This work aims to utilize the increased sensitivity and resolution of the JWST to quantify the HDO/H$_{2}$O ratio in ices toward young stellar objects (YSOs) and to determine if the HDO/H$_{2}$O ratios measured in the gas phase toward massive YSOs (MYSOs) are representative of the ratios in their ice envelopes. Two protostars observed in the Investigating Protostellar Accretion (IPA) program using JWST NIRSpec were analyzed: HOPS 370, an intermediate-mass YSO (IMYSO), and IRAS 20126+4104, a MYSO. The HDO ice toward these sources was detected above the 3$\sigma$ level and quantified via its 4.1 $\mu$m band. The contributions from the CH$_{3}$OH combination modes to the observed optical depth in this spectral region were constrained via the CH$_{3}$OH 3.53 $\mu$m band to ensure that the integrated optical depth of the HDO feature was not overestimated. H$_{2}$O ice was quantified via its 3 $\mu$m band. From these fits, ice HDO/H$_{2}$O abundance ratios of 4.6$\pm$1.8$\times$10$^{-3}$ and 2.6$\pm$1.2$\times$10$^{-3}$ are obtained for HOPS 370 and IRAS 20126+4104, respectively. The simultaneous detections of both crystalline HDO and crystalline H$_{2}$O corroborate the assignment of the observed feature at 4.1 $\mu$m to HDO ice. The ice HDO/H$_{2}$O ratios are similar to the highest reported gas HDO/H$_{2}$O ratios measured toward MYSOs as well as the hot inner regions of isolated low-mass protostars, suggesting that at least some of the gas HDO/H$_{2}$O ratios measured toward massive hot cores are representative of the HDO/H$_{2}$O ratios in ices. The need for an H$_{2}$O-rich CH$_{3}$OH component in the CH$_{3}$OH ice analysis supports recent experimental and observational results that indicate that some CH$_{3}$OH ice may form prior to the CO freeze-out stage in H$_{2}$O-rich ice layers.

Abstract Outbursts from young Class 0 protostars are now being detected using 3–5 μm light curves assembled from Spitzer and WISE/NEOWISE photometry. For comparison, we present a 4–8 μm light curve of the erupting, more evolved protostar V1647 Ori (HOPS 388), assembled from photometry obtained with the ISOCAM camera on ISO, the IRAC camera on Spitzer, and from WISE and NEOWISE. Covering 26 yr, this light curve spans the longest available time interval from infrared space-based telescopes capable of separating individual young stellar objects in nearby molecular clouds. This curve does not include a two year interval where the visible-light photometry shows a large drop in brightness. In the case of V1647 Ori, we find that the increase in brightness (3.1 mag) and duration (16 yr) are similar to infrared (3–5 μm) outbursts found toward Class 0 protostars in Orion.

We present a combined Stratospheric Observatory for Infrared Astronomy (SOFIA) and two-epoch Hubble Space Telescope (HST) study of the region NGC 2071 IR containing the outflow from the protostar HOPS 361-A (NGC 2071 IRS 1). New [O i] 63 mu m spectra, taken with the German REciever for Astronomy at Terahertz frequencies (GREAT) instrument aboard SOFIA, trace the outflow, spectrally resolve line profiles, and give radial velocities of the far-IR emission to yield 3D kinematics, shock properties, and feedback properties. Proper motions and extinction values from HST give a more complete quasi-3D picture that we use to model shock speeds and densities. We identify 14 distinct features that show proper motions. Combined with the GREAT data, we estimate that HOPS 361-A has a mass outflow rate of 3.16 x 10-6 M circle dot yr-1 with shock speeds up to 51 km s-1. The outflow force summed over all knots per area is measured to be 1.45 x 10-4 M circle dot km-1 s-1 yr-1 and a power summed over all knotsper area of 2.37 x 10-2 M circle dot s-3 dissipated assuming constant M , with large uncertainties on the feedback values. The total [O i] luminosity using all SOFIA apertures encompassing the HOPS 361 clump is 0.7 L circle dot, corresponding to a mass outflow rate of 7 x 10-5 M circle dot yr-1. This is the second 3D kinematic study of an outflow in NGC 2071 IR in the near- and far-IR regimes following Rubinstein et al. (2023). The SOFIA [O i] spectra add unique focus to the entrained gas connecting the recent episode of outflows from HOPS 361-A to the outflow cavity and the surrounding NGC 2071 IR star-forming environment.

