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The vector Apodizing Phase Plate (vAPP) is a pupil plane coronagraph that suppresses starlight by forming a dark hole in its point spread function (PSF). The unconventional and non-axisymmetrical PSF arising from the phase modification applied by this coronagraph presents a special challenge to post-processing techniques. We aim to implement a recently developed post-processing algorithm, temporal reference analysis of planets (TRAP) on vAPP coronagraphic data. The property of TRAP that uses non-local training pixels, combined with the unconventional PSF of vAPP, allows for more flexibility than previous spatial algorithms in selecting reference pixels to model systematic noise. Datasets from two types of vAPPs are analysed: a double grating-vAPP (dgvAPP360) that produces a single symmetric PSF and a grating-vAPP (gvAPP180) that produces two D-shaped PSFs. We explore how to choose reference pixels to build temporal systematic noise models in TRAP for them. We then compare the performance of TRAP with previously implemented algorithms that produced the best signal-to-noise ratio (S/N) in companion detections in these datasets. We find that the systematic noise between the two D-shaped PSFs is not as temporally associated as expected. Conversely, there is still a significant number of systematic noise sources that are shared by the dark hole and the bright side in the same PSF. We should choose reference pixels from the same PSF when reducing the dgvAPP360 dataset or the gvAPP180 dataset with TRAP. In these datasets, TRAP achieves results consistent with previous best detections, with an improved S/N for the gvAPP180 dataset., 15 pages, 10 figures, accepted to A&A

Accreting protoplanets represent a window into planet formation processes. We report H{\alpha} differential imaging results from the deepest and most comprehensive accreting protoplanet survey to date, acquired with the Magellan Adaptive Optics (MagAO) system's VisAO camera. The fourteen transitional disks targeted are ideal candidates for protoplanet discovery due to their wide, heavily depleted central cavities, wealth of non-axisymmetric circumstellar disk features evocative of ongoing planet formation, and ongoing stellar accretion. To address the twin challenges of morphological complexity in the target systems and PSF instability, we develop novel approaches for frame selection and optimization of the Karhounen-Loeve Image Processing algorithm pyKLIP. We detect one new candidate protoplanet, CS Cha "c", at a separation of 75mas and a Delta mag of 5.1 and robustly recover the HD142527 B and HD100453 B low mass stellar companions across multiple epochs. Though we cannot rule out a substantial scattered light contribution to its emission, we also recover LkCa 15 b. Its presence inside of the cleared disk cavity and consistency with a forward-modeled point source suggest that it remains a viable protoplanet candidate. The protoplanet PDS 70 c was marginally recovered under our conservative general methodology. However, through targeted optimization in H-alpha} imagery, we tentatively recover PDS 70 c in three epochs and PDS 70 b in one epoch. Of the many other previously-reported companions and companion candidates around objects in the sample, we do not recover any additional robust candidates. However, lack of recovery at moderate H-alpha contrast does not rule out the presence of protoplanets at these locations, and we report limiting H-alpha contrasts in such cases., Comment: Final version, in press at AJ

International audience; The next generation of giant ground and space telescopes will have the light-collect-ing power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of the Giant Segment Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are opti-mized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance and, as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the innovative comprehensive adaptive optics and coronagraph test instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We describe the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. We detail the error budget of the CACTI system, review its operation and calibration procedures, and discuss its current status. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the raw intensity and slopes map signal processing methods. This experiment was repeated for a modulation radius of 1.6 and 3.25 λ∕D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.; La prochaine génération de télescopes terrestres et spatiaux géants aura la capacité de collecter la lumière pour détecter et caractériser des exoplanètes terrestres potentiellement habitables en utilisant pour la première fois une imagerie à contraste élevée. Cela ne sera réalisable que si les performances des systèmes d'optique adaptative extrême (ExAO) des télescopes à miroir à segmentés géants (GSMT) sont optimisées à leur plein potentiel. Un composant clé d'un système ExAO est le senseur de front d'onde (WFS), qui mesure les aberrations de la turbulence atmosphérique. Un choix courant dans les instruments actuels et de prochaine génération est le senseur de front d'onde pyramidal (PWFS). Les systèmes ExAO nécessitent un échantillonnage spatial et temporel élevé des fronts d'onde pour optimiser les performances et en conséquence nécessitent des détecteurs de grande taille pour le WFS. Nous présentons une démonstration de banc d'essai en boucle fermée d'un capteur de front d'onde pyramidal à trois côtés (3PWFS) comme alternative au capteur conventionnel de front d'onde pyramidal à quatre côtés (4PWFS) pour les applications GSMT-ExAO sur l'optique adaptative complète innovante et l'instrument de test coronographe ( CACTUS). Le 3PWFS est moins sensible au bruit de lecture que le 4PWFS car il utilise moins de pixels détecteurs. Le 3PWFS a un avantages supplémentaire : une optique pyramidale à trois côtés de haute qualité est plus facile à fabriquer qu'une pyramide à quatre côtés. Nous décrivons la conception des deux composants du système CACTI, le simulateur d'optique adaptative et le banc d'essai PWFS qui comprend à la fois un 3PWFS et un 4PWFS. Nous détaillons le budget d'erreur du système CACTI, passons en revue ses procédures de fonctionnement et d'étalonnage, et discutons de son état actuel. Une expérience préliminaire a été réalisée sur CACTI pour étudier les performances de la 3PWFS à la 4PWFS dans différentes forces de turbulence en utilisant à la fois l'intensité brute et les méthodes de traitement du signal de la carte des pentes. Cette expérience a été répétée pour un rayon de modulation de 1,6 et 3,25 λ∕D. Nous avons constaté que les performances des deux capteurs de front d'onde sont comparables si les gains de boucle modale sont réglés.

