arXiv subjects

Leon Trapman

Publications and source records attributed to Leon Trapman.

At least 19 recordsLinked to original sources

arXiv2026

exoALMA. XXIV. Formaldehyde Emission in Protoplanetary Disks of exoALMA Compared with Their Properties and Dynamical State

The presence of asymmetries and substructures in protoplanetary disks, revealed by both dust and gas emission, highlights the potential interplay and the broader connection between chemistry and dynamics in disk evolution. We explore multiple relationships using the nonparametric Kendall-$\tau$ correlation to examine formaldehyde (H$_2$CO) emission with relation to stellar and disk properties for a subset of disks from the exoALMA sample. We also retrieve the H$_2$CO column density and excitation temperature using four transitions, measured in radial bins of 100 au, and quantify the level of asymmetry in the resolved peak intensity of the H$_2$CO emission. From our correlation analysis, we find no correlations with sufficient statistical significance. However, we identify tentative relationships that can be tested with larger samples. In particular, we report a proposed correlation ($2.1\sigma$) between stellar effective temperature and the formaldehyde excitation conditions, suggesting that, to first order, the central star dominates the nature of the H$_2$CO emission over possible dynamical asymmetries traced by dust. Although a correlation with the stellar luminosity was also expected, a larger sample is required to confirm or refute this trend. A possible correlation with spectral type, together with the broad range of H$_2$CO excitation temperatures within the inner 100 au of the studied disks, hint at possible multiple chemical formation pathways for H$_2$CO, including both gas-phase reactions and ice-surface chemistry on dust grains.

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arXiv2026

Physical and Chemical Characterization of GY 91's Multi-ringed Protostellar Disk with ALMA

GY 91, commonly categorized as a Class I young stellar object, is notable for disk dust substructures that have been hypothesized to trace early planet formation. Using the ALMA 12-m and ACA arrays, we present new Band 7 dust continuum and molecular line observations of GY 91 at an angular resolution of (~40 au). We report detections of CS $J=6-5$, N$_2$H$^+$ $J=3-2$, C$^{18}$O $J=3-2$, H$_2$CS $J_{K_a, K_c} = 8_{1,7}-7_{1,6}$, H$_2$CO $J_{K_a, K_c} = 4_{0,4}-3_{0,3}$, and H$_2$CO $J_{K_a, K_c} = 4_{2,3}-3_{2,2}$, as well as a tentative detection of $^{13}$C$^{18}$O $J=3-2$. We observe azimuthal asymmetry in CS and H$_2$CS emission, as well as radially structured H$_2$CO $4_{0,4}-3_{0,3}$ emission outside the dust continuum. C$^{18}$O and H$_2$CO 4$_{0,4}-3_{0,3}$ show significant cloud contamination, while CS and N$_2$H$^+$ are good tracers of Keplerian rotation originating from the disk. Envelope emission does not appear to contribute significantly either to the continuum or molecular line observations. GY 91's chemical properties appear in large part to resemble those of Class II disks, although observations of additional molecular probes should be obtained for a fuller comparison. With CS, we estimated a dynamical stellar mass of 0.58 $M_\odot$, which is higher than previous estimates from stellar evolutionary models (0.25 $M_\odot$). Using both radiative transfer modeling of the dust continuum and comparison of the C$^{18}$O and N$_2$H$^+$ fluxes to literature thermochemical models, we estimate a disk mass of $\sim0.01$ $M_\odot$.

