arXiv subjects

Nicholas P. Ballering

Publications and source records attributed to Nicholas P. Ballering.

At least 19 recordsLinked to original sources

arXiv2026

Nascent Embedded-protostar Survey in Taurus (NEST) I: Protostellar Multiplicity

We present new ALMA 0.9 mm and VLA 9 mm observations in the Taurus Molecular Cloud (TMC) of 25 protostellar systems, containing 40 protostars, observed at 0.3" (~20 au) resolution. Within separations of 18-10,000 au, the ALMA/VLA-observed Taurus sample has a multiplicity fraction (MF), defined as the fraction of systems with at least one companion, of 0.50 +/- 0.07, and a companion fraction (CF), defined as the average number of companions per system, of 0.58 +/- 0.20. To build a more complete census of protostellar multiplicity in this region, we supplement the observed sample with 24 protostars (12 protostellar systems and 5 additional companions associated with systems we observed) previously identified through archival infrared or ALMA observations. Together, these 64 individual protostars (37 systems) define our Taurus+ sample, for which we measure higher values of 0.53 +/- 0.06 and 0.72 +/- 0.19 for the MF and CF, respectively. These multiplicity statistics in the TMC are notably higher than those reported in the more clustered star-forming regions of Orion and Perseus at the ~3-4 sigma level, suggesting that Taurus may preserve a larger fraction of primordial multiples. The separation distributions in our samples show populations of both close and wide multiples, but a deficit at intermediate separations of 200-300 au. This pattern may suggest two distinct formation pathways: close binaries (<200 au) arising primarily from disk fragmentation, and wide multiples (>1000 au) from core fragmentation.

astro-ph.SR↗

arXiv2026

Nascent Embedded-protostar Survey in Taurus (NEST) II: Measuring Dust Mass, Disk Size, and Gas Mass

Envelope-embedded protostellar disks represent the earliest stage of protoplanetary disk evolution, but their masses and sizes are difficult to measure because disk emission is entangled with the envelope. We analyze 26 protostellar disk systems in Taurus using ALMA Band 7 (345 GHz; ~0.3'') and VLA Ka-band (33 GHz; ~0.2'') continuum observations, together with molecular-line data to constrain disk gas masses. At 345 GHz, the median flux density, dust mass, and radius are 71 mJy, 5.5 M_Mearth, and 28 AU, with 68% ranges of 54-107 mJy, 3.9-9.4 M_Mearth, and 25-39 AU. At 33 GHz, the corresponding medians are 0.43 mJy, 39 M_Mearth, and 32 AU, with ranges of 0.41-0.80 mJy, 34-52 M_Mearth, and 29-33 AU. Taurus Class I disks are fainter and less massive than those in Orion, comparable to Perseus Class I disks but fainter than Perseus Class 0 disks, and brighter and more massive than those in Ophiuchus. Within Taurus, Class 0/I disks are brighter than Class II disks at both frequencies, although their inferred dust masses are comparable at 345 GHz and slightly higher at 33 GHz. Radiative-transfer modeling of CO isotopologue emission yields a median gas mass of 6.7 x 10^-4 M_Msun. The resulting CO-inferred gas-to-dust ratios span a broad range, with a mean of 147 +/- 75, a median of 26, and a 16th-84th percentile range of 8-147. This distribution overlaps the Taurus Class II population at the low end and ISM-like or higher values, including the AGE-PRO Ophiuchus Class 0/I population, at the high end.

astro-ph.SR↗

arXiv2026

Extreme Debris Disks: Insights into Violent Collisions in Planet Formation and Destruction

Debris disks are dusty structures around mature stars, primarily identified by infrared excesses in the stellar spectra. A subset, known as extreme debris disks (EDDs), exhibits stochastic infrared variability, believed to result from large-scale violent collisions that contribute to the formation or destruction of rocky planetary bodies. We analyze JWST and Spitzer mid-infrared spectra for 21 EDDs to investigate the connection between impact-produced dust mineralogy and the age and dynamical state of these systems during various stages of planet formation and evolution. Our findings indicate that EDDs contain significantly more optically thin, small dust grains compared to those typically seen in protoplanetary and debris disks. Predominantly submicron in size, these grains are thermally altered, as shown by their high levels of silica and crystalline silicate composition. Along with stochastic infrared variability, these features define EDDs as a subclass of debris systems where dust is generated from large collisions between Moon- and Mars-sized bodies. Our results not only provide diagnostic information about the physical conditions of violent events during terrestrial planet formation, aiding in differentiating the complex outcomes of these impacts, but also offer a potential marker for identifying planetary systems experiencing dynamical instability.

