplanet REsearch1) instrument on the VLT. This is a unique data set from an XAO instrument to study its stability on timescales as short as one second and as long as several tens of minutes. We find different temporal regimes of decorrelation. We show that residuals from the atmospheric turbulence induce a fast, partial decorrelation of the PSF over a few seconds, before a transition to a regime with a linear decorrelation with time, at a rate of several tens parts per million per second (ppm/s). We analyze the spatial dependence of this decorrelation within the well-corrected radius of the adaptive optics system and show that the linear decorrelation is faster at short separations. Last, we investigate the influence of the distance to the meridian on the decorrelation.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a second-generation instrument for the VLT,
optimized for very high-contrast imaging around bright stars. Its primary goal is the detection and characterization of
new giant planets around nearby stars, together with the observation of early planetary systems and disks. The Infrared
Dual Imager and Spectrograph (IRDIS), one of the three SPHERE subsystems, will provide dual-band imaging in the
near-infrared, among with other observing modes such as long slit spectroscopy, classical imaging and infrared
polarimetry. IRDIS is able to achieve very high contrast with the help of extreme-AO turbulence compensation,
coronography, exceptional image quality, very accurate calibration strategies and advanced data processing. IRDIS
underwent extensively laboratory testing during the integration and optimization of SPHERE at IPAG and it is now
integrated to the VLT/ESO. We will present the results of performances and operations validations performed with
SPHERE. In particular we present the achievable level of contrast and compare it with on-sky results obtained at the
VLT/ESO.
We present in this paper an overview of the high contrast imaging modes of the wide-field imager MICADO. MICADO is a near-IR camera for the European Extremely Large Telescope (E-ELT), featuring a wide field (75”), spectroscopic and coronagraphic capabilities. It has been chosen by ESO as one of the two first-light instruments. MICADO will be optimized for the multi-conjugate adaptive optics module MAORY and will also work in SCAO mode. This SCAO mode will provide MICADO with a high-level, on-axis correction, making use of the M4 adaptive mirror in the telescope.
After presenting the scientific interest for high contrast imaging modes in MICADO, we describe the technical choices we are studying. We present the hypotheses chosen for our simulation tools and contrast as well as planet detection performance derived from this tool.
We present in this paper an overview of the single-conjugate adaptive optics (SCAO) module of the wide-field imager MICADO. MICADO is a near-IR camera for the European ELT, featuring a wide field (75"), spectroscopic and coronagraphic capabilities. It has been chosen by ESO as one of the two first-light instruments. MICADO will be optimized for the multi-conjugate adaptive optics module MAORY and will also work in SCAO mode. This SCAO mode will provide MICADO with a high-level, on-axis correction, making use of the M4 adaptive mirror in the telescope. We present first the current design of the different subsystems of the SCAO module (namely the optical relay interfacing MICADO to the telescope in its SCAO mode, the wavefront sensor, the real-time computer and the high contrast imaging). We then present the adaptive optics and coronagraphic simulations. The following section is devoted to the presentation of the project organization. We end with the conclusions and perspectives of the project.
MICADO is a near-IR camera for the European ELT, featuring an extended field (75” diameter) for imaging, and also spectrographic and high contrast imaging capabilities. It has been chosen by ESO as one of the two first-light instruments. Although it is ultimately aimed at being fed by the MCAO module called MAORY, MICADO will come with an internal SCAO system that will be complementary to it and will deliver a high performance on axis correction, suitable for coronagraphic and pupil masking applications. The basis of the pupil masking approach is to ensure the stability of the optical transfer function, even in the case of residual errors after AO correction (due to non common path errors and quasi-static aberrations). Preliminary designs of pupil masks are presented. Trade-offs and technical choices, especially regarding redundancy and pupil tracking, are explained.
The instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch), recently installed on the VLT-UT3,
aims to detected and characterize giant extra-solar planets and the circumstellar environments in the very close vicinity
of bright stars. The extreme brightness contrast and small angular separation between the planets or disks and their parent
stars have so far proven very challenging. SPHERE will meet this challenge by using an extreme AO, stellar
coronagraphs, an infrared dual band and polarimetric imager called IRDIS, an integral field spectrograph, and a visible
polarimetric differential imager called ZIMPOL. Polarimetry allows a separation of the light coming from an unpolarized
source such as a star and the polarized source such as a planet or protoplanetary disks. In this paper we present the
performance of the infrared polarimetric imager based on experimental validations performed within SPHERE before the
preliminary acceptance in Europe. We report on the level of instrumental polarization in the infrared and its calibration
limit. Using differential polarimetry technique, we quantify the level of speckle suppression, and hence improved
sensitivity in the context of imaging extended stellar environments.
SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. SPHERE commissioning is foreseen in 2013 on the VLT. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light (600-900 nm) from extrasolar planets. It is located behind an extreme AO system (SAXO) and a stellar coronagraph. We present the first high contrast polarimetric results obtained for the fully integrated SPHERE-ZIMPOL system. We have measured the polarimetric high contrast performance of several coronagraphs: a Classical Lyot on substrate, a suspended Classical Lyot and two 4 Quadrant Phase Mask coronagraphs. We describe the impact of crucial system parameters – Adaptive Optics, Coronagraphy and Polarimetry - on the contrast performance.
Direct imaging of exoplanet is one of the most exciting field of planetology today. The light coming from exoplanet orbiting their host star witnesses for the chemical composition of the atmosphere, and the potential biomarkers for life. However, the faint flux to be imaged, very close to the huge flux of the parent star, makes this kind of observation extremely difficult to perform from the ground. The direct imaging instruments (SPHERE [1], GPI [2]) are nowaday reaching lab maturity. Such instrument imply the coordination of XAO for atmospherical turbulence real-time correction, coronagraphy for star light extinction, IR Dual band camera, IFS, and visible polarimetry. The imaging modes include single and double difference (spectral and angular). The SPHERE project is now at the end of AIT phase. This paper presents the very last results obtained in laboratory, with realistic working conditions. These AIT results allows one to predict on-sky performance, that should come within the next weeks after re-installation at Very Large Telescope at Paranal.
KEYWORDS: Coronagraphy, Stars, Principal component analysis, Point spread functions, L band, Adaptive optics, Exoplanets, Space telescopes, Planets, Observatories
In November 2012, we installed an L-band annular groove phase mask (AGPM) vector vortex coronagraph (VVC) inside NACO, the adaptive optics camera of ESO’s Very Large Telescope. The mask, made out of diamond subwavelength gratings has been commissioned, science qualified, and is now offered to the community. Here we report ground-breaking on-sky performance levels in terms of contrast, inner working angle, and discovery space. This new practical demonstration of the VVC, coming a few years after Palomar’s and recent record-breaking lab experiments in the visible (E. Serabyn et al. 2013, these proceedings), shows once again that this new-generation coronagraph has reached a high level of maturity.
Several small space coronagraphs have been proposed to characterize cold exoplanets in reflected light. Studies
have mainly focused on technical feasibility because of the huge star/planet
flux ratio to achieve in the close-in
stellar environment (108-1010 at 0.2"). However, the main interest of such instruments, the analysis of planet
properties, has remained highly unexplored so far. We performed numerical simulations to assess the ability
of a small space coronagraph to retrieve spectra of mature Jupiters, Neptunes and super-Earths under realistic
assumptions. We describe our assumptions: exoplanetary atmosphere models, instrument numerical simulation
and observing conditions. Then, we define a criterion and use it to determine the required exposure times to
measure several planet parameters from their spectra (separation, metallicity, cloud and surface coverages) for
particular cases. Finally, we attempt to define a parameter space of the potential targets. In the case of a
solar-type star, we show that a small coronagraph can characterize the spectral properties of a 2-AU Jupiter up
to 10 pc and the cloud and surface coverage of super-Earths in the habitable zone for a few stars within 4-5 pc.
Potentially, SPICES could perform analysis of a hypothetical Earth-size planet around α Cen A and B.
The study of the physico-chemical properties of wide-separated exoplanets (> 1 AU) is a major goal of high-contrast
imaging techniques. SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary
Systems) is a project of space coronagraph dedicated to the spectro-polarimetric analysis of gas and ice giant
planets, super-Earths and circumstellar disks in visible light at a spectral resolution of about 40. After recalling
the science cases of the mission, we describe the optical design and the critical subsystems of the instrument.
We then discuss the SPICES performance that we derived from numerical simulations.
Small-angle coronagraphy is technically and scientifically appealing because it enables the use of smaller telescopes,
allows covering wider wavelength ranges, and potentially increases the yield and completeness of circumstellar
environment – exoplanets and disks – detection and characterization campaigns. However, opening up
this new parameter space is challenging. Here we will review the four posts of high contrast imaging and their
intricate interactions at very small angles (within the first 4 resolution elements from the star). The four posts
are: choice of coronagraph, optimized wavefront control, observing strategy, and post-processing methods. After
detailing each of the four foundations, we will present the lessons learned from the 10+ years of operations of
zeroth and first-generation adaptive optics systems. We will then tentatively show how informative the current
integration of second-generation adaptive optics system is, and which lessons can already be drawn from this
fresh experience. Then, we will review the current state of the art, by presenting world record contrasts obtained
in the framework of technological demonstrations for space-based exoplanet imaging and characterization mission
concepts. Finally, we will conclude by emphasizing the importance of the cross-breeding between techniques
developed for both ground-based and space-based projects, which is relevant for future high contrast imaging
instruments and facilities in space or on the ground.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a second generation
instrument for the VLT optimized for very high-contrast imaging around bright stars. Its primary
science goal is the detection and characterization of giant planets, together with observation of
circumstellar environment. The infrared differential imager and spectrograph (IRDIS), one of the
three science instruments for SPHERE, provides simultaneous differential imaging in the near
infrared, among with long slit spectroscopy, classical imaging and infrared polarimetry. IRDIS is
designed to achieve very high contrast with the help of extreme-AO (Strehl < 90%), coronography,
exceptional image quality (including non-common-path aberrations compensation), very accurate
calibration strategies and very advanced data processing for speckle suppression. In this paper, we
report on the latest experimental characterizations of IRDIS performed with SPHERE/SAXO before
the preliminary acceptance in Europe.
