arXiv subjects

John Debes

Publications and source records attributed to John Debes.

At least 19 recordsLinked to original sources

arXiv2026

JWST/NIRCam Imaging of Young Stellar Objects. IV. Detailed Imaging of the Protoplanetary Disk around TW Hya

As the nearest protoplanetary disk to Earth ($d = 60.14$ pc), TW Hya is one of the most studied protoplanetary disks and a critical benchmark for testing planet formation theories. We present high-contrast coronagraphic imaging of the TW Hya disk from JWST/NIRCam across four filters (F187N, F200W, F356W, and F444W). We detect the disk's scattered-light emission in F200W, F356W, and F444W. An elliptical fit to the disk image yields an average inclination of $i = 8.74^{+1.03}_{-0.94}$ degrees and a position angle of $\mathrm{PA} = 75.62^{+7.86}_{-6.56}$ degrees. We find tentative evidence for radial variations in these parameters, a trend consistent with a disk warp. Our companion search yields no new detections, placing the lowest mass limits yet on companions that might be responsible for carving out the dust gap. Assuming no local extinction and a system age of 10 Myr, the F444W data are sensitive to masses down to $\sim 0.4\,M_{\rm Jup}$ at separations of $1$ arcsec ($\sim 60$ AU). Accounting for local disk extinction analogous to the AS 209 system, our limits reach sub-Jupiter masses beyond $2$ arcsec. Furthermore, our analysis provides a detailed view of a previously detected feature in the outer disk at $\sim 120$ AU, confirming its morphology as a distinct bifurcation structure. This feature may indicate the presence of complex substructures arising from dynamical planet-disk interactions. These results demonstrate JWST's ability to characterize the architecture of protoplanetary disks and constrain the properties of forming worlds.

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arXiv2026

COS2035: Extending COS/FUV Operations Through the 2030s

The far-ultraviolet (FUV) detector of the Cosmic Origins Spectrograph (COS) accumulates gain sag where photons land, and without continued mitigation this degradation would render the most used modes unusable. To extend COS FUV operations through the 2030s, the COS team developed the COS2035 strategy, which builds on the existing COS2025 rules with four technical breakthroughs and two new usage policies. First, SPLIT-wavecals decouple wavelength calibration from science exposures and open detector real estate above the Pt-Ne lamp light leak. Second, a hybrid lifetime position (LP) architecture allows different gratings to operate at different LPs simultaneously. Third, the LP-infinity framework removes the dependence on the eight-LP limit in the COS flight software, supported by a new table-based APT and TRANS rules architecture. Fourth, a revised gain-sag flagging method evaluates integrated column count loss against the maximum achievable signal-to-noise (S/N) per mode. The two new usage policies cap per-target S/N at the maximum achievable value set by fixed-pattern noise, and limit any single program to 2\% of the lifetime at any single LP. With LP7 and LP10 enabled in Cycle 33 and LP11 and LP12 in active commissioning for Cycles 34 and 35, the COS2035 strategy positions the FUV channel for continued high productivity through the 2030s.

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arXiv2026

Spectroscopic Monitoring of Metal Lines in Polluted White Dwarfs

The disruption and accretion of planetary material onto white dwarfs is expected to be inherently dynamic and stochastic, potentially driving variability in the accretion rate and therefore the shape and depth of the photospheric metal absorption lines. This paper presents an 18-year optical spectroscopic monitoring campaign of five warm (11,000-23,000K) polluted white dwarfs with sinking timescales of days-months, observed using Magellan/MIKE and SALT/HRS to directly test this prediction. At four of the five systems, no statistically significant variability is detected over baselines of 15-18 years corresponding to hundreds to thousands of diffusion timescales, with inferred accretion rates stable to within 15-30% (1$\sigma$) showing remarkably stable accretion on decadal timescales. This implies that either the processes maintaining the accretion of the disrupted planetary material are stable on the same timescales, or that currently uncharacterized photospheric processes act to smooth observable abundance variations on these timescales. The one exception, WD 0106$-$328, shows statistically significant variability in the 4481A Mg II doublet from the ground-based data. Yet no significant equivalent width or abundance changes are seen between two Hubble Space Telescope ultraviolet spectra taken in 2016 and 2025, despite probing a larger set of transitions. This may imply that the ground-based observations witnessed a stochastic excursion from a stable baseline accretion rate, rather than a sustained change in the bulk accretion rate.

