arXiv subjects

Laird Close

Publications and source records attributed to Laird Close.

At least 19 recordsLinked to original sources

arXiv2026

Visible-Light High-Contrast Polarimetry with MagAO-X: Characterization and Initial Results

MagAO-X is a visible-light extreme adaptive optics instrument on the 6.5 meter Magellan Clay Telescope, recently upgraded to enable high-contrast polarimetric differential imaging (PDI) in r', i', and z' filters. Polarimetry is a powerful technique for suppressing unpolarized starlight and isolating the faint, polarized signal scattered by circumstellar dust, but it demands precise calibration of instrumental polarization effects introduced by the telescope and instrument optics. We present an overview of the MagAO-X polarimeter and characterize its polarimetric response using a purpose-built polarization generator that injects light of a known polarization state. From these measurements, we fit a Mueller-matrix model of the instrument and quantify its polarimetric efficiency and instrumental polarization as a function of the k-mirror image rotator angle and observing filter. The initial characterization revealed significant, dynamic inefficiencies driven by the image rotator, motivating the deployment of a dual rotating quarter-wave plate (DQWP) compensator that dynamically reorients the input polarization to the instrument's eigenpolarization. Following installation of the DQWP, we measured an average increase in polarimetric efficiency of +17.5% (to 87.4%) and a reduction in instrumental polarization of -5.4% (to 8.3%) across all filters. Finally, we demonstrate the on-sky performance of the polarimeter with i' imaging of the debris disk around HR 4796, producing one of the closest inner-working-angle views of the bright, forward-scattering side of the disk. These results help pave the way for polarimeters on future extremely large telescopes such as GMT and ELT.

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arXiv2026

Upgrading LBTI/NOMIC with a quadruple annular groove phase mask and GeoSnap detector for imaging nearby, habitable-zone exoplanets

The Large Binocular Telescope Interferometer (LBTI)'s Nulling-Optimized Mid-Infrared Camera (NOMIC) is among the most capable thermal-infrared imaging systems available for high-contrast, high-angular-resolution astronomical observations. Here we describe two in-progress upgrades to LBTI/NOMIC: (1) the design, fabrication, and installation of a quadruple annular groove phase mask (Q-AGPM) coronagraph, and (2) the installation of a 13 micron-cutoff Teledyne GeoSnap array. The Q-AGPM is the first coronagraph to be installed within NOMIC and one of the first optimized for N-band (~11 micron) observations. It places four annular groove phase masks on a single diamond substrate so that, in the LBTI dual-aperture imaging mode, each of the two telescope beams can be chopped between a pair of masks without loss of observing efficiency. The GeoSnap array will replace NOMIC's original AQUARIUS array, delivering higher quantum efficiency, larger well depth, faster and more linear readout, and freedom from the excess low-frequency noise that requires aggressive chopping. Together these upgrades substantially improve the achievable contrast and sensitivity at small angular separations. We also present a high-contrast Fizeau imaging sequence obtained with LBTI's new FFTCam fringe tracker, which confirms the interferometric gain over a single aperture through injection/recovery tests: relative to an equal-time single aperture exposure, the S/N = 3 contrast is a factor of ~2-4 deeper across 0.2-1 arcsec, spanning the contrast- and background-limited regimes. Finally, we describe the role of the upgraded LBTI/NOMIC instrument within the Breakthrough Watch program at the University of Arizona, which aims to perform the deepest observations yet of the habitable zones of the nearest single Sun-like stars.

