arXiv subjects

Alex Hedglen

Publications and source records attributed to Alex Hedglen.

11 recordsLinked to original sources

arXiv2026

windsoCC: reconstructing the wind-driven halo in MagAO-X images using wavefront sensor telemetry

The wind-driven halo (WDH) is a persistent, low spatial frequency noise artifact that arises due to the servo-lag error inherent to all adaptive optics (AO) instruments. Spatial filtering may be employed to overcome this artifact, however, filtering out the WDH while simultaneously preserving signal from an extended astrophysical object of interest is exceptionally challenging. Additionally, since the WDH changes in intensity and position angle through an observation, data-driven algorithms (e.g., KLIP) that are commonly used to subtract the starlight need to be overly-aggressive to remove both the static and dynamic noise components. Since wavefront sensors (WFSs) continuously track the closed-loop residual wavefront error, WFS telemetry presents the ideal resource for combating this type of noise artifact through postprocessing. Using archival WFS telemetry from MagAO-X, which is the ``extreme" AO instrument for the 6.5-meter Magellan-Clay telescope, we demonstrate a novel workflow for WDH reconstruction and removal in individual coronagraphic science images. MagAO-X is equipped with a pyramid WFS capable of recording wavefront telemetry at a high-cadence which is saved during data acquisition. Given this, we detail how our WFS data processing pipeline, windsoCC, cross-correlates the recorded closed-loop wavefront to measure the wind vectors of several turbulent layers of the atmosphere above Las Campanas Observatory. We then make use of the wind parameters learned through windsoCC to reconstruct the WDH footprint by leveraging a parametric model. Notably, we demonstrate a dramatic improvement in object recovery using on-sky MagAO-X images of the disk around HR~4796A at visible wavelengths.

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arXiv2026

ffortissimo: A Freeform Forward-Modeling Pipeline for High-Contrast Images of Circumstellar Disks Based on Automatic Differentiation

Modeling circumstellar disks in the traditional sense carries the assumption that the dust density distribution can be accurately described with a fixed parametric form. Furthermore, commonly-used algorithms for subtracting the stellar point-spread function (PSF) distort the true morphology of the faint underlying disk structure, especially dusty features that are located at small angular separations. These phenomena often lead to significant residuals with parametric disk models and make it difficult to measure the full realizable range of the scattering function of the dust. We address these challenges with ffortissimo, a novel, pixel-based freeform forward modeling pipeline designed to characterize extended objects in KLIP-reduced images. We built this pipeline within the framework of JAX, which is a machine learning library in Python that enables efficient optimization through automatic differentiation ("autodiff") and GPU-accelerated array computations. Using visible light images of the disk around HR 4796A taken by the "extreme" Magellan Adaptive Optics instrument (MagAO-X), we show that our data-driven freeform models excel at fitting a complex dust distribution and can infer the dust scattering properties even through PSF subtraction artifacts. Additionally, we demonstrate the potential for retrieving spatial dust features beyond the diffraction limit of the telescope. We note that there are remaining challenges to address before precision photometry using these freeform models is advised. These include better background, wind-driven halo, and speckle characterization as preventing the freeform models from learning these noise artifacts is currently difficult.

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arXiv2026

A Multiband Study of the HR 4796A Disk in the Optical Using MagAO-X

We present total intensity images of the debris disk around HR 4796A from observations spanning 2023 to 2025 with the Magellan extreme adaptive optics instrument (MagAO-X). We detected the disk at high signal-to-noise ratios at $g' (527$ nm), $r' (615$ nm), $i' (762$ nm), and $z' (909 $ nm). Additionally, we present images collected using the "star-hopping" technique that show the entirety of the disk, including the dramatic forward-scattering at the minor axis. We subjected our images to a battery of modeling techniques to constrain the geometry and photometry of the disk. Leveraging our clear detections of the disk's minor axis, we modeled the scattering phase function (SPF) using a basis of the Legendre polynomials. To mitigate self-subtraction artifacts in our angular differential imaging, we implemented a forward-modeling pipeline that generates a pixel-based freeform disk forward model leading to a deconvolved image of the disk. Our best-fit disk models reveal: (1) highly forward-scattering SPFs with a minimum at the $\sim65^{\circ}$ scattering angle, (2) a faint halo of dust just exterior to the spine of the disk that is not well-described by a broken power law density profile, (3) a red spectral slope for the dust, and finally (4) a compact, clump-like feature in the freeform disk models. Our empirically-measured SPFs suggest that the scattering is dominated by large, highly-absorptive grains. However, we emphasize the need for testing advanced irregular grain models using our SPFs to learn more about the physical and chemical properties of this complex system.

