Hendrik Linz

Context. The composition of rocky planets depends on the dust in their natal protoplanetary disk (PPD), which may contain water ice. Crystalline water ice was detected in the PPD d216-0939 in the Orion Nebula Cluster (ONC). Aims. We aim to constrain the spatial distribution and crystallization state of water ice in the d216-0939 disk using recent observations of the water ice absorption feature at a wavelength of ∼3 μm collected with JWST. Methods. We performed 3D Monte Carlo radiative transfer (MCRT) simulations to constrain the free parameters of an accretion disk model by fitting the calculated spectrum in the wavelength range from 1.6 μm to 24 μm to the spectral energy distribution (SED) observed with the JWST instruments NIRSpec and MIRI. Additionally, spatially resolved archival HST observations were used to constrain the global spatial structure of the disk, as the parameter space is degenerate with respect to the fit to the SED. Successively, we fitted the water ice absorption feature using polychromatic MCRT simulations with spectral importance sampling to produce synthetic observations at high spectral resolutions. Results. By probing the upper and outer disk layers, we found that a PPD model with dust containing 5.4% crystallized water ice beyond the snowline fits the observations well, necessitating the outward transport of material, since crystalline ice is unlikely to form in situ in the probed disk layers. In the spectral region of the water ice absorption feature, scattering and thermal dust emission both contribute significantly to the total flux.

Accretion-driven outbursts are a fundamental process in star formation, determining the final masses of stars and the chemistry of protoplanetary disks, yet their detection in the youngest, deeply embedded protostars remains challenging. Radiatively pumped methanol masers, to date associated exclusively with high-mass young stellar objects, exhibit flares that are interpreted as signatures of accretion bursts and serve as beacons to identify massive protostellar outbursts. Indeed, for all such methanol maser flares studied thus far, the driving source has been identified as the associated high mass protostar. By combining James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array (ALMA) observations, we prove that the recent methanol maser flare in the massive star-forming region IRAS 18134-194216 was driven by a nearby lower-mass protostar undergoing a strong accretion outburst, rather than the central massive object. Our infrared spectroscopy captures the physical and chemical response of the protostellar core to the accretion burst. Our results demonstrate that methanol masers flares can uncover the hidden population of embedded low-mass bursting protostars in massive clusters, and challenge the standard paradigm where such maser activity is exclusively attributed to massive protostars, demonstrating that cavities opened by low-mass companions can provide a radiative path for triggering flares of pre-existing masers excited by massive protostars.

Context . Although there has been significant progress, the physical properties and potential fragmentation of accretion disks around high-mass protostars remain poorly constrained. Aims . We characterize at high angular resolution one of the most nearby (~700 pc) high-mass accretion disk candidates, CepA HW2. Methods . Using the new long-baseline array configuration (~1700 m) of the Northern Extended Millimeter Array (NOEMA), we study CepA HW2 with a resolution of ≤0.2″ or ≤100 au at 1.3 mm in dust continuum and spectral line emission. Results . The millimeter continuum emission resolves the central disk candidate into several substructures. Conducting a Toomre Q stability analysis based on CH ₃ CN and continuum data, and a comparison to 3D radiation hydrodynamic simulations shows that the data are consistent with an almost edge-on disk whereby the observed substructures may represent fragments within the disk. The CO and SiO spectral line data confirm a second bipolar outflow (in addition to the well-known jet) emanating from the central peak position. This indicates that this central peak should host at least a binary if not even a higher-order multiple system. The usually assumed dense gas tracer CH ₃ CN also shows contributions from the outflows, which complicates further kinematic analysis of the disk. Conclusions . The high-resolution outflow-disk data of CepA reveal a multiply fragmented disk that drives several outflows. These observations reinforce the picture of high-mass star formation in which multiplicity and fragmentation can happen on the smallest spatial scales related to the inner accretion disks.