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arXiv2026

From Hubble to HWO: Bridging the Frontier of White Dwarf Exoplanet Science

White dwarf stars, the endpoint of stellar evolution for 97% of stars in our Milky Way, offer a unique and powerful window into the bulk elemental composition of rocky exoplanetary bodies. Up to 50% of single white dwarfs are observed with photospheric metal lines from accreted exoplanetary bodies (called 'polluted' white dwarfs), and spectroscopic observations reveal the bulk composition of this material. High-resolution (R>15,000) UV spectra are essential for detecting many elements present in the material, such as the volatile elements imperative for habitability studies (C, N, O, P, S) and key rock-forming elements required to constrain interior structure (e.g. Fe, Si, Mg, Al, Ni). HST, through its COS and STIS spectrographs, remains the only facility capable of performing this science in the near future. Looking to the next decade, the scientific case for continued HST UV observations of polluted white dwarfs is compelling on three fronts (i) as a standalone to enable the bulk composition of exoplanetary material to be measured in a statistically significant sample, (ii) as essential groundwork for the Habitable Worlds Observatory (HWO), and (iii) in a powerful synergy with JWST, to enable characterization of the bulk mineralogy and bulk elemental composition of exoplanetary material. This white paper argues that continued UV spectroscopic capabilities with HST is a high-return investment for white dwarf and exoplanet science, and preserving and prioritizing HST's UV capabilities through at least 2035 is crucial to maximize the scientific return from HST, JWST, and HWO.

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arXiv2026

The Hubble Advanced Spectral Product (HASP) Program

The Hubble Advanced Spectral Products (HASP) program is designed to robustly coadd Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS) spectra within the Mikulski Archive for Space Telescopes (MAST) in an automated fashion such that coadds are available for new data or archival data with updated calibrations. For each target within a visit or program, HASP employs a meticulous multi-stage filtering process to ensure data quality and creates coadded products for all central wavelengths (CENWAVEs) within specific gratings, as well as combined products using different gratings and instruments. The project also emphasizes making the code accessible to the user community for custom coaddition. As calibrations improve and new data are added to the archive, HASP products are re-created automatically so that they represent the best reduction of a given visit or program. Automated coadditions like those achieved by HASP can significantly enhance the combination of different CENWAVES, increase signal-to-noise ratios, and increase wavelength coverage. These properties make HASP a vital resource for astronomers using archival spectroscopic data from HST.

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arXiv2026

Overview of the New Hubble Spectroscopic Legacy Archive

The new Hubble Spectroscopic Legacy Archive (HSLA) provides coadded spectra of individual targets that have been observed with the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS) over their operating lifetime. HSLA uses data available in the Mikulski Archive for Space Telescopes (MAST). It automatically produces coadds whenever new data become publicly available or when there is newly recalibrated data. HSLA defines individual targets by their associated coordinates, accounting for proper motions, and uses SIMBAD, NED and the Phase II observing proposals to obtain astronomical classifications for each object. Coadded spectra are produced for each observing mode. In the case of COS far-ultraviolet observations there is one coadded spectrum for each lifetime position (LP). Additionally, a spectrum spanning the entire wavelength range covered by the observations is produced by abutting the spectra from a selection of individual modes. For each individual target, HSLA also provides a human-readable metadata file with key information that can be used in searches or for further exploration of the data. The HSLA project also makes the code used for coadding spectra publicly available along with several other tools (using Jupyter notebooks) for custom coaddition required in special cases. In this report we will describe the main components of HSLA and provide a brief description of how the data and metadata can be accessed.