astro-ph.EP↗

arXiv2026

Protoplanetary disk cavities with JWST-MIRI: a dichotomy in molecular emission

The evolution of planet-forming regions in protoplanetary disks is of fundamental importance to understanding planet formation. Disks with a central deficit in dust emission, a "cavity", have long attracted interest as potential evidence for advanced disk clearing by protoplanets and/or winds. Before JWST, infrared spectra showed that these disks typically lack the strong molecular emission observed in full disks. In this work, we combine a sample of 12 disks with millimeter cavities of a range of sizes ($\sim2$-70 au) and different levels of millimeter and infrared continuum deficits. We analyze their molecular spectra as observed with MIRI on JWST, homogeneously reduced with the new JDISCS pipeline. This analysis demonstrates a stark dichotomy in molecular emission where "molecule-rich" (MR) cavities follow global trends between water, CO, and OH luminosity and accretion luminosity as in full disks, while "molecule-poor" (MP) cavities are significantly sub-luminous in all molecules except sometimes OH. Disk cavities generally show sub-luminous organic emission, higher OH/H$_2$O ratios, and suggest a lower water column density. The sub-thermal excitation of CO and water vibrational lines suggests a decreased gas density in the emitting layer in all cavities, supporting model expectations for C$_2$H$_2$ photodissociation. We discover a bifurcation in infrared index (lower in MR cavities) suggesting that the molecular dichotomy is linked to residual $μ$m-size dust within millimeter disk cavities. Put together, these results suggest a feedback process between dust depletion, gas density decrease, and molecule dissociation. Disk cavities may have a common evolutionary sequence where MR switch into MP over time.

astro-ph.EP↗

arXiv2025

Silicate mineralogy and bulk composition of exoplanetary material in polluted white dwarfs

White dwarf planetary systems uniquely link the bulk elemental composition of exoplanetary material to the mineralogy as photospheric abundances can be compared to circumstellar dust mineralogy. This study re-examines Spitzer/IRS spectra of eight white dwarfs with both circumstellar dust and photospheric metals. All systems show 10$μ$m silicate emission features consistent with a mixture of olivine and pyroxene silicates, with varying dominance. New Hubble Space Telescope ultraviolet spectroscopic observations of two of these systems, GD56 and WD1150-153, reveal that both are accreting dry, rocky material. WD1150-153 is accreting material consistent with Bulk Earth, while GD56 is accreting core-rich material with an inferred core mass fraction of 0.59$^{+0.08}_{-0.09}$ (0.37$^{+0.08}_{-0.08}$ by mole). A comparison between the bulk elemental composition of the accreted planetary material and the dust mineralogy of the eight systems reveals a tentative correlation between the dominant silicate mineralogy and the Mg/Si ratio, indicating that the circumstellar and photospheric material are compositionally similar. This suggests that rapid and well-mixed accretion is occurring with minimal compositional alteration. Furthermore, new GGCHEM equilibrium chemistry models confirm that Mg-rich planetary material preferentially forms olivine-rich dust, highlighting the importance of equilibrium in planetary chemistry and that a host star or rock's Mg/Si can be used to predict whether its silicate mineralogy is olivine- or pyroxene-dominated, influencing its capacity to structurally store water, recycle key nutrients, and possibly habitability.

astro-ph.EP↗

arXiv2025

The past, present and future of observations of externally irradiated disks

Recent years have seen a surge of interest in the community studying the effect of ultraviolet radiation environment, predominantly set by OB stars, on protoplanetary disc evolution and planet formation. This is important because a significant fraction of planetary systems, potentially including our own, formed in close proximity to OB stars. This is a rapidly developing field, with a broad range of observations across many regions recently obtained or recently scheduled. In this paper, stimulated by a series of workshops on the topic, we take stock of the current and upcoming observations. We discuss how the community can build on this recent success with future observations to make progress in answering the big questions of the field, with the broad goal of disentangling how external photoevaporation contributes to shaping the observed (exo)planet population. Both existing and future instruments offer numerous opportunities to make progress towards this goal.

