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Vortex phase masks have been shown to be an efficient means to reduce the blinding stellar light in high-contrast imaging instruments. Once placed at the focal plane of the telescope, the helical phase ramp of a vortex phase mask diffracts the light of a bright on-axis source outside the re-imaged telescope pupil, while transmitting the light of a faint off-axis companion nearly unaffected. The Annular Groove Phase Mask (AGPM) is a broadband metasurface implementation of a vector vortex phase mask using the artificial birefringence of a circular subwavelength grating etched onto a diamond substrate. To date, the AGPM design has been optimized using rigorous coupled-wave analysis (RCWA), which is a valid tool to simulate periodic straight gratings. However, we have now reached a performance level where the curvature of the grating lines at the center becomes a limiting factor. Here, we use a finite-difference time-domain (FDTD) method to correctly describe the AGPM performance, including the effect of the curved grating close to its center. We confirm the validity of this simulation framework by comparing its predictions with experimental results obtained on our infrared coronagraphic test bench, and we show that RCWA fails at reproducing correctly the central AGPM performance, confirming the need for a full 3d simulation tool such as FDTD. Finally, we use FDTD to optimize the grating parameters at the AGPM center, and conclude with a new optimal design.

Correction to: Nature Communications https://doi.org/10.1038/s41467-021-21176-6, published online 10 February 2021.The original version of this Article contained an error in Fig. 1b, in which the units incorrectly read ‘AU,’ instead of the correct ‘au’. This has been corrected in both the PDF and HTML versions of the Article.

Direct imaging is a powerful exoplanet discovery technique that is complimentary to other techniques with great promise in the era of 30-meter class telescopes. Space-based transit surveys have revolutionized our understanding of the frequency of planets at small orbital radii around sun-like stars. The next generation of extremely large ground-based telescopes will have the angular resolution and sensitivity to directly image planets with R < 4 Earth radii around the very nearest stars. Here we predict yields from a direct imaging survey of a volume-limited sample of sun-like stars with the Mid-Infrared ELT Imager and Spectrograph (METIS) instrument, planned for the 39-m European Southern Observatory (ESO) Extremely Large Telescope (ELT) that is expected to be operational towards the end of the decade. Using Kepler occurrence rates, a sample of stars with spectral types A-K within 6.5 pc, and simulated contrast curves based on an advanced model of what is achievable from coronagraphic imaging with adaptive optics, we estimate the expected yield from METIS using Monte Carlo simulations. We find the METIS expected yield of small planets in the N2 band (10.10 - 12.40 μm) is 1.15 planets which is greater than similar observations in the L (3.70 - 3.95 μm) and M (4.70 - 4.90 μm) bands. We also determine a 42% chance of detecting at least one Jovian planet in the background limited regime assuming a 1-hour integration. We calculate the yield per star and estimate optimal observing revisit times to increase the yield. We also analyze this survey if performed in the northern hemisphere and find there are additional targets worth considering. Finally, we present an observing strategy in order to maximize the possible yield for limited telescope time, resulting in 1.52 expected planets in the N2 band.

Direct imaging is a powerful exoplanet discovery technique that is complementary to other techniques and offers great promise in the era of 30 m class telescopes. Space-based transit surveys have revolutionized our understanding of the frequency of planets at small orbital radii around Sun-like stars. The next generation of extremely large ground-based telescopes will have the angular resolution and sensitivity to directly image planets with R, Astronomy & Astrophysics, 653, ISSN:0004-6361, ISSN:1432-0746

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., Comment: 29 pages, 11 figures, published in Nature Communications

METIS is one of the first three instruments for the ELT, Europe’s next-generation ground-based telescope. It will offer imaging, coronagraphy and spectroscopy in the L, M and N bands for general-purpose science in astrophysics. Among its main science drivers are circumstellar disks and extrasolar planets observations, which requires demanding high contrast imaging techniques. In that framework, METIS will be equipped with state-of-the-art phase mask coronagraphs: Apodizing Phase Plate (APP) and Annular Grooves Phase Mask (AGPM). Manufacturing the AGPM coronagraphs is a complex process that requires performance assessment with specific testing before implementation into the instrument. At Department of Astrophysics (CEA Saclay, France), responsible for the testing of the N-band AGPMs, a previously available test bench with a telescope simulator and cryogenic facility has been upgraded to comply with the AGPM tests requirements. This paper presents these requirements and describes the test bench design adopted. Then, based on preliminary results, we discuss the original solutions that permitted to reach our goals.

