arXiv subjects

Audrey Coutens

Publications and source records attributed to Audrey Coutens.

At least 19 recordsLinked to original sources

arXiv2026

A JWST, ALMA and VLA survey of the Ophiuchus-A star-forming region: Unveiling hidden dust mass and connecting infrared outflows to their radio origins

We present an infrared, millimetre, and radio survey of 20 Class 0-III young stellar objects in the Ophiuchus A L1688 star-forming cluster, combining high-resolution (7-25 au) VLA and JWST observations with archival ALMA data. We implement physically motivated models to derive dust and ionised gas properties, spectral behaviour and their relative contributions through the millimetre-centimetre radio spectral energy distribution. Our models reveal circumstellar dust disks that are, on average, tens to hundreds of times more massive than millimetre-only estimates (subject to uncertainties arising from the choice of dust opacity) and contain millimetre-sized grains even at the Class 0 stage. Owing to the VLA's high resolution we are able to connect outflows to their origins, detecting protostellar jet emission on scales of 10s-1000s au. Our results represent a homogeneous characterisation of the dust and ionised gas properties in Ophiuchus and present a potential solution to the long-standing 'missing disk mass' problem. However, our understanding is still limited by resolution and sensitivity at frequencies <40 GHz. Future facilities like the SKA and ngVLA are needed to provide the necessary capabilities to fully spatially resolve this emission (<0.18") even in one of the closest star-forming regions.

astro-ph.GA↗

arXiv2026

Chemical Complexity in the Early Stages of Star Formation in the SKAO Era

About 350 molecules have been identified in the interstellar medium (ISM), including complex molecules relevant to prebiotic chemistry. A remarkable level of molecular diversity has been observed from the earliest stages of star formation, providing the initial chemical inventory inherited by planetary systems. Radio observations have played a pivotal role in these discoveries, starting with the identification of the first polyatomic molecule, $\text{NH}_3$ (Cheung et al. 1968). (Sub-)millimeter observations have revealed complex organic molecules of prebiotic relevance, including formamide ($\text{NH}_2\text{CHO}$), glycolaldehyde ($\text{CH}_2\text{OHCHO}$), and even urea ($(\text{NH}_2)_2\text{CO}$), and hydroxylamine ($\text{NH}_2\text{OH}$), which are possible precursors of RNA nucleotides (Ceccarelli et al. 2023; Jim\'enez-Serra et al. 2020). However, in dense protostellar regions, dust opacity hampers the detection of molecular emission. Additionally, large molecules and those containing heavy atoms, which have rotational transitions at lower frequencies, often remain inaccessible to current instruments. The Square Kilometre Array Observatory (SKAO) will provide an unprecedented combination of sensitivity and angular resolution at radio wavelengths. This will allow for the detection of prebiotic species and offer new insights into the chemical pathways that shape emerging planetary systems (Jim\'enez-Serra et al. 2022). This chapter details the scientific questions and advancements that the SKAO, and more specifically, SKA-Mid equipped with the Band 5 receivers, will pursue in the field of astrochemistry, focusing on the chemical complexity in both high-mass and solar-type star-forming regions.

astro-ph.SR↗

arXiv2026

Unveiling Complex Chemistry in Planet-forming Disks with the SKAO

The chemical composition of planets is inherited from that of the natal protoplanetary disk at the time of planet formation. In recent years, we have made huge progress in characterizing disk chemistry. (Sub-)millimeter interferometers, such as ALMA, allowed us to detect emission lines from simple to complex organic molecules and to probe their radial and vertical distribution in disks. On the other hand, JWST has started to unveil the composition of disk ices, and line emission from the innermost disk regions. The advent of SKA will open new domains in the field, by observing emission lines from heavier molecules including heavy carbon chains and rings, and prebiotic molecules with peak emission in the cm range. Moreover, SKA will probe molecular emission from regions which are obscured by dust opacity at mm wavelengths, hence from the disk midplane, and often from the inner 30 au region. These observations will constrain the initial conditions for disk evolution and planet formation, allowing us to predict the chemical composition of the forming planets and their atmospheres. Comparison with forthcoming results on exoplanet atmospheres and on the chemistry of pristine bodies in the Solar System will provide new hints on the origin and evolution of planetary systems including our own.

astro-ph.SR↗

arXiv2026

The Reaction between Atomic Carbon and Molecular Nitrogen as a Source of Cyanamide and Carbodiimide on Interstellar Ices