Investigating Protostellar Accretion is a Cycle 1 JWST program using the NIRSpec+MIRI integral field units to obtain 2.9-28 mu m spectral cubes of five young protostars with luminosities of 0.2-10,000 L-circle dot in their primary accretion phase. This paper introduces the NIRSpec 2.9-5.3 mu m data of the inner 840-9000 au with spatial resolutions from 28 to 300 au. The spectra show rising continuum emission; deep ice absorption; emission from H-2, H i, and [Fe ii]; and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe ii] for the four <320 L-circle dot protostars, two of which are additionally traced in Br alpha. Knots of [Fe ii] emission are detected toward the most luminous protostar, and knots of [Fe ii] emission with dynamical times of <30 yr are found in the jets of the others. While only one jet is traced in H-2, knots of H-2 and CO are detected in the jets of four protostars. H-2 is seen extending through the cavities, showing that they are filled by warm molecular gas. Bright H-2 emission is seen along the walls of a single cavity, while in three cavities narrow shells of H-2 emission are found, one of which has an [Fe ii] knot at its apex. These data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets.

The structure and composition of simple ices can be severely modified during stellar evolution by protostellar heating. Key to understanding the involved processes are thermal and chemical tracers that can be used to diagnose the history and environment of the ice. The 15.2 µm bending mode of 12CO2 in particular has proven to be a valuable tracer of ice heating events but suffers from grain shape and size effects. A viable alternative tracer is the weaker 13CO2 isotopologue band at 4.39 µm, which has now become accessible at high S/N with the James Webb Space Telescope (JWST). In this study, we present JWST NIRSpec observations of 13CO2 ice in five deeply embedded Class 0 sources that span a wide range in masses and luminosities (0.2–104 L⊙) taken as part of the Investigating Protostellar Accretion Across the Mass Spectrum (IPA) program. The band profiles vary significantly depending on the source, with the most luminous sources showing a distinct narrow peak at 4.38 µm. We first applied a phenomenological approach with which we demonstrate that a minimum of three to four Gaussian profiles are needed to fit the absorption feature of 13CO2. We then combined these findings with laboratory data and show that a 15.2 µm 12CO2 bending-mode-inspired five-component decomposition can be applied to the isotopologue band, with each component representative of CO2 ice in a specific molecular environment. The final solution consists of cold mixtures of CO2 with CH3OH, H2O, and CO as well as segregated heated pure CO2 ice at 80 K. Our results are in agreement with previous studies of the 12CO2 ice band, further confirming that 13CO2 is a useful alternative tracer of protostellar heating and ice composition. We also propose an alternative solution consisting only of heated mixtures of CO2:CH3OH and CO2:H2O ices and warm pure CO2 ice at 80 K (i.e., no cold CO2 ices) for decomposing the ice profiles of HOPS 370 and IRAS 20126, the two most luminous sources in our sample that show strong evidence of ice heating resulting in ice segregation.

Investigating Protostellar Accretion (IPA) is a JWST Cycle 1 GO program that uses NIRSpec integral field units and MIRI Medium Resolution Spectrograph to obtain 2.9–28 μ m spectral cubes of young, deeply embedded protostars with luminosities of 0.2–10,000 L _⊙ and central masses of 0.15–12 M _⊙ . In this Letter, we report the discovery of a highly collimated atomic jet from the Class 0 protostar IRAS 16253−2429, the lowest-luminosity source ( L _bol = 0.2 L _⊙ ) in the IPA program. The collimated jet is detected in multiple [Fe ii ] lines and [Ne ii ], [Ni ii ], and H i lines but not in molecular emission. The atomic jet has a velocity of about 169 ± 15 km s ^−1 , after correcting for inclination. The width of the jet increases with distance from the central protostar from 23 to 60 au, corresponding to an opening angle of 2.°6 ± 0.°5. By comparing the measured flux ratios of various fine-structure lines to those predicted by simple shock models, we derive a shock speed of 54 km s ^−1 and a preshock density of 2.0 × 10 ^3 cm ^−3 at the base of the jet. From these quantities and using a suite of jet models and extinction laws, we compute a mass-loss rate between 0.4 and 1.1 ×10 ^−10 M _⊙ yr ^−1 . The low mass-loss rate is consistent with simultaneous measurements of low mass accretion rate (2.4 ± 0.8 × 10 ^−9 M _⊙ yr ^−1 ) for IRAS 16253−2429 from JWST observations, indicating that the protostar is in a quiescent accretion phase. Our results demonstrate that very low-mass protostars can drive highly collimated, atomic jets, even during the quiescent phase.

