Hannah Calcutt

Context. Dust grains are fundamental components of the interstellar medium (ISM), playing a crucial role in star formation as catalysts for chemical reactions and planetary building blocks. Extinction curves can serve as a tool for characterizing dust properties, however mid-infrared (MIR) extinction remains less constrained in protostellar environments. Gas-phase line ratios from embedded protostellar jets offer a spatially resolved method for measuring the extinction from protostellar envelopes, complementing traditional background starlight techniques. Aims. We aim to derive MIR extinction curves along the lines of sight toward a protostellar jet embedded within an envelope and to assess whether they differ from those inferred from dense molecular clouds. Methods. We analyzed JWST NIRSpec IFU and MIRI MRS observations, focusing on four locations along the blue-shifted TMC1A jet. After extracting observed [Fe II] line intensities, we modeled the intrinsic line ratios using the Cloudy spectral synthesis code across a range of electron densities and temperatures. By comparing observed near-IR (NIR) and MIR line ratios to intrinsic ratios predicted with Cloudy, we were able to infer the relative extinction between the NIR and MIR wavelengths. Results. The electron densities (n_e) derived from NIR [Fe II] lines range from ~5 × 10⁴ to ~5 × 10³ cm⁻³ along the jet axis at scales ≲350 AU, serving as reference points for comparing the relative NIR and MIR extinction. The derived MIR extinction results display a higher reddening than empirical dark cloud curves at the corresponding n_e values and temperatures (from a few 10³ to ~10⁴ K) adopted from shock models. While both the electron density and temperature influence the NIR-to-MIR [Fe II] line ratios, the ratios are more strongly dependent on n_e over the adopted range. If the MIR emission originates from gas that is less dense and cooler than the NIR-emitting region, the inferred extinction curves remain consistent with background star-derived values. Conclusions. This study introduces a new line-based method for deriving spatially resolved MIR extinction curves towards embedded protostellar sources exhibiting a bright [Fe II] jet. These results suggest that protostellar envelopes may contain dust with a modified grain size distribution, such as an increased fraction of larger grains (potentially due to grain growth) if the MIR and NIR lines originate from similar regions along the same sight lines. Alternatively, if the grain size distribution has not changed (i.e., there is no grain growth), the MIR lines may trace cooler, less dense gas than the NIR lines along the same sight lines. This method provides a novel approach for studying dust properties in star-forming regions that could be extended to other protostellar systems to refine extinction models in embedded environments.

Context. Protostellar outflows exhibit large variations in their structure depending on the observed gas emission. To understand the origin of the observed variations, it is important to analyze the differences in the observed morphology and kinematics of the different tracers. The James Webb Space Telescope (JWST) allows us to study the physical structure of the protostellar outflow through well-known near-infrared shock tracers in a manner unrivaled by other existing ground-based and space-based telescopes at these wavelengths. Aims. This study analyzes the atomic jet and molecular outflow in the Class I protostar, TMC1A, utilizing spatially resolved [Fe II] and H₂ lines to characterize the morphology and to identify previously undetected spatial features, and compare them to existing observations of TMC1A and its outflows observed at other wavelengths. Methods. We identified a large number of [Fe II] and H₂ lines within the G140H, G235H, and G395H gratings of the NIRSpec IFU observations. We analyzed their morphology and position-velocity (PV) diagrams. From the observed [Fe II] line ratios, the extinction toward the jet is estimated. Results. We detected the bipolar Fe jet by revealing, for the first time, the presence of a redshifted atomic jet. Similarly, the red-shifted component of the H₂ slower wide-angle outflow was observed. The [Fe II] and H₂ redhifted emission both exhibit significantly lower flux densities compared to their blueshifted counterparts. Additionally, we report the detection of a collimated high-velocity (~100 km s⁻¹), blueshifted H₂ outflow, suggesting the presence of a molecular jet in addition to the well-known wider angle low-velocity structure. The [Fe II] and H₂ jets show multiple intensity peaks along the jet axis, which may be associated with ongoing or recent outburst events. In addition to the variation in their intensities, the H₂ wide-angle outflow exhibits a ring-like structure. The blueshifted H₂ outflow also shows a left-right brightness asymmetry likely due to interactions with the surrounding ambient medium and molecular outflows. Using the [Fe II] line ratios, the extinction along the atomic jet is estimated to be between A_V = 10–30 on the blueshifted side, with a trend of decreasing extinction with distance from the protostar. A similar A_V is found for the redshifted side, supporting the argument for an intrinsic red-blue outflow lobe asymmetry rather than environmental effects such as extinction. This intrinsic difference revealed by the unprecedented sensitivity of JWST, suggests that younger outflows already exhibit the red-blue side asymmetry more commonly observed toward jets associated with Class II disks.

