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Inga Kamp

Publications and source records attributed to Inga Kamp.

At least 55 records · Page 3Linked to original sources
arXiv2024

Mapping the Vertical Gas Structure of the Planet-hosting PDS 70 Disk

PDS 70 hosts two massive, still-accreting planets and the inclined orientation of its protoplanetary disk presents a unique opportunity to directly probe the vertical gas structure of a planet-hosting disk. Here, we use high-spatial-resolution (${\approx}$0."1;10 au) observations in a set of CO isotopologue lines and HCO$^+$ J=4-3 to map the full 2D $(r,z)$ disk structure from the disk atmosphere, as traced by $^{12}$CO, to closer to the midplane, as probed by less abundant isotopologues and HCO$^+$. In the PDS 70 disk, $^{12}$CO traces a height of $z/r\approx0.3$, $^{13}$CO is found at $z/r\approx0.1$, and C$^{18}$O originates at, or near, the midplane. The HCO$^+$ surface arises from $z/r\approx0.2$ and is one of the few non-CO emission surfaces constrained with high fidelity in disks to date. In the $^{12}$CO J=3-2 line, we resolve a vertical dip and steep rise in height at the cavity wall, making PDS 70 the first transition disk where this effect is directly seen in line emitting heights. In the outer disk, the CO emission heights of PDS 70 appear typical for its stellar mass and disk size and are not substantially altered by the two inner embedded planets. By combining CO isotopologue and HCO$^+$ lines, we derive the 2D gas temperature structure and estimate a midplane CO snowline of ${\approx}$56-85 au. This implies that both PDS 70b and 70c are located interior to the CO snowline and are likely accreting gas with a high C/O ratio of ${\approx}$1.0, which provides context for future planetary atmospheric measurements from, e.g., JWST, and for properly modeling their formation histories.

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arXiv2023

15NH3 in the atmosphere of a cool brown dwarf

Brown dwarfs serve as ideal laboratories for studying the atmospheres of giant exoplanets on wide orbits as the governing physical and chemical processes in them are nearly identical. Understanding the formation of gas giant planets is challenging, often involving the endeavour to link atmospheric abundance ratios, such as the carbon-to-oxygen (C/O) ratio, to formation scenarios. However, the complexity of planet formation requires additional tracers, as the unambiguous interpretation of the measured C/O ratio is fraught with complexity. Isotope ratios, such as deuterium-to-hydrogen and 14N/15N, offer a promising avenue to gain further insight into this formation process, mirroring their utility within the solar system. For exoplanets only a handful of constraints on 12C/13C exist, pointing to the accretion of 13C-rich ice from beyond the disks' CO iceline. Here we report on the mid-infrared detection of the 14NH3 and 15NH3 isotopologues in the atmosphere of a cool brown dwarf with an effective temperature of 380 K in a spectrum taken with the Mid-InfraRed Instrument of the James Webb Space Telescope. As expected, our results reveal a 14N/15N value consistent with star-like formation by gravitational collapse, demonstrating that this ratio can be accurately constrained. Since young stars and their planets should be more strongly enriched in the 15N isotope, we expect that 15NH3 will be detectable in a number of cold, wide-separation exoplanets.

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arXiv2023

MINDS. Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI

MIRI/MRS on board the JWST allows us to probe the inner regions of protoplanetary disks. Here we examine the disk around the classical T Tauri star Sz 98, which has an unusually large dust disk in the millimetre with a compact core. We focus on the H$_2$O emission through both its ro-vibrational and pure rotational emission. Furthermore, we compare our chemical findings with those obtained for the outer disk from Atacama Large Millimeter/submillimeter Array (ALMA) observations. In order to model the molecular features in the spectrum, the continuum was subtracted and LTE slab models were fitted. The spectrum was divided into different wavelength regions corresponding to H$_2$O lines of different excitation conditions, and the slab model fits were performed individually per region. We confidently detect CO, H$_2$O, OH, CO$_2$, and HCN in the emitting layers. The isotopologue H$^{18}_2$O is not detected. Additionally, no other organics, including C$_2$H$_2$, are detected. This indicates that the C/O ratio could be substantially below unity, in contrast with the outer disk. The H$_2$O emission traces a large radial disk surface region, as evidenced by the gradually changing excitation temperatures and emitting radii. The OH and CO$_2$ emission are relatively weak. It is likely that H$_2$O is not significantly photodissociated; either due to self-shielding against the stellar irradiation, or UV-shielding from small dust particles. The relative emitting strength of the different identified molecular features point towards UV-shielding of H$_2$O in the inner disk of Sz 98, with a thin layer of OH on top. The majority of the organic molecules are either hidden below the dust continuum, or not present. In general, the inferred composition points to a sub-solar C/O ratio (<0.5) in the inner disk, in contrast with the larger than unity C/O ratio in the gas in the outer disk found with ALMA.