The Vector Vortex Coronagraph (VVC) is one of the most attractive new-generation coronagraphs for ground- and
space-based exoplanet imaging/characterization instruments, as recently demonstrated on sky at Palomar and
in the laboratory at JPL, and Hokkaido University. Manufacturing technologies for devices covering wavelength
ranges from the optical to the mid-infrared, have been maturing quickly. We will review the current status of
technology developments supported by NASA in the USA (Jet Propulsion Laboratory-California Institute of
Technology, University of Arizona, JDSU and BEAMCo), Europe (University of Li`ege, Observatoire de Paris-
Meudon, University of Uppsala) and Japan (Hokkaido University, and Photonics Lattice Inc.), using liquid
crystal polymers, subwavelength gratings, and photonics crystals, respectively. We will then browse concrete
perspectives for the use of the VVC on upcoming ground-based facilities with or without (extreme) adaptive
optics, extremely large ground-based telescopes, and space-based internal coronagraphs.
SPHERE, the extra-solar planet imager for the Very Large Telescope is a program that has been running since 2006. The
instrument is now nearing completion and it is in the final integration stage. The 3 science instruments of SPHERE are
now complete and have passed the internal acceptance review while the complex common path with the extreme
Adaptive optics system, the coronographs and the calibration module is aggressively progressing. This paper reviews the
performance of the Common Path (CP) and three science instruments of SPHERE: IRDIS, the dual band imager; IFS, the
integral field spectrograph and ZIMPOL, the imaging polarimeter. We also present an outlook at the final system
integration.
Phase-mask coronagraphs are known to provide high contrast imaging capabilities while preserving a small inner
working angle, which allows searching for exoplanets or circumstellar disks with smaller telescopes or at longer
wavelengths. The AGPM (Annular Groove Phase Mask, Mawet et al. 20051) is an optical vectorial vortex coronagraph
(or vector vortex) induced by a rotationally symmetric subwavelength grating (i.e. with a period smaller than λ/n, λ being
the observed wavelength and n the refractive index of the grating substrate). In this paper, we present our first midinfrared
AGPM prototypes imprinted on a diamond substrate. We firstly give an extrapolation of the expected
coronagraph performances in the N-band (~10 μm), and prospects for down-scaling the technology to the most wanted L-band
(~3.5 μm). We then present the manufacturing and measurement results, using diamond-optimized microfabrication
techniques such as nano-imprint lithography (NIL) and reactive ion etching (RIE). Finally, the subwavelength grating
profile metrology combines surface metrology (scanning electron microscopy, atomic force microscopy, white light
interferometry) with diffractometry on an optical polarimetric bench and cross correlation with theoretical simulations
using rigorous coupled wave analysis (RCWA).
In the context of exoplanet detection, a large majority of the 400 detected exoplanets have been found by indirect
methods. Today, progress in the field of high contrast and angular resolution imaging has allowed direct images of
several exoplanetary systems to be taken (cf. HR 8799, Fomalhaut and β Pic).1-4 In the near future, several new
instruments are going to dramatically improve our sensitivity to exoplanet detection. Among these, SPHERE
(Spectro Polarimetric High contrast Exoplanet REsearch) at the VLT, MIRI (Mid Infra-Red Instrument) onboard
JWST and EPICS at the ELT will be equipped with coronagraphs to reveal faint objects in the vicinity of nearby
stars. We made use of the Lyon group (COND) evolutionary models of young (sub-)stellar objects and exoplanets
to compare the sensitivities of these different instruments using their estimated coronagraphic profiles. From this
comparison, we present a catalogue of targets which are particularly well suited for the different instruments.
To characterize orbits and atmospheres of exoplanets with large orbits (≥ a few AU), direct imaging is nowadays
the sole way. From space, this involves high contrast imaging techniques as coronagraphy, differential imaging or
wavefront control. Several methods exist or are under development and several small (~1.5m) space telescope
missions are proposed. One of them is See-coast (super-Earth explorer coronagraphic off-axis space telescope)
which will be proposed to the next ESA Cosmic Vision call. It will provide polarimetric and spectral characterization
of giant gazeous planets and possibly Super-Earths in visible light. In this paper, we first detail science
cases of this mission. We then describe the foreseen telescope design and its instrumentation. We finally derive
performance for a particular instrumental configuration from numerical simulation and we show how See-coast
can retrieve planet spectra.