The next generation of giant ground and space telescopes will have the light-collecting power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of Giant Segmented Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are optimized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance, and as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the new Comprehensive Adaptive Optics and Coronagraph Test Instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We detail the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the Raw Intensity and Slopes Map signal processing methods. This experiment was repeated for a modulation radius of 1.6 lambda/D and 3.25 lambda/D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned., 28 Pages, 15 Figures, and 4 Tables

The next generation of Giant Segmented Mirror Telescopes (GSMT) will have large gaps between the segments either caused by the shadow of the mechanical structure of the secondary mirror (E-ELT and TMT) or intrinsically by design (GMT). These gaps are large enough to fragment the aperture into independent segments that are separated by more than the typical Fried parameter. This creates piston and petals modes that are not well sensed by conventional wavefront sensors such as the Shack-Hartmann wavefront sensor or the pyramid wavefront sensor. We propose to use a new optical device, the Holographic Dispersed Fringe Sensor (HDFS), to sense and control these petal/piston modes. The HDFS uses a single pupil-plane hologram to interfere the segments onto different spatial locations in the focal plane. Numerical simulations show that the HDFS is very efficient and that it reaches a differential piston rms smaller than 10 nm for GMT/E-ELT/TMT for guide stars up to 13th J+H band magnitude. The HDFS has also been validated in the lab with MagAO-X and HCAT, the GMT phasing testbed. The lab experiments reached 5 nm rms piston error on the Magellan telescope aperture. The HDFS also reached 50 nm rms of piston error on a segmented GMT-like aperture while the pyramid wavefront sensor was compensating simulated atmosphere under median seeing conditions. The simulations and lab results demonstrate the HDFS as an excellent piston sensor for the GMT. We find that the combination of a pyramid slope sensor with a HDFS piston sensor is a powerful architecture for the GMT., Accepted by JATIS for the special on ELTs

The Giant Magellan Telescope (GMT) design consists of seven circular 8.4-m diameter mirror segments that are separated by large > 30 cm gaps, creating the possibility of fluctuations in optical path differences due to flexure, segment vibrations, wind buffeting, temperature effects, and atmospheric seeing. In order to utilize the full diffraction-limited aperture of the GMT for natural guide star adaptive optics (NGSAO) science, the seven mirror segments must be co-phased to well within a fraction of a wavelength. The current design of the GMT involves seven adaptive secondary mirrors, an off-axis dispersed fringe sensor (part of the AGWS), and a pyramid wavefront sensor (PyWFS; part of the NGWS) to measure and correct the total path length between segment pairs, but these methods have yet to be tested "end-to-end" in a lab environment. We present the design and working prototype of a "GMT High-Contrast Adaptive Optics phasing Testbed" (p-HCAT) which leverages the existing MagAO-X AO instrument to demonstrate segment phase sensing and simultaneous AO-control for GMT NGSAO science. We present the first test results of closed-loop piston control with one GMT segment using MagAO-X's PyWFS and a novel Holographic Dispersed Fringe Sensor (HDFS) with and without simulated atmospheric turbulence. We show that the PyWFS alone was unsuccessful at controlling segment piston with generated ~ 0.6 arcsec and ~ 1.2 arcsec seeing turbulence due to non-linear modal cross-talk and poor pixel sampling of the segment gaps on the PyWFS detector. We report the success of an alternate solution to control piston using the novel HDFS while controlling all other modes with the PyWFS purely as a slope sensor (piston mode removed). This "second channel" WFS method worked well to control piston to within 50 nm RMS and $\pm$ 10 $μ$m dynamic range under simulated 0.6 arcsec atmospheric seeing conditions., 54 pages, 25 figures

Accreting protoplanets enable the direct characterization of planet formation. As part of a high-contrast imaging search for accreting planets with the Hubble Space Telescope (HST) Wide Field Camera 3, we present H$α$ images of AB Aurigae (AB Aur), a Herbig Ae/Be star harboring a transition disk. The data were collected in two epochs of direct-imaging observations using the F656N narrow-band filter. After subtracting the point spread function of the primary star, we identify a point-like source located at a P.A. of $182.5^{\circ}\pm1.4^{\circ}$ and a separation of $600\pm22$~mas relative to the host star. The position is consistent with the recently identified protoplanet candidate AB Aur b. The source is visible in two individual epochs separated by ${\sim}50$ days and the H$α$ intensities in the two epochs agree. The H$α$ flux density is $F_ν=1.5\pm0.4$~mJy, $3.2\pm0.9$ times of the optical continuum determined by published HST/STIS photometry. In comparison to PDS 70 b and c, the H$α$ excess emission is weak. The central star is accreting and the stellar H$α$ emission has a similar line-to-continuum ratio as seen in AB Aur b. We conclude that both planetary accretion and scattered stellar light are possible sources of the H$α$ emission, and the H$α$ detection alone does not validate AB Aur b as an accreting protoplanet. Disentangling the origin of the emission will be crucial for probing planet formation in the AB Aur disk., Accepted for publication in ApJL

Giant exoplanets on 10-100 au orbits have been directly imaged around young stars. The peak of the thermal emission from these warm young planets is in the near-infrared (~1-5 microns), whereas mature, temperate exoplanets (i.e., those within their stars' habitable zones) radiate primarily in the mid-infrared (mid-IR: ~10 microns). If the background noise in the mid-IR can be mitigated, then exoplanets with low masses--including rocky exoplanets--can potentially be imaged in very deep exposures. Here, we review the recent results of the Breakthrough Watch/New Earths in the Alpha Centauri Region (NEAR) program on the Very Large Telescope (VLT) in Chile. NEAR pioneered a ground-based mid-IR observing approach designed to push the capabilities for exoplanet imaging with a specific focus on the closest stellar system, Alpha Centauri. NEAR combined several new optical technologies--including a mid-IR optimized coronagraph, adaptive optics system, and rapid chopping strategy to mitigate noise from the central star and thermal background within the habitable zone. We focus on the lessons of the VLT/NEAR campaign to improve future instrumentation--specifically on strategies to improve noise mitigation through chopping. We also present the design and commissioning of the Large Binocular Telescope's Exploratory Survey for Super-Earths Orbiting Nearby Stars (LESSONS), an experiment in the Northern hemisphere that is building on what was learned from NEAR to further push the sensitivity of mid-IR imaging. Finally, we briefly discuss some of the possibilities that mid-IR imaging will enable for exoplanet science., Submitted proceedings to SPIE Optical Engineering + Applications 2021, Techniques and Instrumentation for Detection of Exoplanets X

