Background stars observed through a circumstellar disk provide valuable benchmarks for investigating the disk's extinction properties. The HD 163296 system is an excellent case study due to its large disk, the clearly visible extinction effects in JWST/NIRCam data, and the presence of numerous background sources within or around its disk. We present the measured contrasts and astrometry of sources surrounding HD 163296 from Cycle 1 JWST/NIRCam coronagraphic observations, which will serve as a useful reference for future studies of the disk's extinction characteristics.

We present the operational capabilities and on-sky performance of the SOAR Adaptive Module Optical Spectrograph (SAMOS) at the completion of its science commissioning phase. SAMOS is a Digital Micromirror Device (DMD)-based multi-object spectrograph and imager installed behind the SOAR Adaptive Module (SAM) ground-layer adaptive optics system. The instrument relays the full 3 x 3 arcmin AO-corrected field onto a large-format DMD, where each micromirror can direct light to either a spectroscopic or a parallel imaging channel. This architecture enables programmable slit-mask patterns that can be generated and reconfigured within seconds. SAMOS provides low-resolution spectroscopy over the 4000-10000 A wavelength range at resolving power R 2500 and high-resolution spectroscopy (R 10,000) in the 4500-5150 A and 6 000-7000 A bands. We summarize the operational workflow established during commissioning, including target acquisition, astrometric registration, DMD slit-mask generation, simultaneous imaging and spectroscopy, and automated data reduction. Science-verification observations demonstrate accurate target acquisition, reliable programmable slit-mask operation, multiplexed spectroscopy of crowded stellar fields, wavelength-calibration accuracy of about 0.3 A, and end-to-end spectrophotometric calibration through the combination of imaging and spectroscopic data. These results establish SAMOS as a unique facility instrument that combines adaptive-optics-assisted imaging, programmable multi-object spectroscopy, and rapid slit-mask reconfiguration for efficient spectroscopic surveys, transient follow-up, and studies of crowded stellar populations.

Understanding the Universe's origins and evolution remains one of the most fundamental challenges in modern cosmology. This white paper explores three key science priorities in this field: unravelling the physics of cosmic inflation, investigating the accelerating expansion of the Universe, and precisely measuring the sum of the neutrino masses. Achieving these goals requires a dedicated survey to map the large-scale structure at high redshift in unprecedented detail. We describe how this can be achieved through a mission concept called SIRMOS, providing a high-throughput, highly multiplexed spectroscopic capability to obtain accurate redshifts for over 100 million galaxies over a wide sky area. Such a survey would leverage the deepest existing wide-area photometric catalogues for targeting, with spectra offering continuous 1.25-2.5 μm wavelength coverage at moderate resolution, allowing precise redshift measurements in the 1<z<4 range with minimal bias. We outline the scientific opportunities this presents. Recent years have seen significant advances in instrumentation, including digital micromirror devices, complex telescope mirrors, large detector arrays, and data processing pipelines. While these technologies have been demonstrated in terrestrial applications, such a survey is a unique opportunity to apply these proven capabilities in space to address fundamental questions in cosmology. Participation in such a mission will simultaneously deliver a compelling science case, help align UK Space Agency and STFC strategies, demonstrate the UK's growing capability in end-to-end space missions, and strengthen the national space economy through high-value industrial participation.

Young (≲ 10 Myr) planetary-mass companions (PMCs) provide valuable insights into the formation and early evolution of planetary systems. To date, only a dozen such objects have been identified through direct imaging. Using JWST/NIRCam observations towards the Orion Nebula, obtained as part of the PDRs4All Early Release Science program, we have identified a faint point source near the M-type star V2376 Ori. Follow-up spectroscopic observations with the MUSE instrument on the VLT confirm that the source, V2376 Ori b, is indeed a young planetary-mass companion. It is a member of Orion D, around 80 pc in the foreground of the Trapezium cluster of Orion and with an age of approximately 7 ± 3 Myr. We fit the SED of V2376 Ori b to infer a mass of ∼ 20 M_ Jup. The MUSE spectrum reveals several accretion tracers. Based on the Hα line intensity, we estimate an accretion rate of ∼10^-6.5 ± 0.7 M_Jup yr^-1, which is comparable to that of young PMCs such as PDS 70b. In addition, the MUSE data cube reveals extended emission in the [O ii] doublet at 7320 and 7330 Å, which is interpreted as evidence of a dynamical interaction between the two sources that, potentially, involves mass transfer between their individual accretion disks. These results demonstrate that JWST/NIRCam imaging surveys of young stellar associations can uncover new PMCs, which can then be confirmed and characterized through ground-based spectroscopic follow-up.

