arXiv subjects

Alycia J. Weinberger

Publications and source records attributed to Alycia J. Weinberger.

At least 19 recordsLinked to original sources

arXiv2026

Comparing realtime optical gain measurement and methods on MagAO-X

A lingering technical challenge for pyramid wavefront sensors (PyWFS) is their change in response between calibration and correction residuals, a quantity known as optical gain (OG). Given the prevalent use of PyWFSs in current and planned high contrast adaptive optics (AO), understanding and reliably measuring OG for realtime control unlocks advanced correction and post processing techniques. The OG quantity as an unknown inhibits a system's ability to stably correct non common path errors, reconstructing wavefronts, and PSF reconstruction. This work compares kinds of optical gain measurement techniques on MagAO-X, a visible light extreme AO instrument on the 6.5m Magellan Clay telescope. We present a set of on-sky measurements of OG across three techniques: 1) An on-sky calibration that acquires OG per spatial mode, 2) realtime measurements of the instantaneous Strehl Ratio (SR) on the pyramid tip, and 3) realtime measurement of known, high-frequency probe signal on the WFS itself. We compare these on-sky results with performance diagnostics to asses how faithfully OG is returned. We conclude with future steps for active control of OG on MagAO-X.

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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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arXiv2026

High Velocity Circumstellar Gas Orbiting a White Dwarf Star

Numerous white dwarf stars are known to be orbited by disks of gas and dust. To date, broad, about 300 km s-1 wide, gaseous circumstellar absorption features have only been reported for the already iconic WD 1145+017, where one is witnessing the breakup of an extrasolar asteroid in real time. We report here the discovery of absorption from circumstellar gas around a second white dwarf (WD J0234-0406) with similarly broad features. The observed lines are carried by ions of Ca, Cr, Fe, Ti, Mg, Mn, Na, O, Si, Sc, Sr, Ti, and V. In addition, deep, non-photospheric lines of Si IV are seen in the ultraviolet; we compare these with Si IV lines previously seen in the ultraviolet spectra of various other white dwarfs. The apparent broadband flux of WD 1145+017 is known to change often and rapidly as chunks of the asteroid pass between the star and Earth. No such variations are seen in the brightness of WD J0234-0406. In addition, while the strength/structure of circumstellar absorption features at WD 1145+017 has changed dramatically with time, nothing similar is seen at WD J0234-0406. Excess infrared emission at WD J0234-0406 indicates the presence of circumstellar dust particles.

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arXiv2025

glitterin: Towards Replacing the Role of Lorenz-Mie Theory in Astronomy Using Neural Networks Trained on Light Scattering of Irregularly Shaped Grains

Light scattering by dust particles is often modeled assuming the dust is spherical for numerical simplicity and speed. However, real dust particles have highly irregular morphologies that significantly affect their scattering properties. We have developed glitterin, a neural network trained to predict light scattering from irregularly shaped dust grains, offering a computationally efficient alternative to Lorenz-Mie theory. We computed scattering properties using the Discrete Dipole Approximation code ADDA for irregularly shaped particles across size parameters x from 0.1 to 65, covering a range in complex refractive index m that includes astrosilicates, pyroxene, enstatite, water-ice, etc. The neural network operates at millisecond timescales while maintaining superior accuracy compared to linear interpolation. Irregular grains exhibit x-dependent deviations from spherical predictions. At small x, cross-sections approach volume-equivalent spheres for low m. At large x, irregular grains show enhanced cross-sections due to greater geometric extension. Increasing m also enhances the absorption cross-section relative to the volume-equivalent spheres. This differential x and m dependence creates mid-IR solid-state features distinct from predictions from spherical grains. Validation against laboratory measurements of forsterite and hematite demonstrates that our neural network captures both qualitative and quantitative behaviors more accurately than spherical models. Millimeter-wavelength applications reveal that spherical grains produce opposite polarization signatures compared to irregular grains, potentially relaxing stringent ~100um grain size constraints in protoplanetary disks. glitterin is publicly available and alleviates the computational barriers to incorporating emission and scattering of realistic grain morphologies.