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arXiv2026

The MIRI Excess around Degenerates (MEAD) Survey II: A Probable Planet detected via IR Excess around WD 0644+025

The MIRI Excess Around Degenerates (MEAD) Survey is a cycle 2 JWST program designed to image nearby white dwarfs with MIRI at 10 and 15 microns. This survey targeted 56 white dwarfs within 25 pc to search for mid-infrared excesses, flux deficits from collision-induced absorption, and resolved substellar companions. In this paper we present our analysis of WD 0644+025, an unusually massive white dwarf (0.95 Msun) and the MEAD target exhibiting the most significant mid-infrared excess. The observed JWST MIRI photometry shows a 7.3 sigma excess at 15 microns and a 3.6 sigma excess at 10 microns, which may be associated with either a planetary companion or a circumstellar dust disk. This excess corresponds to a companion mass of 6.8 Mjup (Teff=261 +/- 9 K) with orbital distance <11.8 au, although substantially lower masses are possible if we consider a closely orbiting insolated companion. No spatially resolved sources are detected within 200 au, with contrast curve analysis excluding planets more massive than 2 Mjup beyond ~12 au. Metal pollution is confirmed in both archival Keck HIRES spectra from 1999 and new observations from 2025, with no evidence suggesting the accretion rate has substantially changed over the decades. We explore possible dust disk morphologies to describe the observed IR excess, and find that traditional debris disks struggle to fit our data. WD 0644+025 thus represents a compelling case study in the growing population of white dwarfs with cold infrared excesses, and highlights JWST's ability to probe planetary system remnants inaccessible to prior infrared observatories.

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arXiv2025

JWST/NIRSpec Detects Warm CO Emission in the Terrestrial-Planet Zone of HD 131488

We have obtained a high-resolution, JWST NIRSpec $2.87$ -- $5.14$ $\mu$m spectrum of the debris disk around HD 131488. We discover CO fundamental emission indicating the presence of warm fluorescent gas within $\sim10$ AU of the star. The large discrepancy in CO's vibrational and rotational temperature indicates that CO is out of thermal equilibrium and is excited with UV fluorescence. Our UV fluorescence model gives a best fit of $1150\,$K with an effective temperature of $450$, $332$, and $125\,$K for the warm CO gas kinetic temperature within $0.5$, $1$, and $10\,$AU to the star and a gas vibrational temperature of $8800\,$K. The newly discovered warm CO gas population likely resides between sub-AU scales and $\sim\,10\,$AU, interior to the cold CO reservoir detected beyond $35\,$AU with HST STIS and ALMA. The discovery of warm, fluorescent gas in a debris disk is the first such detection ever made. The detection of warm CO raises the possibility of unseen molecules (H$_2$O, H$_2$, etc) as collisional partners to excite the warm gas. We estimated a lower mass limit for CO of $1.25\times 10^{-7}\text{M}_{\oplus}$, which is $10^{-5}$ of the cold CO mass detected with ALMA and HST. We demonstrate that UV fluorescence emerges as a promising avenue for detecting tenuous gas at $10^{-7}$ Earth-mass level in debris disks with JWST.

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arXiv2025

Follow-up Observations of Candidate White Dwarf Planets with MIRI

We report on second-epoch imaging of two candidate planet-hosting white dwarfs stars, WD2105-82 and WD1202-232. Both stars showed evidence of resolved, planet-mass candidate companions in observations using the MIRI mid-infrared imager on JWST. WD2105-82 also showed evidence of an infrared excess consistent with an unresolved 1.4 Jupiter mass companion with an orbital separation of <4 au. Our second epoch observations confirm that the source of the excess shares common proper motion with the star. The excess is almost certainly due to a companion planet or debris disk. However, neither of the two resolved sources with projected separations of >1" in the first epoch of JWST observations show measurable proper motion and are thus likely faint, unresolved background galaxies. We also search for common proper motion companions out to hundreds of au, but find no evidence of widely separated companions.