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arXiv2025

A planetary-mass candidate imaged in the Young Suns Exoplanet Survey

Directly imaged exoplanets in wide orbits challenge current gas giant formation theories. They need to form quickly and acquire enough material before the disk dissipates, which cannot be accommodated by in-situ formation by core accretion. We search for wide separation ($>$ 100 au) planetary-mass companions with the Young Suns Exoplanet Survey (YSES). Here, we present a planetary-mass candidate companion discovered in the survey. We conducted follow-up observations of the candidate system after the first epoch observations and obtained six epochs of observations for this system between 2018 and 2024, and integral field spectroscopy of the stellar component. We report the detection of a candidate companion with H=22.04 $\pm$ 0.13 mag at a projected separation of 730 $\pm$ 10 au away from the primary star. High angular resolution imaging observations of the central star show it is a visual binary. Acceleration data, orbital fitting, spectral energy distribution fitting and radial velocity differences all suggest that there is at least one more unresolved low-mass stellar companion in this system. The planetary-mass candidate shows a significant proper motion comparable to that of the primary star. We estimate an age of 19-28 Myr for the primary star. We cannot confirm the companionship of the candidate due to the unknown barycentre of the stars. Long-term imaging and radial velocity monitoring of the central stars, along with spectroscopy of the candidate companion, are key to resolving the nature of this system. If confirmed, the candidate companion would have a mass of 3-5 Mj estimated with the ATMO evolutionary model. It would be another cold low-mass planet imaged similar to 51 Eri b and AF Lep b. Its extremely wide separation from the host star would challenge the formation theory of gas giant exoplanets.

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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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arXiv2022

A Novel Hexpyramid Pupil Slicer for an ExAO Parallel DM for the Giant Magellan Telescope

The 25.4m Giant Magellan Telescope (GMT) will be amongst the first in a new series of segmented extremely large telescopes (ELTs). The 25.4 m pupil is segmented into seven 8.4 m circular segments in a flower petal pattern. At the University of Arizona we have developed a novel pupil slicer that will be used for ELT extreme adaptive optics (ExAO) on the up and coming ExAO instrument, GMagAO-X. This comes in the form of a six-sided reflective pyramid with a hole through the center known as a "hexpyramid". By passing the GMT pupil onto this reflective optic, the six outer petals will be sent outward in six different directions while the central segment passes through the center. Each segment will travel to its own polarization independent flat fold mirror mounted on a piezoelectric piston/tip/tilt controller then onto its own commercial 3,000 actuator deformable mirror (DM) that will be employed for extreme wavefront control. This scheme of seven DMs working in parallel to produce a 21,000 actuator DM is a new ExAO architecture that we named a "parallel DM," in which the hexpyramid is a key optical component. This significantly surpasses any current or near future actuator count for any monolithic DM architecture. The optical system is designed for high-quality wavefront (lambda/10 surface PV) with no polarization errors and no vignetting. The design and fabrication of the invar mechanical mounting structure for this complex optical system is described in this paper.

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arXiv2021

Characterizing deformable mirrors for the MagAO-X instrument

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$α$.

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arXiv2020

Concept for the GMT High-Contrast Exoplanet Instrument GMagAO-X and the GMT High-Contrast Phasing Testbed with MagAO-X

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.

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arXiv2018

Optical and mechanical design of the extreme AO coronagraphic instrument MagAO-X

Here we review the current optical mechanical design of MagAO-X. The project is post-PDR and has finished the design phase. The design presented here is the baseline to which all the optics and mechanics have been fabricated. The optical/mechanical performance of this novel extreme AO design will be presented here for the first time. Some highlights of the design are: 1) a floating, but height stabilized, optical table; 2) a Woofer tweeter (2040 actuator BMC MEMS DM) design where the Woofer can be the current f/16 MagAO ASM or, more likely, fed by the facility f/11 static secondary to an ALPAO DM97 woofer; 3) 22 very compact optical mounts that have a novel locking clamp for additional thermal and vibrational stability; 4) A series of four pairs of super-polished off-axis parabolic (OAP) mirrors with a relatively wide FOV by matched OAP clocking; 5) an advanced very broadband (0.5-1.7micron) ADC design; 6) A Pyramid (PWFS), and post-coronagraphic LOWFS NCP wavefront sensor; 7) a vAPP coronagraph for starlight suppression. Currently all the OAPs have just been delivered, and all the rest of the optics are in the lab. Most of the major mechanical parts are in the lab or instrument, and alignment of the optics has occurred for some of the optics (like the PWFS) and most of the mounts. First light should be in 2019A.

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arXiv2018

MagAO-X: project status and first laboratory results

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$α$. 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$α$ (656 nm). We present an overview of the MagAO-X system, review the system design, and discuss the current project status.

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