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arXiv2026

Direct spectroscopic confirmation of the young embedded proto-planet WISPIT 2c

WISPIT 2 is a nearby young star with a multi-ringed disk which was recently confirmed to host a ~4.9 MJup gas giant planet embedded in a large (60 au) gap at a radial separation of 57 au from the host star. We confirm and characterise a second, close-in planet in the WISPIT 2 system using a combination of new VLT/SPHERE H-band dual-polarisation imaging and VLTI/GRAVITY K-band interferometric observations of the WISPIT 2 system. The GRAVITY detection is consistent with a point-like source while its extracted K-band spectrum shows CO band-head absorption at 2.3 microns and a continuum shape consistent with a young giant planet. From the GRAVITY data we extract a medium resolution K-band spectrum of the companion and fit atmospheric model grids using the species tool with nested sampling to constrain its effective temperature, radius, and luminosity. We infer Teff of 1500-2600 K, a radius of 0.91-2.2 RJup, and a luminosity of (-3.47)-(-3.63). Comparison with evolutionary tracks implies a mass range of 8-12 MJup, approximately twice as massive as the previously confirmed WISPIT 2b. The astrometry rules out a background source and marginally detects orbital motion of WISPIT 2c, which needs further follow-up observations for confirmation. WISPIT 2 now becomes an analogue to PDS 70, offering a second laboratory for studying the formation and early evolution of a multi-planet system within its natal disk.

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arXiv2024

MagAO-X Phase II Upgrades: Implementation and First On-Sky Results of a New Post-AO 1000 Actuator Deformable Mirror

MagAO-X is the extreme coronagraphic adaptive optics (AO) instrument for the 6.5-meter Magellan Clay telescope and is currently undergoing a comprehensive batch of upgrades. One innovation that the instrument features is a deformable mirror (DM) dedicated for non-common path aberration correction (NCPC) within the coronagraph arm. We recently upgraded the 97 actuator NCPC DM with a 1000 actuator Boston Micromachines Kilo-DM which serves to (1) correct non-common path aberrations which hamper performance at small inner-working angles, (2) facilitate focal-plane wavefront control algorithms (e.g., electric field conjugation) and (3) enable 10 kHz correction speeds (up from 2 kHz) to assist post-AO, real-time low-order wavefront control. We present details on the characterization and installation of this new DM on MagAO-X as part of our efforts to improve deep contrast performance for imaging circumstellar objects in reflected light. Pre-installation procedures included use of a Twyman-Green interferometer to build an interaction matrix for commanding the DM surface, in closed-loop, to a flat state for seamless integration into the instrument. With this new NCPC DM now installed, we report on-sky results from the MagAO-X observing run in March -- May 2024 for the Focus Diversity Phase Retrieval and implicit Electric Field Conjugation algorithms for quasistatic speckle removal and in-situ Strehl ratio optimization, respectively.

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arXiv2024

Making the unmodulated Pyramid wavefront sensor smart. Closed-loop demonstration of neural network wavefront reconstruction with MagAO-X

Almost all current and future high-contrast imaging instruments will use a Pyramid wavefront sensor (PWFS) as a primary or secondary wavefront sensor. The main issue with the PWFS is its nonlinear response to large phase aberrations, especially under strong atmospheric turbulence. Most instruments try to increase its linearity range by using dynamic modulation, but this leads to decreased sensitivity, most prominently for low-order modes, and makes it blind to petal-piston modes. In the push toward high-contrast imaging of fainter stars and deeper contrasts, there is a strong interest in using the PWFS in its unmodulated form. Here, we present closed-loop lab results of a nonlinear reconstructor for the unmodulated PWFS of the Magellan Adaptive Optics eXtreme (MagAO-X) system based on convolutional neural networks (CNNs). We show that our nonlinear reconstructor has a dynamic range of >600 nm root-mean-square (RMS), significantly outperforming the linear reconstructor that only has a 50 nm RMS dynamic range. The reconstructor behaves well in closed loop and can obtain >80% Strehl at 875 nm under a large variety of conditions and reaches higher Strehl ratios than the linear reconstructor under all simulated conditions. The CNN reconstructor also achieves the theoretical sensitivity limit of a PWFS, showing that it does not lose its sensitivity in exchange for dynamic range. The current CNN's computational time is 690 microseconds, which enables loop speeds of >1 kHz. On-sky tests are foreseen soon and will be important for pushing future high-contrast imaging instruments toward their limits.