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arXiv2026

Tracing Pebble Drift History in Two Protoplanetary Disks with CO Enhancement

Pebble drift is an important mechanism for supplying the materials needed to build planets in the inner region of protoplanetary disks. Thus, constraining pebble drift's timescales and mass flux is essential to understanding planet formation history. Current pebble drift models suggest pebble fluxes can be constrained from the enhancement of gaseous volatile abundances when icy pebbles sublimate after drifting across key snowlines. In this work, we present ALMA observations of spatially resolved $^{13}$C$^{18}$O J=2-1 line emission inside the midplane CO snowline of the HD 163296 and MWC 480 protoplanetary disks. We use radiative transfer and thermochemical models to constrain the spatial distribution of CO gas column density. We find that both disks display centrally peaked CO abundance enhancement of up to ten times of ISM abundance levels. For HD 163296 and MWC 480, the inferred enhancements require 250-350 and 480-660 Earth Masses of pebbles to have drifted across their CO snowlines, respectively. These ranges fall within cumulative pebble mass flux ranges to grow gas giants in the interior to the CO snowline. The centrally peaked CO enhancement is unexpected in current pebble drift models, which predict CO enhancement peaks at the CO snowline or is uniform inside the snowline. We propose two hypotheses to explain the centrally-peaked CO enhancement, including a large CO desorption distance and CO trapped in water ice. By testing both hypotheses with the 1D gas and dust evolution code chemcomp, we find that volatile trapping (about 30\%) best reproduces the centrally peaked CO enhancement observed.

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arXiv2025

SMA and NOEMA reveal asymmetric sub-structure in the protoplanetary disk of IRAS23077+6707

We present high-resolution data of IRAS 23077+6707 (`Dracula's Chivito') with the Submillimeter Array (SMA at 1.33 mm/225.5 GHz) and the Northern Extended Millimeter Array (NOEMA at 2.7 mm/111.7 GHz and 3.1 mm/96.2 GHz). IRAS 23077+6707 is a highly-inclined and newly discovered protoplanetary disk, first reported in 2024. We combine SMA baselines from the Compact, Extended and Very Extended arrays, and NOEMA baselines from its A and C configurations, and present continuum images with resolution ${\lesssim}0.8''$, which constitute the first sub-arcsecond resolution maps of IRAS 23077+6707. The images show extended linear emission that spans $5.6{-}6.1''$ as expected for a radially extended, highly-inclined protoplanetary disk. Accompanied with lower resolution data, we show that the disk has a steep spectral index, ranging from $\alpha=3.2{-}3.9$. We present evidence of multiple radial emission peaks and troughs in emission, which may originate in disk rings and a central cavity. We further present evidence that these radial structures are asymmetric; hosting a a significant brightness asymmetry, with emission enhanced by up to 50% in the north versus the south. We discuss hypotheses about the potential origins of these features, including the possibility that IRAS 23077+6707 hosts a rare example of an eccentric protoplanetary disk, which can induce these radially asymmetric structures. We present a simple eccentric continuum model of IRAS 23077+6707, and show for an eccentricity of $e \approx 0.26$, that this can reproduce the bulk morphology of the emission.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): II. Dust and Gas Disk Properties in the Ophiuchus Star-forming Region

The ALMA survey of Gas Evolution in PROtoplanetary disks (AGE-PRO) Large Program aims to trace the evolution of gas disk mass and size throughout the lifetime of protoplanetary disks. This paper presents Band-6 ALMA observations of 10 embedded (Class I and Flat Spectrum) sources in the Ophiuchus molecular cloud, with spectral types ranging from M3 to K6 stars, which serve as the evolutionary starting point in the AGE-PRO sample. While we find 4 nearly edge on disks (>70 deg.), and 3 highly inclined disks (>60 deg.) in our sample, we show that, as a population, embedded disks in Ophiuchus are not significantly contaminated by more evolved, but highly inclined sources. We derived dust disk masses from the Band 6 continuum and estimated gas disk masses from the C18O and C17O lines. The mass estimates from the C17O line are slightly higher, suggesting C18O emission might be partially optically thick. While the 12CO and 13CO lines are severely contaminated by extended emission and self-absorption, the C18O and C17O lines allowed us to trace the radial extent of the gaseous disks. From these measurements, we found that the C18O and C17O fluxes correlate well with each other and with the continuum fluxes. Furthermore, the C18O and C17O lines present a larger radial extension than disk dust sizes by factors ranging from 1.5 to 2.5, as it is found for Class II disks using the radial extension of the 12CO. In addition, we have detected outflows in three disks from 12CO observations.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): V. Protoplanetary gas disk masses