Context . Protoplanetary disks are the birthplace of planets and planetary systems. Investigating the molecular inventory of disks is key to linking the chemical evolution of the interstellar medium and the makeup of planets and their atmospheres. In particular, tracing the history of the deuterium enrichment of water along the journey from interstellar clouds through protoplanetary disks to planetary systems provides critical insights into the chemical inheritance. Aims . We aim to investigate the chemical composition of ices in protoplanetary disks; specifically, the presence of HDO ice that ought to be present, but has not been detected in disks thus far. Methods . We analyzed JWST/NIRSpec observations of the 132-1832 edge-on disk located in the Orion Nebula Cluster using the ENIIGMA fitting tool and unique laboratory data. Results . We report on the first detections of HDO ice in a protoplanetary disk. The estimated upper limit for the HDO/H ₂ O ratio for 132-1832 is much higher, compared to HDO/H ₂ O ratios obtained for chondrites, comets, and embedded young stellar objects. In the disk ices, beyond HDO, we detected H ₂ O, CO ₂ , ¹³ CO ₂ , CO, OCN ⁻ , and OCS, species, whose presence has also been detected in other disks. Conclusions . The HDO ice detection may point to the efficient ice processing in the disk and confirm the findings of laboratory experiments on deuterated ices.

Understanding the earliest stage of star and planet formation requires detailed observations to address the connection and interplay between the accretion, outflow, and disk evolution. We present results from the observations of the low luminosity ( L _bol ∼ 0.2 L _⊙ ) and mass ( M _* ∼ 0.15 M _⊙ ) Class 0 protostar IRAS 16253−2429, conducted as part of the eDisk Atacama Large Millimeter/submillimeter Array (ALMA) large program and the JWST cycle-1 GO Investigating Protostellar Accretion program. Observations reveal a wide hourglass-shaped continuum cavity traced in scattered light (at ≤5 μ m), with a brighter, extended northern side. We detect 15 pure rotational H ₂ transitions ( E _up : 1015–21411 K), revealing a wide-angle molecular outflow. The outflow width (as traced in H ₂ 0–0 S(11)) at the protostellar location measures ≤35 au, slightly larger than the dust and Keplerian disk diameters (∼30 au) but wider than the 20–23 au jet width in [Fe II ]. The opening angle narrows from 40° to 35° for the low-J H ₂ lines (up to S(5)) and the cold gas component (ALMA ¹² CO) to ∼28°–19° for the high-J H ₂ lines (S(7)–S(11)). Position–velocity diagrams of H ₂ reveal higher velocities for higher E _up , ranging from 12.5 km s ⁻¹ for H ₂ 0–0 S(1) and S(2) to 28.5 km s ⁻¹ for H ₂ 0–0 S(5) and S(7) with respect to the mean flow velocity. The nested excitation and velocity structure of the collimated jet and wide-angle wind suggest a magnetohydrodynamic wind as a likely launching mechanism, similar to the findings in other protostars and Class II sources. The lower velocity millimeter CO may be gas from the infalling envelope accelerated outwards by the wide-angle wind along the cavity walls.

The earliest stages of star formation are highlighted by complex interactions between accretion, outflow, and radiative processes, which shape the chemical and physical environment of the emerging protostar. James Webb Space Telescope observations of the low-mass, low-luminosity Class 0 protostar IRAS 16253–2429 (I16253) reveal a central compact source. This object exhibits a rich mid-IR emission spectrum of OH pure rotational lines and CO ₂ rovibrational lines. Unusually for a young stellar object, it has no mid-IR line emission from H ₂ O to match the other molecules. We demonstrate that the emitting OH molecules arise from UV photodissociation of H ₂ O in its second absorption band at λ = 114–145 nm, and that the OH emission is a fluorescent cascade starting with highest-excitation rotational states. This situation offers the opportunity of using the IR OH spectrum to measure the UV flux from the central protostar. Thereby, we determine the disk-to-star accretion rate to be 3 × 10 ⁻¹⁰ M _⊙ yr ⁻¹ , and demonstrate that the system luminosity arises mostly from the protostar’s photosphere rather than from accretion luminosity. The result is in accord with the measured outflow rate of I16253 and lies within the outflow/accretion-flow rate trend often inferred for protostars, and with episodic accretion as the dominant mechanism by which this protostar has grown.