The MagAO-X instrument is a new extreme adaptive optics system for high-contrast imaging at visible and near-infrared wavelengths on the Magellan Clay Telescope. A central component of this system is a 2040-actuator microelectromechanical deformable mirror (DM) from Boston Micromachines Corp. that operates at 3.63 kHz for high-order wavefront control (the tweeter). Two additional DMs from ALPAO perform the low-order (the woofer) and non-common-path science-arm wavefront correction (the NCPC DM). Prior to integration with the instrument, we characterized these devices using a Zygo Verifire Interferometer to measure each DM surface. We present the results of the characterization effort here, demonstrating the ability to drive tweeter to a flat of 6.9 nm root mean square (RMS) surface (and 0.56 nm RMS surface within its control bandwidth), the woofer to 2.2 nm RMS surface, and the NCPC DM to 2.1 nm RMS surface over the MagAO-X beam footprint on each device. Using focus-diversity phase retrieval on the MagAO-X science cameras to estimate the internal instrument wavefront error (WFE), we further show that the integrated DMs correct the instrument WFE to 18.7 nm RMS, which, combined with a 11.7% pupil amplitude RMS, produces a Strehl ratio of 0.94 at H$\alpha$., Comment: Accepted for publication in JATIS

We present limits on the lens flux of OGLE-2007-BLG-224 based on MagAO imaging taken seven years after the microlensing event. At the time of the observations, the lens should have been separated from the microlensing source by 292 mas. However, no new sources are detected with MagAO. We place an upper limit on the lens flux of $H>20.57$. This measurement supports the conclusion of Gould et al. (2009) that the lens in this event should be a brown dwarf. This is the first test of a prediction based on the terrestrial microlens parallax effect and the first AO confirmation of a sub-stellar/dark microlens., Submitted to AAS Journals

NaCo was switched off on 2 October 2019, almost 18 years after its first light. The last exposure was of the standard star HD590 as part of the close-out calibrations. To date, 699 papers have been published using NaCo data, including observations of the Galactic centre, direct images of exoplanets orbiting their stars, young stellar objects, brown dwarfs, massive stars, stellar clusters, Solar System objects, SN 1987A and several extragalactic sources. We present a short history of the life and achievements of NaCo from the viewpoint of the Instrument Operation Team, Instrument Scientists, and Instrument Engineers., Published in The Messenger vol. 179, pp. 7-11, March 2020.

Here we review the current conceptual optical mechanical design of GMagAO-X --the extreme AO (ExAO) system for the Giant Magellan Telescope (GMT). The GMagAO-X tweeter deformable mirror (DM) design is novel in that it uses an optically distributed set of pupils that allows seven commercially available 3000 actuator BMC DMs to work "in parallel" to effectively create an ELT-scale ExAO tweeter DM --with all parts commercially available today. The GMagAO-X "parallel DM" tweeter will have 21,000 actuators to be used at ~2kHz update speeds enabling high-contrast science at ~5 mas separations in the visible and NIR of the spectrum (0.6-1.7 microns). To prove our concept for GMagAO-X several items must be lab tested: the optical/mechanical concept for the parallel DM; phasing of the GMT pupil; and solving the GMT's "isolated island effect" will all be demonstrated on an optical testbed at the University of Arizona. Here we outline the current design for this "GMT High-Contrast Testbed" that has been proposed jointly by GMTO and the University of Arizona which leverages the existing, operational, MagAO-X ExAO instrument to verify our approach to phase sensing and AO control for high-contrast GMT NGS science. We will also highlight how GMagAO-X can be mounted on the auxiliary port of the GMT and so remain gravity invariant. Since it is gravity invariant GMagAO-X can utilize a floating optical table to minimize flexure and NCP vibrations., Comment: Proc. Adaptive Optics For Extremely Large Telescopes: AO4ELT6, Quebec City, Canada, June 2019. 12 pages 10 figures. arXiv admin note: substantial text overlap with arXiv:1807.04311, arXiv:1807.05070

Surveys reveal that terrestrial- to Neptune-sized planets (1 $< R, Comment: Astro2020 Science White Paper

The transfer of circumstellar disk mass and momentum onto the protostar and out into the environment occurs via a variety of mechanisms including magnetospheric accretion, jets, outflows, and disk winds. The interplay of these processes determine both the conditions under which planet formation occurs and the lifetime of the disk. Metallic emission lines, along with the Balmer series of hydrogen, probe the kinematics of gas within the planet-forming and central regions of circumstellar disks. High-spectral resolution study of these emission lines provides critical information on mass and momentum loss, turbulence, and disk wind origins., Astro2020 Science White Paper

Gas giants are the most readily detectable exoplanets but fundamental questions about their system architectures, formation, migration, and atmospheres have been unanswerable with the current generation of ground- and space-based facilities. The dominant techniques to detect and characterize giant planets $-$ radial velocities, transits, direct imaging, microlensing, and astrometry $-$ are each isolated to a limited range of planet masses, separations, ages, and temperatures. These windows into the arrangement and physical properties of giant planets have spawned new questions about the timescale and location of their assembly; the distributions of planet mass and orbital separation at young and old ages; the composition and structure of their atmospheres; and their orbital and rotational angular momentum architectures. The ELTs will address these questions by building bridges between these islands of mass, orbital distance, and age. The angular resolution, collecting area, all-sky coverage, and novel instrumentation suite of these facilities are needed to provide a complete map of the orbits and atmospheric evolution of gas giant planets (0.3$-$10 $M_\mathrm{Jup}$) across space (0.1$-$100 AU) and time (1 Myr to 10 Gyr). This white paper highlights the scientific potential of the GMT and TMT to address these outstanding questions, with a particular focus on the role of direct imaging and spectroscopy of large samples of giant planets that will soon be made available with $Gaia$., White paper for the Astro2020 decadal survey

The processes that transform gas and dust in circumstellar disks into diverse exoplanets remain poorly understood. One key pathway is to study exoplanets as they form in their young ($\sim$few~Myr) natal disks. Extremely Large Telescopes (ELTs) such as GMT, TMT, or ELT, can be used to establish the initial chemical conditions, locations, and timescales of planet formation, via (1)~measuring the physical and chemical conditions in protoplanetary disks using infrared spectroscopy and (2)~studying planet-disk interactions using imaging and spectro-astrometry. Our current knowledge is based on a limited sample of targets, representing the brightest, most extreme cases, and thus almost certainly represents an incomplete understanding. ELTs will play a transformational role in this arena, thanks to the high spatial and spectral resolution data they will deliver. We recommend a key science program to conduct a volume-limited survey of high-resolution spectroscopy and high-contrast imaging of the nearest protoplanetary disks that would result in an unbiased, holistic picture of planet formation as it occurs., Comment: Science white paper submitted to the Astro2020 Decadal Survey

