Adwin Boogert

The Barnard 335 (B335) protostar has recently undergone a major, still ongoing, outburst detected in scattered light from its outflow cavity, offering a rare opportunity to study its impact on a protostellar jet. We use James Webb Space Telescope (JWST) NIRCam photometry of background stars behind B335 from 2.7 to 4.4 μ m to map extinction and H ₂ O ice absorption, showing that the outflow has carved a cavity in the molecular core. We measure proper motions of shock fronts emerging from the protostar of 131–227 km s ⁻¹ . The kinematic age of the most prominent shock front, 3E, corresponds to the early phase of the current outburst. JWST/NIRSpec Integral Field Unit data show that the youngest shock, 2E, exhibits ionic lines but no molecular emission. Shock 3E shows strong CO emission together with H ₂ and [Fe ii ], whereas older shocks show weaker CO and are dominated by H ₂ and [Fe ii ]. The feature 0E, closest to the protostar, appears to be a stationary shock. CO-line-removed spectra near the protostar show that the unsaturated absorption features of ¹³ CO ₂ , OCN ^– , and OCS increase strongly toward the source. The ice properties are otherwise similar to those along lower-extinction sight lines. In the central bipolar reflection nebula, CO gas is seen in scattered emission from the immediate protostellar surroundings, but a few arcseconds farther out, absorption by cooler CO gas in the outflow cavity is detected.

Complex organic molecules (COMs) are the key to understanding the chemical evolution from simple interstellar molecules to potential prebiotic material. Although COMs have been extensively studied in the gas phase toward protostars, their counterparts in ices, where they are thought to form at earlier stages, remain far less constrained. A number of diagnostic features of complex ices lie between 6.8 and 8.8 μ m, a region known as the “COM ice fingerprint range,” but previous infrared facilities lacked the sensitivity and spectral resolution required to quantify the weak bands therein. With the unprecedented sensitivity and resolving power of the James Webb Space Telescope, these limitations can now be overcome. Here, we present the first large-sample quantitative study of the absorption features at 7.02, 7.24, 7.40, and 7.67 μ m, using mid-infrared spectra of 21 protostars observed by the Medium Resolution Spectroscopy mode of the Mid-Infrared Instrument. The CH ₄ band at 7.67 μ m is the strongest band and shows remarkably uniform peak positions (7.67–7.68 μ m) and full widths at half-maximum (FWHMs; 0.06–0.08 μ m), suggesting CH ₄ ice as its dominant carrier. The 7.24 and 7.40 μ m bands exhibit larger source-to-source variations in peak positions and FWHMs, but their occurrence and intensities are strongly correlated with each other. Comparisons with existing and new laboratory spectra suggest HCOO ⁻ as the most likely carrier of these two bands, yet HCOO ⁻ cannot fully reproduce their intensity ratios, implying additional contributions from other species such as C ₂ H ₅ OH, CH ₃ CHO, and CH ₃ COCH ₃ . Our results reveal, for the first time, the potential ubiquity of weak features of complex ices in protostars, which have remained largely undetected due to observational limitations.

Nitrogen-bearing molecules are generally more difficult to observe than oxygen-bearing ones in both gas and ice, mainly due to the lower abundance of nitrogen in the interstellar medium. Therefore, the formation pathways of many of these species is still under debate. Studies prior to the launch of the Space Telescope (JWST) did not have the sensitivity to observe ices toward the youngest and most deeply embedded Class 0 objects. The time is now ripe to study nitrogen-bearing molecules toward ice-rich Class 0 and Class I objects with the JWST. Here we focus on OCN-$, CH_3CN, C_2H_5CN, NO, and N$_2O in ices to better understand their formation. James Webb We used the data from JWST Observations of Young protoStars (JOYS+) program. Particularly, we studied the objects that have the JWST NIRSpec-IFU observations (8 Class 0 and 11 Class I) to measure the ice column densities of the targeted molecules. We firmly detect OCN-$ in ices for all these objects, tentatively detect CH_3CN, C_2H_5CN, and N_2O toward three sources, and find upper limits on the NO abundance in ices. The OCN^-/CO_2 ratios are found to be higher by a factor of ∼2-3 for the objects that have a visible CO_2 (15.2,μm) double peak (a sign of ice thermal processing), which points to the moderate effect of temperature on OCN^- production. Considering H_2O, CO_2, and OCN^- relations with A_̊m V, we tentatively find that OCN^- forms at a later stage compared to H_2O and CO_2. We find that the ratios of CH_3CN, C_2H_5CN, and N_2O with respect to OCN^- are relatively constant within one order of magnitude across our objects, likely suggesting that they have similar ice environments. The upper limit abundances of NO are around one order of magnitude lower than what was previously predicted in ices of a mature protoplanetary disk to explain the gas-phase detection of this molecule in the disk. This indicates that gas-phase NO may be a product of another molecule such as N$_2O in the ices. We conclude that after OCN-$ forms, it can increase at higher temperatures by only a factor of ∼2-3, and thus OCN^- detection alone does not imply ice heating. Large-sample studies of OCN$^- toward pre-stellar cores will be useful to further confirm the formation timeline of this molecule.