The planet detection thresholds of space-based coronagraphs are predicted to lie within an order of magnitude from their theoretical (shot-noise) limits. Ground-based telescopes, on the other hand, are limited by larger systematic uncertainties in the point spread function (PSF) of the residual light which rapidly fluctuates due to atmospheric turbulence. The PSF is affected by Adaptive Optics (AO) which reduce the intensity of the speckles but also make them less predictable. Although not a common practice, it is possible to take millisecond exposures of the so-called “frozen” speckles and record the history of AO controls, in which case the collected data resembles that of simulated space coronagraphs. In this work we use the HEEPS simulation of the EELT/METIS to assess the applicability of this newly-developed space-oriented approach to ground-based postprocessing. Unlike intensity-based algorithms, this method formulates the estimation problem in terms of the electric field of the speckles and therefore can incorporate controls history and various temporal models of the electric field variations. In our simulations, we artificially introduced small deformable mirror (DM) probes on top of AO controls, and achieved a post-processing error lower by a factor of 2 than that of Angular Differential Imaging (ADI). However, our attempt at incorporating the AO history without DM probes, has so far resulted in higher errors than ADI.

Vortex coronagraphs have been shown to be a promising avenue for high-contrast imaging in the close-in environment of stars at thermal infrared (IR) wavelengths. They are included in the baseline design of METIS. To ensure good performance of these coronagraphs, a precise control of the centering of the star image in real time is needed. We previously developed and validated the quadrant analysis of coronagraphic images for tip-tilt sensing estimator (QACITS) pointing estimator to address this issue. While this approach is not wavelength-dependent in theory, it was never implemented for mid-IR observations, which leads to specific challenges and limitations. Here, we present the design of the mid-IR vortex coronagraph for the new Earths in the $\alpha$ Cen Region (NEAR) experiment with the VLT/VISIR instrument and assess the performance of the QACITS estimator for the centering control of the star image onto the vortex coronagraph. We use simulated data and on-sky data obtained with VLT/VISIR, which was recently upgraded for observations assisted by adaptive optics in the context of the NEAR experiment. We demonstrate that the QACITS-based correction loop is able to control the centering of the star image onto the NEAR vortex coronagraph with a stability down to $0.015 \lambda/D$ rms over 4h in good conditions. These results show that QACITS is a robust approach for precisely controlling in real time the centering of vortex coronagraphs for mid-IR observations., Comment: Published in JATIS. This version is the manuscript resubmitted before acceptance, 30 pages, 14 figures

The article offers a historiographical look at the “global history phe-nomenon” in France. The aim is to analyse the rise of world-wide/global approaches as a “historiographical event” that reconfig-ures the contemporary “making of history”. Does the examination of the specificities of this historiographical galaxy of world history make it possible to go beyond the heterogeneity of its different compo-nents? The questions of the object (the world, globalization), the method, the choice of scale, the “global turn”, and European cen-trism are thus addressed., Critical Hermeneutics, V. 3, N. 1 (2019): Crisis of Historicity: A Challenge for Historians

We successfully rapid-prototyped a mostly off-the-shelf, partially 3D-printed pathfinder version of an integral field spectrograph (IFS) in order to compress the design/build/test schedule of a final, mostly-custom IFS, by accelerating the start date of data pipeline development, thus allowing this development to progress in parallel with the design, procurement, fabrication, and alignment of the final IFS version. This parallel-path development schedule enabled us to successfully design, build, align, test, and extract a data cube from the new IFS within only 1 year, even in the face of several design setbacks. We have begun using the now-functional IFS for development of IFS sensing and control algorithms, and have also begun implementing motorized alignment upgrades that enable the systematic characterization of the tolerance (or required compensation) of its data cube extraction to misaligned images, in support of NASA’s WFIRST and PISCES IFS.