As we begin to discover rocky planets in the habitable zone of nearby stars with missions like TESS and CHEOPS, we will need quick advancements on instrumentation and observational techniques that will enable us to answer key science questions, such as What are the atmospheric characteristics of habitable zone rocky planets? How common are Earth-like biosignatures in rocky planets?} How similar or dissimilar are those planets to Earth? Over the next decade we expect to have discovered several Earth-analog candidates, but we will not have the tools to study the atmospheres of all of them in detail. Ground-based ELTs can identify biosignatures in the spectra of these candidate exo-Earths and understand how the planets' atmospheres compare to the Earth at different epochs. Transit spectroscopy, high-resolution spectroscopy, and reflected-light direct imaging on ELTs can identify multiple biosignatures for habitable zone, rocky planets around M stars at optical to near-infrared wavelengths. Thermal infrared direct imaging can detect habitable zone, rocky planets around AFGK stars, identifying ozone and motivating reflected-light follow-up observations with NASA missions like HabEx/LUVOIR. Therefore, we recommend that the Astro2020 Decadal Survey Committee support: (1) the search for Earth-like biosignatures on rocky planets around nearby stars as a key science case; (2) the construction over the next decade of ground-based Extremely Large Telecopes (ELTs), which will provide the large aperture and spatial resolution necessary to start revealing the atmospheres of Earth-analogues around nearby stars; (3) the development of instrumentation that optimizes the detection of biosignatures; and (4) the generation of accurate line lists for potential biosignature gases, which are needed as model templates to detect those molecules., Comment: 9 pages, 3 figures. Science White Paper submitted to the Astro2020 Decadal Survey

We are now on a clear trajectory for improvements in exoplanet observations that will revolutionize our ability to characterize their atmospheric structure, composition, and circulation, from gas giants to rocky planets. However, exoplanet atmospheric models capable of interpreting the upcoming observations are often limited by insufficiencies in the laboratory and theoretical data that serve as critical inputs to atmospheric physical and chemical tools. Here we provide an up-to-date and condensed description of areas where laboratory and/or ab initio investigations could fill critical gaps in our ability to model exoplanet atmospheric opacities, clouds, and chemistry, building off a larger 2016 white paper, and endorsed by the NAS Exoplanet Science Strategy report. Now is the ideal time for progress in these areas, but this progress requires better access to, understanding of, and training in the production of spectroscopic data as well as a better insight into chemical reaction kinetics both thermal and radiation-induced at a broad range of temperatures. Given that most published efforts have emphasized relatively Earth-like conditions, we can expect significant and enlightening discoveries as emphasis moves to the exotic atmospheres of exoplanets., Comment: Submitted as an Astro2020 Science White Paper

Direct detection, also known as direct imaging, is a method for discovering and characterizing the atmospheres of planets at intermediate and wide separations. It is the only means of obtaining spectra of non-transiting exoplanets. Characterizing the atmospheres of planets in the, (March 2018) Submitted to the Exoplanet Science Strategy committee of the NAS

The challenges of high contrast imaging (HCI) for detecting exoplanets for both ground and space applications can be met with extreme adaptive optics (ExAO), a high-order adaptive optics system that performs wavefront sensing (WFS) and correction at high speed. We describe two ExAO optical system designs, one each for ground-based telescopes and space-based missions, and examine them using the angular spectrum Fresnel propagation module within the Physical Optics Propagation in Python (POPPY) package. We present an end-to-end (E2E) simulation of the MagAO-X instrument, an ExAO system capable of delivering 6$\times10^{-5}$ visible-light raw contrast for static, noncommon path aberrations without atmosphere. We present a laser guidestar (LGS) companion spacecraft testbed demonstration, which uses a remote beacon to increase the signal available for WFS and control of the primary aperture segments of a future large space telescope, providing on order of a factor of ten factor improvement for relaxing observatory stability requirements. The LGS E2E simulation provides an easily adjustable model to explore parameters, limits, and trade-offs on testbed design and characterization., 11 pages, 12 figures, SPIE Astronomical Telescopes and Instrumentation 2018

Adaptive optics systems correct atmospheric turbulence in real time. Most adaptive optics systems used routinely correct in the near infrared, at wavelengths greater than 1 micron. MagAO- X is a new extreme adaptive optics (ExAO) instrument that will offer corrections at visible-to- near-IR wavelengths. MagAO-X will achieve Strehl ratios greater than 70% at H-alpha when running the 2040 actuator deformable mirror at 3.6 kHz. A visible pyramid wavefront sensor (PWFS) optimized for sensing at 600-1000 nm wavelengths will provide the high-order wavefront sensing on MagAO- X. We present the optical design and predicted performance of the MagAO-X pyramid wavefront sensor., SPIE Conference Proceedings, Telescopes and Instruments 2018 Austin

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 REsearch 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., Comment: 18 pages, 20 figures

MagAO-X is an entirely new "extreme" adaptive optics system for the Magellan Clay 6.5 m telescope, funded by the NSF MRI program starting in Sep 2016. The key science goal of MagAO-X is high-contrast imaging of accreting protoplanets at H$\alpha$. With 2040 actuators operating at up to 3630 Hz, MagAO-X will deliver high Strehls (>70%), high resolution (19 mas), and high contrast ($< 1\times10^{-4}$) at H$\alpha$ (656 nm). We present an overview of the MagAO-X system, review the system design, and discuss the current project status., Comment: Presented at SPIE Astronomical Telescopes and Instrumentation 2018