We introduce our new program to develop two-dimensional MEMS arrays of individually addressable micro-mirrors (”Micro-Mirror Devices”, MMDs) specifically optimized for astronomy, multi-slit spectroscopy in particular. After reviewing the main characteristics and performance of the currently available options, Micro Shutter Arrays by NASA/Goddard and Digital Micromirror Devices by Texas Instruments, we present our planned first generation/baseline devices with 30 micron x 30 miron pixel size arranged in a 1K x 1K format with tilt angle 15 degrees. Our goal is to bring to maturity a technology capable of delivering arrays of 2K x 2K element of 100 micron x 100 micron, buttable on two sides to achieve even larger formats. In additions to MEMS design, we will develop the associated device packaging and electronic control circuitry leveraging on the extensive expertise gained in the last 30+ years by leading experts from digital imaging industry.

Using NIRSpec on JWST, we studied a sample of 15 intermediate-mass (1.8–4.1 M _⊙ ) young stellar objects (YSOs) previously identified with MIRI photometry in the low-metallicity NGC 346 star-forming cluster in the Small Magellanic Cloud. All objects, observed in the 1.7–5.3 μ m range, show strong hydrogen recombination lines in the Paschen, Brackett, Pfund, and Humphreys series, confirming their very young ages. The spectra of 11 YSOs show prominent absorption bands from the three most important ice species (H _2 O, CO _2 , CO), marking the first detection of these ices in intermediate-mass YSOs beyond our Galaxy. In three YSOs, water ice appears to be in crystalline form. In some objects, we also detect ^13 CO _2 and OCS ices—never before observed beyond the Milky Way (MW)—and methanol ice in at least one star. We compared the column densities of H _2 O, CO _2 , and CO ices with those measured in more and less massive protostars in the MW and Large Magellanic Cloud, finding that, in NGC 346, ice column densities reach values nearly an order of magnitude lower than in more massive objects (∼1 × 10 ^17 cm ^−2 for water and ∼1 × 10 ^16 cm ^−2 for CO _2 and CO). However, the relative proportions of the ice species abundances do not differ from those in massive MW YSOs. This suggests that metallicity may not significantly affect ice chemistry in protoplanetary disks and that, shielded by the protostellar envelope or deep in the midplane, circumstellar material is likely impervious to the radiation environment.

A successful theory of star formation should predict the number of objects as a function of their mass produced through star-forming events. Previous studies in star-forming regions and the solar neighborhood have identified a mass function increasing from the hydrogen-burning limit down to about 10 M _J . Theory predicts a limit to the fragmentation process, providing a natural turnover in the mass function down to the opacity limit of turbulent fragmentation, thought to be near 1–10 M _J . Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. We present the first identification of a turnover in the initial mass function below 12 M _J within NGC 2024, a young star-forming region. With JWST/NIRCam deep exposures across 0.7–5 μ m, we identified several free-floating objects down to roughly 3 M _J with sensitivity to 0.5 M _J . We present evidence for a double power-law model increasing from about 60 M _J to roughly 12 M _J , consistent with previous studies, followed by a decrease down to 0.5 M _J . Our results support the predictions of star and brown dwarf formation theory, identifying the theoretical turnover in the mass function and suggesting the fundamental limit of turbulent fragmentation to be near 3 M _J .