astro-ph.SR↗

arXiv2025

Discovery of Radio Recombination Lines from Proplyds in the Orion Nebula Cluster

We present new Atacama Large Millimeter/submillimeter Array observations that, for the first time, detect hydrogen and helium radio recombination lines from a protoplanetary disk. We imaged the Orion Nebula Cluster at 3.1 mm with a spectral setup that covered the $n=42 \rightarrow 41$ transitions of hydrogen (H41$α$) and helium (He41$α$). The unprecedented sensitivity of these observations enables us to search for radio recombination lines toward the positions of ${\sim}200$ protoplanetary disks. We detect H41$α$ from 17 disks, all of which are HST-identified `proplyds.' The detected H41$α$ emission is spatially coincident with the locations of proplyd ionization fronts, indicating that proplyd H41$α$ emission is produced by gas that has been photoevaporated off the disk and ionized by UV radiation from massive stars. We measure the fluxes and widths of the detected H41$α$ lines and find line fluxes of ${\sim}30-800$ mJy km s$^{-1}$ and line widths of ${\sim}30-90$ km s$^{-1}$. The derived line widths indicate that the broadening of proplyd H41$α$ emission is dominated by outflowing gas motions associated with external photoevaporation. The derived line fluxes, when compared with measurements of 3.1 mm free-free flux, imply that the ionization fronts of H41$α$-detected proplyds have electron temperatures of ${\sim}6,000-11,000$ K and electron densities of ${\sim}10^6-10^7$ cm$^{-3}$. Finally, we detect He41$α$ towards one H41$α$-detected source and find evidence that this system is helium-rich. Our study demonstrates that radio recombination lines are readily detectable in ionized photoevaporating disks, providing a new way to measure disk properties in clustered star-forming regions.

astro-ph.EP↗

arXiv2025

Water Ice in the Edge-On Orion Silhouette Disk 114--426 from JWST NIRCam Images

We examine images of the protoplanetary disk 114--426 with JWST/NIRCam in 12 bands. This large disk is oriented edge-on with a dark midplane flanked by lobes of scattered light. The outer edges of the midplane are seen in silhouette against the Orion Nebula, providing a unique opportunity to study planet-forming material in absorption. We discover a dip in the scattered light of the disk at 3\,$\micron$ -- compelling evidence for the presence of water ice. The 3\,$\micron$ dip is also seen in the silhouette of the disk, where we quantify the ice abundance with models of pure absorption and avoid the complications of disk scattering effects. We find grain ice-to-refractory mass ratios of up to $\sim$0.2, maximum grain sizes of 0.25 to 5\,$\micron$, and a total dust plus ice mass of 0.46\,$M_\oplus$ in the silhouette region. We also discover excess absorption in the NIRCam bands that include the Paschen $α$ line, suggesting there may be excited atomic hydrogen in the disk. Examining the morphology of the scattered light lobes reveals that they are laterally offset from each other and exhibit a brightness asymmetry that flips with wavelength -- both evidence for a tilted inner disk in this system.

astro-ph.EP↗

arXiv2024

Deep Search for a scattered light dust halo around Vega with the Hubble Space Telescope

We present a provisory scattered light detection of the Vega debris disk using deep Hubble Space Telescope coronagraphy (PID 16666). At only 7.7 parsecs, Vega is immensely important in debris disk studies both for its prominence and also because it allows the highest physical resolution among all debris systems relative to temperature zones around the star. We employ the STIS coronagraph's widest wedge position and classical Reference Differential Imaging to achieve among the lowest surface brightness sensitivities to date ($\sim 4\,μJy/arcsec^{2}$) at wide separations using 32 orbits in Cycle 29. We detect a halo extending from the inner edge of our effective inner working angle at $10^{\prime\prime}.5$ out to the photon noise floor at $30^{\prime\prime}$ (80 - 230 au). The face-on orientation of the system and the lack of a perfectly color-matched PSF star have provided significant challenges to the reductions, particularly regarding artifacts from the imperfect color matching. However, we find that a halo of small dust grains provides the best explanation for the observed signal. Unlike Fomalhaut (a close twin to Vega in luminosity, distance, and age), there is no clear distinction in scattered light between the parent planetesimal belt observed with ALMA and the extended dust halo. These HST observations complement JWST GTO Cycle 1 observations of the system with NIRCam and MIRI.