International audience; SPHERE is the VLT second generation planet hunter instrument. Installed since May 2014 on UT3, the system has been commissioned and verified for more than one year now and routinely delivers unprecedented images of star surroundings, exoplanets and dust disks. The exceptional performance required for this kind of observation makes the appointment: a repeatable Strehl Ratio of 90% in H band, a rough contrast level of 10-5@0.5 arcsec, and reaches 10-6 at the same separation after differential imaging (SDI, ADI). The instrument also presents high contrast levels in the visible and an unprecedented 17mas diffraction-limited resolution at 0.65 microns wavelength. SAXO is the SPHERE XAO system, allowing the system to reach its final detectivity. Its high performance and therefore highly sensitive capacities turns a new eye on telescope environment. Even if XAO performance are reached as expected, some unexpected limitations are here described and a first work around is proposed and discussed. Spatial limitation: wave-front aberrations have been identified, deviating from kolmogorov statistics, and therefore not easily seen and compensated for by the XAO system. The impact of this limitations results in a degraded performance in some particular low wind conditions. Solutions are developed and tested on sky to propose a new operation procedure reducing this limitation. Temporal limitation: high amplitude vibrations on the low order modes have been issued, due to telescope environment and XAO behaviour. Again, a solution is developed and an assessment of its performance is dressed. The potential application of these solutions to E-ELT is proposed.

Direct imaging of exoplanet systems requires the use of coronagraphs to reach high contrast levels (10^-8 to 10^-11) at small angular separations (0.1"). However, the performance of these devices is drastically limited by aberrations (in phase or in amplitude, introduced either by atmosphere or by the optics). Coronagraphs must therefore be combined with extreme adaptive optic systems, composed of a focal plane wavefront sensor and of a high order deformable mirror. These adaptive optic systems must reach a residual error in the corrected wavefront of less than 0.1 nm (RMS) with a rate of 1 kHz. In addition, the surface defects of the deformable mirror, inherent from the fabrication process, must be limited in order to avoid the introduction of amplitude aberrations. An experimental high contrast bench has been developed at the Paris Observatory (LESIA). This bench includes a Boston Micromachine deformable mirror composed of 1024 actuators. For a precise analysis of its surface and performance, we characterized this mirror on the interferometric bench developed since 2004 at the Marseille Observatory (LAM). In this paper, we present this interferometric bench as well as the results of the analysis. This will include a precise surface characterization and a description of the behavior of the actuators, on a 10 by 10 actuator range (behavior of a single actuator, study of the cross-talk between neighbor actuators, influence of a stuck actuator) and on full mirror scale (general surface shape)., Comment: Proceedings Volume 9148, Adaptive Optics Systems IV; 914846 (2014); doi: 10.1117/12.2057833 Event: SPIE Astronomical Telescopes + Instrumentation, 2014, Montr\'eal, Quebec, Canada

International audience; The extreme AO system, SAXO (SPHERE AO for eXoplanet Observation), is the heart of the SPHERE system, feeding the scientific instruments with flat wave front corrected from all the atmospheric turbulence and internal defects. We will present the final performance of SAXO obtained during the instrument AIT in Europe as well as the very first on-sky results. The main requirements and system characteristics will be recalled and the full AO loop performance will be quantified and compared to original specifications. It will be demonstrated that SAXO meets or even exceeds (especially its limit magnitude and its jitter residuals) its challenging requirements (more than 90% of SR in H band and a 3 mas residual jitter). Finally, after 10 years of AO developments, from early design to final on-sky implementations, some critical system aspects as well as some important lesson-learned will be presented in the perspective of the future generation of complex AO systems for VLTs and ELTs.

HARMONI is a visible and NIR integral field spectrograph, providing the E-ELT's core spectroscopic capability at first light. HARMONI will work at the diffraction limit of the E-ELT, thanks to a Classical and a Laser Tomographic AO system. In this paper, we present the system choices that have been made for these SCAO and LTAO modules. In particular, we describe the strategy developed for the different Wave-Front Sensors: pyramid for SCAO, the LGSWFS concept, the NGSWFS path, and the truth sensor capabilities. We present first potential implementations. And we asses the first system performance., Comment: SPIE proceeding, 2016

International audience; The high-contrast imaging instruments VLT/SPHERE and GPI have been routinely observing gas giant planets, brown dwarfs, and debris disks around nearby stars since 2013-2014. In these facilities, low-wind effects or differential aberrations between the extreme Adaptive Optics sensing path and the science path represent critical limitations for the observation of exoplanets orbiting their host star with a contrast ratio larger than 106 at small separations. To circumvent this problem, we proposed ZELDA, a Zernike wavefront sensor to measure these quasistatic aberrations at a nanometric level. A prototype was installed on VLT/SPHERE during its integration in Chile. We recently performed measurements on an internal source with ZELDA in the presence of Zernike or Fourier modes introduced with the deformable mirror of the instrument. In this communication, we present the results of our experiment and report on the contrast gain obtained with a first ZELDA-based wavefront correction. We finally discuss the suitability of such a solution for a possible upgrade of VLT/SPHERE and for its use with future E-ELT instruments or space missions with high-contrast capabilities (e.g. WFIRST-AFTA, HDST).

International audience; The SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) instrument aims at detecting extremely faint sources (giant extrasolar planets) in the vicinity of bright stars1. Such a challenging goal requires the use of a very-high-order performance Adaptive Optics [AO] system feeding the scientific instruments with a quasi-perfect flat wave front corrected from all the atmospheric turbulence and internal defects. This AO system, called SAXO (Sphere Ao for eXoplanet Observation) is the heart of the instrument, a heart beating 1200 time per second and providing unprecedented image quality for a large ground based telescope at optical/near infrared wavelength. We will present the latest results obtained on-sky, demonstrating its exceptional performance (in terms of correction quality, stability and robustness) and tremendous potentiality for high contrast imaging and more specifically for exoplanet discovery.

International audience; We propose and apply two methods for estimating phase discontinuities for two realistic scenarios on VLT and Keck. The methods use both phase diversity and a form of image sharpening. For the case of VLT, we simulate the `low wind effect' (LWE) which is responsible for focal plane errors in low wind and good seeing conditions. We successfully estimate the LWE using both methods, and show that using both methods both independently and together yields promising results. We also show the use of single image phase diversity in the LWE estimation, and show that it too yields promising results. Finally, we simulate segmented piston effects on Keck/NIRC2 images and successfully recover the induced phase errors using single image phase diversity. We also show that on Keck we can estimate both the segmented piston errors and any Zernike modes affiliated with the non-common path.