Context . How dense clouds and star-forming regions form out of the dynamical interstellar medium is at the heart of star formation research. Aims . The G28.37+0.07 star-forming region is a prototypical infrared dark cloud (IRDC) located at the interface of a converging gas flow. This study characterizes the properties of this dynamic gas flow. Methods . Combining data from the Northern Extended Millimeter Array (NOEMA) with single-dish data from the IRAM 30 m observatory, we mapped large spatial scales (~81 pc ² ) at high angular resolution (7.0″ × 2.6″ corresponding ~2.3×10 ⁴ au or ~0.1 pc) down to core scales. The spectral setup in the 3 mm band covers many spectral lines as well as the continuum emission. Results . The data clearly reveal the proposed west–east converging gas flow in all observed dense gas tracers. We estimate a mass-flow rate along that flow around 10 ⁻³ M _⊙ yr ⁻¹ . Comparing these west–east flow rates to infall rates toward sources along the line of sight, the gas flow rates are roughly a factor of 25 greater than those along the line of sight (roughly perpendicular to the west–east flow). This confirms the dominance of longitudinal motions along the converging gas flow in this region. For comparison, in the main north–south IRDC formed by the west–east converging gas flow, infall rates along the line of sight are about an order of magnitude greater than those along the west–east flow. In addition to the kinematic analysis, a comparison of CH ₃ CN-derived gas temperatures with Herschel- derived dust temperatures typically show higher gas temperatures toward high-density sources. We discuss whether mechanical heating from the conversion of the flow’s kinetic energy into thermal energy may explain some of the observed temperature differences. Conclusions . Our analysis of the G28.37+0.07 converging gas flow shows that such structures can indeed form and feed typical highmass star-forming regions in the Milky Way. The differences between flow rates along the converging flow, perpendicular to it, and toward the sources at the IRDC center indicate that at the interfaces of converging gas flows – where most of the active star formation takes place – originally more directed gas flows can convert into multidirectional infall motions.

Context. While the number of detected molecules, particularly complex organic molecules, in the solid state in astrophysical environments is still rather limited, laboratory experiments and astrochemical models predict many potential candidates. Detection of molecules in protoplanetary disks provides a bridge between the chemical evolution of the interstellar medium and the chemistry of planets and their atmospheres. Aims. The excellent spectral sensitivity, broad wavelength coverage, and high spatial resolution of the James Webb Space Telescope (JWST) allows us to make progress in exploring chemical compositions of various astrophysical environments, including planet-forming disks. They are a prerequisite for probing the disk content by means of sensitive absorption studies. Methods. In this paper we present the initial results of the JWST Cycle 1 GO programme 1741 on d216-0939, a highly inclined TTauri disk located in the outskirts of the Orion Nebula Cluster. We utilised the NIRSpec and MIRI integral field unit spectrographs to cover its spectrum from 1.7 to 28 μm. Results. The spectra of the d216-0939 disk show clear absorption signatures of amorphous silicates and ices. We unambiguously detected the solid-state features of H₂O, CO₂, ¹³CO₂, CO, OCN⁻, and tentatively OCS ices, species that had also been detected recently in other circumstellar disks. For the first time in disks, we provide unique detections of ices carrying NH₄⁺ and the complex organic molecule ammonium carbamate (NH₄⁺NH₂COO⁻). Conclusions. The latter detections speak for a very efficient NH₃ chemistry in the disk. We also show the very important role of scattering in the analysis of observational spectra of highly inclined disks.

The composition of protoplanetary disks, and hence the initial conditions of planet formation, may be strongly influenced by the infall and thermal processing of material during the protostellar phase. The composition of dust and ice in protostellar envelopes, shaped by energetic processes driven by the protostar, serves as the fundamental building material for planets and complex organic molecules. As part of the JWST General Observers program, “Investigating Protostellar Accretion,” we observed an intermediate-mass protostar HOPS 370 (OMC2-FIR3) using NIRSpec integral field unit and Mid-Infrared Instrument medium-resolution spectroscopy. This study presents the gas and ice phase chemical inventory revealed with the JWST in the spectral range of ∼2.9–28 μm and explores the spatial variation of volatile ice species in the protostellar envelope. We find evidence for the thermal processing of ice species throughout the inner envelope. We present the first high-spatial resolution (∼80 au) maps of key volatile ice species H₂O, CO₂, ¹³CO₂, CO, and OCN⁻, which reveal a highly structured and inhomogeneous density distribution of the protostellar envelope, with a deficiency of ice column density that coincides with the jet/outflow shocked knots. Further, we observe high relative crystallinity of H₂O ice around the shocked knot seen in the H₂ and OH wind/outflow, which can be explained by a lack of outer colder material in the envelope along the line of sight due to the irregular structure of the envelope. These observations show clear evidence of thermal processing of the ices in the inner envelope, close to the outflow cavity walls, heated by the luminous protostar.