Tyler L. Bourke

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.

Envelope-embedded protostellar disks represent the earliest stage of protoplanetary disk evolution, but their masses and sizes are difficult to measure because disk emission is entangled with the envelope. We analyze 26 protostellar disk systems in Taurus using Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 (345 GHz; ∼0 . ″ 3) and Very Large Array (VLA) Ka -band (33 GHz; ∼0 . ″ 2) observations that trace compact disk emission, together with molecular line data to constrain the disk gas masses. At 345 GHz, the median flux density, dust mass, and radius are 71 mJy, 5.5 M _⊕ , and 28 au, with 68% ranges of 54–107 mJy, 3.9–9.4 M _⊕ , and 25–39 au. At 33 GHz, the corresponding medians are 0.43 mJy, 39 M _⊕ , and 32 au, with ranges of 0.41–0.80 mJy, 34–52 M _⊕ , and 29–33 au. Taurus Class I disks are fainter and less massive than those in Orion, comparable to Perseus Class I disks but fainter than Perseus Class 0 disks, and brighter and more massive than those in Ophiuchus. Within Taurus, Class 0/I disks are brighter than Class II disks at both frequencies, although their inferred dust masses are comparable at 345 GHz and slightly higher at 33 GHz. Radiative-transfer modeling of CO isotopologue emission yields a median gas mass of M _gas,med = 6.7 × 10 ⁻⁴ M _⊙ . The resulting CO-inferred gas-to-dust ratios span a broad range, with a mean of 147 ± 75, a median of 26, and a 16th–84th percentile range of 8–147. This distribution overlaps the Taurus Class II population at the low end and interstellar medium (ISM)-like or higher values, including the AGE-PRO Ophiuchus Class 0/I population, at the high end.

We present an infrared, millimeter, and radio survey of 20 Class 0–III young stellar objects in the Ophiuchus A L1688 star-forming cluster, combining high-resolution (7–25 au) Very Large Array (VLA) and James Webb Space Telescope observations with archival Atacama Large Millimeter/submillimeter Array data. We implement physically motivated models to derive dust and ionized gas properties, spectral behaviour, and their relative contributions through the millimeter-to-centimeter radio spectral energy distribution. Our models reveal circumstellar dust disks that are, on average, tens to hundreds of times more massive than millimeter-only estimates (subject to uncertainties arising from the choice of dust opacity) and contain millimeter-sized grains even at the Class 0 stage. Owing to the VLA’s high resolution, we are able to connect outflows to their origins, detecting protostellar jet emission on scales of tens to thousands of au. Our results represent a homogeneous characterization of the dust and ionized gas properties in Ophiuchus and present a potential solution to the long-standing “missing disk mass” problem. However, our understanding is still limited by resolution and sensitivity at frequencies . ″ 18) even in one of the closest star-forming regions.

We present new Atacama Large Millimeter/submillimeter Array (ALMA) 0.9 mm and Very Large Array (VLA) 9 mm observations in the Taurus Molecular Cloud (TMC) of 25 protostellar systems, containing 40 protostars, observed at 0 . ″ 3 (∼20 au) resolution. Within separations of 18–10,000 au, the ALMA/VLA-observed Taurus sample has a multiplicity fraction (MF), defined as the fraction of systems with at least one companion, of 0.50 ± 0.07, and a companion fraction (CF), defined as the average number of companions per system, of 0.58 ± 0.20. To build a more complete census of protostellar multiplicity in this region, we supplement the observed sample with 24 protostars (12 protostellar systems and five additional companions associated with systems we observed) previously identified through archival infrared or ALMA observations. Together, these 64 individual protostars (37 systems) define our Taurus+ sample, for which we measure higher values of 0.53 ± 0.06 and 0.72 ± 0.19 for the MF and CF, respectively. These multiplicity statistics in the TMC are notably higher than those reported in the more clustered star-forming regions of Orion and Perseus at the ∼3 σ –4 σ level, suggesting that Taurus may preserve a larger fraction of primordial multiples. The separation distributions in our samples show populations of both close and wide multiples, but a deficit at intermediate separations of 200–300 au. This pattern may suggest two distinct formation pathways: close binaries (1000 au) from core fragmentation.

We present high-resolution magnetic field maps of the M17 SW molecular cloud using JCMT 850 μ m dust polarization at scale of 14″. The magnetic field exhibits a distinct arc-like structure that encircles three dense clumps (C1, C2, and C3). By combining polarization data with ammonia line observations, the plane-of-sky magnetic field strength, measured using the Skalidis–Tassis method to minimize angle dispersion errors, ranges from 0.1 to 2.4 mG (mean: 0.54 mG). Energy budget analysis reveals a hierarchy dominated by gravity ( e _G ≈ 10 ^−7.8 erg cm ⁻³ ), which exceeds both magnetic ( e _B ≈ 10 ^−8.3 erg cm ⁻³ ) and turbulent ( e _k ≈ 10 ^−8.7 erg cm ⁻³ ) energies. Since all three energy densities lie within 1 order of magnitude, gravitational dominance acts primarily as the global driver, while the system remains in a state of near equipartition. Structurally, the northeastern boundary shows magnetic field lines perpendicular to the shock front, consistent with compression from the adjacent H II region. Within the cloud, magnetic field lines generally align with gravity to assist collapse, but turn perpendicular to gravity within curved accretion bridges. This configuration provides support against radial collapse while guiding gas flow. Kinematic evidence suggests that these channels transport material from clump C3 onto the massive clump C2. Star formation in M17 SW is globally driven by gravity but locally regulated by the magnetic field structure.

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.

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.

We present observations of jets within 2000 au of three deeply embedded protostars using 2.9-27 micron 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 IFUs. We find that [Fe II] emission traces the full extent of the inner 1000 to 2000 au of the jets, depending on 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 red-shifted lobes. The widths of the jets increase non-monotonically with distance from the central protostar, with opening angles ranging from 2.1 degrees to < 10.1 degrees for the three protostars in the sample. The jets have total velocities ranging from 147 to 184 km/s after correcting for disk inclination. For B335, an 8-month gap between NIRSpec and MIRI MRS 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 blue- and red-shifted lobes strongly suggest complex interactions between the circumstellar disks and magnetic fields.