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arXiv2025

Tracing Planetary Accretion in a 3 Gyr-old Hydrogen-Rich White Dwarf: The Extremely Polluted Atmosphere of LSPM J0207+3331

We report the detection of 13 heavy elements (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, and Sr) in the photosphere of LSPM J0207+3331, a ~3 Gyr old hydrogen-rich white dwarf with an effective temperature comparable to that of the Sun. Upper limits on carbon, obtained through the absence of molecular CH, suggest accretion from a carbon-volatile-depleted source. The accreted parent body exhibits slight deficits of Mg and Si relative to Fe but otherwise bulk Earth-like abundance patterns; a reasonable interpretation is that LSPM J0207+3331 is accreting a massive differentiated rocky body that had a core mass fraction higher than the Earth's. The high level of pollution indicates that substantial accretion events can still occur even after 3 Gyr of cooling. We also detect weak Ca II H & K line-core emission, making this only the second known isolated polluted white dwarf to exhibit this phenomenon and suggesting the presence of additional physical processes in or above the upper atmosphere. Our analysis also highlights the critical importance of including heavy elements in the model atmosphere structure calculations for highly polluted hydrogen-rich white dwarfs. Neglecting their contribution significantly impacts the inferred thermodynamic structure, leading to inaccuracies in derived stellar parameters. Finally, we show that the observed 11.3 microns infrared excess can be explained by a single silicate dust disk rather than a two-ring disk model.

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arXiv2025

Do White Dwarfs Sample Water-Rich Planetary Material?

Polluted white dwarfs offer a unique way to directly probe the compositions of exoplanetary bodies. We examine the water content of accreted material using the oxygen abundances of 51 highly polluted white dwarfs. Within this sample, we present new abundances for three H-dominated atmosphere white dwarfs that showed promise for accreting water-rich material. Throughout, we explore the impact of the observed phase and lifetime of accretion disks on the inferred elemental abundances of the parent bodies that pollute each white dwarf. Our results indicate that white dwarfs sample a range of dry to water-rich material, with median uncertainties in water mass fractions of $\approx$15\%. Amongst the He-dominated white dwarfs, 35/39 water abundances are consistent with corresponding H abundances. While for any individual white dwarf it may be ambiguous as to whether or not water is present in the accreted parent body, when considered as a population the prevalence of water-rich bodies is statistically robust. The population as a whole has a median water mass fraction of $\approx$25\%, and enforcing chondritic parent body compositions, we find that 31/51 WDs are likely to have non-zero water concentrations. This conclusion is different from a similar previous analysis of white dwarf pollution and we discuss reasons why this might be the case. Pollution in H-dominated white dwarfs continues to be more water-poor than in their He-dominated cousins, although the sample size of H-dominated white dwarfs remains small and the two samples still suffer a disjunction in the range of host star temperatures being probed.

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arXiv2025

Wide Separation Planets In Time (WISPIT): Discovery of a Gap H$α$ Protoplanet WISPIT 2b with MagAO-X

Excellent (<25 mas) H$_α$ images of the star TYC 5709-354-1 led to the discovery of a rare H$_α$ protoplanet. This star was discovered by the WISPIT survey to have a large multi-ring transitional disk, and is hereafter WISPIT 2. Our H$_α$ images of 2025, April 13 and April 16 discovered an accreting (H$_α$ in emission) protoplanet: WISPIT 2b (r=309.43$\pm$1.56 mas; (~54 au deprojected), PA=242.21$\pm$0.41 degrees) likely clearing a dust-free gap between the two brightest dust rings in the transitional disk. Our SNR=12.5 detection gave an H$_α$ ASDI contrast of (6.5$\pm$0.5)x10$^{-4}$ and a H$_α$ line flux of (1.29$\pm$0.28)x10$^{-15}$ erg/s/cm$^2$. We also present L' photometry from LBT/LMIRcam of the planet (L'=15.30$\pm$0.05 mag) which, when coupled with an age of 5.1$^{+2.4}_{-1.3}$ Myr, yields a planet mass estimate of 5.3$\pm$1.0 Mjup from the DUSTY evolutionary models. WISPIT 2b is accreting at 2.25$^{-0.17}_{+3.75}$x10$^{-12}$ Msun/yr. WISPIT 2b is very similar to the other H$_α$ protoplanets in terms of mass, age, flux, and accretion rate. The inclination of the system (${\it i}$=44 degrees) is also, surprisingly, very similar to the other known H$α$ protoplanet systems which all cluster from 37$\leq{\it i}\leq$52 degrees. We argue this clustering has only a ~1.0% (2.6 sigma) probability of occurring randomly, and so we speculate that magnetospherical accretion might have a preferred inclination range (~37-52 degrees) for the direct (cloud free, low extinction) line of sight to the H-alpha line formation/shock region. We also find at 110mas (~15au deprojected) a close companion candidate (CC1) which may be consistent with an inner dusty 9$\pm$4 Mjup planet.