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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

Flight masks of the Roman Space Telescope Coronagraph Instrument

Over the past two decades, thousands of confirmed exoplanets have been detected. The next major challenge is to characterize these other worlds and their stellar systems. Much information on the composition and formation of exoplanets and circumstellar debris disks can only be achieved via direct imaging. Direct imaging is challenging because of the small angular separations (< 1 arcsec) and high star-to-planet flux ratios such as ~1e9 for a Jupiter analog or ~1e10 for an Earth analog in the visible. Atmospheric turbulence prohibits reaching such high flux ratios on the ground, so observations must be made above the Earth's atmosphere. The Nancy Grace Roman Space Telescope (Roman), planned to launch in late 2026, will be the first space-based observatory to demonstrate high-contrast imaging with active wavefront control using its Coronagraph Instrument. The instrument's main purpose is to mature the various technologies needed for a future flagship mission to image and characterize Earth-like exoplanets. These technologies include two high-actuator-count deformable mirrors, photon-counting detectors, two complementary wavefront sensing and control loops, and two different coronagraph types. In this paper, we describe the complete set of flight masks in the Roman Coronagraph Instrument, their intended combinations, and how they were laid out, fabricated, and measured.

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arXiv2025

Exozodiacal dust as a limitation to exoplanet imaging and spectroscopy

In addition to planets and other small bodies, stellar systems will likely also host exozodiacal dust, or exozodi. This warm dust primarily resides in or near the habitable zone of a star, and scatters stellar light in visible to NIR wavelengths, possibly acting as a spatially inhomogeneous fog that can impede our ability to detect and characterize Earth-like exoplanets. By improving our knowledge of exozodi in the near term with strategic precursor observations and model development, we may be able to mitigate these effects to support a future search for signs of habitability and life with a direct imaging mission. This white paper introduces exozodi, summarizes its impact on directly imaging Earth-like exoplanets, and outlines several key knowledge gaps and near-term solutions to maximize the science return of future observations.

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arXiv2024

The MIRI Exoplanets Orbiting White Dwarfs (MEOW) Survey: Mid-Infrared Excess Reveals a Giant Planet Candidate around a Nearby White Dwarf

The MIRI Exoplanets Orbiting White dwarfs (MEOW) Survey is a cycle 2 JWST program to search for exoplanets around dozens of nearby white dwarfs via infrared excess and direct imaging. In this paper, we present the detection of mid-infrared excess at 18 and 21 microns towards the bright (V = 11.4) metal-polluted white dwarf WD 0310-688. The source of the IR excess is almost certainly within the system; the probability of background contamination is $<0.1\%$. While the IR excess could be due to an unprecedentedly small and cold debris disk, it is best explained by a $3.0^{+5.5}_{-1.9}$ M$_{\rm Jup}$ cold (248$^{+84}_{-61}$ K) giant planet orbiting the white dwarf within the forbidden zone (the region where planets are expected to be destroyed during the star's red giant phase). We constrain the source of the IR excess to an orbital separation of 0.1-2 AU, marking the first discovery of a white dwarf planet candidate within this range of separations. WD 0310-688 is a young remnant of an A or late B-type star, and at just 10.4 pc it is now the closest white dwarf with a known planet candidate. Future JWST observations could distinguish the two scenarios by either detecting or ruling out spectral features indicative of a planet atmosphere.

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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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arXiv2024

JWST Directly Images Giant Planet Candidates Around Two Metal-Polluted White Dwarf Stars

We report the discovery of two directly imaged, giant planet candidates orbiting the metal-rich DAZ white dwarfs WD 1202-232 and WD 2105-82. JWST's Mid-Infrared Instrument (MIRI) data on these two stars show a nearby resolved source at a projected separation of 11.47 and 34.62 au, respectively. Assuming the planets formed at the same time as their host stars, with total ages of 5.3 and 1.6Gyr, the MIRI photometry is consistent with giant planets with masses about 1-7 Jupiter Masses. The probability of both candidates being false positives due to red background sources is approximately 1 in 3000. If confirmed, these would be the first directly imaged planets that are similar in both age and separation to the giant planets in our own solar system, and they would demonstrate that widely separated giant planets like Jupiter survive stellar evolution. Giant planet perturbers are widely used to explain the tidal disruption of asteroids around metal-polluted white dwarfs. Confirmation of these two planet candidates with future MIRI imaging would provide evidence that directly links giant planets to metal pollution in white dwarf stars.

