arXiv subjects

Edwin A. Bergin

Publications and source records attributed to Edwin A. Bergin.

At least 37 records · Page 2Linked to original sources

arXiv2025

Cosmic cascades: How disk substructure regulates the flow of water to inner planetary systems

The influx of icy pebbles to the inner regions of protoplanetary disks constitutes a fundamental ingredient in most planet formation theories. The observational determination of the magnitude of this pebble flux and its dependence on disk substructure (disk gaps as pebble traps) would be a significant step forward. In this work we analyze a sample of 21 T Tauri disks (with ages $\approx 0.5{-}2\mathrm{~Myr}$) using JWST/MIRI spectra homogeneously reduced with the JDISCS pipeline and high-angular-resolution ALMA continuum data. We find that the 1500/6000 K water line flux ratio measured with JWST - a tracer of cold water vapor and pebble drift near the snowline - correlates with the radial location of the innermost dust gap in ALMA continuum observations (ranging from 8.7 to 69 au), confirming predictions from recent models that study connections between the inner and outer disk reservoirs. We develop a population synthesis exploration of pebble drift in gapped disks and find a good match to the observed trend for early and relatively effective gaps, while scenarios where pebble drift happens quickly, gaps are very leaky, or where gaps form late are disfavored on a population level. Inferred snowline pebble mass fluxes (ranging between $10^{-6}$ and $10^{-3}~M_\oplus/\mathrm{yr}$ depending on gap position) are comparable to fluxes used in pebble accretion studies and those proposed for the inner Solar System, while system-to-system variations suggest differences in the emerging planetary system architectures and water budgets.

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arXiv2025

Grand Design Spiral Arms in the Compact, Embedded Protoplanetary Disk of Haro 6-13

Millimeter continuum spiral arms have so far only been detected in a handful of protoplanetary disks, and thus we have a limited understanding of the circumstances in which they can form. In particular, substructures in small disks ($R\lessapprox 50$ au) have not been well-characterized in comparison with large disks. We present ALMA 1.3 mm continuum observations of the disk around the T Tauri star Haro 6-13 at a resolution of $\sim0.04''$ ($\sim5$ au). A pair of low-contrast spiral arms are detected at disk radii from $\sim10-35$ au. They can be approximated as Archimedean spirals with pitch angles ranging from $\sim10-30^\circ$. The low value of the disk-averaged spectral index between 1.3 and 3 mm ($α=2.1$) and the high brightness temperatures suggest that the millimeter continuum is likely optically thick and thus may hide sufficient mass for the disk to become gravitationally unstable and form spiral arms. CO observations have shown that Haro 6-13 is surrounded by an envelope, raising the possibility that infall is facilitating spiral arm formation.

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arXiv2025

The JDISC Survey: Linking the Physics and Chemistry of Inner and Outer Protoplanetary Disk Zones

Mid-infrared spectroscopy of protoplanetary disks provides a chemical inventory of gas within a few au, where planets are readily detected around older stars. With the JWST Disk Infrared Spectral Chemistry Survey (JDISCS), we explore demographic trends among 31 disks observed with MIRI (MRS) and with previous ALMA millimeter continuum imaging at high angular resolution (5-10 au). With these S/N $\sim$200-450 spectra, we report emission from H$_2$O, OH, CO, C$_2$H$_2$, HCN, CO$_2$, [Ne II], [Ne III], and [Ar II]. Emission from H$_2$O, OH and CO is nearly ubiquitous for low-mass stars, and detection rates of all molecules are higher than for similar disks observed with Spitzer-IRS. Slab model fits to the molecular emission lines demonstrate that emission from C$_2$H$_2$, HCN, and possibly CO$_2$ is optically thin; thus since column densities and emitting radii are degenerate, observations are actually sensitive to the total molecular mass. C$_2$H$_2$ and HCN emission also typically originate in a hotter region ($920^{+70}_{-130}$, $820^{+70}_{-130}$ K, respectively) than CO$_2$ ($600^{+200}_{-160}$ K). The HCN to cold H$_2$O luminosity ratios are generally smaller in smooth disks, consistent with more efficient water delivery via icy pebbles in the absence of large dust substructures. The molecular emission line luminosities are also correlated with mass accretion rates and infrared spectral indices, similar to trends reported from Spitzer-IRS surveys. This work demonstrates the power of combining multi-wavelength observations to explore inner disk chemistry as a function of outer disk and stellar properties, which will continue to grow as the sample of observed Class II systems expands in the coming JWST observation cycles.