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arXiv2023

Monitoring H$\alpha$ Emission from the Wide-orbit Brown-dwarf Companion FU Tau B

Monitoring mass accretion onto substellar objects provides insights into the geometry of the accretion flows. We use the Lulin One-meter Telescope to monitor H$\alpha$ emission from FU Tau B, a $\sim$19 $M_{\rm Jup}$ brown-dwarf companion at 5.7" (719 au) from the host star, for six consecutive nights. This is the longest continuous H$\alpha$ monitoring for a substellar companion near the deuterium-burning limit. We aim to investigate if accretion near the planetary regime could be rotationally modulated as suggested by magnetospheric accretion models. We find tentative evidence that H$\alpha$ mildly varies on hourly and daily timescales, though our sensitivity is not sufficient to definitively establish any rotational modulation. No burst-like events are detected, implying that accretion onto FU Tau B is overall stable during the time baseline and sampling windows over which it was observed. The primary star FU Tau A also exhibits H$\alpha$ variations over timescales from minutes to days. This program highlights the potential of monitoring accretion onto substellar objects with small telescopes.

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arXiv2021

Imaging low-mass planets within the habitable zones of nearby stars with ground-based mid-infrared imaging

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.

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arXiv2019

New Spatially Resolved Imaging of the SR 21 Transition Disk and Constraints on the Small-Grain Disk Geometry

We present new 0.6 - 4 $\mu$m imaging of the SR 21 transition disk from Keck/NIRC2 and Magellan/MagAO. The protoplanetary disk around SR 21 has a large (~ 30 - 40 AU) clearing first inferred from its spectral energy distribution and later detected in sub-millimeter imaging. Both the gas and small dust grains are known to have a different morphology, with an inner truncation in CO at ~7 AU, and micron-sized dust detected within the millimeter clearing. Previous near-infrared imaging could not distinguish between an inner dust disk with a truncation at ~7 AU or one that extended to the sublimation radius. The imaging data presented here require an inner dust disk radius of a few AU, and complex structure such as a warp or spiral. We present a parametric warped disk model that can reproduce the observations. Reconciling the images with the spectral energy distribution gathered from the literature suggests grain growth to ~2 - 5 $\mu$m within the sub-millimeter clearing. The complex disk structure and possible grain growth can be connected to dynamical shaping by a giant-planet mass companion, a scenario supported by previous observational and theoretical studies.

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arXiv2019

The Need for Laboratory Measurements and Ab Initio Studies to Aid Understanding of Exoplanetary Atmospheres

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.

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arXiv2019

Detecting Earth-like Biosignatures on Rocky Exoplanets around Nearby Stars with Ground-based Extremely Large Telescopes

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.

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arXiv2019

New Frontiers for Terrestrial-sized to Neptune-sized Exoplanets In the Era of Extremely Large Telescopes

Surveys reveal that terrestrial- to Neptune-sized planets (1 $< R <$ 4 R$_{\rm{Earth}}$) are the most common type of planets in our galaxy. Detecting and characterizing such small planets around nearby stars holds the key to understanding the diversity of exoplanets and will ultimately address the ubiquitousness of life in the universe. The following fundamental questions will drive research in the next decade and beyond: (1) how common are terrestrial to Neptune-sized planets within a few AU of their host star, as a function of stellar mass? (2) How does planet composition depend on planet mass, orbital radius, and host star properties? (3) What are the energy budgets, atmospheric dynamics, and climates of the nearest worlds? Addressing these questions requires: a) diffraction-limited spatial resolution; b) stability and achievable contrast delivered by adaptive optics; and c) the light-gathering power of extremely large telescopes (ELTs), as well as multi-wavelength observations and all-sky coverage enabled by a comprehensive US ELT Program. Here we provide an overview of the challenge, and promise of success, in detecting and comprehensively characterizing small worlds around the very nearest stars to the Sun with ELTs. This white paper extends and complements the material presented in the findings and recommendations published in the National Academy reports on Exoplanet Science Strategy and Astrobiology Strategy for the Search for Life in the Universe.