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arXiv2025

Five New Sirius-Like White Dwarf + Main Sequence Star Systems with MagAO-X

Most known white dwarfs in multiple systems with main sequence stars have been discovered with M-type companions, because the white dwarf causes detectable UV excess and bluer colors than expected from a single M star. Surveys have shown that the number of white dwarfs in Sirius-like systems within 100 pc of the Sun is lower than expected, suggesting that white dwarfs are being missed in the glare of their main sequence companions. In this work we have leveraged the angular resolution and high-contrast capabilities, as well as optimization for visible wavelengths, of the extreme adaptive optics instrument MagAO-X to detect new white dwarf companions to AFGK stars. We present the first results of our survey with the extreme AO instrument MagAO-X, called the Pup Search, of 18 targets with seven new candidate companions, five of which are confirmed to be white dwarfs. We discuss the new detections in the context of previous surveys and other detection metric sensitivities and show that we are sensitive to a region not probed by other surveys. Finally we discuss the future of the Pup Search in light of developing technologies.

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arXiv2025

The Proxima Centauri Campaign -- First Constraints On Millimeter Flare Rates from ALMA

Proxima Centauri (Cen) has been the subject of many flaring studies due to its proximity and potential to host habitable planets. The discovery of millimeter flares from this M dwarf with ALMA has opened a new window into the flaring process and the space-weather environments of exoplanets like Proxima b. Using a total of ~50 hours of ALMA observations of Proxima Cen at 1.3 mm (233 GHz), we add a new piece to the stellar flaring picture and report the first cumulative flare frequency distribution (FFD) at millimeter wavelengths of any M dwarf. We detect 463 flares ranging from energies 10$^{24}$ erg to 10$^{27}$ erg. The brightest and most energetic flare in our sample reached a flux density of 119 $\pm$ 7 mJy, increasing by a factor of 1000x the quiescent flux, and reaching an energy of 10$^{27}$ erg in the ALMA bandpass, with t$_{1/2}$~16s. From a log-log linear regression fit to the FFD, we obtain a power law index of $α_\mathrm{FFD}$ = 2.92 $\pm$ 0.02, much steeper than $α_\mathrm{FFD}$ values (~2) observed at X-ray to optical wavelengths. If millimeter flare rates are predictive of flare rates at extreme-UV wavelengths, the contribution of small flares to the radiation environment of Proxima b may be much higher than expected based on the shallower power-law slopes observed at optical wavelengths.

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arXiv2025

Three Years of High-Contrast Imaging of the PDS 70 b and c Exoplanets at Hα with MagAO-X: Evidence of Strong Protoplanet Hα Variability and Circumplanetary Dust