Reactions occurring on the ice-covered surfaces of interstellar dust grains are considered to be among the most important sources of complex species in the interstellar medium. Despite this, molecules such as cyanamide, NH2CN, are largely underpredicted by current astrochemical models suggesting that the network of reactions currently used to describe this species and its tautomer carbodiimide, HNCNH, are incomplete. Here, we performed a theoretical investigation of the reaction of ground state atomic carbon C(3P) with molecular nitrogen N2 in both the gas-phase and on the surface of amorphous solid water (ASW) clusters to examine its potential importance in the formation of NH2CN and HNCNH. We show that the reaction of gas-phase C-atoms with N2 molecules already present on the ASW surface results in the barrierless formation of CNN. Following exothermic hydrogenation reactions, the N-N bond of the C-N-N bearing intermediates is broken allowing the formation of molecules with N-C-N backbones through cyclic intermediates over low barriers. To test the importance of these processes to NH2CN and HNCNH formation, these reactions were included in a three-phase astrochemical model of low-mass protostellar evolution employing a reaction network that was updated to better describe the formation and destruction pathways of related small nitrogen bearing molecules. These simulations demonstrate that the ice surface reaction between C and N2 represents by far the dominant source of NH2CN and HNCNH in protostellar environments and in dense clouds.

astro-ph.GA↗

arXiv2026

One-dimensional and time-dependent modelling of complex organic molecules in protostars

Complex organic molecules (COMs), the building blocks of life, have been extensively detected under various physical conditions, from quiescent clouds to star-forming regions. They therefore serve as excellent tracers for the local physical and chemical properties of these environments. Proper models that are capable of grasping the formation and destruction of COMs are crucial to understanding observations. However, given that distinct COMs may be detected from different locations and at varying times, we improve UCLCHEM - a gas-grain chemical code - to a one-dimensional, time-dependent model, tailored to protostars. In this update, we examine two stages of a protostar: the prestellar and heating stages, incorporating a simple radiative mechanism for both the internal and external radiation fields of the cloud. This approach relies on the key assumption that the dust and gas temperatures are completely coupled. Ultimately, we implement an updated version of our model to interpret observations obtained through both single-dish and interferometry under varying conditions, including a SgrB2(N1) hot core, massive Galactic clumps and a hot core in Orion. We show that our model could reproduce these observations well, highlighting that some COMs are positioned at a higher temperature in the envelope, whereas others are from the lower temperature, potentially leading to misinterpretation when using a single-point model. In a particular case of SgrB2(N1), the best model indicates that the cosmic-ray ionisation rate significantly exceeds the value typically used for the standard interstellar medium. Our model shows as an efficient computational tool particularly useful for better insights into observations of COMs.

astro-ph.GA↗

arXiv2025

The evolution of complex organic molecules during star formation

Complex organic molecules (COMs) are thought to be the precursors of pre-biotic molecules and are observed in many protostellar sources. For this paper we studied the formation of COMs during star formation and their evolution in the midplane of the circumstellar disk up to the end of the Class I stage. We used the Analytical Protostellar Environment (APE) code to perform analytical simulations of star formation and the Nautilus code to model the chemical evolution. Most COMs mainly form during the collapse or in the disk, except the lightest (CH3CCH, C3H6, CH3OH, CH3CHO, CH3OCH3, C2H5OH, CH3CN, CH3NC, C2H3CN, and CH3SH), which are significantly inherited by the disk from the prestellar phase. Over the first 150 kyr of the disk, the abundances of several COMs in the midplane vary negligibly (e.g., CH3CCH, CH3OH, and CH3CN), while others experience a variation of one order of magnitude (e.g., C2H3CHO HOCH2CHO, and CH3COCH2OH). Changing physical conditions also have an impact on the abundance profiles of COMs in the disk, and their inheritance. For example, increasing the temperature of the molecular cloud from 10 K to 15 K significantly promotes the formation of COMs in the prestellar phase, notably c-C2H4O and N-bearing species. Conversely, increasing the cloud mass from 2 Msol to 5 Msol only has a minor effect on the disk abundances in the early stages.

astro-ph.GA↗

arXiv2025

APE: An analytical protostellar environment to provide physical conditions to chemical models and synthetic observations