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arXiv2023

A MIRI Search for Planets and Dust Around WD 2149+02

The launch of JWST has ushered in a new era of high precision infrared astronomy, allowing us to probe nearby white dwarfs for cold dust, exoplanets, and tidally heated exomoons. While previous searches for these exoplanets have successfully ruled out companions as small as 7-10 Jupiter masses, no instrument prior to JWST has been sensitive to the likely more common sub-Jovian mass planets around white dwarfs. In this paper, we present the first multi-band photometry (F560W, F770W, F1500W, F2100W) taken of WD 2149+021 with the Mid-Infrared Instrument (MIRI) on JWST. After a careful search for both resolved and unresolved planets, we do not identify any compelling candidates around WD 2149+021. Our analysis indicates that we are sensitive to companions as small as ~0.34 MJup outwards of 1."263 (28.3 au) and ~0.64 MJup at the innermost working angle (0."654, 14.7 au) with 5 sigma confidence, placing significant constraints on any undetected companions around this white dwarf. The results of these observations emphasize the exciting future of sub-Jovian planet detection limits by JWST, which can begin to constrain how often these planets survive their host stars evolution.

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arXiv2023

WD0141-675: A case study on how to follow-up astrometric planet candidates around white dwarfs

This work combines spectroscopic and photometric data of the polluted white dwarf WD0141-675 which has a now retracted astrometric super-Jupiter candidate and investigates the most promising ways to confirm Gaia astrometric planetary candidates and obtain follow-up data. Obtaining precise radial velocity measurement for white dwarfs is challenging due to their intrinsic faint magnitudes, lack of spectral absorption lines, and broad spectral features. However, dedicated radial velocity campaigns are capable of confirming close in giant exoplanets (a few M$_{\textrm{Jup}}$) around polluted white dwarfs, where additional metal lines aid radial velocity measurements. Infrared emission from these giant exoplanets is shown to be detectable with JWST MIRI and will provide constraints on the formation of the planet. Using the initial Gaia astrometric solution for WD0141-675 as a case study, if there were a planet with a 33.65 d period or less with a nearly edge on orbit, 1) ground-based radial velocity monitoring limits the mass to $<$ 15.4 M$_{\textrm{Jup}}$, and 2) space-based infrared photometry shows a lack of infrared excess and in a cloud-free planetary cooling scenario, a sub-stellar companion would have to be $<$ 16 M$_{\textrm{Jup}}$ and be older than 3.7 Gyr. These results demonstrate how radial velocities and infrared photometry can probe the mass of the objects producing some of the astrometric signals, and rule out parts of the brown dwarf and planet mass parameter space. Therefore, combining astrometric data with spectroscopic and photometric data is crucial to both confirm, and characterise astrometric planet candidates around white dwarfs.

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arXiv2023

NMF-based GPU accelerated coronagraphy pipeline

We present a generalized Non-negative factorization (NMF)-based data reduction pipeline for circumstellar disk and exoplanet detection. By using an adaptable pre-processing routine that applies algorithmic masks and corrections to improper data, we are able to easily offload the computationally-intensive NMF algorithm to a graphics processing unit (GPU), significantly increasing computational efficiency. NMF has been shown to better preserve disk structural features compared to other post-processing approaches and has demonstrated improvements in the analysis of archival data. The adaptive pre-processing routine of this pipeline, which automatically aligns and applies image corrections to the raw data, is shown to significantly improve chromatic halo suppression. Utilizing HST-STIS and JWST-MIRI coronagraphic datasets, we demonstrate a factor of five increase in real-time computational efficiency by using GPUs to perform NMF compared to using CPUs. Additionally, we demonstrate the usefulness of higher numbers of NMF components with SNR and contrast improvements, which necessitates the use of a more computationally efficient approach for data reduction.

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