The evolution of the gas mass of planet-forming disks around young stars is crucial for our understanding of planet formation, yet it has proven hard to constrain observationally, due both to the difficulties of measuring gas masses and the lack of a homogeneous sample. Here we present a large grid of thermochemical models which we use to measure protoplanetary gas disk masses of AGE-PRO, the ALMA survey of Gas Evolution in PROtoplanetary disks. AGE-PRO covers a sample of 30 disks around similar spectral type (M3-K6) stars with ages between 0.1 and 10 Myr. Our approach is to simultaneously fit observations of CO isotopologues and N2H+, a complementary molecule produced when CO freezes out. We find that the median gas mass of the three regions decreases over time, from 7.0(+4.4,-2.6)x10^-3 Msun in Ophiuchus (<1 Myr) to 9.4(+5.4,-3.4)x10^-4 Msun for Lupus (~1-3 Myr) and 6.8(+5.1,-2.8)x10^-4 Msun for Upper Sco (~2-6 Myr), with ~1 dex scatter in gas mass in each region. We note that the gas mass distributions for Lupus and Upper Sco look very similar, which could be due to survivorship bias for the latter. The median bulk CO abundance in the CO emitting layer is found to be a factor ~10 lower than the ISM value but does not significantly change between Lupus and Upper Sco. From Lupus to Upper Sco the median gas-to-dust mass ratio increases by a factor ~3 from ~40 to ~120, suggesting efficient inward pebble drift and/or the formation of planetesimals.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): VII. Testing accretion mechanisms from disk population synthesis

The architecture of planetary systems depends on the evolution of the disks in which they form. In this work, we develop a population synthesis approach to interpret the AGE-PRO measurements of disk gas mass and size considering two scenarios: turbulence-driven evolution with photoevaporative winds and MHD disk-wind-driven evolution. A systematic method is proposed to constrain the distribution of disk parameters from the disk fractions, accretion rates, disk gas masses, and CO gas sizes. We find that turbulence-driven accretion with initially compact disks ($R_0 \simeq 5-20~$au), low mass-loss rates, and relatively long viscous timescales ($t_{\nu,0} \simeq 0.4-3~$Myr or $\alpha_{SS} \simeq 2-4 \times 10^{-4}$) can reproduce the disk fraction and gas sizes. However, the distribution of apparent disk lifetime defined as the $M_D/\dot{M}_*$ ratio is severely overestimated by turbulence-driven models. On the other hand, MHD wind-driven accretion can reproduce the bulk properties of the disk populations from Ophiuchus to Upper Sco assuming compact disks with an initial magnetization of about $\beta \simeq 10^5$ ($\alpha_{DW} \simeq 0.5-1 \times 10^{-3}$) and a magnetic field that declines with time. More studies are needed to confirm the low masses found by AGE-PRO, notably for compact disks that question turbulence-driven accretion. The constrained synthetic disk populations can now be used for realistic planet population models to interpret the properties of planetary systems on a statistical basis.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): X. Dust Substructures, Disk Geometries, and Dust-disk Radii