We present 3 years of high-contrast imaging of the PDS 70 b and c accreting protoplanets with the new extreme AO system MagAO-X as part of the MaxProtoPlanetS survey of H$α$ protoplanets. In 2023 and 2024 our sharp (25-27 mas FWHM); well AO corrected (20-26% Strehl), deep (2-3.6hr) images detect compact (r~30 mas; r~3 au) circumplanetary disks (CPDs) surrounding both protoplanets. Starlight scattering off the dusty outer edges of these CPDs is the likely source of the bright compact continuum light detected within ~30 mas of both planets in our simultaneously obtained continuum 668 nm filter images. After subtraction of contaminating continuum and PSF residuals with pyKLIP ADI and SDI we obtained high-contrast ASDI H$α$ images of both planets in 2022, 2023 and 2024. We find the H$α$ line flux of planet b fell by (8.1$\pm$1.6)x10$^{-16}$ ergs/s/cm$^2$ a factor of 4.6 drop in flux from 2022 to 2023. In March 2024, planet b continued to be faint with just a slight 1.6x rise to an H$α$ line flux of (3.64$\pm$0.87)x10$^{-16}$ ergs/s/cm$^2$. For c we measure a significant increase of (2.74$\pm$0.51)x10$^{-16}$ ergs/s/cm$^2$ from 2023 to 2024 which is a factor of 2.3x increase. So both protoplanets have recently experienced significant H$α$ variability with ~1 yr sampling. In 2024, planet c is brighter than b: as c is brightening and b generally fading. We also tentatively detect one new point source "CC3" inside the inner disk (~49 mas; at PA~295 deg; 2024) with orbital motion roughly consistent with a ~5.6 au orbit.

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arXiv2024

MagAO-X: Commissioning Results and Status of Ongoing Upgrades

MagAO-X is the coronagraphic extreme adaptive optics system for the 6.5 m Magellan Clay Telescope. We report the results of commissioning the first phase of MagAO-X. Components now available for routine observations include: the >2 kHz high-order control loop consisting of a 97 actuator woofer deformable mirror (DM), a 2040 actuator tweeter DM, and a modulated pyramid wavefront sensor (WFS); classical Lyot coronagraphs with integrated low-order (LO) WFS and control using a third 97-actuator non-common path correcting (NCPC) DM; broad band imaging in g, r, i, and z filters with two EMCCDs; simultaneous differential imaging in H-alpha; and integral field spectroscopy with the VIS-X module. Early science results include the discovery of an H-alpha jet, images of accreting protoplanets at H-alpha, images of young extrasolar giant planets in the optical, discovery of new white dwarf companions, resolved images of evolved stars, and high-contrast images of circumstellar disks in scattered light in g-band (500 nm). We have commenced an upgrade program, called "Phase II", to enable high-contrast observations at the smallest inner working angles possible. These upgrades include a new 952 actuator NCPC DM to enable coronagraphic wavefront control; phase induced amplitude apodization coronagraphs; new fast cameras for LOWFS and Lyot-LOWFS; and real-time computer upgrades. We will report the status of these upgrades and results of first on-sky testing in March-May 2024.

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arXiv2024

More data than you want, less data than you need: machine learning approaches to starlight subtraction with MagAO-X

High-contrast imaging data analysis depends on removing residual starlight from the host star to reveal planets and disks. Most observers do this with principal components analysis (i.e. KLIP) using modes computed from the science images themselves. These modes may not be orthogonal to planet and disk signals, leading to over-subtraction. The wavefront sensor data recorded during the observation provide an independent signal with which to predict the instrument point-spread function (PSF). MagAO-X is an extreme adaptive optics (ExAO) system for the 6.5-meter Magellan Clay telescope and a technology pathfinder for ExAO with GMagAO-X on the upcoming Giant Magellan Telescope. MagAO-X is designed to save all sensor information, including kHz-speed wavefront measurements. Our software and compressed data formats were designed to record the millions of training samples required for machine learning with high throughput. The large volume of image and sensor data lets us learn a PSF model incorporating all the information available. This will eventually allow us to probe smaller star-planet separations at greater sensitivities, which will be needed for rocky planet imaging.

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arXiv2024

Debris Disks can Contaminate Mid-Infrared Exoplanet Spectra: Evidence for a Circumstellar Debris Disk around Exoplanet Host WASP-39

The signal from a transiting planet can be diluted by astrophysical contamination. In the case of circumstellar debris disks, this contamination could start in the mid-infrared and vary as a function of wavelength, which would then change the observed transmission spectrum for any planet in the system. The MIRI/LRS WASP-39b transmission spectrum shows an unexplained dip starting at $\sim$10 $μ$m that could be caused by astrophysical contamination. The spectral energy distribution displays excess flux at similar levels to that which are needed to create the dip in the transmission spectrum. In this article, we show that this dip is consistent with the presence of a bright circumstellar debris disk, at a distance of $>$2 au. We discuss how a circumstellar debris disk like that could affect the atmosphere of WASP-39b. We also show that even faint debris disks can be a source of contamination in MIRI exoplanet spectra.