We present an algorithm, effective over a broad range of planet populations and instruments, for optimizing integration times of an exoplanet direct imaging observation schedule, to maximize the number of unique exoplanet detections under realistic mission constraints. Our planning process uses “completeness” as a reward metric and the nonlinear combination of optimal integration time per target and constant overhead time per target as a cost metric constrained by a total mission time. We validate our planned target list and integration times for a specific telescope by running a Monte Carlo of full mission simulations using EXOSIMS, a code base for simulating telescope survey missions. These simulations encapsulate dynamic details such as time-varying local zodiacal light for each star, planet keep-out regions, exoplanet positions, and strict enforcement of observatory use over time. We test our methods on the Wide-Field Infrared Survey Telescope (WFIRST) coronagraphic instrument (CGI). We find that planet, Sun, and solar panel keep-out regions limit some target per-annum visibility to

Future space-based observatories such as WFIRST will be equipped with high contrast imaging instruments designed to study extrasolar planets and disks in the absence of atmospheric perturbations. One of the most efficient techniques to achieve this goal is the combination of wavefront control and broadband coronagraphy. Being able to achieve a high contrast over a wide spectral bandwidth allows us to characterize the chemical composition of exoplanet atmospheres using an integral field spectrograph (IFS). In this paper, we report on the development of such an IFS for the High Contrast Imaging Lab (HCIL) at Princeton University, downstream of a Shaped Pupil coronagraph. Our final lensletbased design calls for the light in an 18% band around 660 nm to be dispersed with a spectral resolution of 50. We also present our new laboratory control software written in Python, allowing the import of open-source packages such as CRISPY to ultimately reconstruct 3D datacubes from IFS spatio-spectral science images. Finally, we show and discuss our preliminary first light results, reaching a contrast of ~10-5 using in-house focal-plane wavefront control and estimation algorithms with two deformable mirrors.

Since its first light at the VLT in 2012, the Annular Groove Phase Mask (AGPM) has been used to implement vortex coronagraphy into AO-assisted infrared cameras at two additional world-leading observatories: the Keck Observatory and the LBT. In this paper, we review the status of these endeavors, and briefly highlight the main scientific results obtained so far. We explore the performance of the AGPM vortex coronagraph as a function of instrumental constraints, and identify the main limitations to the sensitivity to faint, off-axis companions in high-contrast imaging. These limitations include the AGPM itself, non-common path aberrations, as well as the data processing pipeline; we briefly describe our on-going efforts to further improve these various aspects. Based on the lessons learned from the first five years of on-sky exploitation of the AGPM, we are now preparing its implementation in a new generation of high-contrast imaging instruments. We detail the specificities of these instruments, and how they will enable the full potential of vortex coronagraphy to be unleashed in the future. In particular, we explain how the AGPM will be used to hunt for planets in the habitable zone of alpha Centauri A and B with a refurbished, AO-assisted version of the VISIR mid-infrared camera at the VLT (aka the NEAR project), and how this project paves the way towards mid-infrared coronagraphy on the ELT with the METIS instrument. We also discuss future LM-band applications of the AGPM with VLT/ERIS, ELT/METIS, and with a proposed upgrade of Keck/NIRC2, as well as future applications at shorter wavelengths, such as a possible upgrade of VLT/SPHERE with a K-band AGPM.

An exoplanet direct imaging mission using an external occulter for starlight suppression could potentially achieve higher contrasts and throughputs than an equivalently sized telescope with an internal coronagraph. We consider a formation flying mission where the starshade must station-keep with a telescope, assumed to be on a halo orbit about the Sun-Earth L2 point, during observations and slew between observations as the telescope re-orients to target the next star. We use a parameterization of the slew fuel cost calculation based on interpolation of exact solutions of boundary value problem in the circular restricted three body formalism. Time constraints are imposed based on when stars are observable due to the motion of bright sources in the solar system, integration times, and mission lifetime constraints. Finally, we present a comprehensive cost function incorporating star completeness values as a reward heuristic and retargeting fuel costs to sequentially select the next best star to observe. Ensembles of simulations are conducted for different selection schemes; for a 3 year mission, taking two steps of the linear cost function produces the most unique detections with an average of 7.08± 2.55.