We present recent developments of the CAOS problem-solving environment (PSE), an IDL-based software tool
whose original aim was to define and simulate as realistically as possible the behavior of a generic adaptive
optics (AO) system -from the atmospheric propagation of light, to the sensing of the wave-front aberrations
and the correction through a deformable mirror- but which results in a widely more general tool now. In
fact, the different developments made through the last years result in a very versatile numerical tool complete
of a global graphical interface (the CAOS Application Builder), a general utilities library (the CAOS
Library), and different packages dedicated to a wide range of astronomical-optics-related scientific topics: the
original package designed for end-to-end AO system simulations (the Software Package CAOS), an image simulation/
reconstruction package with interferometric capabilities (the Software Package AIRY), an extension of
the latter specialized for the LBT instrument LINC-NIRVANA (the Software Package AIRY-LN), an ad hoc
package dedicated to the VLT instrument SPHERE (the Software Package SPHERE), and an embedment of the
analytical AO simulation code PAOLA (the Software Package PAOLAC).We present the status of the whole CAOS
PSE, together with the most recent developments, and plans for the future of the overall tool.
In the context of the SPHERE planet finder project, we further develop and characterize a recently proposed
method for the efficient direct detection of exoplanets from the ground using spectral and angular differential
imaging. The method, called ANDROMEDA, combines images appropriately into "pseudo-data", then uses all
of them in a Maximum-Likelihood framework to estimate the position and flux of potential planets orbiting
the observed star. The method's performance is assessed on realistic simulations of images performed by the
SPHERE consortium, and it is applied to experimental data taken by the VLT/NAOS-CONICA instrument.
ESO and a large European consortium completed the phase-A study of EPICS, an instrument dedicated to exoplanets
direct imaging for the EELT. The very ambitious science goals of EPICS, the imaging of reflected light of mature gas
giant exoplanets around bright stars, sets extremely strong requirements in terms of instrumental contrast achievable. The
segmented nature of an ELT appears as a very large source of quasi-static high order speckles that can impair the
detection of faint sources with small brightness contrast with respect to their parent star. The paper shows how the
overall system has been designed in order to maximize the efficiency of quasi-static speckles rejection by calibration and
post-processing using the spectral and polarization dependency of light waves. The trade-offs that led to the choice of the
concepts for common path and diffraction suppression system is presented. The performance of the instrument is
predicted using simulations of the extreme Adaptive Optics system and polychromatic wave-front propagation through
the various optical elements.
The ESO planet-finder VLT instrument SPHERE (Spectro-Polarimetric High-contrast Exoplanet
REsearch), scheduled for first light in 2011, aims to detected and characterize giant extra-solar
planet and the circumstellar environments in the very close vicinity of bright stars. The extreme
brightness contrast and small angular separation between the planets or disks and their parent stars
have so far proven very challenging. SPHERE will meet this challenge by using an extreme AO
system, stellar coronagraphs, an infrared dual band and polarimetric imager called IRDIS, an integral
field spectrograph, and a visible polarimetric differential imager called ZIMPOL. Additional smart
imaging techniques such has differential imaging and differential polarimetry will be also included
to cancel out the light from the parent star and reach typical contrasts of 10-5. We describe here the
performances and the detection limit of IRDIS polarimetric mode for imaging extended stellar
environments.
In the framework of exoplanet direct imaging, a few coronagraphs have been proposed to overcome the large flux ratio
that exists between the star and its planet. However, there are very few solutions that gather in the same time broad band
achromaticity, a small inner working angle (shortest angular distance for planet detection), a good throughput for the
planet light, and a mature technical feasibility. Here, we propose to use a combination of chromatic Four Quadrant Phase
Mask coronagraphs to achromatize the dephasing of this well-studied monochromatic coronagraph. After describing the
principle of the technique, we present preliminary results for a compact prototype. Contrast larger than 10000 are
reached with more than 250 nm of spectral bandwidth in the visible. Stability over time and effect of the filtering is also
discussed.
ZIMPOL is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to
detect the very faint reflected and hence polarized visible light from extrasolar planets. ZIMPOL is located behind an
extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of
2011. ZIMPOL is currently in the manufacturing, integration and testing phase. We describe the optical, polarimetric,
mechanical, thermal and electronic design as well as the design trade offs. Specifically emphasized is the optical quality
of the key performance component: the Ferro-electric Liquid Crystal polarization modulator (FLC). Furthermore, we
describe the ZIMPOL test setup and the first test results on the achieved polarimetric sensitivity and accuracy. These
results will give first indications for the expected overall high contrast system performance. SPHERE is an instrument
designed and built by a consortium consisting of LAOG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève,
ETH, NOVA, ONERA and ASTRON in collaboration with ESO.
The detection and characterization of extrasolar planets by direct imaging is becoming more and
more promising with the preparation of dedicated high-contrast instruments and the help of new data
analysis techniques. SPHERE (Spectro-Polarimetric High-contrast imager for Exoplanets REsearch)
is currently being developed as part of the second generation instruments of the ESO-VLT. IRDIS,
one of the SPHERE subsystems, will provide dual-band imaging with several filter pairs covering
the near-infrared from 0.95 to 2.3 microns, among with other observing modes such as long slit
spectroscopy and infrared polarimetry. This paper describes the instrument performances and the
impact of instrumental calibrations on finding and characterizing extrasolar planets, and on
observing strategies. It discusses constraints to achieve the required contrast of ~106 within few
hours of exposure time.