We perform visibility fitting to the dust continuum Band 6 1.3 mm data of the 30 protoplanetary disks in the AGE-PRO ALMA Large Program. We obtain disk geometries, dust-disk radii, and azimuthally symmetric radial profiles of the intensity of the dust continuum emission. We examine the presence of continuum substructures in the AGE-PRO sample by using these radial profiles and their residuals. We detect substructures in 15 out of 30 disks. We report five disks with large ($>$15 au) inner dust cavities. The Ophiuchus Class I disks show dust-disk substructures in $\sim80\%$ of the resolved sources. This evidences the early formation of substructures in protoplanetary disks. A spiral is identified in IRS 63, hinting to gravitational instability in this massive disk. We compare our dust-disk brightness radial profiles with gas-disk brightness radial profiles and discuss colocal substructures in both tracers. In addition, we discuss the evolution of dust-disk radii and substructures across Ophiuchus, Lupus, and Upper Scorpius. We find that disks in Lupus and Upper Scorpius with large inner dust cavities have typical gas-disk masses, suggesting an abundance of dust cavities in these regions. The prevalence of pressure dust traps at later ages is supported by a potential trend with time with more disks with large inner dust cavities (or "transition disks") in Upper Scorpius and the absence of evolution of dust-disk sizes with time in the AGE-PRO sample. We propose this is caused by an evolutionary sequence with a high fraction of protoplanetary disks with inner protoplanets carving dust cavities.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): XI. Beam-corrected gas disk sizes from fitting 12CO moment zero maps

The inward drift of mm-cm sized pebbles in protoplanetary disks has become an important part of our current theories of planet formation and, more recently, planet composition as well. The gas-to-dust size ratio of protoplanetary disks can provide an important constraint on how pebbles have drifted inward provided that observational effects, especially resolution, can be accounted for. Here we present a method for fitting beam-convolved models to integrated intensity maps of line emission using the astropy python package and use it to fit 12 CO moment zero maps of ten Lupus and ten Upper Scorpius protoplanetary disks from the AGE-PRO ALMA Large Program, a sample of disks around M3-K6 stars that cover the ~1 to 6 Myr of gas disk evolution. From the unconvolved best fit models we measure the gas disk size (RCO,90%[model]), which we combine with the dust disk size (Rdust,90%[FRANK]) from continuum visibility fits from Vioque et al. (2025, in press.) to compute beam-corrected gas-to-dust size ratios. In our sample we find gas-to-dust size ratios between ~1 and ~5.5, with a median value of 2.78(+0.37,-0.32). Contrary to models of dust evolution that predict an increasing size ratio with time, we find that the younger disks in Lupus have similar (or even larger) median ratios (3.02(+0.33,-0.33)) than the older disks in Upper Sco (2.46(+0.53,-0.38)). A possible explanation to this discrepancy is that pebble drift is halted in dust traps combined with truncation of the gas disk by external photo-evaporation in Upper Sco, although survivorship bias could also play a role.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): XII. Extreme millimetre variability detected in a Class II disc

Variability of millimetre wavelength continuum emission from Class II protoplanetary disks is extremely rare, and when detected it is usually interpreted as originating from non-thermal emission mechanisms that relate to the host star itself rather than its disk. During observations made as part of the AGE-PRO ALMA Large program, significant variability in the brightness of the 2MASS J16202863-2442087 system was detected between individual executions. We report the observed properties of the variability detected at millimetre wavelengths and investigate potential driving mechanisms. To investigate the nature of the variability we construct a light curve from the continuum observations and analyse imaged constructed from both flaring and quiescent emission. We characterise the dust disk around the star through analysis in the image and visibility plane, and carry out kinematic analysis of the CO(2-1) emission from the gas disk. The continuum flux decays by a factor of 8 in less than an hour, and by a factor of 13 within 8 days. The peak brightness coincides with an expected brightness maximum extrapolated from the periodicity of previously observed optical variability. The flare is most likely the product of synchrotron emission in the close vicinity of the star. The nature of the millimetre flare closely resembles those detected in very close binary systems, and may be due to the interaction of magnetic fields in an as yet undetected binary. Alternatively if the central host is a single-star object, the flare may be due to the interaction of magnetic field loops at the stellar surface or a strong accretion burst.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): VIII. The impact of external photoevaporation on disk masses and radii in Upper Scorpius