astro-ph.EP↗

arXiv2024

High-contrast JWST-MIRI spectroscopy of planet-forming disks for the JDISC Survey

The JWST Disk Infrared Spectral Chemistry Survey (JDISCS) aims to understand the evolution of the chemistry of inner protoplanetary disks using the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST). With a growing sample of >30 disks, the survey implements a custom method to calibrate the MIRI Medium Resolution Spectrometer (MRS) to contrasts of better than 1:300 across its 4.9-28 micron spectral range. This is achieved using observations of Themis-family asteroids as precise empirical reference sources. High spectral contrast enables precise retrievals of physical parameters, searches for rare molecular species and isotopologues, and constraints on the inventories of carbon- and nitrogen-bearing species. JDISCS also offers significant improvements to the MRS wavelength and resolving power calibration. We describe the JDISCS calibrated data and demonstrate its quality using observations of the disk around the solar-mass young star FZ Tau. The FZ Tau MIRI spectrum is dominated by strong emission from warm water vapor. We show that the water and CO line emission originates from the disk surface and traces a range of gas temperatures of ~500-1500 K. We retrieve parameters for the observed CO and H2O lines, and show that they are consistent with a radial distribution represented by two temperature components. A high water abundance of n(H2O)~10^-4 fills the disk surface at least out to the 350 K isotherm at 1.5 au. We search the FZ Tau environs for extended emission detecting a large (radius of ~300 au) ring of emission from H2 gas surrounding FZ Tau, and discuss its origin.

astro-ph.EP↗

arXiv2023

Water-Rich Disks around Late M-stars Unveiled: Exploring the Remarkable Case of Sz114

We present an analysis of the JDISC JWST/MIRI-MRS spectrum of Sz~114, an accreting M5 star surrounded by a large dust disk with a shallow gap at $\sim 39$ au. The spectrum is molecular-rich: we report the detection of water, CO, CO$_2$, HCN, C$_2$H$_2$, and H$_2$. The only identified atomic/ionic transition is from [NeII] at 12.81 micron. A distinct feature of this spectrum is the forest of water lines with the 17.22 micron emission surpassing that of most mid-to-late M-star disks by an order of magnitude in flux and aligning instead with disks of earlier-type stars. Moreover, flux ratios of C$_2$H$_2$/H$_2$O and HCN/H$_2$O in Sz~114 also resemble those of earlier-type disks, with a slightly elevated CO$_2$/H$_2$O ratio. While accretional heating can boost all infrared lines, the unusual properties of Sz~114 could be explained by the young age of the source, its formation under unusual initial conditions (a large massive disk), and the presence of dust substructures. The latter delays the inward drift of icy pebbles and help preserve a lower C/O ratio over an extended period. In contrast, mid-to-late M-star disks--which are typically faint, small in size, and likely lack significant substructures--may have more quickly depleted the outer icy reservoir and already evolved out of a water-rich inner disk phase. Our findings underscore the unexpected diversity within mid-infrared spectra of mid-to-late M-star disks, highlighting the need to expand the observational sample for a comprehensive understanding of their variations and thoroughly test pebble drift and planet formation models.

astro-ph.EP↗

arXiv2023

Isolating Dust and Free-Free Emission in ONC Proplyds with ALMA Band 3 Observations

The Orion Nebula Cluster (ONC) hosts protoplanetary disks experiencing external photoevaporation by the cluster's intense UV field. These ``proplyds" are comprised of a disk surrounded by an ionization front. We present ALMA Band 3 (3.1 mm) continuum observations of 12 proplyds. Thermal emission from the dust disks and free-free emission from the ionization fronts are both detected, and the high-resolution (0.057") of the observations allows us to spatially isolate these two components. The morphology is unique compared to images at shorter (sub)millimeter wavelengths, which only detect the disks, and images at longer centimeter wavelengths, which only detect the ionization fronts. The disks are small ($r_d$ = 6.4--38 au), likely due to truncation by ongoing photoevaporation. They have low spectral indices ($α\lesssim 2.1$) measured between Bands 7 and 3, suggesting the dust emission is optically thick. They harbor tens of Earth masses of dust as computed from the millimeter flux using the standard method, although their true masses may be larger due to the high optical depth. We derive their photoevaporative mass-loss rates in two ways: first, by invoking ionization equilibrium, and second using the brightness of the free-free emission to compute the density of the outflow. We find decent agreement between these measurements and $\dot M$ = 0.6--18.4 $\times$ 10$^{-7}$ $M_\odot$ yr$^{-1}$. The photoevaporation timescales are generally shorter than the $\sim$1 Myr age of the ONC, underscoring the known ``proplyd lifetime problem." Disk masses that are underestimated due to being optically thick remains one explanation to ease this discrepancy.