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arXiv2024

Modeling Circumstellar Gas Emission around a White Dwarf Using Cloudy

The chemical composition of an extrasolar planet is fundamental to its formation, evolution and habitability. In this study, we explore a new way to measure the chemical composition of the building blocks of extrasolar planets, by measuring the gas composition of the disrupted planetesimals around white dwarf stars. As a first attempt, we used the photo-ionization code Cloudy to model the circumstellar gas emission around a white dwarf Gaia J0611$-$6931 under some simplified assumptions. We found most of the emission lines are saturated and the line ratios approaching the ratios of thermal emission; therefore only lower limits to the number density can be derived. Silicon is the best constrained element in the circumstellar gas and we derived a lower limit of 10$^{10.3}$ cm$^{-3}$. In addition, we placed a lower limit on the total amount of gas to be 1.8 $\times$ 10$^{19}$ g. Further study is needed to better constrain the parameters of the gas disk and connect it to other white dwarfs with circumstellar gas absorption.

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arXiv2024

A Uniform Analysis of Debris Disks with the Gemini Planet Imager II: Constraints on Dust Density Distribution Using Empirically-Informed Scattering Phase Functions

Spatially-resolved images of debris disks are necessary to determine disk morphological properties and the scattering phase function (SPF) which quantifies the brightness of scattered light as a function of phase angle. Current high-contrast imaging instruments have successfully resolved several dozens of debris disks around other stars, but few studies have investigated trends in the scattered-light, resolved population of debris disks in a uniform and consistent manner. We have combined Karhunen-Loeve Image Projection (KLIP) with radiative-transfer disk forward modeling in order to obtain the highest quality image reductions and constrain disk morphological properties of eight debris disks imaged by the Gemini Planet Imager at H-band with a consistent and uniformly-applied approach. In describing the scattering properties of our models, we assume a common SPF informed from solar system dust scattering measurements and apply it to all systems. We identify a diverse range of dust density properties among the sample, including critical radius, radial width, and vertical width. We also identify radially narrow and vertically extended disks that may have resulted from substellar companion perturbations, along with a tentative positive trend in disk eccentricity with relative disk width. We also find that using a common SPF can achieve reasonable model fits for disks that are axisymmetric and asymmetric when fitting models to each side of the disk independently, suggesting that scattering behavior from debris disks may be similar to Solar System dust.

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arXiv2023

Probing Disk Ice Content and PAH Emission Through Multiband MagAO+Clio Images of HD 141569

We present resolved images of the inner disk component around HD 141569 using the Magellan adaptive optics system with the Clio2 1 - 5 $μ$m camera, offering a glimpse of a complex system thought to be in a short evolutionary phase between protoplanetary and debris disk stages. We use a reference star along with the KLIP algorithm for PSF subtraction to detect the disk inward to about 0.24" (~25 au assuming a distance of 111 pc) at high signal-to-noise ratios at $L'$ (3.8 $μ$m), $Ls$ (3.3 $μ$m), and narrowband $Ice$ (3.1 $μ$m). We identify an arc or spiral arm structure at the southeast extremity, consistent with previous studies. We implement forward modeling with a simple disk model within the framework of an MCMC sampler to better constrain the geometrical attributes and photometry using our KLIP-reduced disk images. We then leverage these modeling results to facilitate a comparison of the measured brightness in each passband to find a reduction in scattered light from the disk in the $Ice$ filter, implying significant absorption due to water ice in the dust. Additionally, our best-fit disk models exhibit peak brightness in the southwestern, back-scattering region of the disk, which we suggest to be possible evidence of 3.3 $μ$m PAH emission. However, we point out the need for additional observations with bluer filters and more complex modeling to confirm these hypotheses.

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