Transition disks offer the extraordinary opportunity to look for newly born planets and investigate the early stages of planet formation. In this context we observed the Herbig A5 star MWC 758 with the L band vector vortex coronagraph installed in the near-infrared camera and spectrograph NIRC2 at the Keck II telescope, with the aim of unveiling the nature of the spiral structure by constraining the presence of planetary companions in the system. Our high-contrast imaging observations show a bright (delta L=7.0+/-0.3 mag) point-like emission, south of MWC 758 at a deprojected separation of about 20 au (r=0.111+/- 0. 004 arcsec) from the central star. We also recover the two spiral arms (south-east and north-west), already imaged by previous studies in polarized light, and discover a third one to the south-west of the star. No additional companions were detected in the system down to 5 Jupiter masses beyond 0.6 arcsec from the star. We propose that the bright L band emission could be caused by the presence of an embedded and accreting protoplanet, although the possibility of it being an asymmetric disk feature cannot be excluded. The spiral structure is probably not related to the protoplanet candidate, unless on an inclined and eccentric orbit, and it could be due to one (or more) yet undetected planetary companions at the edge of or outside the spiral pattern. Future observations and additional simulations will be needed to shed light on the true nature of the point-like source and its link with the spiral arms., Comment: 10 pages, 9 figures, Accepted for publication in Astronomy & Astrophysics

The “scientific” and “educational” questions raised by the relationship between research and the teaching of history have returned to the spotlight with the current reform of teacher training in France. Undertaken as part of the “Refounding the School System” project initiated in 2012 by minister of education Vincent Peillon, this reform accords a central place to pedagogical approaches and “professionalization.” This article analyzes some of the issues at stake in this “pedagogical turn” for the training of history and geography teachers, particularly with regard to renewed questions about the social function of history and the recurrent challenges and reservations on the part of academic historians about binding the notions of “scientific” and “educational” together.

Les questions soulevees par les rapports entre recherche et enseignement de l’histoire, entre le «scientifique» et le «pedagogique», sont de nouveau d’actualite avec la reforme en cours de la formation des enseignants. Menee dans le cadre du projet de «Refondation de l’ecole» lance par Vincent Peillon en 2012, elle entend mettre la demarche pedagogique et la professionnalisation au cœur de la reforme. L’article se propose d’analyser quelquesuns des enjeux de ce «tournant pedagogique» de la formation des enseignants d’histoiregeographie en France au regard notamment des interrogations renouvelees sur la fonction sociale de l’histoire ainsi que des difficultes recurrentes et des reticences, dans la discipline, a articuler «scientifique» et «pedagogique». Abstract: The “scientific” and “educational” questions raised by the relationship between research and the teaching of history have been put back on the agenda with the current reform of teacher training in France. Undertaken as part of the “Refounding Schools” project initiated in 2012 by Vincent Peillon, then minister of Education, this reform accords a central place to pedagogical approaches and “professionalization.” This article analyzes some of the issues at stake in this “pedagogical turning-point” for the training of history and geography teachers, particularly with regard to renewed questions about the social function of history, as well as the recurrent challenges and reservations on the part of academic historians about binding the notions of “scientific” and “pedagogical” together.

We present yield modeling results for the HabEx concept study using EXOSIMS. EXOSIMS (Exoplanet Open-Source Imaging Mission Simulator) provides a parametric estimate of science yield of mission concepts using contrast curves from physics-based diffraction model codes and Monte Carlo simulations of design reference missions using realistic observing constraints. Two baseline architecture configurations and two extended configurations are compared. We compare a configuration with a coronagraph to a configuration with a starshade for both detection and spectral characterization. The input parameters, including astrophysical assumptions, are detailed. We show sensitivity to key design parameters around design space local to the point designs. The yield results provide an analysis of the relative performance of telescope and instrument design that enable system engineering decisions.