Future high-contrast imagers on ground-based extremely large telescopes will have to deal with the segmentation of the primary mirrors. Residual phase errors coming from the phase steps at the edges of the segments will have to be minimized in order to reach the highest possible wavefront correction and thus the best contrast performance. To study these effects, we have developed the MITHIC high-contrast testbed, which is designed to test various strategies for wavefront sensing, including the Zernike sensor for Extremely accurate measurements of Low-level Differential Aberrations (ZELDA) and COronagraphic Focal-plane wave-Front Estimation for Exoplanet detection (COFFEE). We recently equipped the bench with a new atmospheric turbulence simulation module that offers both static phase patterns representing segmented primary mirrors and continuous phase strips representing atmospheric turbulence filtered by an AO or an XAO system. We present a characterisation of the module using different instruments and wavefront sensors, and the first coronagraphic measurements obtained on MITHIC., Comment: Presented at SPIE Astronomical Instrumentation + Telescope 2016

A new coronagraphic instrument for the Large Binocular Telescope (LBT) has successfully passed the conceptual design phase. SHARK-NIR channel will be installed in one arm of the Large Binocular Telescope and it is designed to use different coronagraphic techniques, both to match as much as possible the different requirements of the different science cases and to explore the capabilities of such techniques for the next-generation of ELTs. By exploiting the combination with SHARK-VIS channel mounted at the other LBT arm, the instrument will offer simultaneous coronagraphic observations at different wavelengths, characterized by high contrast, even for relatively faint targets. This will be achievable thanks to the very efficient Adaptive Optics (AO) systems already operating at LBT (First Light AO, FLAO). Furthermore, the latter will be soon upgraded with new detectors, promising even better performance in terms of limiting magnitude. In this paper we present the status of the SHARK-NIR channel design.

International audience; The exoplanet direct imagers Gemini/GPI and VLT/SPHERE are built around extreme adaptive optics (ExAO) to correct the atmospheric turbulence and the aberrations associated with the optical surfaces. However, additional strategies are necessary to correct the non-common path aberrations (NCPA) between the ExAO and science paths that can limit the instrument contrast performance. To perform an adequate calibration, we have developed ZELDA, a Zernike sensor to achieve NCPA measurements with nanometric accuracy. We report the results of a new design analysis that maximizes the dynamic range, and from laboratory demonstrations on the LAM high-contrast testbed and on VLT/SPHERE during its integration.

We present the first ground-based CCD ($��< 1��$m) image of an extrasolar planet. Using MagAO's VisAO camera we detected the extrasolar giant planet (EGP) $��$ Pictoris b in $Y$-short ($Y_S$, 0.985 $��$m), at a separation of $0.470 \pm 0.010''$ and a contrast of $(1.63 \pm 0.49) \times 10^{-5}$. This detection has a signal-to-noise ratio of 4.1, with an empirically estimated upper-limit on false alarm probability of 1.0%. We also present new photometry from the NICI instrument on the Gemini-South telescope, in $CH_{4S,1\%}$ ($1.58$ $��m$), $K_S$ ($2.18��m$), and $K_{cont}$ (2.27 $��m$). A thorough analysis of our photometry combined with previous measurements yields an estimated near-IR spectral type of L$2.5\pm1.5$, consistent with previous estimates. We estimate log$(L_{bol}/L_{Sun})$ = $-3.86 \pm 0.04$, which is consistent with prior estimates for $��$ Pic b and with field early-L brown dwarfs. This yields a hot-start mass estimate of $11.9 \pm 0.7$ $M_{Jup}$ for an age of $21\pm4$ Myr, with an upper limit below the deuterium burning mass. Our $L_{bol}$ based hot-start estimate for temperature is $T_{eff}=1643\pm32$ K (not including model dependent uncertainty). Due to the large corresponding model-derived radius of $R=1.43\pm0.02$ $R_{Jup}$, this $T_{eff}$ is $\sim$$250$ K cooler than would be expected for a field L2.5 brown dwarf. Other young, low-gravity (large radius), ultracool dwarfs and directly-imaged EGPs also have lower effective temperatures than are implied by their spectral types. However, such objects tend to be anomalously red in the near-IR compared to field brown dwarfs. In contrast, $��$ Pic b has near-IR colors more typical of an early-L dwarf despite its lower inferred temperature., 40 pages, 20 figures. Accepted to ApJ

This article presents a proposal aimed at investigating the technical feasibility and the scientific capabilities of high contrast cameras to be implemented at LBT. Such an instrument will fully exploit the unique LBT capabilities in Adaptive Optics (AO) as demonstrated by the First Light Adaptive Optics (FLAO) system, which is obtaining excellent results in terms of performance and reliability. The aim of this proposal is to show the scientific interest of such a project, together with a conceptual opto-mechanical study which shows its technical feasibility, taking advantage of the already existing AO systems, which are delivering the highest Strehl experienced in nowadays existing telescopes. Two channels are foreseen for SHARK, a near infrared channel (2.5-0.9 um) and a visible one (0.9 – 0.6 um), both providing imaging and coronagraphic modes. The visible channel is equipped with a very fast and low noise detector running at 1.0 kfps and an IFU spectroscopic port to provide low and medium resolution spectra of 1.5 x 1.5 arcsec fields. The search of extra solar giant planets is the main science case and the driver for the technical choices of SHARK, but leaving room for several other interesting scientific topics, which will be briefly depicted here.