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arXiv2019

Astro2020 Science White Paper: Dynamical Processes in the Planet-Forming Environment

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.

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arXiv2019

The Demographics and Atmospheres of Giant Planets with the ELTs

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 $Gaia$.

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arXiv2019

Imaging Giant Protoplanets with the ELTs

We have now accumulated a wealth of observations of the planet-formation environment and of mature planetary systems. These data allow us to test and refine theories of gas-giant planet formation by placing constraints on the conditions and timescale of this process. Yet a number of fundamental questions remain unanswered about how protoplanets accumulate material, their photospheric properties and compositions, and how they interact with protoplanetary disks. While we have begun to detect protoplanet candidates during the last several years, we are presently only sensitive to the widest separation, highest mass / accretion rate cases. Current observing facilities lack the angular resolution and inner working angle to probe the few-AU orbital separations where giant planet formation is thought to be most efficient. They also lack the contrast to detect accretion rates that would form lower mass gas giants and ice giants. Instruments and telescopes coming online over the next decade will provide high contrast in the inner giant-planet-forming regions around young stars, allowing us to build a protoplanet census and to characterize planet formation in detail for the first time.

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arXiv2019

Protoplanetary Disk Science Enabled by Extremely Large Telescopes

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.

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arXiv2018

Direct Imaging in Reflected Light: Characterization of Older, Temperate Exoplanets With 30-m Telescopes

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 <5 AU regime, where RV surveys have revealed an abundance of other worlds, requires a 30-m-class aperture in combination with an advanced adaptive optics system, coronagraph, and suite of spectrometers and imagers - this concept underlies planned instruments for both TMT (the Planetary Systems Imager, or PSI) and the GMT (GMagAO-X). These instruments could provide astrometry, photometry, and spectroscopy of an unprecedented sample of rocky planets, ice giants, and gas giants. For the first time habitable zone exoplanets will become accessible to direct imaging, and these instruments have the potential to detect and characterize the innermost regions of nearby M-dwarf planetary systems in reflected light. High-resolution spectroscopy will not only illuminate the physics and chemistry of exo-atmospheres, but may also probe rocky, temperate worlds for signs of life in the form of atmospheric biomarkers (combinations of water, oxygen and other molecular species). By completing the census of non-transiting worlds at a range of separations from their host stars, these instruments will provide the final pieces to the puzzle of planetary demographics. This whitepaper explores the science goals of direct imaging on 30-m telescopes and the technology development needed to achieve them.

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arXiv2018

SHARK-NIR, the coronagraphic camera for LBT, moving toward construction

SHARK-NIR is one of the two coronagraphic instruments proposed for the Large Binocular Telescope. Together with SHARK-VIS (performing coronagraphic imaging in the visible domain), it will offer the possibility to do binocular observations combining direct imaging, coronagraphic imaging and coronagraphic low resolution spectroscopy in a wide wavelength domain, going from 0.5{\mu}m to 1.7{\mu}m. Additionally, the contemporary usage of LMIRCam, the coronagraphic LBTI NIR camera, working from K to L band, will extend even more the covered wavelength range. In January 2017 SHARK-NIR underwent a successful final design review, which endorsed the instrument for construction and future implementation at LBT. We report here the final design of the instrument, which foresees two intermediate pupil planes and three focal planes to accomodate a certain number of coronagraphic techniques, selected to maximize the instrument contrast at various distances from the star. Exo-Planets search and characterization has been the science case driving the instrument design, but the SOUL upgrade of the LBT AO will increase the instrument performance in the faint end regime, allowing to do galactic (jets and disks) and extra-galactic (AGN and QSO) science on a relatively wide sample of targets, normally not reachable in other similar facilities.

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arXiv2018

Modeling coronagraphic extreme wavefront control systems for high contrast imaging in ground and space telescope missions

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.

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