EXOSIMS is an open-source simulation tool for parametric modeling of the detection yield and characterization of exoplanets. EXOSIMS has been adopted by the Exoplanet Exploration Programs Standards Definition and Evaluation Team (ExSDET) as a common mechanism for comparison of exoplanet mission concept studies. To ensure trustworthiness of the tool, we developed a validation test plan that leverages the Python-language unit-test framework, utilizes integration tests for selected module interactions, and performs end-to-end crossvalidation with other yield tools. This paper presents the test methods and results, with the physics-based tests such as photometry and integration time calculation treated in detail and the functional tests treated summarily. The test case utilized a 4m unobscured telescope with an idealized coronagraph and an exoplanet population from the IPAC radial velocity (RV) exoplanet catalog. The known RV planets were set at quadrature to allow deterministic validation of the calculation of physical parameters, such as working angle, photon counts and integration time. The observing keepout region was tested by generating plots and movies of the targets and the keepout zone over a year. Although the keepout integration test required the interpretation of a user, the test revealed problems in the L2 halo orbit and the parameterization of keepout applied to some solar system bodies, which the development team was able to address. The validation testing of EXOSIMS was performed iteratively with the developers of EXOSIMS and resulted in a more robust, stable, and trustworthy tool that the exoplanet community can use to simulate exoplanet direct-detection missions from probe class, to WFIRST, up to large mission concepts such as HabEx and LUVOIR.

The Wide Field Infrared Survey Telescope (WFIRST) mission, scheduled for launch in the mid-2020s will perform exoplanet science via both direct imaging and a microlensing survey. An internal coronagraph is planned to perform starlight suppression for exoplanet imaging, but an external starshade could be used to achieve the required high contrasts with potentially higher throughput. This approach would require a separately-launched occulter spacecraft to be positioned at exact distances from the telescope along the line of sight to a target star system. We present a detailed study to quantify the Δv requirements and feasibility of deploying this additional spacecraft as a means of exoplanet imaging. The primary focus of this study is the fuel use of the occulter while repositioning between targets. Based on its design, the occulter is given an offset distance from the nominal WFIRST halo orbit. Target star systems and look vectors are generated using Exoplanet Open-Source Imaging Simulator (EXOSIMS); a boundary value problem is then solved between successive targets. On average, 50 observations are achievable with randomly selected targets given a 30-day transfer time. Individual trajectories can be optimized for transfer time as well as fuel usage to be used in mission scheduling. Minimizing transfer time reduces the total mission time by up to 4.5 times in some simulations before expending the entire fuel budget. Minimizing Δv can generate starshade missions that achieve over 100 unique observations within the designated mission lifetime of WFIRST.

In addition to the Wide-Field Infrared Survey Telescope Coronagraphic Imager (WFIRST CGI), which is currently scheduled for launch in the mid 2020s, there is an extensive, ongoing design effort for next-generation, space-based, exoplanet imaging instrumentation. This work involves mission concepts such as the Large UV/ Optical/Infrared Surveyor (LUVOIR), the Habitable Exoplanet Imaging Misson (HabEx), and a starshade rendezvous mission for WFIRST, among others. While each of these efforts includes detailed mission analysis targeted at the specifics of each design, there is also interest in being able to analyze all such concepts in a unified way (to the extent that this is possible) and to draw specific comparisons between projected concept capabilities. Here, we discuss and compare two fundamental approaches to mission analysis, full mission simulation and depth of search analysis, in the specific context of simulating and comparing multiple different mission concepts. We present strategies for mission analysis at varying stages of concept definition, using WFIRST as a motivating example, and discuss useful metrics for cross-mission comparison, as well as strategies for evaluating these metrics.

Uncovering the ingredients and the architecture of planetary systems is a very active field of research that has fuelled many new theories on giant planet formation, migration, composition, and interaction with the circumstellar environment. We aim at discovering and studying new such systems, to further expand our knowledge of how low-mass companions form and evolve. We obtained high-contrast H-band images of the circumstellar environment of the F5V star HD206893, known to host a debris disc never detected in scattered light. These observations are part of the SPHERE High Angular Resolution Debris Disc Survey (SHARDDS) using the InfraRed Dual-band Imager and Spectrograph (IRDIS) installed on VLT/SPHERE. We report the detection of a source with a contrast of 3.6x10^{-5} in the H-band, orbiting at a projected separation of 270 milliarcsecond or 10 au, corresponding to a mass in the range 24 to 73 Mjup for an age of the system in the range 0.2 to 2 Gyr. The detection was confirmed ten months later with VLT/NaCo, ruling out a background object with no proper motion. A faint extended emission compatible with the disc scattered light signal is also observed. The detection of a low-mass companion inside a massive debris disc makes this system an analog of other young planetary systems such as beta Pictoris, HR8799 or HD95086 and requires now further characterisation of both components to understand their interactions., 7 pages, 6 figures

HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and complex circumstellar disk, likely still in a transition stage from protoplanetary to debris disk phase. Here, we present a new image of the third inner disk component of HD 141569 A made in the L' band (3.8 micron) during the commissioning of the vector vortex coronagraph recently installed in the near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory Keck II adaptive optics system. We used reference point spread function subtraction, which reveals the innermost disk component from the inner working distance of $\simeq 23$ AU and up to $\simeq 70$ AU. The spatial scale of our detection roughly corresponds to the optical and near-infrared scattered light, thermal Q, N and 8.6 micron PAH emission reported earlier. We also see an outward progression in dust location from the L'-band to the H-band (VLT/SPHERE image) to the visible (HST/STIS image), likely indicative of dust blowout. The warm disk component is nested deep inside the two outer belts imaged by HST NICMOS in 1999 (respectively at 406 and 245 AU). We fit our new L'-band image and spectral energy distribution of HD 141569 A with the radiative transfer code MCFOST. Our best-fit models favor pure olivine grains, and are consistent with the composition of the outer belts. While our image shows a putative very-faint point-like clump or source embedded in the inner disk, we did not detect any true companion within the gap between the inner disk and the first outer ring, at a sensitivity of a few Jupiter masses., 12 pages, 6 figures

Context. The Annular Groove Phase Mask (AGPM) is one possible implementation of the vector vortex coronagraph, where the helical phase ramp is produced by a concentric subwavelength grating. For several years, we have been manufacturing AGPMs by etching gratings into synthetic diamond substrates using inductively coupled plasma etching. Aims. We aim to design, fabricate, optimize, and evaluate new L-band AGPMs that reach the highest possible coronagraphic performance, for applications in current and forthcoming infrared high-contrast imagers. Methods. Rigorous coupled wave analysis (RCWA) is used for designing the subwavelength grating of the phase mask. Coronagraphic performance evaluation is performed on a dedicated optical test bench. The experimental results of the performance evaluation are then used to accurately determine the actual profile of the fabricated gratings, based on RCWA modeling. Results. The AGPM coronagraphic performance is very sensitive to small errors in etch depth and grating profile. Most of the fabricated components therefore show moderate performance in terms of starlight rejection (a few 100:1 in the best cases). Here we present new processes for re-etching the fabricated components in order to optimize the parameters of the grating and hence significantly increase their coronagraphic performance. Starlight rejection up to 1000:1 is demonstrated in a broadband L filter on the coronagraphic test bench, which corresponds to a raw contrast of about 1e-5 at two resolution elements from the star for a perfect input wave front on a circular, unobstructed aperture. Conclusions. Thanks to their exquisite performance, our latest L-band AGPMs are good candidates for installation in state-of-the-art and future high-contrast thermal infrared imagers, such as METIS for the E-ELT., Comment: Accepted for publication in A&A

We report on our ongoing development of EXOSIMS and mission simulation results for WFIRST. We present the interface control and the modular structure of the software, along with corresponding prototypes and class definitions for some of the software modules. More specifically, we focus on describing the main steps of our high-fidelity mission simulator EXOSIMS, i.e., the completeness, optical system and zodiacal light modules definition, the target list module filtering, and the creation of a planet population within our simulated universe module. For the latter, we introduce the integration of a recent mass-radius model from the FORECASTER software. We also provide custom modules dedicated to WFIRST using both the Hybrid Lyot Coronagraph (HLC) and the Shaped Pupil Coronagraph (SPC) for detection and characterization, respectively. In that context, we show and discuss the results of some preliminary WFIRST simulations, focusing on comparing different methods of integration time calculation, through ensembles (large numbers) of survey simulations.