We present high resolution adaptive optics (AO) corrected images of the silhouette disk Orion 218-354 taken with Magellan AO (MagAO) and its visible light camera, VisAO, in simultaneous differential imaging (SDI) mode at H-alpha. This is the first image of a circumstellar disk seen in silhouette with adaptive optics and is among the first visible light adaptive optics results in the literature. We derive the disk extent, geometry, intensity and extinction profiles and find, in contrast with previous work, that the disk is likely optically-thin at H-alpha. Our data provide an estimate of the column density in primitive, ISM-like grains as a function of radius in the disk. We estimate that only ~10% of the total sub-mm derived disk mass lies in primitive, unprocessed grains. We use our data, Monte Carlo radiative transfer modeling and previous results from the literature to make the first self-consistent multiwavelength model of Orion 218-354. We find that we are able to reproduce the 1-1000micron SED with a ~2-540AU disk of the size, geometry, small vs. large grain proportion and radial mass profile indicated by our data. This inner radius is a factor of ~15 larger than the sublimation radius of the disk, suggesting that it is likely cleared in the very interior., 14 pages, 4 figures, ApJL accepted

As the only directly imaged multiple planet system, HR 8799 provides a unique opportunity to study the physical properties of several planets in parallel. In this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images offer an unprecedented view of the system, allowing us to obtain H and 3.3$ micron photometry of the innermost planet (for the first time) and put strong upper-limits on the presence of a hypothetical fifth companion. We find that all four planets are unexpectedly bright at 3.3 microns compared to the equilibrium chemistry models used for field brown dwarfs, which predict that planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find that removing CH4 to fit the 3.3 micron photometry increases the predicted L' (3.8 microns) flux enough that it is inconsistent with observations. In an effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy atmospheres, which are intended to represent planets covered by clouds of varying opacity. In this scenario, regions with low opacity look hot and bright, while regions with high opacity look faint, similar to the patchy cloud structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models reproduce all of the available data, but self-consistent models are still necessary to demonstrate their viability., Accepted to ApJ

The Adaptive Optics Scientific Working Group of the Large Binocular Telescope produced this document. It was distributed accompanying the LBT call for the Science Verification and Science Demonstration time in 2011 and 2012. It is also available following this link: https://wiki.lbto.org/AdaptiveOptics/AOGuidelines This document describes the best practices for imaging with PISCES+FLAO@LBT, emphasizing the main differences with common Near InfraRed (NIR) imaging. This document is based on the experience made on the first run of the PISCES+FLAO @ LBT commissioning that did not cover all the possible aspects.

In addition to the BLINC/MIRAC IR science instruments, the Magellan adaptive secondary AO system will have an EEV CCD47 that can be used both for visible AO science and as a wide-field acquisition camera. The effects of atmospheric dispersion on the elongation of the diffraction limited Magellan adaptive optics system point spread function (PSF) are significant in the near IR. This elongation becomes particularly egregious at visible wavelengths, culminating in a PSF that is 2000\{mu}m long in one direction and diffraction limited (30-60 \{mu}m) in the other over the wavelength band 0.5-1.0\{mu}m for a source at 45\pm zenith angle. The planned Magellan AO system consists of a deformable secondary mirror with 585 actuators. This number of actuators should be sufficient to nyquist sample the atmospheric turbulence and correct images to the diffraction limit at wavelengths as short as 0.7\{mu}m, with useful science being possible as low as 0.5\{mu}m. In order to achieve diffraction limited performance over this broad band, 2000\{mu}m of lateral color must be corrected to better than 10\{mu}m. The traditional atmospheric dispersion corrector (ADC) consists of two identical counter-rotating cemented doublet prisms that correct the primary chromatic aberration. We propose two new ADC designs: the first consisting of two identical counter-rotating prism triplets, and the second consisting of two pairs of cemented counter-rotating prism doublets that use both normal dispersion and anomalous dispersion glass in order to correct both primary and secondary chromatic aberration. The two designs perform 58% and 68%, respectively, better than the traditional two-doublet design. We also present our design for a custom removable wide-field lens that will allow our CCD47 to switch back and forth between an 8.6" FOV for AO science and a 28.5" FOV for acquisition., Comment: Proceedings of the SPIE, 2008, Vol. 7015, 70156M

Using an optical vortex coronagraph and simple adaptive optics techniques we have made the first convincing demonstration of an optical vortex coronagraph that is coupled to a star gazing telescope. In particular we suppressed by 97% the primary star of a barely resolvable binary system, Cor Caroli, having an effective angular separation of only 1.4 lambda/D. The secondary star suffered no suppression., Keywords: Coronagraph, Optical Vortex, High Contrast Imaging, Binary Star, Extrasolar Planet, Fourier Optics, Electron Beam Lithography. 7 pages, 7 figures, 28 references

Although T Tauri is one of the most studied young objects in astronomy, the nature of its circumstellar environment remains elusive due, in part, to the small angular separation of its three components (North-South and South a-b are separated by 0.68" and 0.12" respectively). Taking advantage of incredibly stable, high Strehl, PSFs obtained with Mid-IR adaptive optics at the 6.5 meter MMT, we are able to resolve the system on and off the 10um silicate dust feature (8.7um, 10.55um, and 11.86um; 10% bandwidth), and broad N. At these wavelengths, South a-b are separated by only ~0.3 lambda/D. This paper describes a robust Markov Chain Monte Carlo technique to separate all three components astrometrically and photometrically, for the first time, in the mid-IR. Our results show that the silicate feature previously observed in the unresolved T Tau South binary is dominated by T Tau Sa's absorption, while Sb does not appear to have a significant feature. This suggests that a large circumbinary disk around Sa-Sb is not likely the primary source of cool dust in our line-of-sight, and that T Tau Sa is enshrouded by a nearly edge-on circumstellar disk. Surprisingly, T Tau Sb does not appear to have a similarly oriented disk., 11 pages, 5 figures, accepted to ApJ

We present the results of a survey of 45 young ( 10 mag (5 sigma) at a separation of 0.5" from the primary star on 45% of our targets and H band contrasts of > 9 mag at a separation of 0.5'' on 80% of our targets. With this degree of attenuation, we should be able to image (5sigma detection) a 5 M_{Jup} planet 15 AU from a 70 Myr K1 star at 15 pc or a 5 M_{Jup} planet at 2 AU from a 12 Myr M star at 10 pc. We believe that our SDI images are the highest contrast astronomical images ever made from ground or space for methane rich companions, 69 pages, 25 figures, accepted to ApJS, supplemental materials available at http://exoplanet.as.arizona.edu/~lclose/SDI.html