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arXiv2025

Solar C/O ratio in planet-forming gas at 1 au in a highly irradiated disk

The chemical composition of exoplanets is thought to be influenced by the composition of the disks in which they form. JWST observations have unveiled a variety of species in numerous nearby disks, showing significant variations in the C/O abundance ratio. However, little is known about the composition and C/O ratio of disks around young stars in clusters exposed to strong ultraviolet (UV) radiation from nearby massive stars, which are representative of the environments where most planetary systems form, including ours. We present JWST spectroscopy of d203-504, a young 0.7 $\rm M_{\odot}$ star in the Orion Nebula with a 30 au disk irradiated by nearby massive stars. These observations reveal spectroscopic signatures of CO, H$_2$O, CH$_3^+$, and PAHs. Water and CO are detected in absorption in the inner disk ($r\lesssim 1$ au), where the estimated gas-phase C/O ratio is 0.48, consistent with the Solar value and that of the Orion Nebula. In contrast, \ch{CH3+} and PAHs are found in the extended surface layers of the disk. These results suggest that gas in the inner disk is chemically shielded from UV radiation while the surface layers of the disk experience UV-induced chemistry, potentially depleting their carbon content.

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arXiv2025

Discovery of the 7-ring PAH Cyanocoronene (C$_{24}$H$_{11}$CN) in GOTHAM Observations of TMC-1

We present the synthesis and laboratory rotational spectroscopy of the 7-ring polycyclic aromatic hydrocarbon (PAH) cyanocoronene (C$_{24}$H$_{11}$CN) using a laser-ablation assisted cavity-enhanced Fourier transform microwave spectrometer. A total of 71 transitions were measured and assigned between 6.8--10.6\,GHz. Using these assignments, we searched for emission from cyanocoronene in the GBT Observations of TMC-1: Hunting Aromatic Molecules (GOTHAM) project observations of the cold dark molecular cloud TMC-1 using the 100\,m Green Bank Telescope (GBT). We detect a number of individually resolved transitions in ultrasensitive X-band observations and perform a Markov Chain Monte Carlo analysis to derive best-fit parameters, including a total column density of $N(\mathrm{C}_{24}\mathrm{H}_{11}\mathrm{CN}) = 2.69^{+0.26}_{-0.23} \times 10^{12}\,\mathrm{cm}^{-2}$ at a temperature of $6.05^{+0.38}_{-0.37}\,$K. A spectral stacking and matched filtering analysis provides a robust 17.3$\,σ$ significance to the overall detection. The derived column density is comparable to that of cyano-substituted naphthalene, acenaphthylene, and pyrene, defying the trend of decreasing abundance with increasing molecular size and complexity found for carbon chains. We discuss the implications of the detection for our understanding of interstellar PAH chemistry and highlight major open questions and next steps.

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arXiv2025

Tracking the Chemical Evolution of Hydrocarbons Through Carbon Grain Supply in Protoplanetary Disks

The gas present in planet-forming disks typically exhibits strong emission features of abundant carbon and oxygen molecular carriers. In some instances, protoplanetary disks show an elevated C/O ratio above interstellar values, which leads to a rich hydrocarbon chemistry evidenced in the mid-infrared spectra. The origin of this strengthened C/O ratio may stem from the release of less complex hydrocarbons from the chemical processing of carbonaceous grains. We have explored a set of 42 single-cell models in which we match the physical conditions to the inner regions of planet-forming disks, while varying the C/O ratio by exploring different levels of CH$_4$, C, H$_2$O, and CO to the gas-phase chemistry, which we evaluate in both the cosmic/X-ray and UV-driven limit. We find that the carbon-bearing species in our models exhibit high dependencies on the driver of the chemistry, where both CO and long chain hydrocarbons act as carbon sinks in the cosmic/X-ray-driven chemistry limit, while the vast majority ends up in atomic carbon and CO in the UV-driven limit. We also find moderate dependencies upon the C/O ratio, where this and the ionization rate/UV field determines the point of peak production of a species as well as its equilibrium abundance. We also find that the production of several hydrocarbons, specifically C$_2$H$_2$, is strongly dependent up to an order of magnitude on the initial water abundance. We lastly find that in the X-ray-driven limit, both CH$_4$ and C serve as highly transient donor species to the carbon chemistry.