Context. The typically large distances, extinction, and crowding of Galactic supermassive star clusters (stellar clusters more massive than 10(4) M-circle dot) have so far hampered the identification of their very low mass members, required to extend our understanding of star and planet formation, and early stellar evolution, to the extremely energetic star-forming environment typical of starbursts. This situation has now evolved thanks to the James Webb Space Telescope (JWST), and its unmatched resolution and sensitivity in the infrared. Aims. In this paper, the third of the series of the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS), we present JWST/NIRCam and JWST/MIRI observations of the supermassive star cluster Westerlund 1. These observations are specifically designed to unveil the cluster members down to the brown dwarf mass regime, and to allow us to select and study the protoplane-tary disks in the cluster and to study the mutual feedback between the cluster members and the surrounding environment. Methods. Westerlund 1 was observed as part of JWST GO-1905 for 23.6 hours. The data have been reduced using the JWST calibration pipeline, together with specific tools necessary to remove artifacts, such as the 1/f random noise in NIRCam images. Source identification and photometry were performed with DOLPHOT. Results. The MIRI images show a plethora of different features. Diffuse nebular emission is observed around the cluster, which is typically composed of myriads of droplet-like features pointing toward the cluster center or the group of massive stars surrounding the Wolf-Rayet star W72/A. A long pillar is also observed in the northwest. The MIRI images also show resolved shells and outflows surrounding the M-type supergiants W20, W26, W75, and W237, the sgB[e] star W9 and the yellow hypergiant W4. Some of these shells have been observed before at other wavelengths, but never with the level of detail provided by JWST. The color-magnitude diagrams built using the NIRCam photometry show a clear cluster sequence, which is marked in its upper part by the 1828 NIRCam stars with X-ray counterparts. NIRCam observations using the F115W filter have reached the 23.8 mag limit with 50% completeness (roughly corresponding to a 0.06 M-circle dot brown dwarf).

Age-benchmark brown dwarf and planetary-mass-object spectroscopy is key to characterizing substellar evolution. In this paper, we present the JHK medium-resolution ( R ∼ 3000) spectra of 25 7–76 M _Jup (spectral types L3.0–M6.0) brown dwarfs and planetary mass objects in the Orion Nebula Cluster, obtained with MOSFIRE installed at the W. M. Keck I telescope. We obtained the spectral types of the targets in our sample using template brown dwarf and planetary-mass-object spectra. We confirmed their extreme youth (<5 Myr) and membership of the cluster using spectral indices as well as the diversity of their spectra, even for targets with similar spectral types. Six of our targets presented Paschen β and Brackett γ emission lines, suggesting the existence of accreting protoplanetary disks for objects with masses as low as 7 M _Jup . After analyzing the emission lines of those objects, and measuring their accretion rates, we compared them to those of stars, brown dwarfs, and planetary mass objects, confirming that planetary mass young objects deplete their disks quickly at young ages. Finally, we illustrate the spectral evolution of a 7–10 M _Jup planetary mass object through its life from 1–3 to 200 Myr old, using one of our latest spectral type targets and other targets from the literature with older ages but similar estimated masses. The spectra are publicly available for the community’s use as data behind the figures.

We present a new program aimed at developing a new generation of micromirror devices specifically tailored for astronomical applications, multi-slit spectroscopy in particular. We first overview the general characteristics of Multi-Object-Spectrographs based on the current Digital Micromirror Devices (DMDs), with particular focus on the newly deployed SAMOS instrument at the 4.1 m SOAR telescope on Cerro Pachon. We illustrate the operational advantages of DMD-based instruments and the technical limitations of the currently available devices, the DMDs produced by Texas Instruments (TI). We then introduce the baseline and target parameters of the new Micro-Mirror-Devices (MMDs) that we plan to develop with the goal of reaching TRL-5 by mid-2029 as required by the Habitable Worlds Observatory (HWO) timeline. We conclude with a brief illustration of the exciting potential of MMD-based spectrographs for an 8 m class space telescope like HWO.

Star formation is a fundamental, yet poorly understood, process of the Universe. It is important to study how star formation occurs in different galactic environments. Thus, here, in the first of a series of papers, we introduce the Low-metallicity Star Formation (LZ-STAR) survey of the Sh2-284 (hereafter S284) region, which, at Z ∼ 0.3–0.5 Z _⊙ , is one of the lowest-metallicity star-forming regions of our Galaxy. LZ-STAR is a multifacility survey, including observations with JWST, the Atacama Large Millimeter/submillimeter Array (ALMA), Hubble Space Telescope, Chandra, and Gemini. As a starting point, we report JWST and ALMA observations of one of the most massive protostars in the region, S284p1. The observations of shock-excited molecular hydrogen reveal a symmetric, bipolar outflow originating from the protostar, spanning several parsecs, and fully covered by the JWST field of view and ALMA observations of CO(2–1) emission. These allow us to infer that the protostar has maintained a relatively stable orientation of disk accretion over its formation history. The JWST near-infrared continuum observations detect a centrally illuminated bipolar outflow cavity around the protostar, as well as a surrounding cluster of low-mass young stars. We develop new radiative transfer models of massive protostars designed for the low metallicity of S284. Fitting these models to the protostar’s spectral energy distribution implies a current protostellar mass of ∼10 M _⊙ has formed from an initial ∼100 M _⊙ core over the last ∼3 × 10 ^5 yr. Overall, these results indicate that massive stars can form in an ordered manner in low-metallicity, protocluster environments.