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arXiv2023

XUE. Molecular inventory in the inner region of an extremely irradiated Protoplanetary Disk

We present the first results of the eXtreme UV Environments (XUE) James Webb Space Telescope (JWST) program, that focuses on the characterization of planet forming disks in massive star forming regions. These regions are likely representative of the environment in which most planetary systems formed. Understanding the impact of environment on planet formation is critical in order to gain insights into the diversity of the observed exoplanet populations. XUE targets 15 disks in three areas of NGC 6357, which hosts numerous massive OB stars, among which some of the most massive stars in our Galaxy. Thanks to JWST we can, for the first time, study the effect of external irradiation on the inner ($< 10$ au), terrestrial-planet forming regions of proto-planetary disks. In this study, we report on the detection of abundant water, CO, CO$_2$, HCN and C$_2$H$_2$ in the inner few au of XUE 1, a highly irradiated disk in NGC 6357. In addition, small, partially crystalline silicate dust is present at the disk surface. The derived column densities, the oxygen-dominated gas-phase chemistry, and the presence of silicate dust are surprisingly similar to those found in inner disks located in nearby, relatively isolated low-mass star-forming regions. Our findings imply that the inner regions of highly irradiated disks can retain similar physical and chemical conditions as disks in low-mass star-forming regions, thus broadening the range of environments with similar conditions for inner disk rocky planet formation to the most extreme star-forming regions in our Galaxy.

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arXiv2023

Hydrocarbon chemistry in inner regions of planet forming disks

The analysis of the mid-infrared spectra helps understanding the composition of the gas in the inner, dense and warm terrestrial planet forming region of disks around young stars. ALMA has detected hydrocarbons in the outer regions of the planet forming disk and Spitzer detected \ce{C2H2} in the inner regions. JWST- MIRI provides high spectral resolution observations of \ce{C2H2} and a suite of more complex hydrocarbons are now reported. Interpreting the fluxes observed in the spectra is challenging and radiation thermo-chemical codes are needed to properly take into account the disk structure, radiative transfer, chemistry and thermal balance. Various disk physical parameters like the gas-to-dust ratio, dust evolution including radial drift, dust growth and settling can affect the fluxes observed in the mid-IR. Still, thermo-chemical disk models were not always successful in matching all observed molecular emission bands simultaneously. The goal of this project is two-fold. We analyse the warm carbon chemistry in the inner regions of the disk, i.e. within 10 au to find pathways forming \ce{C2H2} potentially missing from the existing chemical networks. Second, we analyse the effect of the new chemistry on the line fluxes of acetylene. We use radiative thermo-chemical disk code {P{\small RO}D{\small I}M{\small O}} to expand the hydrocarbon chemistry that occurs in a typical standard T Tauri disks. We used the UMIST and the KIDA rate databases for collecting reactions for the species. We include a number of three-body and thermal decomposition reactions from STAND2020 network. We included isotopomers for the species that were present in the databases. The chemistry is then analysed in the regions that produce observable features in the mid-infrared spectra. The effect of expanding the hydrocarbon chemistry on the mid-infrared spectra is studied. Acetylene is formed via two ....

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arXiv2023

The Chemical Inventory of the Inner Regions of Planet-forming Disks -- The JWST/MINDS Program

The understanding of planet formation has changed recently, embracing the new idea of pebble accretion. This means that the influx of pebbles from the outer regions of planet-forming disks to their inner zones could determine the composition of planets and their atmospheres. The solid and molecular components delivered to the planet-forming region can be best characterized by mid-infrared spectroscopy. With Spitzer low-resolution (R=100, 600) spectroscopy, this approach was limited to the detection of abundant molecules such as H2O, C2H2, HCN and CO2. This contribution will present first results of the MINDS (MIRI mid-IR Disk Survey, PI: Th. Henning) project. Due do the sensitivity and spectral resolution (R~1500-3500) provided by JWST we now have a unique tool to obtain the full inventory of chemistry in the inner disks of solar-types stars and brown dwarfs, including also less abundant hydrocarbons and isotopologues. The Integral Field Unit (IFU) capabilities enable at the same time spatial studies of the continuum and line emission in extended sources such as debris disks, the flying saucer and also the search for mid-IR signatures of forming planets in systems such as PDS70. These JWST observations are complementary to ALMA and NOEMA observations of the outer disk chemistry; together these datasets provide an integral view of the processes occurring during the planet formation phase.