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arXiv2024

Water in protoplanetary disks with JWST-MIRI: spectral excitation atlas and radial distribution from temperature diagnostic diagrams and Doppler mapping

This work aims at providing fundamental general tools for the analysis of water spectra as observed in protoplanetary disks with JWST-MIRI. We analyze 25 high-quality spectra from the JDISC Survey reduced with asteroid calibrators as presented in Pontoppidan et al. (2024). First, we present a spectral atlas to illustrate the clustering of H$_2$O transitions from different upper level energies ($E_u$) and identify single (un-blended) transitions that provide the most reliable measurements. With that, we demonstrate two important excitation effects: the opacity saturation of ortho-para line pairs that overlap, and the non-LTE excitation of $v=1-1$ lines scattered across the $v=0-0$ rotational band. Second, we define a shorter list of fundamental lines spanning $E_u=$ 1500-6000 K to develop simple line-ratio diagnostic diagrams for the radial temperature distribution of water in inner disks, which can be interpreted using discrete temperature components or a radial gradient. Third, we report the detection of disk-rotation Doppler broadening of molecular lines, which confirms the radial distribution of water emission including, for the first time, the radially-extended $\approx$ 170-220 K reservoir close to the snowline. The combination of measured line ratios and broadening suggests that drift-dominated disks have shallower temperature gradients with an extended cooler disk surface enriched by ice sublimation. We also report the first detection of a H$_2$O-rich inner disk wind from narrow blue-shifted absorption in the ro-vibrational lines. We summarize these findings and tools into a general recipe to make the study of water in planet-forming regions reliable, effective, and sustainable for samples of $> 100$ disks.

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arXiv2024

Constraints on the gas-phase C/O ratio of DR Tau's outer disk from CS, SO, and C$_2$H observations

Millimeter wavelength observations of Class II protoplanetary disks often display strong emission from hydrocarbons and high CS/SO values, providing evidence that the gas-phase C/O ratio commonly exceeds 1 in their outer regions. We present new NOEMA observations of CS $5-4$, SO $7_6-6_5$ and $5_6-4_5$, C$_2$H $N=3-2$, HCN $3-2$, HCO$^+$ $3-2$, and H$^{13}$CO$^+$ $3-2$ in the DR Tau protoplanetary disk at a resolution of $\sim0.4''$ (80 au). Estimates for the disk-averaged CS/SO ratio range from $\sim0.4-0.5$, the lowest value reported thus far for a T Tauri disk. At a projected separation of $\sim180$ au northeast of the star, the SO moment maps exhibit a clump that has no counterpart in the other lines, and the CS/SO value decreases to $<0.2$ at its location. Thermochemical models calculated with DALI indicate that DR Tau's low CS/SO ratio and faint C$_2$H emission can be explained by a gas-phase C/O ratio that is $<1$ at the disk radii traced by NOEMA. Comparisons of DR Tau's SO emission to maps of extended structures traced by $^{13}$CO suggest that late infall may contribute to driving down the gas-phase C/O ratio of its disk.