Protoplanetary disk evolution can be deeply influenced by the UV radiation emitted by neighboring massive stars (mainly of spectral type O and B). We show that the process of external photoevaporation, which causes an outside-in depletion of disk material due to environmental UV radiation, can lead to a significant decrease in disk size, and moderate in disk mass and lifetime even at moderate irradiation levels (1-10 G$_{0}$). In this work we investigate the role of external photoevaporation in shaping the masses and sizes of the ten AGE-PRO disks in the Upper Scorpius region, which we estimate to be subject to FUV fluxes ranging between 2 and 12 G$_{0}$, on average. We compare the disk masses and sizes resulting from 1D numerical viscous evolution simulations in which the effect of external photoevaporation is included, to the values retrieved from the AGE-PRO observations. While the pure viscous framework fails in adequately explaining the observed disk properties in Upper Scorpius, with the inclusion of external photoevaporation we can successfully reproduce gas disk sizes for 7 out of 10 sources within a factor <2, when the initial disk mass is 1-10% of the stellar mass. We emphasize the importance of accounting for the environmental irradiation when comparing star-forming regions of different ages, even when moderate FUV irradiation fields are experienced, as in the case of Upper Scorpius.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): IV. Dust and Gas Disk Properties in the Upper Scorpius Star-forming Region

The Atacama Large Millimeter/submillimeter Array (ALMA) large program AGE-PRO explores protoplanetary disk evolution by studying gas and dust across various ages. This work focuses on ten evolved disks in Upper Scorpius, observed in dust continuum emission, CO and its isotopologues, and N$_2$H$^+$ with ALMA Bands 6 and 7. Disk radii, from the radial location enclosing 68% of the flux, are comparable to those in the younger Lupus region for both gas and dust tracers. However, solid masses are about an order of magnitude below those in Lupus and Ophiuchus, while the dust spectral index suggests some level of dust evolution. These empirical findings align with a combination of radial drift, dust trapping, and grain growth into larger bodies. A moderate correlation between CO and continuum fluxes suggests a link between gas and dust content, through the increased scatter compared to younger regions, possibly due to age variations, gas-to-dust ratio differences, or CO depletion. Additionally, the correlation between C$^{18}$O and N$_2$H$^+$ fluxes observed in Lupus persists in Upper Sco, indicating a relatively stable CO gas abundance over the Class II stage of disk evolution. In conclusion, the AGE-PRO survey of Upper Scorpius disks reveals intriguing trends in disk evolution. The findings point towards potential gas evolution and the presence of dust traps in these older disks. Future high-resolution observations are needed to confirm these possibilities and further refine our understanding of disk evolution and planet formation in older environments.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): VI. Comparison of Dust Evolution Models to AGE-PRO Observations

The potential for planet formation of a circumstellar disk depends on the dust and gas reservoirs, which evolve as a function of the disk age. The ALMA Large Program AGE-PRO has measured several disk properties across three star-forming regions of different ages, and in this study we compare the observational results to dust evolution simulations. Using DustPy for the dust evolution, and RADMC-3D for the radiative transfer, we ran a large grid of models spanning stellar masses of 0.25, 0.50, 0.75, and 1.0 $M_\odot$, with different initial conditions, including: disk sizes, disk gas masses, and dust-to-gas ratio, and viscosity. Our models are performed assuming smooth, weakly, or strongly substructured disks, aiming to investigate if any observational trend can favor or exclude the presence of dust traps. The observed gas masses in the disks of the AGE-PRO sample are not reproducible with our models, which only consider viscous evolution with constant $\alpha$, suggesting that additional physical mechanisms play a role in the evolution of the gas mass of disks. When comparing the dust continuum emission fluxes and sizes at 1.3 mm, we find that most of the disks in the AGE-PRO sample are consistent with simulations that have either weak or strong dust traps. The evolution of spectral index in the AGE-PRO sample is also suggestive of an unresolved population of dust traps. Future observations at high angular resolution are still needed to test several hypotheses that result from comparing the observations to our simulations, including that more massive disks in gas mass have the potential to form dust traps at larger disk radii.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): III. Dust and Gas Disk Properties in the Lupus Star-forming Region