Using the MIRI/MRS spectrometer on JWST, we have detected pure rotational, suprathermal OH emissions from the vicinity of the intermediate-mass protostar HOPS 370 (OMC2/FIR3). These emissions are observed from shocked knots in a jet/outflow, and originate in states of rotational quantum number as high as 46 that possess excitation energies as large as E-U/k=4.65x10(4) K. The relative strengths of the observed OH lines provide a powerful diagnostic of the ultraviolet radiation field in a heavily-extinguished region (A(V)similar to 10-20) where direct UV observations are impossible. To high precision, the OH line strengths are consistent with a picture in which the suprathermal OH states are populated following the photodissociation of water in its (B) over bar - X band by ultraviolet radiation produced by fast (similar to 80kms(-1)) shocks along the jet. The observed dominance of emission from symmetric (A ') OH states over that from antisymmetric (A '') states provides a distinctive signature of this particular population mechanism. Moreover, the variation of intensity with rotational quantum number suggests specifically that Ly alpha radiation is responsible for the photodissociation of water, an alternative model with photodissociation by a 10(4) K blackbody being disfavored at a high level of significance. Using measurements of the Br alpha flux to estimate the Ly alpha production rate, we find that similar to 4% of the Ly alpha photons are absorbed by water. Combined with direct measurements of water emissions in the nu(2)=1-0 band, the OH observations promise to provide key constraints on future models for the diffusion of Ly alpha photons in the vicinity of a shock front.

We investigate the bright CO fundamental emission in the central regions of five protostars in their primary mass assembly phase using new observations from JWST's Near-Infrared Spectrograph and Mid-Infrared Instrument. CO line emission images and fluxes are extracted for a forest of similar to 150 rovibrational transitions from two vibrational bands, v = 1-0 and v = 2-1. However, 13CO is undetected, indicating that 12CO emission is optically thin. We use H2 emission lines to correct fluxes for extinction and then construct rotation diagrams for the CO lines with the highest spectral resolution and sensitivity to estimate rotational temperatures and numbers of CO molecules. Two distinct rotational temperature components are required for v = 1 (similar to 600 to 1000 K and 2000 to similar to 104 K), while one hotter component is required for v = 2 (greater than or similar to 3500 K). 13CO is depleted compared to the abundances found in the interstellar medium, indicating selective UV photodissociation of 13CO; therefore, UV radiative pumping may explain the higher rotational temperatures in v = 2. The average vibrational temperature is similar to 1000 K for our sources and is similar to the lowest rotational temperature components. Using the measured rotational and vibrational temperatures to infer a total number of CO molecules, we find that the total gas masses range from lower limits of similar to 1022 g for the lowest mass protostars to similar to 1026 g for the highest mass protostars. Our gas mass lower limits are compatible with those in more evolved systems, which suggest the lowest rotational temperature component comes from the inner disk, scattered into our line of sight, but we also cannot exclude the contribution to the CO emission from disk winds for higher mass targets.

Context. Tracing the origin and evolution of interstellar water is key to understanding many of the physical and chemical processes involved in star and planet formation. Deuterium fractionation offers a window into the physicochemical history of water due to its sensitivity to local conditions. Aims. The aim of this work is to utilize the increased sensitivity and resolution of the James Webb Space Telescope (JWST) to quantify the HDO/H2O ratio in ices toward young stellar objects (YSOs) and to determine if the HDO/H2O ratios measured in the gas phase toward massive YSOs (MYSOs) are representative of the ratios in their ice envelopes. Methods. Two protostars observed in the Investigating Protostellar Accretion (IPA) program using JWST NIRSpec were analyzed: HOPS 370, an intermediate-mass YSO (IMYSO), and IRAS 20126+4104, a MYSO. The HDO ice toward these sources was quantified via its 4.1 µm band. The contributions from the CH3OH combination modes to the observed optical depth in this spectral region were constrained via the CH3OH 3.53 µm band to ensure that the integrated optical depth of the HDO feature was not overestimated. H2O ice was quantified via its 3 µm band. New laboratory IR spectra of ice mixtures containing HDO, H2O, CH3OH, and CO were collected to aid in the fitting and chemical interpretation of the observed spectra. Results. HDO ice is detected above the 3σ level in both sources. It requires a minimum of two components, one amorphous and one crystalline, to obtain satisfactory fits. The H2O ice band at 3 µm similarly requires both amorphous and crystalline components. The observed peak positions of the crystalline HDO component are consistent with those of annealed laboratory ices, which could be evidence of heating and subsequent recooling of the ice envelope (i.e., thermal cycling). The CH3OH 3.53 µm band is fit best with two cold components, one consisting of pure CH3OH and the other of CH3OH in an H2O-rich mixture. From these fits, ice HDO/H2O abundance ratios of 4.6 ± 1.8 × 10−3 and 2.6 ± 1.2 × 10−3 are obtained for HOPS 370 and IRAS 20126+4104, respectively. Conclusions. The simultaneous detections of both crystalline HDO and crystalline H2O corroborate the assignment of the observed feature at 4.1 µm to HDO ice. The ice HDO/H2O ratios are similar to the highest reported gas HDO/H2O ratios measured toward MYSOs and the hot inner regions of isolated low-mass protostars, suggesting that at least some of the gas HDO/H2O ratios measured toward massive hot cores are representative of the HDO/H2O ratios in ices. The need for an H2O-rich CH3OH component in the CH3OH ice analysis supports recent experimental and observational results that indicate that some CH3OH ice may form prior to the CO freeze-out stage in H2O-rich ice layers.