Controlling the amplitude of light is crucial for many scientific applications, such as imaging systems, astronomical
instruments, optical testing, or laser physics. We provide an overview of the halftoning technique - the process of
displaying a continuous image with binary dots - for application to coronagraphy. Customized filters with spatially
varying transmission are produced using a binary array of metal pixels (namely microdot masks) that offers excellent
control of the local transmission, with intrinsic achromaticity. Applications, design guidelines, and tests of near-IR
prototypes for both pupil and focal plane coronagraphic devices are presented in the context of the VLT-SPHERE and EELT
EPICS instruments.
SPHERE is a second generation instrument for the Very Large Telescope (VLT) which will aim at directly
detecting the intrinsic flux of young giant exoplanets thanks to a dedicated extreme adaptive optics system
and coronagraphs. Exoplanet detection in the near-infrared will be performed in parallel with an integral
field spectrograph and a differential imager, IRDIS. IRDIS main mode for exoplanet detection will be Dual-
Band Imaging (DBI) where two images are acquired simultaneously at close wavelengths around expected sharp
features in cold planetary objects spectra. We present here the end-to-end simulations performed to obtain
realistic data for IRDIS in DBI mode with temporal evolution of the quasi-static speckle pattern. Data cubes
have been generated to represent 4 hour observations in IRDIS filter pairs for various star magnitudes and planets
at angular separations from 0."2 to 2".0. Using this unique set of data, we present a comparison of various data
analysis methods for high-contrast imaging with IRDIS in DBI mode both in terms of detection limits and of
estimation of the exoplanet flux after speckle noise attenuation.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is VLT instrument for the discovery and
study of new extra-solar giant planets orbiting nearby stars by direct imaging of their circumstellar environment.
SPHERE is a complex instrument containing more than 50 optical surfaces. The optical imperfections of each of
these surfaces might influence the final contrast. SPHERE has several observing modes in Visible and Infrared,
and therefore several optical paths.
FOROS is an end-to-end optical propagation code for SPHERE, which includes almost all surfaces of the
instrument. It models the instrument by the sequential blocks: VLT, Foreoptics, Corrective Optics, Coronagraph
and so on, such that the beam quality can be studied at several selected locations. The Vis and IR paths are
separated in the model. It incorporates the real data of surface measurement, according to the availability of this
data. Each surface error can be switched on and off; therefore the influence of each surface on the contrast can be
studied independently.
FOROS is an IDL-PROPER-based code, the main power of which is Fresnel propagation. Therefore it represents
a numerical tool to study the Fresnel diffraction effects in SPHERE. In the paper we describe the structure and
philosophy of the code. The phase screens are not yet implemented.
Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and
explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based
telescopes, the Extremely Large Telescopes (ELTs), have the potential to dramatically enlarge the discovery space
towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. EPICS is a
proposed instrument for the European ELT, dedicated to the detection and characterization of Exoplanets by direct
imaging, spectroscopy and polarimetry. ESO completed a phase-A study for EPICS with a large European consortium
which - by simulations and demonstration experiments - investigated state-of-the-art diffraction and speckle suppression
techniques to deliver highest contrasts. The paper presents the instrument concept and analysis as well as its main
innovations and science capabilities. EPICS is capable of discovering hundreds of giant planets, and dozens of lower
mass planets down to the rocky planets domain.
SPHERE, the ESO extra-solar planet imager for the VLT is aimed at the direct detection and spectral characterization of
extra-solar planets. Its whole design is optimized towards reaching the highest contrast in a limited field of view and at
short distances from the central star. SPHERE has passed its Final Design Review (FDR) in December 2008 and it is in
the manufacturing and integration phase. We review the most challenging specifications and expected performance of
this instrument; then we present the latest stage of the design chosen to meet the specifications, the progress in the
manufacturing as well as the integration and test strategy to insure gradual verification of performances at all levels.
Integral field spectroscopy (IFS) is extremely useful for high-contrast imaging purposes and integral field units (IFU)
based on a matrix of lenses are suitable to guarantee low level of differential aberrations among the array of light
footprints reaching the detector. To this purpose a new optical concept (BIGRE) for the lenses array adopted in integral
field spectroscopy is here fully described, and characterized in the working case of two IFS instruments devoted to high-contrast
imaging of extrasolar planets: SPHERE and EPICS, respectively for a 10 meter class telescope (VLT) and a 40
meter class (E-ELT) telescope. The aim of this work is the explanation of the BIGRE optical concept and its
implementation on two IFS optical designs, optimized respectively for SPHERE and EPICS.