Supernova remnants (SNRs) can strongly affect the chemical composition of the interstellar dust. In this paper, we investigate to what degree the dust and ices are modified by observing four stars expected to be absorbed by a giant molecular cloud interacting with SNR W44, using medium-resolution spectroscopy in 2–5 μ m. Absorption from H ₂ O ice around 3.0 μ m and aliphatic hydrocarbon dust around 3.4 μ m were detected toward two stars, while probable CO ice at 4.67 μ m was detected toward one of them. Millimeter gas-phase CO J = 1–0 lines and three-dimensional (3D) dust extinction maps show that the dense molecular gas associated with W44 dominates (≳60%) the total interstellar extinction ( A _K ∼ 2.6) along these two sight lines. The H ₂ O ice column densities are a factor of 1.5–3 lower than nearby molecular clouds at similar extinctions, possibly because of the destruction of ice by shocks and cosmic rays (CRs) from W44, consistent with the low CO ice abundance relative to H ₂ O (≲12%). One of the sight lines shows an unusually strong 3.4 μ m aliphatic hydrocarbon absorption. If the carriers are located in diffuse dust along the sight line, unrelated to W44, their strength is ∼4 times larger than that typically observed for diffuse dust clouds. Alternatively, the carriers may be enhanced in the W44 environment. We discuss several possible explanations, including shock formation of aliphatic hydrocarbons in diffuse clouds associated with W44, contribution from aliphatic hydrocarbons in shocked and CR-bombarded molecular clouds, and changes in the extinction law due to the SNR interaction.

As the James Webb Space Telescope (JWST) pursues its observing journey, several thousands of icy-grain spectra are expected to be measured and analysed. The inventory of ices in particular, via the observations of background sources, is accessible for hundreds of lines of sight (LOSs) per molecular-cloud region, opening the possibility to add strong constraints on the solid phase chemistry in a vast domain of cloud densities. SynthIceSpec is a synthetic infrared (IR) spectrum generator that has been designed as a tool to support observing proposals and to test the outcome of chemical models. It is based on laboratory measurements of pure and mixed ices, where each vibrational component is fitted by a sum of Gaussian profiles. Given an initial ice chemical composition (either set by the user or the outputs of a chemical model), a full JWST spectrum is generated, to which the contribution of silicates; continuum, stellar photospheric absorption bands; and extinction law can be added. For the continuum, stellar photospheric models for a wide range of spectral types can be selected by the program, or, Spectral Energy Distribution (SEDs). We present a few use cases of SynthIceSpec: we probed the impact of dust temperature on CO ₂ ice formation using IR data and gas-grain modelling. Next, we used SynthIceSpec to explore the detectability of the main feature of CH ₃ CN at 4.45 µm in a cold core environment with the JWST, which was previously tentatively detected in YSOs. The detection thresholds we derive are reasonably low and observable, but identification is directly impacted by the photosphere absorptions that can greatly hinder identification. For some photostellar types, it could remain feasible. Coupled with the Estimated Time Calculator of the Space Telescope Science Institute, SynthIceSpec can be used to find the optimum observational setup for new observations.