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arXiv2023

MINDS. The detection of $^{13}$CO$_{2}$ with JWST-MIRI indicates abundant CO$_{2}$ in a protoplanetary disk

We present JWST-MIRI MRS spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey (MINDS) GTO program. Emission from $^{12}$CO$_{2}$, $^{13}$CO$_{2}$, H$_{2}$O, HCN, C$_{2}$H$_{2}$, and OH is identified with $^{13}$CO$_{2}$ being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few au of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The $Q$-branches of these molecules, including those of hot-bands, are particularly sensitive to temperature and column density. We find that the $^{12}$CO$_{2}$ emission in the GW Lup disk is coming from optically thick emission at a temperature of $\sim$400 K. $^{13}$CO$_{2}$ is optically thinner and based on a lower temperature of $\sim$325 K, may be tracing deeper into the disk and/or a larger emitting radius than $^{12}$CO$_{2}$. The derived $N_{\rm{CO_{2}}}$/$N_{\rm{H_{2}O}}$ ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on \textit{Spitzer}-IRS data. This high column density ratio may be due to an inner cavity with a radius in between the H$_{2}$O and CO$_{2}$ snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.

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arXiv2023

Circumplanetary disk ices II. Composition

The subsurface oceans of icy satellites are among the most compelling among the potentially habitable environments in our Solar System. The question of whether a liquid subsurface layer can be maintained over geological timescales depends on its chemical composition. The composition of icy satellites is linked to that of the circumplanetary disk (CPD) in which they form. The CPD accretes material from the surrounding circumstellar disk in the vicinity of the planet, however, the degree of chemical inheritance is unclear. We aim to investigate the composition of ices in chemically reset or inherited circumplanetary disks to inform interior modeling and the interpretation of in situ measurements of icy solar system satellites, with an emphasis on the Galilean moon system. We used a radiation-thermochemical code to produce circumplanetary disk models and extract the ice composition from time-dependent chemistry, incorporating gas-phase and grain-surface reactions. The initial sublimation of ices during accretion may result in a CO2-rich ice composition. Sublimated ammonia ice is destroyed by background radiation while drifting towards the CPD midplane. Liberated nitrogen becomes locked in N2 due to efficient self-shielding, leaving ices depleted of ammonia. A significant ammonia ice component remains only when ices are inherited from the circumstellar disk. The observed composition of the Galilean moons is consistent with the sublimation of ices during accretion onto the CPD. In this scenario, the Galilean moon ices are nitrogen-poor and CO2 on Callisto is endogenous and primordial. The ice composition is significantly altered after an initial reset of accreted circumstellar ice. The chemical history of the Galilean moons stands in contrast to the Saturnian system, where the composition of the moons corresponds more closely with the directly inherited circumstellar disk material.

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arXiv2022

Observing Circumplanetary Disks with METIS

Context: A full understanding of the planet and moon formation process requires observations that probe the circumplanetary environment of accreting giant planets. The mid-infrared ELT imager and spectrograph (METIS) will provide a unique capability to detect warm-gas emission lines from circumplanetary disks. Aims: We aim to demonstrate the capability of the METIS instrument on the Extremely Large Telescope (ELT) to detect circumplanetary disks (CPDs) with fundamental v=1-0 transitions of $^{12}$CO from 4.5-5 $μ$m. Methods: We consider the case of the well-studied HD 100546 pre-transitional disk to inform our disk modeling approach. We use the radiation-thermochemical disk modeling code ProDiMo to produce synthetic spectral channel maps. The observational simulator SimMETIS is employed to produce realistic data products with the integral field spectroscopic (IFU) mode. Results: The detectability of the CPD depends strongly on the level of external irradiation and the physical extent of the disk, favoring massive (~10 M$_{\rm J}$) planets and spatially extended disks with radii approaching the planetary Hill radius. The majority of $^{12}$CO line emission originates from the outer disk surface, and thus the CO line profiles are centrally peaked. The planetary luminosity does not contribute significantly to exciting disk gas line emission. If CPDs are dust-depleted, the $^{12}$CO line emission is enhanced as external radiation can penetrate deeper into the line emitting region. Conclusions: UV-bright star systems with pre-transitional disks are ideal candidates to search for CO-emitting CPDs with ELT/METIS. METIS will be able to detect a variety of circumplanetary disks via their fundamental $^{12}$CO ro-vibrational line emission in only 60 s of total detector integration time.