The ESO planet finder instrument SPHERE will search for the polarimetric signature of the reflected light from
extrasolar planets, using a VLT telescope, an extreme AO system (SAXO), a stellar coronagraph, and an imaging
polarimeter (ZIMPOL). We present the design concept of the ZIMPOL instrument, a single-beam polarimeter
that achieves very high polarimetric accuracy using fast polarization modulation and demodulating CCD detectors.
Furthermore, we describe comprehensive performance simulations made with the CAOS problem-solving
environment. We conclude that direct detection of Jupiter-sized planets in close orbit around the brightest nearby
stars is achievable with imaging polarimetry, signal-switching calibration, and angular differential imaging.
Direct detection and spectral characterization of extra-solar planets is one of the most exciting but also one of the most
challenging areas in modern astronomy. The challenge consists in the very large contrast between the host star and the
planet, larger than 12.5 magnitudes at very small angular separations, typically inside the seeing halo. The whole design
of a "Planet Finder" instrument is therefore optimized towards reaching the highest contrast in a limited field of view and
at short distances from the central star. Both evolved and young planetary systems can be detected, respectively through
their reflected light and through the intrinsic planet emission. We present the science objectives, conceptual design and
expected performance of the SPHERE instrument.
A large number of coronagraphs have been proposed to overcome the ratio that exists between the star and its planet.
The planet finder of the Extremely Large Telescope, which is called EPICS, will certainly need a more efficient
coronagraph than the ones that have been developed so far. We propose to use a combination of chromatic Four
Quadrant Phase Mask coronagraph to achromatize the dephasing of the device while maintaining a high rejection
performance. After describing this multi-stage FQPM coronagraph, we show preliminary results of a study on its
capabilities in the framework of the EPICS instrument, the planet finder of the European Extremely Large Telescope.
Eventually, we present laboratory tests of a rough prototype of a multi-stage four-quadrant phase mask. On one hand, we
deduce from our laboratory data that a detection at the 10-10 level is feasible in monochromatic light. On the other hand,
we show the detection of a laboratory companion fainter than 10-8 with a spectral bandwidth larger than 20%.
Exoplanet direct imaging involves very low signal-to-noise ratio data that need to be carefully acquired and
processed. This paper deals with data processing for the VLT planet finder SPHERE, that will include extreme
adaptive optics and high-contrast coronagraphy, and where field rotation will occur. First, we propose estimators
of the intensity, the intensity estimate uncertainty, and the initial position of a potential exoplanet. Because of
the very large amount of data to process, they are derived from a simple gaussian data model relying on the
time-stationarity of the background, where the so-called background is everything but the exoplanet. Analytical
properties of the estimators are given, under the gaussian data model and under a more sophisticated data model.
Then, in order to relate the detection procedure to a probabillity of false alarm, the detection consists simply
in thresholding the intensity estimate at a given initial position. Finally, this detection-estimation algorithm is
applied on a dataset simulated using the CAOS-based Software Package SPHERE, including time evolution of
the atmospheric, pre-, and post-coronagraphic quasi-static aberrations. As a preliminary result, the detectionestimation
algorithm proves to be totally satisfactory for a 8 × 10-5 intensity ratio for exoplanets located from
0".2 to 2". The stationarity assumption is discussed.
SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) is the second-generation VLT instrument
devoted primarily to direct imaging and characterization of exoplanets, and allowing a large number of promising
observation modes. In this framework, an IDL-based end-to-end numerical tool has been developed within the
problem-solving environment CAOS (or CAOS "system"): the Software Package SPHERE, dedicated to the complete and detailed simulation of the whole instrument. It hence includes detailed instrumental modeling of the extreme adaptive optics system SAXO, the dual-band imaging camera IRDIS, the Integral Field Spectrograph (IFS), and the Zürich IMaging POLarimeter (ZIMPOL). The status of the whole package (which has now reached version 3.0) is exposed. An example of application is also detailed: a sub-system study aspect concerning the near-infrared apodized Lyot coronagraph.
SPHERE (Spectro Polarimetric High contrast Exoplanet REsearch), the planet finder instrument for the VLT is designed
to study relatively bright extrasolar giant planets around young or nearby stars. SPHERE is a set of three instruments fed
by the same AO-system, two of them share the same coronagraph. This complex system has been modeled with Fourier
Optics to investigate the performance of the whole instrument. In turns, this end-to-end model was useful to analyze the
sensitivity to various parameters (WFE, alignment of the coronagraph, differential aberrations) and to put some
specifications on the sub-systems. This paper presents some example of sensitivity analysis and some contrast
performance of the instruments as a function of the flux for the main observing mode of SPHERE: the Dual Band
Imaging (DBI), equivalent to the Spectral Differential Imaging technique.