We present mid-infrared spectroscopic observations of intermediate-to-high-mass young stellar objects (YSOs) in the low-metallicity star-forming region NGC 346 located within the Small Magellanic Cloud (SMC). We conduct these integral field unit observations with the Medium Resolution Spectroscopy mode of the Mid-Infrared Instrument on board JWST. The brightest and most active star-forming region in the SMC, NGC 346, has a metallicity of ∼1/5 Z _⊙ , analogous to the era when star formation in the early Universe ( z ≃ 2) peaked. We discuss the emission and absorption features present in the spectral energy distributions (SEDs) of five YSOs with coverage from 4.9 to 27.9 μ m and three other sources with partial spectral coverage. Via SED model fitting, we estimate their parameters, finding masses ranging from 2.9 to 18.0 M _⊙ . These targets show dusty silicates, polycyclic aromatic hydrocarbons, and ices of CO _2 , CO, H _2 O, and CH _3 OH in their protostellar envelopes. We measure emission from H _2 and atomic fine-structure lines, suggesting the presence of protostellar jets and outflows. We detect H i lines, indicating ongoing accretion, and estimate accretion rates for each source that range from 2.50 × 10 ^−6 to 2.23 × 10 ^−4 M _⊙ yr ^−1 , based on the H i (7–6) line emission. We present evidence for a ∼30,000 au protostellar jet traced by fine-structure, H i , and H _2 emission about YSO Y535—the first mid-infrared detection of a resolved protostellar outflow in the SMC and the most distant yet detected by JWST.

HD 163296 is a Herbig Ae/Be star with multiple signposts of ongoing planet formation on its disk, such as prominent rings and gaps, as well as kinematic features as identified by previous Atacama Large Millimeter/submillimeter Array (ALMA) observations. We carried out JWST/NIRCam coronagraphic imaging using the F410M and F200W NIRCam filters, with the goal of detecting the emission from the putative young planets in this system. Our F410M observations did not detect the putative planets at the predicted locations of the ALMA velocity kinks, but they did detect a point-like source candidate at a separation of ≈ 0 . ″ 75 and a position angle of ≈ 231 . ° 4 that is unlikely a background star because of the measured flux in the F410M filter and the detection limit in the F200W filter. These data achieved unprecedented contrast levels at ∼4 μ m at stellocentric separations ρ ≳ 0 . ″ 8 . This allowed us to derive stringent constraints at the outer velocity kink (ΔF410M = 15.2 mag) on the mass of the putative planet with or without a circumplanetary disk, and considering different possible initial entropies for the planet.

The near-infrared (NIR) emission of the youngest protostars still needs to be characterized to better understand the evolution of their accretion and ejection activity. We analyze James Webb Space Telescope NIRSpec 1.7–5.3 μ m observations of two deeply embedded sources in the S68N protostellar core in Serpens. The North Central source exhibits a highly obscured spectrum ( A K ∼ 4.8 mag) that is modeled with a pre-main-sequence photosphere and a hot disk component. The photospheric parameters are consistent with a young, low-mass photosphere, as suggested by the low surface gravity, log g of 1.95 ±0.15 cm s −2 . The hot disk suggests that accretion onto the central protostellar embryo is ongoing, although prototypical accretion-tracing emission lines H i are not detected. The South Central source, which is even more embedded ( A K ∼ 8 mag; no continuum is detected shortward of 3.6 μ m) appears to be driving the large-scale S68N protostellar outflow, and launches a collimated hot molecular jet detected in H 2 and CO rovibrational lines. Shock modeling of the H 2 (ro)vibrational lines establishes that fast C -type shocks (≥30 km s −1 ), with high pre-shock density (≥10 7 cm −3 ), and strong magnetic field ( b ∼ 3–10, where B = b × n H ( cm − 3 ) μ G ) best match the data. The bright CO fundamental line forest suggests energetic excitation, with the contribution of non-LTE effects, i.e., irradiation pumping. Detected OH and CH + rovibrational lines support this hypothesis. These two Class 0 protostars seem to be in very young evolutionary stages and still have to acquire the bulk of their final stellar masses. These results demonstrate that JWST enables unprecedented diagnostics of these first stages of the protostellar evolutionary phase.

