Doug Johnstone

We report the discovery of a nearby FU Ori–type outburst (FUor), PR Ori B, in the L1641 cluster of the Orion star-forming region. The high-amplitude variability was first identified in the NEOWISE (3–5 μ m) photometry of the unresolved PR Ori binary system. Long-term, resolved optical photometric monitoring demonstrates that PR Ori B is the driver of a Δ G = 5 mag outburst, while PR Ori A has remained constant over the past 20 yr. The near-IR spectrum of PR Ori B changes from a late K-type spectral type during quiescence to a viscously heated disk during outburst, including deep absorption in ¹² CO and H ₂ O bands. The optical spectrum also exhibits features that are commonly associated with FUors, including P Cygni profiles in Na i D lines and absorption in the Ca ii infrared triplet. The luminosity of the outburst ( L _acc ∼ 30–40 L _⊙ ) is similar to that commonly observed in FUors. The comparison of Spitzer/Infrared Spectrograph and Very Large Telescope/VISIR spectroscopy shows some evidence of silicate crystallization during the outburst. PR Ori B is one of the closest and brightest FUors discovered over the past few years, only one magnitude fainter than the archetype of the class FU Ori. The proximity and brightness will allow for future high angular resolution observations to probe the physics of the inner disk and to evaluate changes in the disk due to the increased luminosity.

In just over 3 yr of operation, JWST has observed all seven planets of the TRAPPIST-1 system. The two innermost planets were found to have little to no atmosphere, barring the presence of high-altitude aerosols. Here we present the first JWST transit spectra of the habitable-zone exoplanet TRAPPIST-1 f, which were obtained with NIRISS SOSS over the course of five transits. At least one stellar flare occurred in each visit, but unlike observations of closer-in TRAPPIST-1 planets, no evidence for contamination of the transit spectra from unocculted stellar surface heterogeneities was found. This nondetection does not guarantee the absence of unocculted heterogeneities in all future transit observations of this planet, and it could be explained by the transit chord of TRAPPIST-1 f having properties similar to the average, out-of-transit, visible stellar hemisphere at the time of observation. The transit spectra exhibit slopes ranging from −365 ppm μ m ⁻¹ down to 15 ppm μ m ⁻¹ , which we attribute to stellar variability, that is, flares and/or smaller-scale events. The visits least affected by flares rule out H ₂ /He-dominated atmospheres with surface pressures higher than about 20 mbar at 95% confidence. For high-mean-molecular-mass atmospheres, the exact upper limits on surface pressures depend on the reduction pipeline and on the treatment of the residual slopes in the transit spectra.

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.

As the nearest protoplanetary disk to Earth ( d = 60.14 pc), TW Hya is one of the most studied protoplanetary disks and a critical benchmark for testing planet formation theories. We present high-contrast coronagraphic imaging of the TW Hya disk from JWST/NIRCam across four filters (F187N, F200W, F356W, and F444W). We detect the disk’s scattered-light emission in F200W, F356W, and F444W. An elliptical fit to the disk image yields an average inclination of i = 8 . ° 74 − 0 . ° 94 + 1 . ° 03 and a position angle of PA = 75 . ° 62 − 6 . ° 56 + 7 . ° 86 . We find tentative evidence for radial variations in these parameters, a trend consistent with a disk warp. Our companion search yields no new detections, placing the lowest mass limits yet on companions that might be responsible for carving out the dust gap. Assuming no local extinction and a system age of 10 Myr, the F444W data are sensitive to masses down to ∼0.4 M _Jup at separations of 1″ (∼60 au). Accounting for local disk extinction analogous to the AS 209 system, our limits reach sub-Jupiter masses beyond 2″. Furthermore, our analysis provides a detailed view of a previously detected feature in the outer disk at ∼120 au, confirming its morphology as a distinct bifurcation structure. This feature may indicate the presence of complex substructures arising from dynamical planet–disk interactions. These results demonstrate JWST’s ability to characterize the architecture of protoplanetary disks and constrain the properties of forming worlds.

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.

Erratum: “Tracking Protostellar Variability in Massive Protoclusters with ALMA. I. Insights from QUARKS and MaMMOtH” (2026, ApJ, 1003, 60), Yang, Yuhan, Liu, Tie, Liu, Sheng-Yuan, Johnstone, Doug, Herczeg, Gregory, Jiao, Wenyu, Su, Yu-Nung, Mai, Xiaofeng, Xu, Fengwei, Meyer, D. M.-A., Zhang, Siju, Vorobyov, Eduard, Zhang, Suinan, Luo, Qiuyi, Garay, Guido, Chen, Xi, Jiao, Yunfan, Gu, Qilao, Zhang, Yankun, Tatematsu, Ken’ichi, Kim, Kee-Tae, Sobolev, Andrey M., Parfenov, Sergey, Ladeyschikov, Dmitry A., Bronfman, Leonardo Erratum: “Tracking Protostellar Variability in Massive Protoclusters with ALMA. I. Insights from QUARKS and MaMMOtH” (2026, ApJ, 1003, 60), Yang, Yuhan, Liu, Tie, Liu, Sheng-Yuan, Johnstone, Doug, Herczeg, Gregory, Jiao, Wenyu, Su, Yu-Nung, Mai, Xiaofeng, Xu, Fengwei, Meyer, D. M.-A., Zhang, Siju, Vorobyov, Eduard, Zhang, Suinan, Luo, Qiuyi, Garay, Guido, Chen, Xi, Jiao, Yunfan, Gu, Qilao, Zhang, Yankun, Tatematsu, Ken’ichi, Kim, Kee-Tae, Sobolev, Andrey M., Parfenov, Sergey, Ladeyschikov, Dmitry A., Bronfman, Leonardo

Aims . To advance our understanding of dust properties in class 0/I young stellar objects, it is essential to resolve and characterize their structures at multiple wavelengths and investigate how both grain growth and environmental factors shape their spectral properties. Methods . We present 0.″5 angular resolution ALMA observations of the GSS 30 complex at 1.2–3.0 mm, collected as part of the FAUST large programme, with a linear resolution of 69 au. We analysed the dust continuum emission and performed model fitting to constrain the dust mass and the disk structure. Results . For IRS3, the spectral index increases radially from 2.0 at the centre to 2.5 at the disk edge. In contrast, it decreases from 2.0 to as low as 1.6–1.8 along the outflow direction. An asymmetric distribution shows α as low as 1.6 to the northeastern blueshifted lobe, possibly due to cold outer envelope dust obscuring warmer inner regions. Spectral energy distribution fitting indicates maximum dust grain sizes of tens of microns and a dust mass of 650–1510 M _⊕ . IRS1 is connected with an extended structure to the north-east. It may be an outflow–disk complex or a trailing structure associated with a circumbinary disk, although we cannot rule out the possibility that it could also be a gas streamer accreting onto IRS1. At the centre of IRS1, the spectral index is < 0.8, which is consistent with marginally optically thick free-free emission. IRS2 exhibits brightness variations over 420 seconds of observation, with a multi-epoch comparison suggesting a flare lasting tens of minutes, indicating magnetic activity in the central star. Conclusions . This study presents a detailed millimetre multi-wavelength analysis of the GSS 30 IRS3 and IRS1 systems, highlighting the crucial role of environmental factors – specifically dust obscuration and the connecting streamer structures – in shaping the observed morphology of these early-stage disks. We also find that the IRS2 exhibits millimetre variability, which may originate from magnetic flares at the surface of the protostar.

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 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.