We report laboratory development of coronagraphic devices to be implemented on the High Order Testbench (HOT) to
assess intensity reduction between them at a high Strehl ratio regime. The high order test bench implements extreme
adaptive optics with realistic telescope conditions reproduced by star and turbulence generators. A 32×32 actuator micro
deformable mirror, one pyramid wave front sensor, one Shack-Hartmann wave front sensor and the ESO SPARTA real-time
computer. This will enable characterization and comparative study of different types of coronagraphs in realistic
conditions. We have developed several prototypes of promising coronagraphs concepts: Four Quadrants Phase Mask1
(FQPM), Lyot2 coronagraphs and Apodized Pupil Lyot Coronagraph3 (APLC). We will describe the design of the IR
coronagraphic path on HOT, prototyping processes used for each coronagraph and discuss quality control and first
results obtained on a IR coronagraphic testbench (Strehl ratio ~ 94%). Finally, we will present our experiment plan and
future coronagraph developments.
KEYWORDS: Coronagraphy, Point spread functions, Device simulation, Signal attenuation, Mid-IR, Telescopes, Signal to noise ratio, James Webb Space Telescope, Space telescopes, Imaging systems
One of the main objectives of the instrument MIRI, the Mid-InfraRed Instrument, of the JWST is the direct
detection and characterization of extrasolar giant planets. For that purpose, a coronagraphic device including
three Four-Quadrant Phase Masks and a Lyot coronagraph working in mid-infrared, has been developed. We
present here the results of the first test campaign of the coronagraphic system in the mid-infrared in the facility
developed at the CEA. The performances are compared to the expected ones from the coronagraphic simulations.
The accuracy of the centering procedures is also evaluated to validate the choice of the on-board centering
algorithm.
Presently, dedicated instrument developments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to
discover and explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m
ground-based telescopes, the Extremely Large Telescopes (ELTs), have the potential to dramatically enlarge the
discovery space towards older giant planets seen in reflected light and ultimately even a small number of rocky planets.
EPICS is a proposed instrument for the European ELT, dedicated to the detection and characterization of expolanets by
direct imaging and spectroscopy. ESO recently launched a phase-A study for EPICS with a large European consortium
which - by simulations and demonstration experiments - will investigate state-of-the-art diffraction and speckle
suppression techniques to deliver highest contrasts. The final result of the study in 2010 will be a conceptual design and
a development plan for the instrument. Here we present first results from the phase-A study and discuss the main
challenges and science capabilities of EPICS.
The SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) planet finder instrument for ESO's VLT
telescope, scheduled for first light in 2011, aims to detect giant extra-solar planets in the vicinity of bright stars by the aid
of an extreme-AO turbulence compensation system and to characterize the objects found through spectroscopic and
polarimetric observations. Dual imaging observations within the Y, J, H and Ks atmospheric windows (~0.95 - 2.32μm)
will be done by the aid of the IRDIS cryogenic camera. We describe briefly the science goals of IRDIS and present its
system architecture. Current status of the instrument design is presented, and expected performance is described in terms
of end-to-end simulations.
One of the main science objectives of the European ELT is the direct imaging of extrasolar planets. The large aperture of
the telescope has the potential to significantly enlarge the discovery space towards older gas giant exo-planets seen in
reflected light. In this paper, we give an overview of the EPICS system design strategy during the phase A study. In
order to tackle the critical limitations to high contrast, extensive end-to-end simulations will be developed since the start
to test different scenarios and guide the overall design.
The detection and characterization of extrasolar planets with SPHERE (Spectro Polarimetric High contrast Exoplanet
REsearch) is challenging and in particular relies on the ability of a coronagraph to attenuate the diffracted starlight.
SPHERE includes 3 instruments, 2 of which can be operated simultaneously in the near IR from 0.95 to 1.8 microns.
This requirements is extremely critical for coronagraphy. This paper briefly introduces the concepts of 2 coronagraphs,
the Half-Wave Plate Four Quadrant Phase Masks and the Apodized Pupil Lyot Coronagraph, prototyped within the
SPHERE consortium by LESIA (Observatory of Paris) and FIZEAU (University of Nice) respectively. Then, we present
the measurements of contrast and sensitivity analysis. The comparison with technical specifications allows to validate
the technology for manufacturing these coronagraphs.
The SPHERE is an exo-solar planet imager, which goal is to detect giant exo-solar planets in the vicinity of bright stars
and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made
of an extreme-Adaptive Optics (AO) turbulence correction, pupil tracker and interferential coronagraphs. At its back
end, an Infra-Red Dual-beam Imaging and Spectroscopy science module and an integral field spectrograph work in
the Near Infrared (NIR) Y, J, H and Ks bands (0.95 - 2.32μm) and a high resolution polarization camera covers the
visible (0.6 - 0.9 μm) region. We describe briefly the science goals of the instrument and deduce the top-level
requirements. This paper presents the system architecture, and reviews each of the main sub-systems. The results of the
latest end-to-end simulations are shown and an update of the expected performance is given. The project has been
officially kicked-off in March 2006, it is presently undergoing Preliminary Design Review and is scheduled for 1st
light in early 2011. This paper reviews the present design of SPHERE but focuses on the changes implemented since
this project was presented the last time to this audience.