Chemical modeling and synthetic observations are powerful methods to interpret observations, both requiring a knowledge of the physical conditions. In this paper, we present the Analytical Protostellar Environment (APE) code, which aims at making chemical simulations and synthetic observations accessible. APE contains a physical model of protostellar evolution (including the central object, the envelope, the protoplanetary disk and the outflow) as well as interfaces to publicly available codes to perform chemical simulations, radiative transfer calculations, and synthetic interferometry imaging. APE produces density and temperature maps of protostellar systems. The code can also follow individual particles throughout their journey in a collapsing core. APE includes a treatment of the dust grain size-distribution to compute opacities self-consistently for subsequent radiative transfer. We show an example of application of APE by computing chemical abundance maps of CO, CN, CS, H2CO, and CH3OH in a Class I protostellar system. We also performed synthetic ALMA observations of their molecular emission assuming an edge-on source inclination. The moment 0 maps of CO, CS, and H2CO display an X-shaped emission similar to what is observed toward the Class I source IRAS 04302+2247.

astro-ph.SR↗

arXiv2025

The hot corino-like chemistry of four FUor-like protostars

Context: Compared to Class 0 protostars, the higher densities and lower temperatures of the disk midplanes of Class I young stellar objects (YSOs) limit the detectability of complex organic molecules (COMs). The elevated luminosities of eruptive YSOs increase disk temperatures sublimating frozen molecules and easing their detection. Aims: Our aim is to investigate the chemical composition of four FUor-like Class I YSOs: L1551 IRS 5, Haro 5a IRS, V346 Nor, and OO Ser, and to compare their abundances of COMs with other YSOs in the literature. Methods: We search for COMs line emission in ALMA Band 6 observations. We use the CASSIS software to determine their column densities (N) and excitation temperatures (T_ex) assuming local thermodynamical equilibrium. Results: We detect 249 transitions from 12 COMs. In L1551 IRS 5 we identified CH3OH, 13CH3OH, CH318OH, CH2DOH, CH3CHO, CH3OCH3, CH3OCHO, CH3COCH3, C2H5OH, C2H5CN, 13CH3CN, and CH3C15)N. Haro 5a IRS and OO Ser have emission from CH3OH, CH3CHO, CH3OCH3, and CH3OCHO. CH3COCH3 is also detected in OO Ser. In V346 Nor we found CH3OH, CH2DOH, CH3CHO, CH3OCH3, CH3OCHO, and C2H5CN. The emission of COMs is compact in all targets. The analysis indicates their temperatures are above 100K. The abundance ratios of COMs derived for these eruptive YSOs, as well as for other protostars in the literature, span several orders of magnitude without any clear differentiation between the eruptive and quiescent YSOs. The column density of the main isotopologue of CH3OH should not be used as a reference, as most of the lines are optically thick. Conclusions: The hot and compact emission of COMs indicates that the four FUor-like targets are hot corino-like. Spectral studies of such objects can be useful to investigate the complex organic chemistry at later evolutionary stages than the usual Class 0 stage.

astro-ph.GA↗

arXiv2024

Chemistry in the GG Tau A Disk: Constraints from H2D+, N2H+, and DCO+ High Angular Resolution ALMA Observations

Resolved molecular line observations are essential for gaining insight into the physical and chemical structure of protoplanetary disks, particularly in cold, dense regions where planets form and acquire their chemical compositions. However, tracing these regions is challenging because most molecules freeze onto grain surfaces and are not observable in the gas phase. We investigated cold molecular chemistry in the triple stellar T Tauri disk GG Tau A, which harbours a massive gas and dust ring and an outer disk, using ALMA Band 7 observations. We present high angular resolution maps of N2H+ and DCO+ emission, with upper limits reported for H2D+, 13CS, and SO2. The radial intensity profile of N2H+ shows most emission near the ring outer edge, while DCO+ exhibits double peaks, one near the ring inner edge and the other in the outer disk. With complementary observations of lower-lying transitions, we constrained the molecular surface densities and rotation temperatures. We compared the derived quantities with model predictions across different cosmic ray ionization (CRI) rates, carbon-to-oxygen (C/O) ratios, and stellar UV fluxes. Cold molecular chemistry, affecting N2H+, DCO+, and H2D+ abundances, is most sensitive to CRI rates, while stellar UV flux and C/O ratios have minimal impact on these three ions. Our best model requires a low cosmic ray ionization rate of 1e-18 s-1. However, it fails to match the low temperatures derived from N2H+ and DCO+, 12 to 16 K, which are much lower than the CO freezing temperature.

astro-ph.EP↗

arXiv2024

Unveiling gas phase H2NCO radical: Laboratory rotational spectroscopy and interstellar search toward IRAS 16293-2422