astro-ph.EP↗

arXiv2022

The Geometry of the G29-38 White Dwarf Dust Disk from Radiative Transfer Modeling

Many white dwarfs host disks of dust produced by disintegrating planetesimals and revealed by infrared excesses. The disk around G29-38 was the first to be discovered and is now well-observed, yet we lack a cohesive picture of its geometry and dust properties. Here we model the G29-38 disk for the first time using radiative transfer calculations that account for radial and vertical temperature and optical depth gradients. We arrive at a set of models that can match the available infrared measurements well, although they overpredict the width of the 10 $μm$ silicate feature. The resulting set of models has a disk inner edge located at 92-100 $R_\text{WD}$ (where $R_\text{WD}$ is the white dwarf radius). This is farther from the star than inferred by previous modeling efforts due to the presence of a directly illuminated front edge to the disk. The radial width of the disk is narrow ($\leq$10 $R_\text{WD}$); such a feature could be explained by inefficient spreading or the proximity of the tidal disruption radius to the sublimation radius. The models have a half-opening angle of $\geq$1.4$^\circ$. Such structure would be in strong contradiction with the commonly employed flat-disk model analogous to the rings of Saturn, and in line with the vertical structure of main-sequence debris disks. Our results are consistent with the idea that disks are collisionally active and continuously fed with new material, rather than evolving passively after the disintegration of a single planetesimal.

astro-ph.EP↗

arXiv2021

Simulating Observations of Ices in Protoplanetary Disks

Ices are an important constituent of protoplanetary disks. New observational facilities, notably the James Webb Space Telescope (JWST), will greatly enhance our view of disk ices by measuring their infrared spectral features. We present a suite of models to complement these upcoming observations. Our models use a kinetics-based gas-grain chemical evolution code to simulate the distribution of ices in a disk, followed by a radiative transfer code using a subset of key ice species to simulate the observations. We present models reflecting both molecular inheritance and chemical reset initial conditions. We find that near-to-mid-IR absorption features of H$_2$O, CO$_2$, and CH$_3$OH are readily observable in disk-integrated spectra of highly inclined disks while CO, NH$_3$, and CH$_4$ ice do not show prominent features. CH$_3$OH ice has low abundance and is not observable in the reset model, making this species an excellent diagnostic of initial chemical conditions. CO$_2$ ice features exhibit the greatest change over disk lifetime, decreasing and increasing for the inheritance and reset models, respectively. Spatially resolved spectra of edge-on disks, possible with JWST's integral field unit observing modes, are ideal for constraining the vertical distribution of ices and may be able to isolate features from ices closer to the midplane (e.g., CO) given sufficient sensitivity. Spatially-resolved spectra of face-on disks can trace scattered-light features from H$_2$O, CO$_2$, and CH$_3$OH, plus CO and CH$_4$ from the outermost regions. We additionally simulate far-IR H$_2$O ice emission features and find they are strongest for disks viewed face-on.

astro-ph.EP↗

arXiv2021

Small Protoplanetary Disks in the Orion Nebula Cluster and OMC1 with ALMA

The Orion Nebula Cluster (ONC) is the nearest dense star-forming region at $\sim$400 pc away, making it an ideal target to study the impact of high stellar density and proximity to massive stars (the Trapezium) on protoplanetary disk evolution. The OMC1 molecular cloud is a region of high extinction situated behind the Trapezium in which actively forming stars are shielded from the Trapezium's strong radiation. In this work, we survey disks at high resolution with ALMA at three wavelengths with resolutions of 0.095\arcsec (3 mm; Band 3), 0.048\arcsec (1.3 mm; Band 6), and 0.030\arcsec (0.85 mm; Band 7) centered on radio Source I. We detect 127 sources, including 15 new sources that have not previously been detected at any wavelength. 72 sources are spatially resolved at 3 mm, with sizes from $\sim$8 - 100 AU. We classify 76 infrared-detected sources as foreground ONC disks and the remainder as embedded OMC1 disks. The two samples have similar disk sizes, but the OMC1 sources have a dense and centrally concentrated spatial distribution, indicating they may constitute a spatially distinct subcluster. We find smaller disk sizes and a lack of large (>75 AU) disks in both our samples compared to other nearby star-forming regions, indicating that environmental disk truncation processes are significant. While photoevaporation from nearby massive Trapezium stars may account for the smaller disks in the ONC, the embedded sources in OMC1 are hidden from this radiation and thus must truncated by some other mechanism, possibly dynamical truncation or accretion-driven contraction.