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arXiv2022

The kinematics and excitation of infrared water vapor emission from planet-forming disks: results from spectrally-resolved surveys and guidelines for JWST spectra

This work presents ground-based spectrally-resolved water emission at R = 30000-100000 over infrared wavelengths covered by JWST (2.9-12.8 $μ$m). Two new surveys with iSHELL and VISIR are combined with previous spectra from CRIRES and TEXES to cover parts of multiple ro-vibrational and rotational bands observable within telluric transmission bands, for a total of $\approx160$ spectra and 85 disks (30 of which are JWST targets in Cycle 1). The general expectation of a range of regions and excitation conditions traced by infrared water spectra is for the first time supported by the combined kinematics and excitation as spectrally resolved at multiple wavelengths. The main findings from this analysis are: 1) water lines are progressively narrower from the ro-vibrational bands at 2-9 $μ$m to the rotational lines at 12 $μ$m, and partly match a broad (BC) and narrow (NC) emission components, respectively, as extracted from ro-vibrational CO spectra; 2) rotation diagrams of resolved water lines from upper level energies of 4000-9500 K show vertical spread and curvatures indicative of optically thick emission ($\approx 10^{18}$ cm$^{-2}$) from a range of excitation temperatures ($\approx 800$-1100 K); 3) the new 5 $μ$m spectra demonstrate that slab model fits to the rotational lines at $> 10$ $μ$m strongly over-predict the ro-vibrational emission bands at $< 9$ $μ$m, implying non-LTE vibrational excitation. We discuss these findings in the context of emission from a disk surface and a molecular inner disk wind, and provide a list of guidelines to support the analysis of spectrally-unresolved JWST spectra.

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arXiv2022

Ices in planet-forming disks: Self-consistent ice opacities in disk models

In cold and shielded environments, molecules freeze out on dust grain surfaces to form ices such as H2O, CO, CO2, CH4, CH3OH, and NH3. In protoplanetary disks, the exact radial and vertical ice extension depend on disk mass, geometry, and stellar UV irradiation. The goal of this work is to present a computationally efficient method to compute ice and bare-grain opacities in protoplanetary disk models consistently with the chemistry and to investigate the effect of ice opacities on the physico-chemical state and optical appearance of the disk. A matrix of Mie efficiencies is pre-calculated for different ice species and thicknesses, from which the position dependent opacities of icy grains are then interpolated. This is implemented in the PRODIMO code by a self-consistent solution of ice opacities and the local composition of ices, which are obtained from our chemical network. Locally, the opacity can change significantly, for example, an increase by a factor of more than 200 in the midplane, especially at UV and optical wavelengths, due to ice formation. This is mainly due to changes in the size distribution of dust grains resulting from ice formation. However, since the opacity only changes in the optically thick regions of the disk, the thermal disk structure does not change significantly. For the same reason, the spectral energy distributions computed with our disk models with ice opacities generally show only faint ice emission features at far-IR wavelengths. The ice absorption features are only seen in the edgeon orientation. The assumption made on how the ice is distributed across the grain size distribution influences the far-IR and millimeter slope of the SED. The ice features and their strengths are influenced by the ice power law and the type of chemistry. Our models predict stronger ice features for observations that can spatially resolve the disk, particularly in absorption.

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arXiv2022

Circumplanetary disk ices. I. Ice formation vs. viscous evolution and grain drift