Context. The carbamoyl radical (H2NCO) is believed to play a central role in the ice-grain chemistry of crucial interstellar complex organic molecules as formamide and acetamide. Yet, little is known about this radical that remains elusive in laboratory gas-phase experiments. Aims. In order to enable interstellar searches of H2NCO, we have undertaken a mandatory laboratory characterisation of its pure rotational spectrum. Methods. We report the gas-phase laboratory detection of H2NCO, produced by H-atom abstraction from formamide, using pure rotational spectroscopy at millimetre and submillimetre wavelengths. Millimetre-wave data were acquired using chirped-pulse Fourier-transform spectroscopy while submillimetre-wave ones were obtained using Zeeman-modulated spectroscopy. Experimental measurements were guided by quantum-chemical calculations at the $ω$B97X-D/cc-pVQZ level of theory. Interstellar searches for the radical have been undertaken on the Protostellar Interferometric Line Survey (PILS) towards the solar-type protostar IRAS 16293-2422. Results. From the assignment and fit of experimental transitions up to 660 GHz, reliable spectroscopic parameters for H2NCO in its ground vibrational state have been derived, enabling accurate spectral predictions. No transitions of the radical were detected on the PILS survey. The inferred upper limit shows that H2NCO abundance is at least 60 times below that of formamide and 160 times below that of HNCO in this source; a value that is in agreement with predictions from a physico-chemical model of this young protostar.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2024

A far-ultraviolet-driven photoevaporation flow observed in a protoplanetary disk

Most low-mass stars form in stellar clusters that also contain massive stars, which are sources of far-ultraviolet (FUV) radiation. Theoretical models predict that this FUV radiation produces photo-dissociation regions (PDRs) on the surfaces of protoplanetary disks around low-mass stars, impacting planet formation within the disks. We report JWST and Atacama Large Millimetere Array observations of a FUV-irradiated protoplanetary disk in the Orion Nebula. Emission lines are detected from the PDR; modelling their kinematics and excitation allows us to constrain the physical conditions within the gas. We quantify the mass-loss rate induced by the FUV irradiation, finding it is sufficient to remove gas from the disk in less than a million years. This is rapid enough to affect giant planet formation in the disk.

astro-ph.GA↗

arXiv2023

PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar

(Abridged) We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the HII region to the atomic PDR (crossing the ionisation front (IF)), and the subsequent transition to the molecular PDR (crossing the dissociation front (DF)). We use high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science Program. The NIRSpec data reveal a forest of lines including, but not limited to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. We observe numerous smaller scale structures whose typical size decreases with distance from Ori C and IR lines from CI, if solely arising from radiative recombination and cascade, reveal very high gas temperatures consistent with the hot irradiated surface of small-scale dense clumps deep inside the PDR. The H2 lines reveal multiple, prominent filaments which exhibit different characteristics. This leaves the impression of a "terraced" transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star- and planet formation as well as galaxy evolution.

astro-ph.GA↗

arXiv2023

PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $μ$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $μ$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $μ$m AIB emission from class B$_{11.2}$ in the molecular PDR to class A$_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'.

astro-ph.GA↗

arXiv2023

A high HDO/H$_{2}$O ratio in the Class I protostar L1551 IRS5

Water is a very abundant molecule in star-forming regions. Its deuterium fractionation is an important tool for understanding its formation and evolution during the star and planet formation processes. While the HDO/H$_2$O ratio has been determined toward several Class 0 protostars and comets, the number of studies toward Class I protostars is limited. We aim to study the water deuteration toward the Class I binary protostar L1551 IRS5 and to investigate the effect of evolutionary stage and environment on variations in the water D/H ratio. Observations were made using the NOEMA interferometer. The HDO 3$_{1,2}$-2$_{2,1}$ transition at 225.9 GHz and the H$_2^{18}$O 3$_{1,3}$-2$_{2,0}$ transition at 203.4 GHz were covered with a spatial resolution of 0.5'' $\times$ 0.8'', while the HDO 4$_{2,2}$-4$_{2,3}$ transition at 143.7 GHz was observed with a resolution of 2.0'' $\times$ 2.5''. We used both LTE and non-LTE models. The three transitions are detected. The line profiles display two peaks, one at $\sim$6 km s$^{-1}$ and one at $\sim$9 km s$^{-1}$. We derive an HDO/H$_2$O ratio of (2.1 $\pm$ 0.8) $\times$ 10$^{-3}$ for the redshifted component and a lower limit of $>$ 0.3 $\times$ 10$^{-3}$ for the blueshifted component due to the blending with the redshifted CH$_3$OCH$_3$ emission. The HDO/H$_2$O in L1551 IRS5 is similar to the ratios in isolated Class 0 sources and to the Class I V883 Ori, while it is significantly higher than in the clustered Class 0 sources and the comets. This suggests that the chemistry of protostars in low source densities clouds share more similarities with the isolated sources than the protostars of very dense clusters. If Class 0 protostars with few sources around and isolated Class 0 objects are comparable in the HDO/H$_2$O ratio, it would mean that there is little water reprocessing from the Class 0 to Class I protostellar stage.