We present a two-epoch Hubble Space Telescope study of NGC 2071 IR highlighting HOPS 361-C, a protostar producing an arced 0.2 parsec-scale jet. The proper motions for the brightest knots decrease from 350 to 100 km s−1 with increasing distance from the source. The [Fe ii] and Paβ emission line intensity ratio gives a velocity jump through each knot of 40–50 km s−1. A new [O i] 63 μm spectrum, taken with the German REciever for Astronomy at Terahertz frequencies instrument aboard Stratospheric Observatory for Infrared Astronomy, shows a low line-of-sight velocity indicative of high jet inclination. Proper motions and jump velocities then estimate 3D flow speed for knots. Subsequently, we model knot positions and speeds with a precessing jet that decelerates. The measurements are matched with a precession period of 1000–3000 yr and half opening angle of 15°. The [Fe ii] 1.26-to-1.64 μm line intensity ratio determines visual extinction to each knot from 5 to 30 mag. Relative to ∼14 mag of extinction through the cloud from C18O emission maps, the jet is embedded at a 1/5–4/5 fractional cloud depth. Our model suggests the jet is dissipated over a 0.2 pc arc. This short distance may result from the jet sweeping through a wide angle, allowing the cloud time to fill cavities opened by the jet. Precessing jets contrast with nearly unidirectional protostellar jets that puncture host clouds and can propagate significantly farther.

We present an 870 μ m continuum survey of 300 protostars from the Herschel Orion Protostar Survey using the Atacama Compact Array (ACA). These data measure protostellar flux densities on envelope scales ≤8000 au (20″) and resolve the structure of envelopes with 1600 au (4″) resolution, a factor of 3–5 improvement in angular resolution over existing single-dish 870 μ m observations. We compare the ACA observations to Atacama Large Millimeter/submillimeter Array 12 m array observations at 870 μ m with ∼0.″1 (40 au) resolution. Using the 12 m data to measure the fluxes from disks and the ACA data within 2500 au to measure the combined disk plus envelope fluxes, we calculate the 12 m/ACA 870 μ m flux ratios. Our sample shows a clear evolution in this ratio. Class 0 protostars are mostly envelope-dominated with ratios <0.5. In contrast, Flat Spectrum protostars are primarily disk-dominated with ratios near 1, although with a number of face-on protostars dominated by their envelopes. Class I protostars span the range from envelope to disk-dominated. The increase in ratio is accompanied by a decrease in the envelope fluxes and estimated mass infall rates. We estimate that 80% of the mass is accreted during the envelope-dominated phase. We find that the 12 m/ACA flux ratio is an evolutionary indicator that largely avoids the inclination and foreground extinction dependence of spectral energy distribution-based indicators.

We present a Spitzer/Herschel focused survey of the Aquila molecular clouds ( d ∼ 436 pc) as part of the eHOPS (extension of the Herschel orion protostar survey, or HOPS, Out to 500 ParSecs) census of nearby protostars. For every source detected in the Herschel/PACS bands, the eHOPS-Aquila catalog contains 1–850 μ m SEDs assembled from the Two Micron All Sky Survey, Spitzer, Herschel, the Wide-field Infrared Survey Explorer, and James Clerk Maxwell Telescope/SCUBA-2 data. Using a newly developed set of criteria, we classify objects by their SEDs as protostars, pre-main-sequence stars with disks, and galaxies. A total of 172 protostars are found in Aquila, tightly concentrated in the molecular filaments that thread the clouds. Of these, 71 (42%) are Class 0 protostars, 54 (31%) are Class I protostars, 43 (25%) are flat-spectrum protostars, and four (2%) are Class II sources. Ten of the Class 0 protostars are young PACS bright red sources similar to those discovered in Orion. We compare the SEDs to a grid of radiative transfer models to constrain the luminosities, envelope densities, and envelope masses of the protostars. A comparison of the eHOPS-Aquila to the HOPS protostars in Orion finds that the protostellar luminosity functions in the two star-forming regions are statistically indistinguishable, the bolometric temperatures/envelope masses of eHOPS-Aquila protostars are shifted to cooler temperatures/higher masses, and the eHOPS-Aquila protostars do not show the decline in luminosity with evolution found in Orion. We briefly discuss whether these differences are due to biases between the samples, diverging star formation histories, or the influence of environment on protostellar evolution.