Joel David Green

Molecular winds may play a key role in governing angular momentum transport and accretion during the early evolution of protostars. We present the morphology and kinematic properties of the H ₂ emission in five young, envelope-dominated protostars across a broad bolometric luminosity range, from 0.2 to 10 ⁴ L _⊙ , observed with the NIRSpec/integral field unit and MIRI/Medium Resolution Spectrograph on board JWST as part of the Investigating Protostellar Accretion (IPA) program. A rich set of pure rotational lines of H ₂ , up to v = 0–0 S (18), and a few rovibrational lines are detected in the winds, revealing bipolar structures. The H ₂ lines show a stratified/onion-like structure morphologically and kinematically, where the lines with higher E _u / k show a higher degree of collimation and higher velocities. Additionally, the wind velocity scales with the L _bol of the host protostellar system. In four out of five protostars, H ₂ emission fills the outflow cavity without showing pronounced limb brightening. We also report a tentative detection of H ₂ wind rotation in IRAS 16253, which suggests a launch radius of ∼4 au and a magnetic lever arm parameter of ∼5–10. Taken together, these properties of the H ₂ winds can be explained by the magnetohydrodynamic disk wind models. We detect a collimated, high-velocity H ₂ jet toward HOPS 370, which is more evolved than the extremely young source HH 211 but is accreting at a high accretion rate. This suggests that the presence of collimated molecular jets in protostars is more closely connected to accretion rate than system age.

We present two-epoch JWST NIRSpec and MIRI observations of the young protostar EC 53 (V371 Ser), a periodically variable source with well-characterized quiescent and burst phases. The spectra in both epochs show absorption in the CO overtone (∼2.3 μ m) and fundamental (∼4.6 μ m) bands and the H ₂ O stretching (∼2.7 μ m) and bending (∼6.0 μ m) modes. We also obtained high-resolution ( R ≈ 45,000) IGRINS spectra during the burst to constrain the CO overtone line profiles. Local thermodynamic equilibrium (LTE) slab modeling yields gas temperatures of ∼1800 K (CO overtone) and ∼1200 K (CO fundamental), consistent with the overtone tracing hotter gas at smaller radii. The H ₂ O stretching-mode absorption shows no compelling evidence for variability, and the current JWST CO overtone data do not provide a robust constraint on overtone variability. In contrast, the CO fundamental and H ₂ O bending-mode features weaken by a factor of ∼2 during the burst, which is most naturally explained by continuum changes rather than large variations in absorbing gas. To quantify continuum dilution, we introduce a “relative veiling” that treats the quiescent spectrum as an internal reference and measures the change in the continuum excess between the two epochs. This formalism yields burst-to-quiescent hot-continuum ratios of 2.9 ± 0.2 for the CO overtone and 1.71 ± 0.11 for the CO fundamental. Using a viscous-disk prescription, these imply representative accretion-rate ratios of ∼3.6 and ∼2.0, respectively. The differing ratios suggest that inner-disk regions traced at different temperatures, and thus radii, respond differently across the burst cycle, consistent with episodic mass buildup in the inner disk during quiescence followed by more efficient transport through the innermost disk onto the protostar during the burst.