astro-ph.SR↗

arXiv2023

PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula

The JWST has captured the most detailed and sharpest infrared images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR). We investigate the fundamental interaction of far-ultraviolet photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of 0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. A complex, structured, and folded DF surface was traced by the H2 lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate.

astro-ph.GA↗

arXiv2022

The prebiotic molecular inventory of Serpens SMM1: II. The building blocks of peptide chains

This work aims to constrain the abundances of interstellar amides, by searching for this group of prebiotic molecules in the intermediate-mass protostar Serpens SMM1-a. ALMA observations are conducted toward Serpens SMM1. A spectrum is extracted toward the SMM1-a position and analyzed with the CASSIS line analysis software for the presence of characteristic rotational lines of a number of amides and other molecules. NH$_{2}$CHO, NH$_{2}$CHO $ν_{12}$=1, NH$_{2}^{13}$CHO, CH$_{3}$C(O)NH$_{2}$ $ν$=0,1, CH$_{2}$DOH, CH$_{3}$CHO, and CH$_{3}$C(O)CH$_{3}$ are securely detected, while trans-NHDCHO, NH$_{2}$CDO, CH$_{3}$NHCHO $ν$=0,1, CH$_{3}$COOH, and HOCH$_{2}$CHO are tentatively identified. The results of this work are compared with detections presented in the literature. A uniform CH$_{3}$C(O)NH$_{2}$/NH$_{2}$CHO ratio is found for a group of interstellar sources with vast physical differences. A similar ratio is seen for CH$_{3}$NHCHO, based on a smaller data sample. The D/H ratio of NH$_{2}$CHO is about 1--3\% and is close to values found in the low-mass source IRAS~16293--2422B. The formation of CH$_{3}$C(O)NH$_{2}$ and NH$_{2}$CHO is likely linked. Formation of these molecules on grain surfaces during the dark cloud stage is a likely scenario. The high D/H ratio of NH$_{2}$CHO is also seen as an indication that these molecules are formed on icy dust grains. As a direct consequence, amides are expected to be present in the most pristine material from which planetary systems form, thus providing a reservoir of prebiotic material.

astro-ph.GA↗

arXiv2022

Thermal desorption of interstellar ices. A review on the controlling parameters and their implications fromsnowlines to chemical complexity

The evolution of star-forming regions and their thermal balance are strongly influenced by their chemical composition, that, in turn, is determined by the physico-chemical processes that govern the transition between the gas phase and the solid state, specifically icy dust grains (e.g., particles adsorption and desorption). Gas-grain and grain-gas transitions as well as formation and sublimation of interstellar ices are thus essential elements of understanding astrophysical observations of cold environments (e.g., pre-stellar cores) where unexpected amounts of a large variety of chemical species have been observed in the gas phase. Adsorbed atoms and molecules also undergo chemical reactions which are not efficient in the gas phase. Therefore, the parameterization of the physical properties of atoms and molecules interacting with dust grain particles is clearly a key aspect to interpret astronomical observations and to build realistic and predictive astrochemical models. In this consensus evaluation, we focus on parameters controlling the thermal desorption of ices and how these determine pathways towards molecular complexity and define the location of snowlines, which ultimately influence the planet formation process. We review different crucial aspects of desorption parameters both from a theoretical and experimental point of view. We critically assess the desorption parameters commonly used in the astrochemical community for astrophysical relevant species and provide tables with recommended values. In addition, we show that a non-trivial determination of the pre-exponential factor nu using the Transition State Theory can affect the binding energy value. Finally, we conclude this work by discussing the limitations of theoretical and experimental approaches currently used to determine the desorption properties with suggestions for future improvements.

astro-ph.GA↗