Context . The Central Molecular Zone (CMZ) of the Milky Way contains a substantial reservoir of dense molecular gas, where numerous young stellar objects (YSOs) and dense cloud cores have been identified, offering valuable opportunities to investigate star formation in the nuclear regions of spiral galaxies. However, the large distance and severe foreground extinction complicate detailed interpretation, particularly of infrared absorption features from various ice species that trace the chemical composition and evolutionary state of these embedded objects. Aims . To better characterise YSOs and dense cores in this region, we combined spectra from multiple YSOs, each likely backlit by a giant star, allowing us to probe their outer layers and derive an ensemble-averaged ice abundance profile. Methods . We obtained L -band spectra of 15 point-like sources with extremely red colours using GNIRS on Gemini North, enabling measurements of the CH ₃ OH absorption feature at 3.535 μm. A subset of these sources was also observed in the K band. To better constrain the foreground extinction and H ₂ O ice column densities, we combined these data with K -band and mid-infrared spectra from our previous observations using NASA/IRTF and Spitzer /IRS. Results . We found that the CH ₃ OH abundance in the CH ₃ OH-CO ₂ ice mixture (traced by the 15.4 μm shoulder) lies between 2-5%, reaffirming previous findings and confirming that it is systematically lower than the 5-15% typically observed in the Galactic disc. Furthermore, by using the local excess of foreground extinction as a proxy for the projected distance between a backlit source and the centre of a YSO, we found that the CH ₃ OH abundance relative to solid CO ₂ remains at the ∼10% level in the inner regions of the envelope, but increases sharply to ∼30% in the outer regions. Conclusions . The relatively low methanol ice abundance may reflect the unique chemical environment of the CMZ, including variations in elemental abundances and surface reaction pathways on dust grains. However, our results offer an alternative interpretation: since our sample is biased towards massive and luminous YSOs, intense heating from the central protostar may have caused substantial sublimation of methanol ice in the inner regions of their envelopes, thereby systematically lowering the observed CH ₃ OH/H ₂ O ice ratios.

Most exoplanets known orbit stars that will evolve into red giants, then white dwarfs (WDs). Understanding the population of substellar WD companions informs the common-envelope evolution process (E. Villaver & M. Livio 2009), thereby shedding light on the current and future planetary population of the Milky Way. Here, we report the discovery of a low-mass (25 ± 5M _Jup) brown dwarf (BD) fully eclipsing every 2.93 hr the WD J0404+1112, which we found to be an unexpectedly large host WD (2R _Earth). The eclipsing nature of the system, the low masses of the primary (∼0.3M _Sun) and secondary, and the large day–night temperature contrast for the BD ( ⪭ 2000 K) make it a prime target amongst the dozen WD+BD systems known for a detailed study via JWST phase-curve observations.

We present an analysis of CO rovibrational emission lines in the 183 infrared spectra of nearby Class II objects obtained with the NIRSPEC instrument on the Keck II telescope over the past two decades. The sample includes a broad range of stellar mass (both T Tauri and Herbig Ae/Be) and disk evolutionary states (from full to debris disks). We find that 53% of the sample has CO rovibrational emission lines present in their spectrum with disk/stellar subtype detection rates of 82% for transition disks, 61% for Herbigs, and 77% for classical T Tauri stars. Although there is no discernible difference between T Tauri and Herbig Ae/Be star CO detection rates, the detection of accretion and of CO are statistically correlated in T Tauri stars but not in Herbig Ae/Be objects. Within the sample of T Tauri stars, we find that no weak-line T Tauri stars have CO rovibrational emission lines. We use slab modeling to analyze the density, temperature, and emitting area of the sample. The retrieval results imply that Herbig Ae/Be objects tend to have cooler and larger CO emitting regions than T Tauri stars. We find that the CO emitting area is not a thin ring as defined by temperature, but a ring of varying size, likely dependent on the structure of the disk. We also present guidelines on how to approach CO rovibrational emission lines in JWST spectra and present methods for linking ground-based observations with JWST spectra. This includes line-to-continuum ratio estimates based on stellar mass and accretion rate.

We present an analysis of CO rovibrational emission lines in the 183 infrared spectra of nearby Class II objects obtained with the NIRSPEC instrument on the Keck II telescope over the past two decades. The sample includes a broad range of stellar mass (both T Tauri and Herbig Ae/Be) and disk evolutionary states (from full to debris disks). We find that 53% of the sample has CO rovibrational emission lines present in their spectrum with disk/stellar subtype detection rates of 82% for transition disks, 61% for Herbigs, and 77% for CTTSs. Although there is no discernible difference between T Tauri and Herbig Ae/Be star CO detection rates, the detection of accretion and of CO are statistically correlated in T Tauri stars but not in Herbig Ae/Be objects. Within the sample of T Tauri stars, we find that no weak-line T Tauri stars have CO rovibrational emission lines. We use slab modeling to analyze the density, temperature, and emitting area of the sample. The retrieval results imply that Herbig Ae/Be objects tend to have cooler and larger CO emitting regions than T Tauri stars. We find that the CO emitting area is not a thin ring as defined by temperature, but a ring of varying size likely dependent on the structure of the disk. We also present guidelines on how to approach CO rovibrational emission lines in JWST spectra and present methods for linking ground-based observations with JWST spectra. This includes line-to-continuum ratio estimates based on stellar mass and accretion rate.