We present a comprehensive analysis of extended H ₂ emission from 34 protoplanetary disks observed with the JWST Disk Infrared Spectroscopic Chemistry Survey, supplemented by archival data. We investigated the morphology, kinematics, excitation conditions, and mass dynamics of H ₂ . Extended emission from pure rotational H ₂ lines is found to be common, with 16 sources exhibiting clear signatures of disk winds. These include monopolar and bipolar structures in inclined disks and ring-like or bubble-like morphologies in face-on system features, indicative of wide-angle disk winds. Our analysis shows that the H ₂ is consistent with slow (4.2 − 3.0 + 6.7 km s ⁻¹ ) magnetohydrodynamical driven winds. For 10 disks, we model the wind morphology and find a median half-opening angle of 4 5 − 4 ° + 5 and a characteristic power-law index of α ∼ 1.6. Excitation analysis yields a median gas temperature of 624 ± 130 K and a column density of log ( N tot [ cm − 2 ] ) = 18.6 ± 0.6 . The median wind mass-loss rate, log 10 ( M ̇ wind tot ) = − 9 − 0.4 + 0.8 M ⊙ yr − 1 , implies that if molecular winds are the dominant mechanism responsible for disk dispersal, a typical disk with a mass of 2–3 M _Jup would dissipate on a ∼2–3 Myr timescale, consistent with observed disk lifetimes. The M ̇ wind tot span a relatively narrow range (∼2 dex) and do not correlate strongly with accretion rates onto the star, suggesting that the mass-loss rate and the accretion rates are probing different timescales. Our findings demonstrate that spatially extended warm H ₂ emission is a widespread and reliable tracer of molecular disk winds in protoplanetary systems.

We present a Hubble Space Telescope (HST) imaging survey of a 1.1 deg ² sky area toward the Milky Way Galactic bulge. This field significantly overlaps with the upcoming Nancy Grace Roman Galactic Bulge Time Domain Survey. High angular resolution imaging of this area with HST before the start of the Roman Galactic Exoplanet Survey will greatly strengthen Roman’s ability to characterize detected exoplanet systems, as well as provide a rich and wide-field archive for use as a legacy dataset toward the Galactic bulge for the broader community. We conduct coordinated parallel imaging with both wide-field cameras on HST, the Wide Field Camera 3 and Advanced Camera for Surveys, utilizing the F606W and F814W passbands. Approximately 70% of the survey was conducted during HST Cycle 32, with the remaining 30% conducted during Cycle 33. In this Letter, the first in a series, we give a general overview of the program and the observing strategy and present early results. This campaign secures HST’s lasting impact on the high-precision study of stellar populations, dynamics, exoplanet systems, interstellar extinction, metallicities, cluster associations, and more toward the center of our Galaxy.

We present the 1.6–28 μ m spectra of the young protostar EC 53, obtained with the James Webb Space Telescope (JWST) Near Infrared Spectograph Integral Field Unit and MIRI Medium Resolution Spectroscopy during the quiescent and burst phases of its periodic brightness variations. To isolate ice absorption features, we modeled and removed the mid-infrared silicate dust absorption using a dedicated continuum-fitting procedure. In the optical depth spectrum, we first fit the broad H ₂ O ice features and then decomposed the major ice components, including NH ₃ , CO ₂ , CH ₃ OH, CO, and CH ₄ , by matching laboratory profiles for both pure and H ₂ O-mixed ices. The 4.62 μ m and 6.85 μ m bands are attributed to OCN ^– and NH ₄ ⁺ ions, respectively. Minor or tentative contributions from complex species (HCOOH, H ₂ CO, CH ₃ COOH, CH ₃ CHO, CH ₃ CH ₂ OH, and NH ₂ CHO) are also considered for our global ice analysis. The silicate-corrected spectra reveal no measurable change in any ice absorption band between the two phases, indicating that moderate and short-period accretion bursts in EC 53 do not significantly alter the physical or chemical state of the ices within its envelope. The derived abundances of these major species relative to H ₂ O significantly exceed the values typically observed toward other embedded protostars. Finally, we place the ice inventory of EC 53 in the context of other protostellar systems observed with JWST, highlighting that its chemically rich, thermally quiescent ice reservoir provides a benchmark for studying ice evolution under episodic accretion.

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.