We present Band 6 and Band 7 observations of 10 Lupus disks around M3-K6 stars from the ALMA survey of Gas Evolution in PROtoplanetary disks (AGE-PRO) Large Program. In addition to continuum emission in both bands, our Band 6 setup covers the $\mathrm{{}^{12}CO}$, $\mathrm{{}^{13}CO}$ and $\mathrm{C^{18}O}\,J$=2-1 lines, while our Band 7 setup covers the $\mathrm{N_2H^+}\,J$=3-2 line. All of our sources are detected in $\mathrm{{}^{12}CO}$ and $\mathrm{{}^{13}CO}$, 7 out of 10 are detected in $\mathrm{C^{18}O}$, and 3 are detected in $\mathrm{N_2H^+}$. We find strong correlations between the CO isotopologue line fluxes and the continuum flux densities. With the exception of one disk, we also identify a strong correlation between the $\mathrm{C^{18}O}\,J$=2-1 and $\mathrm{N_2H^+}\,J$=3-2 fluxes, indicating similar CO abundances across this sample. For the two sources with well-resolved continuum and $\mathrm{{}^{12}CO}\,J$=2-1 images, we find that their gas-to-dust size ratio is consistent with the median value of $\sim 2$ inferred from a larger sample of Lupus disks. We derive dust disk masses from continuum flux densities. We estimate gas disk masses by comparing $\mathrm{C^{18}O}\,J$=2-1 line fluxes with those predicted by the limited grid of self-consistent disk models of Ruaud et al. (2022). A comparison of these mass estimates with those derived by Trapman et al. (2025), using a combination of CO isotopologue and $\mathrm{N_2H^+}$ line emission, shows that the masses are consistent with each other. Some discrepancies appear for small and faint disks, but they are still within the uncertainties. Both methods find gas disk masses increase with dust disk masses, and gas-to-dust mass ratios are between $10-100$ in the AGE-PRO Lupus sample.

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arXiv2025

The ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO): I. Program Overview and Summary of First Results

We present the ALMA Survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO), a Large Program of the Atacama Large Millimeter/submillimeter Array (ALMA). AGE-PRO aims to systematically trace the evolution of gas disk mass and size throughout the lifetime of protoplanetary disks. It uses a carefully selected sample of 30 disks around M3-K6 stars in three nearby star-forming regions: Ophiuchus (0.5-1 Myr), Lupus (1-3 Myr), and Upper Sco (2-6 Myr). Assuming the three regions had similar initial conditions and evolutionary paths, we find the median gas disk mass appears to decrease with age. Ophiuchus disks have the highest median gas mass (6 M$_{\rm Jup}$), while the Lupus and Upper Sco disks have significantly lower median masses (0.68 and 0.44 M$_{\rm Jup}$, respectively). Notably, the gas and dust disk masses appear to evolve on different timescales. This is evidenced by the median gas-to-dust mass ratio, which decreases from 122 in the youngest disks ($<$1 Myr) to 46 in Lupus disks, and then increases to 120 in the Upper Sco disks. The median gas disk sizes range between 74-110 au, suggesting that typical gas disks are much smaller than those of well-studied, massive disks. Population synthesis models suggest that magneto-hydrodynamic wind-driven accretion can reproduce median disk properties across all three regions, when assuming compact disks with a declining magnetic field over time. In contrast, turbulent-driven models overestimate gas masses of $>$1 Myr disks by an order of magnitude. Here we discuss the program's motivation, survey design, sample selection, observation and data calibration processes, and highlight the initial results.