astro-ph.GA↗

arXiv2019

Protoplanetary Disk Masses from Radiative Transfer Modeling: A Case Study in Taurus

Measuring the masses of protoplanetary disks is crucial for understanding their planet-forming potential. Typically, dust masses are derived from (sub-)millimeter flux density measurements plus assumptions for the opacity, temperature, and optical depth of the dust. Here we use radiative transfer models to quantify the validity of these assumptions with the aim of improving the accuracy of disk dust mass measurements. We first carry out a controlled exploration of disk parameter space. We find that the disk temperature is a strong function of disk size, while the optical depth depends on both disk size and dust mass. The millimeter-wavelength spectral index can be significantly shallower than the naive expectation due to a combination of optical depth and deviations from the Rayleigh-Jeans regime. We fit radiative transfer models to the spectral energy distributions (SEDs) of 132 disks in the Taurus-Auriga region using a Markov chain Monte Carlo approach. We used all available data to produce the most complete SEDs used in any extant modeling study. We perform the fitting twice: first with unconstrained disk sizes and again imposing the disk size--brightness relation inferred for sources in Taurus. This constraint generally forces the disks to be smaller, warmer, and more optically thick. From both sets of fits, we find disks to be $\sim$1--5 times more massive than when derived using (sub-)millimeter measurements and common assumptions. With the uncertainties derived from our model fitting, the previously measured dust mass--stellar mass correlation is present in our study but only significant at the 2$σ$ level.

astro-ph.EP↗

arXiv2017

What Sets the Radial Locations of Warm Debris Disks?

The architectures of debris disks encode the history of planet formation in these systems. Studies of debris disks via their spectral energy distributions (SEDs) have found infrared excesses arising from cold dust, warm dust, or a combination of the two. The cold outer belts of many systems have been imaged, facilitating their study in great detail. Far less is known about the warm components, including the origin of the dust. The regularity of the disk temperatures indicates an underlying structure that may be linked to the water snow line. If the dust is generated from collisions in an exo-asteroid belt, the dust will likely trace the location of the water snow line in the primordial protoplanetary disk where planetesimal growth was enhanced. If instead the warm dust arises from the inward transport from a reservoir of icy material farther out in the system, the dust location is expected to be set by the current snow line. We analyze the SEDs of a large sample of debris disks with warm components. We find that warm components in single-component systems (those without detectable cold components) follow the primordial snow line rather than the current snow line, so they likely arise from exo-asteroid belts. While the locations of many warm components in two-component systems are also consistent with the primordial snow line, there is more diversity among these systems, suggesting additional effects play a role.

astro-ph.EP↗

arXiv2017

The Inner 25 AU Debris Distribution in the epsilon Eri System

Debris disk morphology is wavelength dependent due to the wide range of particle sizes and size-dependent dynamics influenced by various forces. Resolved images of nearby debris disks reveal complex disk structures that are difficult to distinguish from their spectral energy distributions. Therefore, multi-wavelength resolved images of nearby debris systems provide an essential foundation to understand the intricate interplay between collisional, gravitational, and radiative forces that govern debris disk structures. We present the SOFIA 35 um resolved disk image of epsilon Eri, the closest debris disk around a star similar to the early Sun. Combining with the Spitzer resolved image at 24 um and 15-38 um excess spectrum, we examine two proposed origins of the inner debris in epsilon Eri: (1) in-situ planetesimal belt(s) and (2) dragged-in grains from the cold outer belt. We find that the presence of in-situ dust-producing planetesmial belt(s) is the most likely source of the excess emission in the inner 25 au region. Although a small amount of dragged-in grains from the cold belt could contribute to the excess emission in the inner region, the resolution of the SOFIA data is high enough to rule out the possibility that the entire inner warm excess results from dragged-in grains, but not enough to distinguish one broad inner disk from two narrow belts.

astro-ph.SR↗