Context. Molecular lines are commonly detected towards protostellar sources. However, to get a better understanding of the chemistry of these sources we need unbiased molecular surveys over a wide frequency range for as many sources as possible to shed light on the origin of this chemistry, particularly any influence from the external environment. Aims. We present results from the PILS-Cygnus survey of ten intermediate- to high-mass protostellar sources in the nearby Cygnus-X complex, through high angular resolution interferometric observations over a wide frequency range. Methods. Using the Submillimeter Array (SMA), a spectral line survey of ten sources was performed in the frequency range 329–361 GHz, with an angular resolution of ~1″.5, or ~2000 AU at a source distance of 1.3 kpc from the Sun. Spectral modelling was performed to identify molecular emission and determine column densities and excitation temperatures for each source. Emission maps were made to study the morphology of emission. Finally, emission properties were compared across the sample. Results. We detect CH₃OH towards nine of the ten sources, with CH₃OCH₃ and CH₃OCHO towards three sources. We further detect CH₃CN towards four sources. Towards five sources the chemistry is spatially differentiated, meaning that different species peak at different positions and are offset from the peak continuum emission. Low levels of deuteration are detected towards four sources in HDO emission, whereas deuterated complex organic molecule emission is detected towards one source (CH₂DOH towards N63). The chemical properties of each source do not correlate with their position in the Cygnus-X complex, nor do the distance or direction to the nearest OB associations. However, the five sources located in the DR21 filament do appear to show less line emission compared to the five sources outside the filament. Conclusions. This work shows how important wide frequency coverage observations are combined with high angular resolution observations for studying the protostellar environment. Furthermore, based on the ten sources observed here, the external environment appears to only play a minor role in setting the chemical environment on these small scales (<2000 AU).

Context. Previous observations of the isolated Class 0 source B335 have presented evidence of ongoing infall in various molecular lines, such as HCO⁺, HCN, and CO. There have been no confirmed observations of a rotationally supported disk on scales greater than ~12 au. Aims. The presence of an outflow in B335 suggests that a disk is also expected to be present or undergoing formation. To constrain the earliest stages of protostellar evolution and disk formation, we aim to map the region where gas falls inwards and observationally constrain its kinematics. Furthermore, we aim to put strong limits on the size and orientation of any disk-like structure in B335. Methods. We used high angular resolution ¹³CO data from the Atacama Large Millimeter/submillimeter Array (ALMA) and combined it with shorter-baseline archival data to produce a high-fidelity image of the infall in B335. We also revisited the imaging of high-angular resolution Band 6 continuum data to study the dust distribution in the immediate vicinity of B335. Results. Continuum emission shows an elliptical structure (10 by 7 au) with a position angle 5 degrees east of north, consistent with the expectation for a forming disk in B335. A map of the infall velocity (as estimated from the ¹³CO emission), shows evidence of asymmetric infall, predominantly from the north and south. Close to the protostar, infall velocities appear to exceed free-fall velocities. Three-dimensional (3D) radiative transfer models, where the infall velocity is allowed to vary within the infall region, may explain the observed kinematics. Conclusions. The data suggest that a disk has started to form in B335 and that gas is falling towards that disk. However, kinematically-resolved line data towards the disk itself is needed to confirm the presence of a rotationally supported disk around this young protostar. The high infall velocities we measured are not easily reconcilable with a magnetic braking scenario, suggesting that there is a pressure gradient that allows the infall velocity to vary in the region.

Outflows and winds launched from young stars play a crucial role in the evolution of protostars and the early stages of planet formation. However, the specific details of the mechanism behind these phenomena, including how they affect the protoplanetary disk structure, are still debated. We present JWST NIRSpec integral field unit observations of atomic and H₂ lines from 1 to 5.1 μm toward the low-mass protostar TMC1A. For the first time, a collimated atomic jet is detected from TMC1A in the [Fe ii] line at 1.644 μm along with corresponding extended H₂ 2.12 μm emission. Toward the protostar, we detected spectrally broad H i and He i emissions with velocities up to 300 km s⁻¹ that can be explained by a combination of protostellar accretion and a wide-angle wind. The 2 μm continuum dust emission, H i, He i, and O i all show emission from the illuminated outflow cavity wall and scattered line emission. These observations demonstrate the potential of JWST to characterize and reveal new information about the hot inner regions of nearby protostars; in this case, a previously undetected atomic wind and ionized jet in a well-known outflow.

Context. Complex organic molecules (COMs) are commonly detected in and near star-forming regions. However, the dominant process in the release of these COMs from the icy grains – where they predominately form – to the gas phase is still an open question. Aims. We investigate the origin of COM emission in a high-mass protostellar source, CygX-N30 MM1, through high-angular-resolution interferometric observations over a continuous broad frequency range. Methods. We used 32 GHz Submillimeter Array observations with continuous frequency coverage from 329 to 361 GHz at an angular resolution of ~1″ to do a line survey and obtain a chemical inventory of the source. The line emission in the frequency range was used to determine column densities and excitation temperatures for the COMs. We also mapped out the intensity distribution of the different species. Results. We identified approximately 400 lines that can be attributed to 29 different molecular species and their isotopologues. We find that the molecular peak emission is along a linear gradient, and coincides with the axis of red- and blueshifted H₂CO and CS emission. Chemical differentiation is detected along this gradient, with the O-bearing molecular species peaking towards one component of the system and the N- and S-bearing species peaking towards the other. The chemical gradient is offset from but parallel to the axis through the two continuum sources. The inferred column densities and excitation temperatures are compared to other sources where COMs are abundant. Only one deuterated molecule is detected, HDO, while an upper limit for CH₂DOH is derived, leading to a D/H ratio of Conclusions. We conclude that the origin of the observed COM emission is probably a combination of the young stellar sources along with accretion of infalling material onto a disc-like structure surrounding a young protostar and located close to one of the continuum sources. This disc and protostar are associated with the O-bearing molecular species, while the S- and N-bearing species on the other hand are associated with the other continuum core, which is probably a protostar that is slightly more evolved than the other component of the system. The low D/H ratio likely reflects a pre-stellar phase where the COMs formed on the ices at warm temperatures (~30 K), where the deuterium fractionation would have been inefficient. The observations and results presented here demonstrate the importance of good frequency coverage and high angular resolution when disentangling the origin of COM emission.