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arXiv2025

ExoALMA XIII. gas masses from N2H+ and C18O: a comparison of protoplanetary gas disk mass measurement techniques

The gas masses of protoplanetary disks are important but elusive quantities. In this work we present new ALMA observations of N2H+ (3-2) for 11 exoALMA disks. N2H+ is a molecule sensitive to CO freeze-out and has recently been shown to significantly improve the accuracy of gas masses estimated from CO line emission. We combine these new observations with archival N2H+ and CO isotopologue observations to measure gas masses for 19 disks, predominantly from the exoALMA Large program. For 15 of these disks the gas mass has also been measured using gas rotation curves. We show that the CO + N2H+ line emission-based gas masses typically agree with the kinematically measured ones within a factor 3 (1-2{\sigma}). Gas disk masses from CO + N2H+ are on average a factor 2.3(+0.7,-1.0) x lower than the kinematic disk masses, which could suggest slightly lower N2 abundances and/or lower midplane ionization rates than typically assumed. Herbig disks are found to have ISM level CO gas abundances based on their CO and N2H+ fluxes, which sets them apart from T-Tauri disks where abundances are typically 3-30x lower. The agreement between CO + N2H+ -based and kinematically measured gas masses is promising and shows that multi-molecule line fluxes are a robust tool to accurately measure disk masses at least for extended disks.

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arXiv2025

Smuggling unnoticed: Towards a 2D view of water and dust delivery to the inner regions of protoplanetary discs

Infrared spectroscopy, e.g., with JWST, provides a glimpse into the chemical inventory of the innermost region of protoplanetary discs, where terrestrial planets eventually form. The chemical make-up of regions inside snowlines is connected to the material drifting from the outer regions, which can be modeled with dust evolution models. However, infrared observations are limited by the high dust extinction in the inner disc, and only probes the abundances of gaseous species in the disc surface layers. As a result, the bulk mass of delivered volatiles is not directly relatable to what is measured through infrared spectra. In this paper, we investigate how the delivery of dust and ice after prolonged pebble drift affects the observable reservoir of water vapor in the inner disc. We develop a 1+1D approach based on dust evolution models to determine the delivery and distribution of vapor compared to the height of the $\tau = 1$ surface in the dust continuum. We find that the observable column density of water vapor at wavelengths probed by JWST spans many orders of magnitude over time, exhibiting different radial profiles depending on dust properties, drift rate, and local processing. In the presence of a traffic-jam effect inside the snowline, the observable vapor reservoir appears constant in time despite the ongoing delivery by pebble drift, such that water is effectively smuggled unnoticed. Differences in measured column densities then originate not only from variations in bulk vapor content, but also from differences in the properties and distribution of dust particles.

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arXiv2024

JWST/MIRI detection of a carbon-rich chemistry in a solar nebula analog

It has been proposed, and confirmed by multiple observations, that disks around low mass stars display a molecule-rich emission and carbon-rich disk chemistry as compared to their hotter, more massive solar counterparts. In this work, we present JWST Disk Infrared Spectral Chemistry Survey (JDISCS) MIRI-MRS observations of the solar-mass star DoAr 33, a low-accretion rate T Tauri star showing an exceptional carbon-rich inner disk. We report detections of H$_2$O, OH, and CO$_2$, as well as the more complex hydrocarbons, C$_2$H$_2$ and C$_4$H$_2$. Through the use of thermochemical models, we explore different spatial distributions of carbon and oxygen across the inner disk and compare the column densities and temperatures obtained from LTE slab model retrievals. We find a best match to the observed column densities with models that have carbon enrichment, and the retrieved emitting temperature and area of C$_2$H$_2$ with models that have C/O $=$ 2$-$4 inside the 500 K carbon-rich dust sublimation line. This suggests that the origin of the carbon-rich chemistry is likely due to the sublimation of carbon rich grains near the soot line. This would be consistent with the presence of dust processing as indicated by the detection of crystalline silicates. We propose that this long-lived hydrocarbon rich chemistry observed around a solar-mass star is a consequence of the unusually low M-star-like accretion rate of the central star, which lengthens the radial mixing timescale of the inner disk allowing the chemistry powered by carbon grain destruction to linger.

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