The Planet Finder instrument for ESO's VLT telescope, scheduled for first light in 2010, aims to detect giant extra-solar planets in the vicinity of bright stars and to characterise the objects found through spectroscopic and polarimetric observations. The observations will be done both within the Y, J, H and Ks atmospheric windows (~0.95 - 2.32μm) by the aid of a dual imaging camera (IRDIS) and an integral field spectrograph (IFS), and in the visible using a fast-modulation polarization camera (ZIMPOL). The instrument employs an extreme-AO turbulence compensation system, focal plane tip-tilt correction, and interferential coronagraphs. We describe briefly the science goals of the instrument and deduce the top-level requirements. The system architecture is presented, including brief descriptions of each of the main sub-systems. Expected performance is described in terms of end-to-end simulations, and a semi-analytic performance-estimation tool for system-level sensitivity analysis is presented.
The Exo-Planets Imaging Camera and Spectrograph (EPICS), is the Planet Finder Instrument concept for the European
Extremely Large Telescope (ELT). The study made in the frame of the OWL 100-m telescope concept is being up-dated
in direct relation with the re-baselining activities of the European Extremely Large Telescope.
Extremely Large Telescopes are very promising to detect and characterize Earth-like planets because of their high angular resolution and the increased number of collected photons. We study the impact of aberrations on this detection and the limitations they impose. We consider an extreme adaptive optic device upstream of a perfect coronagraph. Even with the high Strehl ratio provided, the coronagraphic image is not sufficient to detect Earth-like planet. Indeed the contrast between this kind of planet and its star is about 10-10 in the near infra-red. As a consequence, a calibration device downstream of the coronagraph must be used to reach this contrast. We modelize a realistic system taking into account dynamic aberrations left uncorrected by the adaptive optics, static aberrations of optical system and differential static aberrations due to the calibration channel. Numerical simulations compare the respective assets of a 30 meter telescope in a median site to these of a 15 meter telescope in the dome C. In both cases, we must control common static aberrations at 8 nm and differential aberrations at 0.1 nm. Beyond this limitation due to the speckle noise and despite the great collecting area, another limitation is set by the photon noise. We also compare these results to simulations made with real coronagraphs and with an obstructed pupil.
Amplitude apodization of a telescope's pupil can be used to reduce the diffraction rings (Airy rings) in the PSF to allow high contrast imaging. Rather than achieving this apodization by selectively removing light at the edges of the pupil, we propose to produce the desired apodized pupil by redistributing the pupil's light. This lossless apodization concept can yield a high contrast PSF which allows the efficient detection of Earth-sized planets around stars at ~10pc with a 2m visible telescope in space. We review the current status of a JPL-funded study of this concept for the Terrestrial Planet Finder (TPF) mission, including a lab experiment and extensive computer simulations.
The Four Quadrant Phase Mask is a key component for the design of advanced coronagraphs that may be used to search exo-planets. The validity of this concept has been demonstrated in the visible and need now to be demonstrated in the mid infrared. For this purpose, two components are manufactured for wavelengths 4.75 and 16.25 μm. This manufacturing requires the deposition of ZnSe layers using Ion Assisted Deposition, followed by a lift off process.
Numerical simulations have been carried out to assess the opportunity to detect extrasolar planets with MIRI: the mid-IR instrument of NGST. Several coronagraphs and telescope designs have been investigated. As a result, we found that very young planets (50Myr) as well as old planets (5Gyr) can be imaged in the thermal-IR (5μm to 20μm) down to a few Jupiter masses if an appropriate high-contrast coronagraph is in used. Promising results of numerical simulations are presented.
The concept we recently introduced of a coronagraph using a four-quadrant phase mask has been the subject of detailed model calculations and of laboratory validation proving its great potential in planet finding. A nulling factor of 12500 is already demonstrated in the laboratory (Riaud et al., this conference). We first remind the principle of the 4QC: a destructive interference between the two equal fractions of the amplitude with opposite signs produces a very efficient nulling of the_star light. We propose to install such a device on several ground-based and space instruments, including present (NAOS/CONICA) or future (Planet Finder) VLT instruments and MIRI, the mid-IR camera of the NGST. The present paper focus on the question of direct imaging of exoplanets using this type of device. Indeed, one advantage of the four-quadrant coronagraph is to permit probing the vicinity of a star down to smaller angular distances than a classical Lyot mask. We examine the sources of uncertainties in different cases of optimized ground-based and space experiments and different situations of planet/star couples, using as far as possible realistic models of planetary evolution. On the VLT, even with an extremely powerful adaptive optics system, the speckle noise will be the main limitation: contrast in magnitude as large as Dm = 15 are however possible in the K band. The combination of a 4QC and differential imaging at two wavelength is likely the most promising concept for direct planet Detection from the ground. On the other hand, we show that with a 4QC on MIRI, a classical Jupiter is indeed detectable from space and at 20 μm for a star closer than 10 pc, while the more favorable cases of a young (hot) giant planet allows detection at 6 μm for a star belonging to the closest star forming region at 50 pc.
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