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arXiv2024

Discovery of interstellar 1-cyanopyrene: a four-ring polycyclic aromatic hydrocarbon in TMC-1

Polycyclic aromatic hydrocarbons (PAHs) are expected to be the most abundant class of organic molecules in space. Their interstellar lifecycle is not well understood, and progress is hampered by difficulties detecting individual PAH molecules. Here, we present the discovery of CN-functionalized pyrene, a 4-ring PAH, in the dense cloud TMC-1 using the 100-m Green Bank Telescope. We derive an abundance of 1-cyanopyrene of ~1.52 x $10^{12}$ cm$^{-2}$, and from this estimate that the un-substituted pyrene accounts for up to ~0.03-0.3% of the carbon budget in the dense interstellar medium which trace the birth sites of stars and planets. The presence of pyrene in this cold (~10 K) molecular cloud agrees with its recent measurement in asteroid Ryugu where isotopic clumping suggest a cold, interstellar origin. The direct link to the birth site of our solar system is strengthened when we consider the solid state pyrene content in the pre-stellar materials compared to comets, which represent the most pristine material in the solar system. We estimate that solid state pyrene can account for 1% of the carbon within comets carried by this one single organic molecule. The abundance indicates pyrene is an "island of stability" in interstellar PAH chemistry and suggests a potential cold molecular cloud origin of the carbon carried by PAHs that is supplied to forming planetary systems, including habitable worlds such as our own.

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arXiv2024

Detections of interstellar 2-cyanopyrene and 4-cyanopyrene in TMC-1

Polycyclic aromatic hydrocarbons (PAHs) are among the most ubiquitous compounds in the universe, accounting for up to ~25% of all interstellar carbon. Since most unsubstituted PAHs do not possess permanent dipole moments, they are invisible to radio astronomy. Constraining their abundances relies on the detection of polar chemical proxies, such as aromatic nitriles. We report the detection of 2- and 4-cyanopyrene, isomers of the recently detected 1-cyanopyrene. We find that these isomers are present in an abundance ratio of ~2:1:2, which mirrors the number of equivalent sites available for CN addition. We conclude that there is evidence that the cyanopyrene isomers formed by direct CN addition to pyrene under kinetic control in hydrogen-rich gas at 10 K and discuss constraints on the H/CN ratio for PAHs in TMC-1.

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arXiv2024

High Mass Inner Regions Found in Five Outbursting Sources

Young stellar objects are thought to commonly undergo sudden accretion events that result in a rise in bolometric luminosity. These outbursts likely coincide with the onset of planet formation, and could impact the formation of planets. The reason behind this dramatic enhancement of accretion is an active area of research, and the mass of the system is a critical parameter. Using Northern Extended Millimeter Array, we survey five outbursting sources (three FU Ori, one EX Or, one 'peculiar' source) with the primary goal of determining the system's mass using an optically thin line of CO. We estimate the mass of a central region for each object that using both continuum emission and C17O J=2-1. The C17O emission likely includes both disk and inner envelope material, thus acts as an upper limit on the disk mass, ranging from 0.33-3.4 Msun for our sources. These derived masses suggest that the inner approx. 1000 au contains enough mass along the line of sight for these sources to be gravitationally unstable.

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arXiv2024

Complex Organics Surrounding the FU Ori-Type Object V1057 Cyg Indicative of Sublimated Ices

FU Ori and EX Lup type objects present natural experiments for understanding a critical stage in the star and planet formation process. These objects offer insight into the diversity of molecules available to forming planetary systems due to a sudden increase in accretion and central luminosity causes the disk and surrounding material to increase in temperature. This allows for volatiles to sublimate off of grains and exist in the gas-phase for tens to hundreds of years post initial outburst. While this dynamic stage may be common for solar-type protostars, observations of the chemical impact of these bursts are rare. In this article, we present observations from the NOrthern Extended Millimeter Array (NOEMA) of five Young Stellar Objects (YSOs) that have undergone outbursts within the past 100 years and catalog the volatile chemistry found within approx 1000 au of the YSO. Only one source clearly shows a line rich spectra with >11 molecules detected including complex organics and water, as is an expected spectra signature for a post-outburst source. This source is V1057 Cyg, and we present it as the northern analog to the well studied and molecule-rich FU Ori source, V883 Ori. Our conclusions on the chemical inventory of the other four sources in our sample are sensitivity limited, as V1057 Cyg contains the highest disk/envelope gas mass.