We present an extension of the spectral deconvolution method (Sparks & Ford 2002) to achieve very high contrast at small inner working radii. We apply the method to the specific case of ground based adaptive optics fed integral field spectroscopy (without a coronagraph). Utilising the wavelength dependence of the Airy and speckle patterns, we make an accurate estimate of the PSF that can be scaled and subtracted from the data cube. The residual noise in the resulting spectra is very close to the photon noise from the starlight halo. We utilise the technique to extract a very high SNR H & K band spectrum of AB Dor C, the low mass companion to AB Dor A. By effectively eliminating all contamination from AB Dor A, the extracted spectrum retains both continuum and spectral features. The achieved 1 sigma contrast is 9 mag at 0.2", 11 mag at 0.5", in 20 mins exposure time, at an effective spectral bandwidth of 5.5 nm, proving that the method is applicable even in low Strehl regimes. The spectral deconvolution method clearly demonstrates the efficacy of image slicer based IFUs in achieving very high contrast imaging spectroscopy at small angular separations, validating their use as high contrast spectrographs/imagers for extreme adaptive optics systems., 9 pages, 5 figures, accepted for publication in MNRAS. This is a joint submission with astro-ph/0703564 by L. Close et al

We present results of a high-resolution, near-infrared survey of 41 nearby, young (= M6 very low-mass, VLM) populations. We find that the separation distribution of the binaries in this sample peaks at 13+14-9 AU, which is consistent with previous measurements of early-M binaries. Hence, early-M binaries seem to occur in--on average--tighter systems than G binaries. At the same time they are significantly wider than field VLM binary stars. The distribution of mass ratios q of primary and secondary stars was found to show an intermediate distribution between the strongly q-->1 peaked distribution of field VLM systems and the almost flat distribution of earlier-type stars. Consequently, we show evidence for relatively young, early-M binaries representing a transition between the well known earlier star distributions and the recently examined field VLM population characteristics. Despite the fact that this survey was dedicated to the search for faint brown dwarf and planetary mass companions, all planetary mass candidates were background objects. We exclude the existence of physical companions with masses greater than 10 Jupiter masses (M_Jup) at separations of >~40 AU and masses greater than 24 M_Jup for separations >~10 AU around 37 of the 41 observed objects., Comment: To appear in the January 1, 2007 issue of the Astrophysical Journal, 12 pages, 13 figures. Minor typographical and grammatical changes. Wrong round off in binary fraction corrected

International audience

We discuss the preliminary results of a survey of young (25000 (5 sigma Delta F1(1.575 um) > 10 mag, Delta H > 11.5 mag for a T6 spectral type) at a separation of 0.5" from the primary star. With this degree of attenuation, we should be able to image (5 sigma detection) a 2-4 Jupiter mass planet at 5 AU around a 30 Myr star at 10 pc. We are currently completing our survey of young, nearby stars. We have obtained complete datasets for 35 stars in the southern sky (VLT) and 7 stars in the northern sky (MMT). We believe that our SDI images are the highest contrast astronomical images ever made from ground or space for methane rich companions., 7 pages, 3 figures, 1 table. Presented at IAU Colloquium 200, Direct Imaging of Exoplanets: Science and Techniques. For high resolution figures, see IAUC 200 conference proceedings

We utilized the MMT's unique deformable secondary adaptive optics system to produce high-resolution (FWHM=0.3"), very high Strehl mid-infrared (9.8, 11.7 & 18 micron) images of the post-AGB star AC Her. The very high (98+/-2%) Strehls achieved with Mid-IR AO led naturally to an ultra-stable PSF independent of airmass, seeing, or location on the sky. We find no significant difference between AC Her's morphology and our unresolved PSF calibration stars (mu UMa & alpha Her) at 9.8, 11.7, & 18 microns. Our current observations do not confirm any extended Mid-IR structure around AC Her. These observations are in conflict with previously reported Keck (seeing-limited) 11.7 and 18 micron images which suggested the presence of a resolved ~0.6" edge-on circumbinary disk. We conclude that AC Her has no extended Mid-IR structure on scales greater than 0.2" (R, To appear in the November 20, 2003 issue of the Astrophysical Journal Letters. The preprint has 7 pages and 3 figures (one in color; but prints OK in B&W)

We present the first scientific images obtained with a deformable secondary mirror adaptive optics system. We utilized the 6.5m MMT AO system to produce high-resolution (FWHM=0.07'') near infrared (1.6 um) images of the young (~1 Myr) Orion Trapezium theta 1 Ori cluster members. A combination of high spatial resolution and high signal to noise allowed the positions of these stars to be measured to within ~0.003'' accuracies. Including previous speckle data (Weigelt et al. 1999), we analyze a six year baseline of high-resolution observations of this cluster. Over this baseline we are sensitive to relative proper motions of only ~0.002''/yr (4.2 km/s at 450 pc). At such sensitivities we detect orbital motion in the very tight theta 1 Ori B2B3 (52 AU separation) and theta 1 Ori A1A2 (94 AU separation) systems. Such motions are consistent with those independently observed by Schertl et al. (2003) with speckle interferometry, giving us confidence that these very small (~0.002''/yr) orbital motions are real. All five members of the theta 1 Ori B system appear likely gravitationally bound. The very lowest mass member of the theta 1 Ori B system (B4) has K' ~11.66 and an estimated mass of ~0.2 Msun. There was very little motion (4+/-15 km/s) detected of B4 w.r.t B1 or B2, hence B4 is possibly part of the theta 1 Ori B group. We suspect that if this very low mass member is physically associated it most likely is in an unstable (non-hierarchical) orbital position and will soon be ejected from the group. The theta 1 Ori B system appears to be a good example of a star formation ``mini-cluster'' which may eject the lowest mass members of the cluster in the near future. This ``ejection'' process could play a major role in the formation of low mass stars and brown dwarfs., Comment: To appear in the December 10, 2003 issue of the Astrophysical Journal 21 pages, 14 figures (some in color, but print OK in B&W)

Use of the highly sensitive Hokupa'a/Gemini curvature wavefront sensor has allowed for the first time direct adaptive optics (AO) guiding on M8-M9 very low mass (VLM) stars. An initial survey of 20 such objects (SpT=M8-M9) discovered 4 binaries. Three of the systems have separations of less than 4.2 AU and similar mass ratios (Delta K3 AU. This is likely consistent with the 23+/-5% measured for more massive (M0-M6) stars over the same separation range. It appears M8-M9 binaries have a much smaller semi-major axis distribution peak (~4 AU; with no systems wider than 15 AU) compared to M and G stars which have a broad peak at larger \~30 AU separations., Comment: Accepted in Astrophysical Letters (March). 12 pages, 2 figures