The large icy moons of Jupiter formed in a circumplanetary disk (CPD). CPDs are fed by infalling circumstellar gas and dust which may be shock-heated upon accretion or sublimated while passing through an optically thin gap. Accreted material is then either incorporated into moons, falls into the planet, or is lost beyond the disk edge on relatively short timescales. If ices are sublimated during accretion onto the CPD we know there must be sufficient time for them to recondense or moons such as Ganymede or Callisto could not form. The chemical timescale to form sufficiently icy solids places a novel constraint on the dynamical behaviour and properties of CPDs. We use the radiation thermochemical code ProDiMo to analyze how the radial ice abundance evolves in CPDs. We consider different initial chemical conditions of the disk to explore the consequences of infalling material being inherited from the circumstellar disk or being reset to atomic conditions by shock-heating. We contrast the timescales of ice formation with those of viscous evolution and radial dust drift. Water ice can form very efficiently in the CPD from initially atomic conditions, as a significant fraction is efficiently re-deposited on dust grains within < 1 yr. Radial grain drift timescales are in general longer than those of ice formation on grains. Icy grains of size $a < 3$ mm retain their icy mantles while crossing an optically thin circumstellar disk gap at 5 au for $L_* < 10 $ L$_{\odot}$. Three-body reactions play an important role in water formation in the dense midplane condition of CPDs. The CPD midplane must be depleted in dust relative to the circumstellar disk by a factor 10-50 to produce solids with the ice to rock ratio of the icy Galilean satellites. The CPD snowline is not erased by radial grain drift, which is consistent with the compositional gradient of the Galilean satellites being primordial.

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arXiv2022

An unusual reservoir of water emission in the VV CrA A protoplanetary disk

We present an analysis of an unusual pattern of water vapor emission from the $\sim$2 Myr-old low-mass binary system VV CrA, as observed in infrared spectra obtained with VLT-CRIRES, VLT-VISIR, and Spitzer-IRS. Each component of the binary shows emission from water vapor in both the L ($\sim3\,μ$m) and N ($\sim 12\,μ$m) bands. The N-band and Spitzer spectra are similar to those previously observed from young stars with disks, and are consistent with emission from an extended protoplanetary disk. Conversely, the CRIRES L-band data of VV CrA A show an unusual spectrum, which requires the presence of a water reservoir with high temperature ($T\gtrsim1500$ K), column density ($N_\mathrm{H2O}\sim 3\times10^{20}\ \mathrm{cm}^{-2}$), and turbulent broadening ($v\sim 10$ km s$^{-1}$), but very small emitting area ($A\lesssim0.005$ AU$^2$). Similarity with previously observed water emission from V1331 Cyg (Doppmann et al. 2011) and SVS 13 (Carr et al. 2004) suggests that the presence of such a reservoir may be linked to evolutionary state, perhaps related to the presence of high accretion rates or winds. While the inner disk may harbor such a reservoir, simple Keplerian models do not match well with emitting line shapes, and alternative velocity fields must be considered. We also present a new idea, that the unusual emission could arise in a circumplanetary disk, embedded within the larger VV CrA A protoplanetary disk. Additional data are likely required to determine the true physical origin of this unusual spectral pattern.

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arXiv2022

Convolutional neural networks as an alternative to Bayesian retrievals

Exoplanet observations are currently analysed with Bayesian retrieval techniques. Due to the computational load of the models used, a compromise is needed between model complexity and computing time. Analysis of data from future facilities, will need more complex models which will increase the computational load of retrievals, prompting the search for a faster approach for interpreting exoplanet observations. Our goal is to compare machine learning retrievals of exoplanet transmission spectra with nested sampling, and understand if machine learning can be as reliable as Bayesian retrievals for a statistically significant sample of spectra while being orders of magnitude faster. We generate grids of synthetic transmission spectra and their corresponding planetary and atmospheric parameters, one using free chemistry models, and the other using equilibrium chemistry models. Each grid is subsequently rebinned to simulate both HST/WFC3 and JWST/NIRSpec observations, yielding four datasets in total. Convolutional neural networks (CNNs) are trained with each of the datasets. We perform retrievals on a 1,000 simulated observations for each combination of model type and instrument with nested sampling and machine learning. We also use both methods to perform retrievals on real WFC3 transmission spectra. Finally, we test how robust machine learning and nested sampling are against incorrect assumptions in our models. CNNs reach a lower coefficient of determination between predicted and true values of the parameters. Nested sampling underestimates the uncertainty in ~8% of retrievals, whereas CNNs estimate them correctly. For real WFC3 observations, nested sampling and machine learning agree within $2σ$ for ~86% of spectra. When doing retrievals with incorrect assumptions, nested sampling underestimates the uncertainty in ~12% to ~41% of cases, whereas this is always below ~10% for the CNN.