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arXiv2024

Chemical abundance gradients of organic molecules within a protostellar disk

Observations of low-mass protostellar systems show evidence of rich complex organic chemistry. Their low luminosity, however, makes determining abundance distributions of complex organic molecules (COMs) within the water snowline challenging. However, the excitation conditions sampled by differing molecular distributions may produce substantive changes in the resulting emission. Thus, molecular excitation may recover spatial information from spatially unresolved data. By analyzing spatially-unresolved NOrthern Extended Millimeter Array (NOEMA) observations of CH$_3$OH and CH$_3$CN, we aim to determine if CH$_3$OH and CH$_3$CN are distributed differently in the protostellar disk around HOPS-370, a highly-luminous intermediate mass protostar. Rotational diagram analysis of CH$_3$OH and CH$_3$CN yields rotational temperatures of $198 \pm 1.2$ K and $448 \pm 19$ K, respectively, suggesting the two molecules have different spatial distributions. Source-specific 3D LTE radiative transfer models are used to constrain the spatial distribution of CH$_3$OH and CH$_3$CN within the disk. A uniform distribution with an abundance of $4\times10^{-8}$ reproduces the CH$_3$OH observations. In contrast, the spatial distribution of CH$_3$CN needs to be either more compact (within $\sim120$ au versus $\sim240$ au for CH$_3$OH) or exhibiting a factor of $\gtrsim 15$ increase in abundance in the inner $\sim55$ au. A possible explanation for the difference in spatial abundance distributions of CH$_3$OH and CH$_3$CN is carbon-grain sublimation.

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arXiv2024

Constraining the Stellar Masses and Origin of the Protostellar VLA 1623 System

We present ALMA Band 7 molecular line observations of the protostars within the VLA 1623 system. We map C$^{17}$O (3 - 2) in the circumbinary disk around VLA 1623A and the outflow cavity walls of the collimated outflow. We further detect red-shifted and blue-shifted velocity gradients in the circumstellar disks around VLA 1623B and VLA 1623W that are consistent with Keplerian rotation. We use the radiative transfer modeling code, pdspy, and simple flared disk models to measure stellar masses of $0.27 \pm 0.03$ M$_\odot$, $1.9^{+0.3}_{-0.2}$ M$_\odot$, and $0.64 \pm 0.06$ M$_\odot$ for the VLA 1623A binary, VLA 1623B, and VLA 1623W, respectively. These results represent the strongest constraints on stellar mass for both VLA 1623B and VLA 1623W, and the first measurement of mass for all stellar components using the same tracer and methodology. We use these masses to discuss the relationship between the young stellar objects (YSOs) in the VLA 1623 system. We find that VLA 1623W is unlikely to be an ejected YSO, as has been previously proposed. While we cannot rule out that VLA 1623W is a unrelated YSO, we propose that it is a true companion star to the VLA 1623A/B system and that the these stars formed in situ through turbulent fragmentation and have had only some dynamical interactions since their inception.

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arXiv2024

Exploring the Complex Ionization Environment of the Turbulent DM Tau Disk

Ionization drives important chemical and dynamical processes within protoplanetary disks, including the formation of organics and water in the cold midplane and the transportation of material via accretion and magneto-hydrodynamic (MHD) flows. Understanding these ionization-driven processes is crucial for understanding disk evolution and planet formation. We use new and archival ALMA observations of HCO+, H13CO+, and N2H+ to produce the first forward-modeled 2D ionization constraints for the DM Tau protoplanetary disk. We include ionization from multiple sources and explore the disk chemistry under a range of ionizing conditions. Abundances from our 2D chemical models are post-processed using non-LTE radiative transfer, visibility sampling, and imaging, and are compared directly to the observed radial emission profiles. The observations are best fit by a modestly reduced CR ionization rate ($ζ_{CR}$ ~ 10$^{-18}$ s$^{-1}$) and a hard X-ray spectrum (hardness ratio [HR] = 0.3), which we associate with stellar flaring conditions. Our best-fit model under-produces emission in the inner disk, suggesting that there may be an additional mechanism enhancing ionization in DM Tau's inner disk. Overall, our findings highlight the complexity of ionization in protoplanetary disks and the need for high resolution multi-line studies.