Context.Mid-infrared emission features are important probes of the properties of ionized gas and hot or warm molecular gas, which are difficult to probe at other wavelengths. The Orion Bar photodissociation region (PDR) is a bright, nearby, and frequently studied target containing large amounts of gas under these conditions. Under the “PDRs4All” Early Release Science Program for JWST, a part of the Orion Bar was observed with MIRI integral field unit (IFU) spectroscopy, and these high-sensitivity IR spectroscopic images of very high angular resolution (0.2″) provide a rich observational inventory of the mid-infrared (MIR) emission lines, while resolving the HIIregion, the ionization front, and multiple dissociation fronts.Aims.We list, identify, and measure the most prominent gas emission lines in the Orion Bar using the new MIRI IFU data. An initial analysis summarizes the physical conditions of the gas and demonstrates the potential of these new data and future IFU observations with JWST.Methods.The MIRI IFU mosaic spatially resolves the substructure of the PDR, its footprint cutting perpendicularly across the ionization front and three dissociation fronts. We performed an up-to-date data reduction, and extracted five spectra that represent the ionized, atomic, and molecular gas layers. We identified the observed lines through a comparison with theoretical line lists derived from atomic data and simulated PDR models. The identified species and transitions are summarized in the main table of this work, with measurements of the line intensities and central wavelengths.Results.We identified around 100 lines and report an additional 18 lines that remain unidentified. The majority consists of HIrecombination lines arising from the ionized gas layer bordering the PDR. The HIline ratios are well matched by emissivity coefficients from H recombination theory, but deviate by up to 10% because of contamination by HeIlines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni. We show how the NeIII/NeII, SIV/SIII, and ArIII/ArIIratios trace the conditions in the ionized layer bordering the PDR, while FeIII/FeIIand NiIII/NiIIexhibit a different behavior, as there are significant contributions to FeIIand NiIIfrom the neutral PDR gas. We observe the pure-rotational H2lines in the vibrational ground state from 0–0S(1) to 0–0S(8), and in the first vibrationally excited state from 1–1S(5) to 1–1 S(9). We derive H2excitation diagrams, and for the three observed dissociation fronts, the rotational excitation can be approximated with one thermal (~700 K) component representative of an average gas temperature, and one nonthermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model of the Orion Bar PDR, and find that the predicted excitation matches the data qualitatively, while adjustments to the parameters of the PDR model are required to reproduce the intensity of the 0–0 S (6) to S (8) lines.

We performed an HST/WFC3-IR imaging survey of the young stellar cluster NGC 2024 in three filters probing the 1.4 μ m H _2 O absorption feature, characteristic of the population of low-mass and substellar-mass objects down to a few Jupiter masses. We detect 812 point sources, 550 of them in all three filters with signal-to-noise ratio greater than 5. Using a distance-independent two-color diagram, we determine extinction values as high as A _V ≃ 40. We also find that the change of effective wavelengths in our filters results in higher A _V values as the reddening increases. Reconstructing a dereddened color–magnitude diagram, we derive a luminosity histogram both for the full sample of candidate cluster members and for an extinction-limited subsample containing the 50% of sources with A _V ≲ 15. Assuming a standard extinction law like Cardelli et al. with a nominal R _V = 3.1, we produce a luminosity function in good agreement with the one resulting from a Salpeter-like initial mass function for a 1 Myr isochrone. There is some evidence of an excess of luminous stars in the most embedded region. We posit that the correlation may be due to those sources being younger, and therefore overluminous, than the more evolved and less extincted cluster's stars. We compare our classification scheme based on the depth of the 1.4 μ m photometric feature with the results from the spectroscopic survey of Levine et al., and we report a few peculiar sources and morphological features typical of the rich phenomenology commonly encountered in young star-forming regions.