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arXiv2022

Observations of PAHs in the atmospheres of discs and exoplanets

Polycyclic aromatic hydrocarbons (PAHs) play a key role in the chemical and hydrodynamical evolution of the atmospheres of exoplanets and planet-forming discs. If they can survive the planet formation process, PAHs are likely to be involved in pre-biotic chemical reactions eventually leading to more complex molecules such as amino acids and nucleotides, which form the basis for life as we know it. However, the abundance and specific role of PAHs in these environments is largely unknown due to limitations in sensitivity and range of wavelength of current and previous space-borne facilities. Upcoming infrared space spectroscopy missions, such as Twinkle and Ariel, present a unique opportunity to detect PAHs in the atmospheres of exoplanets and planet-forming discs. In this work we present synthetic observations based on conservative numerical modeling of typical planet-forming discs and a transiting hot Saturnian planet around solar type star. Our models show that Twinkle and Ariel might both be able to detect the 3.3 micron PAH feature within reasonable observing time in discs and transiting planets, assuming that PAHs are present with an abundance of at least one tenth of the interstellar medium value.

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arXiv2020

The surprisingly low carbon mass in the debris disk around HD 32297

Gas has been detected in a number of debris disks. It is likely secondary, i.e. produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk around the 15--30 Myr old A-type star HD 32297. We find that C$^0$ is located in a ring at $\sim$110 au with a FWHM of $\sim$80 au, and has a mass of $(3.5\pm0.2)\times10^{-3}$ M$_\oplus$. Naively, such a surprisingly small mass can be accumulated from CO photo-dissociation in a time as short as $\sim$10$^4$ yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C$^0$ and CO observations, is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of $\sim$15 M$_\oplus$ Myr$^{-1}$, much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and re-release. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks.

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arXiv2019

The role of atom tunneling in gas-phase reactions in planet-forming disks

This paper investigates the impact of the increased reaction rate constant due to tunneling effects on planet-forming disks. Our aim is to quantify the astrophysical implications of atom tunneling for simple molecules that are frequently used to infer disk structure information or to define the initial conditions for planet (atmosphere) formation. We explain the tunneling effect on reaction rates by using a scholarly example in comparison to previous UMIST2012 rate constants. In a chemical network with 1299 reactions, we identify all reactions that could show atom tunneling. We devise a simple formulation of reaction rate constants that overestimates tunneling and screen a standard T Tauri disk model for changes in species abundances. For those reactions found to be relevant, we find values of the most recent literature for the rate constants including tunneling and compare the resulting disk chemistry to the standard disk models. The rate constants in the UMIST2012 database in many cases already capture tunneling effects implicitly. A rigorous screening procedure identified three neutral-neutral reactions where atom tunneling could change simple molecule abundances. However, by adopting recent values of the rate constants of these reactions and due to the layered structure of planet-forming disks, the effects are limited to a small region where cold neutral-neutral chemistry dominates. Abundances of water close to the midplane snowline can increase by a factor of two at most compared to previous results with UMIST2012 rates. Observables from the disk surface, such as high excitation (> 500 K) water line fluxes, decrease by 60% at most when tunneling effects are explicitly excluded. On the other hand, disk midplane quantities relevant for planet formation such as the C-to-O ratio and also the ice-to-rock ratio are clearly affected by these gas-phase tunneling effects.

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arXiv2018

On water delivery in the inner solar nebula: Monte Carlo simulations of forsterite hydration

Endogenous or exogenous, dry or wet, various scenarios have been so far depicted for the origin of water on our Solar Systems rocky bodies. Hydrated silicates found in meteorites and in interplanetary dust particles together with observations of abundant water reservoirs in the habitable zone of protoplanetary disks are evidences that support aqueous alteration of silicate dust grains by water vapor condensation in a nebular setting. We investigate the thermodynamics (temperature and pressure dependencies) and kinetics (adsorption rates and energies, surface diffusion and cluster formation) of water adsorption on surfaces of forsterite grains. (abbreviated) The protoplanetary disk model (ProDiMo) code is tuned to simulate the thermochemical disk structure of the early solar nebula at three evolutionary stages. Pressure, temperature and water vapor abundance within 1 au from the protosun were extracted and used as input for a Monte Carlo code to model water associative adsorption using adsorption energies that resemble the forsterite [100] crystal lattice. Hydration of forsterite surfaces by water vapor adsorption could have occurred within the nebula lifetime already at a density of 1e8 cm-3, with increasing surface coverage for higher water vapor densities. Full surface coverage is attained for temperatures lower than 500 K, while for hotter grain surfaces water cluster formation plays a crucial role. (abbreviated) This work shows that water cluster formation enhances the water surface coverage and enables a stable water layer to form at high temperature and low water vapor density conditions. Finally, surface diffusion of physisorbed water molecules shortens the timescale for reaching steady state, enabling phyllosilicate formation within the solar nebula timescale.

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