We present an extensive study of the structure and kinematics of the jet and outflow of EC 53, a Class I protostar with a quasiperiodic variability, using combined James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array (ALMA) observations. ALMA continuum observations resolve a compact disk with a radius of ∼0 . ″ 14 (60 au). Scattered light from the outflow cavity is prominent in the short-wavelength NIRCam and NIRSpec observations, revealing only the southeast nearside lobe. We detect 27 H ₂ emission lines tracing a narrow cone-shaped structure within the outflow cavity. A high-velocity ionized jet is detected in several forbidden atomic lines, characterized by a position angle of 142 ^∘ , an opening angle of 1 . ° 4, and an estimated geometric launching radius of at most ∼40 au. Mid-IR CO rovibrational emission lines, stronger in the P-branch, show a similar distribution to the H ₂ emission and are likely to originate from hot gas within the outflow cavity. CO and C ₂ H emission lines detected by ALMA trace slower, colder outflow components and cavity walls. The spatial and kinematic stratification between the hot atomic and molecular components and the colder molecular gas is consistent with predictions from MHD disk wind models, although envelope material entrained by a wide-angle wind or jet may also contribute. Our analysis highlights the powerful synergy between JWST and ALMA in advancing the understanding of protostellar jets and outflows across multiple spatial and physical scales.

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.

Isotopologues play an important role in solar system cosmochemistry studies, revealing details of early planet formation physics and chemistry. Oxygen isotopes, as measured in solar system materials, reveal evidence for both mass-dependent fractionation processes and a mass-independent process commonly attributed to isotope-selective photodissociation of CO in the solar nebula. The sensitivity of JWST’s MIRI-MRS enables studies of isotopologues in the terrestrial planet-forming regions around nearby young stars. We report here on a search for H 2 18 O in 22 disks from the JDISC Survey with evidence for substantial water vapor reservoirs, with the goal of measuring H 2 16 O/H 2 18 O ratios, and potentially revealing the predicted enhancement of H 2 18 O caused by isotope-selective photodissociation. We find marginal detections of H 2 18 O in six disks, and a more significant detection of H 2 18 O in the disk around WSB 52. Modeling of the detected H 2 18 O lines assuming an interstellar medium (ISM) ratio of H 2 16 O/H 2 18 O predicts H 2 18 O features consistent with observations for four of the modeled disks, but stronger H 2 18 O features than are observed in three of the modeled disks, which includes WSB 52. Therefore, these latter three disks require a higher H 2 16 O/H 2 18 O ratio than the ISM in the water-emitting region, in contrast to long-standing theoretical expectations. We suggest that either the H 2 18 O-rich water has been removed from the emitting region and replaced by H 2 18 O-poor water formed by reactions with ¹⁸ O-poor CO, or that the gas-phase water is depleted in ¹⁸ O via mass-dependent fractionation processes at the water snowline.

We present observations of jets within 2000 au of three deeply embedded protostars using 2.9–27 μ m observations with JWST. These observations show the morphologies and kinematics of the collimated jets from three protostars, the low-mass Class 0 protostars B335 and HOPS 153, and the intermediate-mass protostar HOPS 370. These jets are traced by shock-ionized fine-structure line emission observed with the JWST NIRSpec and MIRI integral field units. We find that [Fe II ] emission traces the full extent of the inner 1000–2000 au of the jets, depending on the distance to the protostar, while other ions mostly trace isolated shocked knots. The jets show evidence of wiggling motion in the plane of the sky as well as asymmetries between blue- and redshifted lobes. The widths of the jets increase nonmonotonically with distance from the central protostar, with opening angles ranging from 2 . ° 1 to < 10 . ° 1 for the three protostars in the sample. The jets have total velocities ranging from 147 to 184 km s ⁻¹ after correcting for disk inclination. For B335, an 8 month gap between NIRSpec and MIRI Medium Resolution Spectroscopy observations enabled measurement of the tangential velocity of a shocked knot; in combination with the radial velocity, this shows that the jet has a different inclination than the outflow cavity. We find multiple knots before and during a recent outburst in B335, although the knots were more frequent during the burst. The asymmetries between the blue- and redshifted lobes strongly suggest complex interactions between the circumstellar disks and magnetic fields.