Aims. Methyl isocyanate (CH₃NCO) and glycolonitrile (HOCH₂CN) are isomers and prebiotic molecules that are involved in the formation of peptide structures and the nucleobase adenine, respectively. These two species are investigated to study the interstellar chemistry of cyanides (CN) and isocyanates (NCO) and to gain insight into the reservoir of interstellar prebiotic molecules. Methods. ALMA observations of the intermediate-mass Class 0 protostar Serpens SMM1-a and ALMA-PILS data of the low-mass Class 0 protostar IRAS 16293B are used. Spectra are analysed with the CASSIS line analysis software package in order to identify and characterise molecules. Results. CH₃NCO, HOCH₂CN, and various other molecules are detected towards SMM1-a. HOCH₂CN is identified in the PILS data towards IRAS 16293B in a spectrum extracted at a half-beam offset position from the peak continuum. CH₃NCO and HOCH₂CN are equally abundant in SMM1-a at [X]/[CH₃OH] of 5.3 × 10⁻⁴ and 6.2 × 10⁻⁴, respectively. A comparison between SMM1-a and IRAS 16293B shows that HOCH₂CN and HNCO are more abundant in the former source, but CH₃NCO abundances do not differ significantly. Data from other sources are used to show that the [CH₃NCO]/[HNCO] ratio is similar in all these sources within ~10%. Conclusions. The new detections of CH₃NCO and HOCH₂CN are additional evidence for a large interstellar reservoir of prebiotic molecules that can contribute to the formation of biomolecules on planets. The equal abundances of these molecules in SMM1-a indicate that their formation is driven by kinetic processes instead of thermodynamic equilibrium, which would drive the chemistry to one product. HOCH₂CN is found to be much more abundant in SMM1-a than in IRAS 16293B. From the observational data, it is difficult to indicate a formation pathway for HOCH₂CN, but the thermal Strecker-like reaction of CN⁻ with H₂CO is a possibility. The similar [CH₃NCO]/[HNCO] ratios found in the available sample of studied interstellar sources indicate that these two species are either chemically related or their formation is affected by physical conditions in the same way. Both species likely form early during star formation, presumably via ice mantle reactions taking place in the dark cloud or when ice mantles are being heated in the hot core. The relatively high abundances of HOCH₂CN and HNCO in SMM1-a may be explained by a prolonged stage of relatively warm ice mantles, where thermal and energetic processing of HCN in the ice results in the efficient formation of both species.

Context.Physical processes that govern the star and planet formation sequence influence the chemical composition and evolution of protoplanetary disks. Recent studies allude to an early start to planet formation already during the formation of a disk. To understand the chemical composition of protoplanets, we need to constrain the composition and structure of the disks from whence they are formed.Aims.We aim to determine the molecular abundance structure of the young disk around the TMC1A protostar on au scales in order to understand its chemical structure and any possible implications for disk formation.Methods.We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of CO, HCO⁺, HCN, DCN, and SO line emission, as well as dust continuum emission, in the vicinity of TMC1A. Molecular column densities are estimated both under the assumption of optically thin emission from molecules in local thermodynamical equilibrium (LTE) as well as through more detailed non-LTE radiative transfer calculations.Results.Resolved dust continuum emission from the disk is detected between 220 and 260 GHz. Rotational transitions from HCO⁺, HCN, and SO are also detected from the inner 100 au region. We further report on upper limits to vibrational HCNυ₂= 1, DCN, and N₂D⁺lines. The HCO⁺emission appears to trace both the Keplerian disk and the surrounding infalling rotating envelope. HCN emission peaks toward the outflow cavity region connected with the CO disk wind and toward the red-shifted part of the Keplerian disk. From the derived HCO⁺abundance, we estimate the ionization fraction of the disk surface, and find values that imply that the accretion process is not driven by the magneto-rotational instability. The molecular abundances averaged over the TMC1A disk are similar to its protostellar envelope and other, older Class II disks. We meanwhile find a discrepancy between the young disk’s molecular abundances relative to Solar System objects.Conclusions.Abundance comparisons between the disk and its surrounding envelope for several molecular species reveal that the bulk of planet-forming material enters the disk unaltered. Differences in HCN and H₂O molecular abundances between the disk around TMC1A, Class II disks, and Solar System objects trace the chemical evolution during disk and planet formation.