On March 2015 an L'-band vortex coronagraph based on an Annular Groove Phase Mask made up of a diamond sub-wavelength grating was installed on NIRC2 as a demonstration project. This vortex coronagraph operates in the L' band not only in order to take advantage from the favorable star/planet contrast ratio when observing beyond the K band, but also to exploit the fact that the Keck II Adaptive Optics (AO) system delivers nearly extreme adaptive optics image quality (Strehl ratios values near 90%) at 3.7μm. We describe the hardware installation of the vortex phase mask during a routine NIRC2 service mission. The success of the project depends on extensive software development which has allowed the achievement of exquisite real-time pointing control as well as further contrast improvements by using speckle nulling to mitigate the effect of static speckles. First light of the new coronagraphic mode was on June 2015 with already very good initial results. Subsequent commissioning nights were interlaced with science nights by members of the VORTEX team with their respective scientific programs. The new capability and excellent results so far have motivated the VORTEX team and the Keck Science Steering Committee (KSSC) to offer the new mode in shared risk mode for 2016B.

For several years, we have been developing vortex phase masks based on sub-wavelength gratings, known as Annular Groove Phase Masks. Etched onto diamond substrates, these AGPMs are currently designed to be used in the thermal infrared (ranging from 3 to 13 {\mu}m). Our AGPMs were first installed on VLT/NACO and VLT/VISIR in 2012, followed by LBT/LMIRCam in 2013 and Keck/NIRC2 in 2015. In this paper, we review the development, commissioning, on-sky performance, and early scientific results of these new coronagraphic modes and report on the lessons learned. We conclude with perspectives for future developments and applications., Comment: To appear in SPIE proceedings vol. 9908

The Annular Groove Phase Mask (AGPM) is a vectorial vortex phase mask. It acts as a half-wave plate with a radial fast axis orientation operating in the mid infrared domain. When placed at the focus of a telescope element provides a continuous helical phase ramp for an on axis sources, which creates the orbital angular momentum. Thanks to that phase, the intensity of the central source is canceled by a down-stream pupil stop, while the off axis sources are not affected. However due to experimental conditions the nulling is hardly perfect. To improve the null, a Mach-Zehnder interferometer containing Dove prisms differently oriented can be proposed to sort out light based on its orbital angular momentum (OAM). Thanks to the differential rotation of the beam, a {\pi} phase shift is achieved for the on axis light affected by a non zero OAM. Therefore the contrast between the star and its faint companion is enhanced. Nevertheless, due the Dove prisms birefringence, the performance of the interferometer is relatively poor. To solve this problem, we propose to add a birefringent wave-plate in each arm to compensate this birefringence. In this paper, we will develop the mathematical model of the wave front using the Jones formalism. The performance of the interferometer is at first computed for the simple version without the birefringent plate. Then the effect of the birefringent plate is be mathematically described and the performance is re-computed.

An optical vortex coronagraph has been implemented within the NIRC2 camera on the Keck II telescope and used to carry out on-sky tests and observations. The development of this new L'-band observational mode is described, and an initial demonstration of the new capability is presented: a resolved image of the low-mass companion to HIP79124, which had previously been detected by means of interferometry. With HIP79124 B at a projected separation of 186.5 mas, both the small inner working angle of the vortex coronagraph and the related imaging improvements were crucial in imaging this close companion directly. Due to higher Strehl ratios and more relaxed contrasts in L' band versus H band, this new coronagraphic capability will enable high-contrast small-angle observations of nearby young exoplanets and disks on a par with those of shorter-wavelength extreme adaptive optics coronagraphs., Comment: 21 pages, 5 figures

The mid-infrared region is well suited for exoplanet detection thanks to the reduced contrast between the planet and its host star with respect to the visible and near-infrared wavelength regimes. This contrast may be further improved with Vector Vortex Coronagraphs (VVCs), which allow us to cancel the starlight. One flavour of the VVC is the AGPM (Annular Groove Phase Mask), which adds the interesting properties of subwavelength gratings (achromaticity, robustness) to the already known properties of the VVC. In this paper, we present the optimized designs, as well as the expected performances of mid-IR AGPMs etched onto synthetic diamond substrates, which are considered for the E-ELT/METIS instrument., Comment: 8 pages, 5 figures, Proc. of SPIE Vol. 9147 (2014)