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arXiv2024

C/O Ratios and the formation of wide separation exoplanets

The gas and solid-state C/O ratios provide context to potentially link the atmospheric composition of planets to that of the natal disk. We provide a synthesis of extant estimates of the gaseous C/O and C/H ratios in planet-forming disks obtained primarily through analysis of Atacama Large Millimeter Array observations. These estimates are compared to atmospheric abundances of wide separation (> 10 au) gas giants. The resolved disk gas C/O ratios, from seven systems, generally exhibit C/O > 1 with sub-solar, or depleted, carbon content. In contrast, wide separation gas giants have atmospheric C/O ratios that cluster near or slightly above the presumed stellar value with a range of elemental C/H. From the existing disk composition, we infer that the solid-state mm/cm-sized pebbles have a total C/O ratio (solid cores and ices) that is solar (stellar) in content. We explore simple models that reconstruct the exoplanet atmospheric composition from the disk, while accounting for silicate cloud formation in the planet atmosphere. If wide separate planets formed via the core-accretion mechanism, they must acquire their metals from pebble or planetesimal accretion. Further, the dispersion in giant planet C/H content is best matched by a disk composition with modest and variable factors of carbon depletion. An origin of the wide separation gas giants via gravitational instability cannot be ruled out as stellar C/O ratios should natively form in this scenario. However, the variation in planet metallicity with a stellar C/O ratio potentially presents challenges to these models.

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arXiv2024

Identification of hot gas around low-mass protostars

The low carbon content of Earth and primitive meteorites compared to the Sun and interstellar grains suggests that carbon-rich grains were destroyed in the inner few astronomical units of the young solar system. A promising mechanism to selectively destroy carbonaceous grains is thermal sublimation within the soot line at $\gtrsim$ 300 K. To address whether such hot conditions are common amongst low-mass protostars, we observe CH$_3$CN transitions at 1, 2 and 3 mm with the NOrthern Extended Millimeter Array (NOEMA) toward seven low-mass and one intermediate-mass protostar ($L_{\rm{bol}} \sim2-300 L_\odot$), as CH$_3$CN is an excellent temperature tracer. We find $>$ 300 K gas toward all sources, indicating that hot gas may be prevalent. Moreover, the excitation temperature for CH$_3$OH obtained with the same observations is always lower ($\sim$135-250 K), suggesting that CH$_3$CN and CH$_3$OH have a different spatial distribution. A comparison of the column densities at 1 and 3 mm shows a stronger increase at 3 mm for CH$_3$CN than for CH$_3$OH. Since the dust opacity is lower at longer wavelengths, this indicates that CH$_3$CN is enhanced in the hot gas compared to CH$_3$OH. If this CH$_3$CN enhancement is the result of carbon-grain sublimation, these results suggests that Earth's initial formation conditions may not be rare.

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arXiv2024

PDRs4All VIII: Mid-IR emission line inventory of the Orion Bar

Mid-infrared emission features probe the properties of ionized gas, and hot or warm molecular gas. The Orion Bar is a frequently studied photodissociation region (PDR) containing large amounts of gas under these conditions, and was observed with the MIRI IFU aboard JWST as part of the "PDRs4All" program. The resulting IR spectroscopic images of high angular resolution (0.2") reveal a rich observational inventory of mid-IR emission lines, and spatially resolve the substructure of the PDR, with a mosaic cutting perpendicularly across the ionization front and three dissociation fronts. We extracted five spectra that represent the ionized, atomic, and molecular gas layers, and measured the most prominent gas emission lines. An initial analysis summarizes the physical conditions of the gas and the potential of these data. We identified around 100 lines, report an additional 18 lines that remain unidentified, and measured the line intensities and central wavelengths. The H I recombination lines originating from the ionized gas layer bordering the PDR, have intensity ratios that are well matched by emissivity coefficients from H recombination theory, but deviate up to 10% due contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni, and show how certain line ratios vary between the five regions. We observe the pure-rotational H$_2$ lines in the vibrational ground state from 0-0 S(1) to 0-0 S(8), and in the first vibrationally excited state from 1-1 S(5) to 1-1 S(9). We derive H$_2$ excitation diagrams, and approximate the excitation with one thermal (~700 K) component representative of an average gas temperature, and one non-thermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model for the Orion Bar PDR and highlight the differences with the observations.

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