We present an overview and first results from a M-band spectroscopic survey of planet-forming disks performed with iSHELL on the Infrared Telescope Facility, using two slits that provide resolving power R ≈ 60,000–92,000 (5–3.3 km s−1). iSHELL provides a nearly complete coverage at 4.52–5.24 μm in one shot, covering >50 lines from the R and P branches of 12CO and 13CO for each of multiple vibrational levels, and providing unprecedented information on the excitation of multiple emission and absorption components. Some of the most notable new findings of this survey are: (1) the detection of two CO Keplerian rings at <2 au (in HD 259431), (2) the detection of H2O rovibrational lines at 5 μm (in AS 205 N), and (3) the common kinematic variability of CO lines over timescales of 1–14 yr. By homogeneously analyzing this survey together with a previous survey of cooler stars, we discuss a unified view of CO spectra where emission and absorption components scan the disk surface across radii from a dust-free region within dust sublimation out to ≈10 au. We classify two fundamental types of CO line shapes interpreted as emission from Keplerian rings (double-peak lines) and a disk surface plus a low-velocity part of a wind (triangular lines), where CO excitation reflects different emitting regions (and their gas-to-dust ratio) rather than just the irradiation spectrum. A disk+wind interpretation for the triangular lines naturally explains several properties observed in CO spectra, including the line blueshifts, line shapes that turn into narrow absorption at high inclinations, and the frequency of disk winds as a function of the stellar type.

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We present ALMA observations of 101 protoplanetary disks within the star-forming region Lynds 1641 in the Orion Molecular Cloud A. Our observations include 1.33 mm continuum emission and spectral windows covering the J = 2–1 transition of 12CO, 13CO, and C18O. We detect 89 protoplanetary disks in the dust continuum at the 4σ level (∼88% detection rate) and 31 in 12CO, 13 in 13CO, and 4 in C18O. Our sample contains 23 transitional disks, 20 of which are detected in the continuum. We target infrared-bright Class II objects, which biases our sample toward massive disks. We determine dust masses or upper limits for all sources in our sample and compare our sample to protostars in this region. We find a decrease in dust mass with evolutionary state. We also compare this sample to other regions surveyed in the (sub)millimeter and find that Lynds 1641 has a relatively massive dust disk population compared to regions of similar and older ages, with a median dust mass of M ⊕ and 27% with dust masses equal to or greater than the minimum solar nebula dust mass value of ∼30 M ⊕. We analyze the disk mass–accretion rate relationship in this sample and find that the viscous disk lifetimes are similar to the age of the region, though with a large spread. One object, [MGM2012] 512, shows a large-scale (>5000 au) structure in both the dust continuum and the three gas lines. We discuss potential origins for this emission, including an accretion streamer with large dust grains.

This work presents ground-based spectrally resolved water emission at R = 30,000–100,000 over infrared wavelengths covered by the JWST (2.9–12.8 μm). Two new surveys with iSHELL and the VISIR are combined with previous spectra from the CRIRES to cover parts of multiple rovibrational and rotational bands observable within telluric transmission bands, for a total of ≈160 spectra and 85 disks (30 of which are JWST targets in Cycle 1). The general expectation of a range of regions and excitation conditions traced by infrared water spectra is for the first time supported by the combined kinematics and excitation as spectrally resolved at multiple wavelengths. The main findings from this analysis are: (1) water lines are progressively narrower from the rovibrational bands at 2–9 μm to the rotational lines at 12 μm, and partly match broad and narrow emission components, respectively, as extracted from rovibrational CO spectra; (2) rotation diagrams of resolved water lines from upper-level energies of 4000–9500 K show vertical spread and curvatures indicative of optically thick emission (≈1018 cm−2) from a range of excitation temperatures (≈800–1100 K); and (3) the new 5 μm spectra demonstrate that slab model fits to the rotational lines at >10 μm strongly overpredict the rovibrational emission bands at <9 μm, implying vibrational excitation not in thermodynamic equilibrium. We discuss these findings in the context of emission from a disk surface and a molecular inner disk wind, and provide a list of guidelines to support the analysis of spectrally unresolved JWST spectra.

We present JWST-MIRI Medium Resolution Spectrometer (MRS) spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey Guaranteed Time Observations program. Emission from 12CO2, 13CO2, H2O, HCN, C2H2, and OH is identified with 13CO2 being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few astronomical units of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The Q branches of these molecules, including those of hot bands, are particularly sensitive to temperature and column density. We find that the 12CO2 emission in the GW Lup disk is coming from optically thick emission at a temperature of ∼400 K. 13CO2 is optically thinner and based on a lower temperature of ∼325 K, and thus may be tracing deeper into the disk and/or a larger emitting radius than 12CO2. The derived N CO 2 / N H 2 O ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on Spitzer-InfraRed-Spectrograph data. This high column density ratio may be due to an inner cavity with a radius in between the H2O and CO2 snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.

Terrestrial and sub-Neptune planets are expected to form in the inner (less than 10 au) regions of protoplanetary disks1. Water plays a key role in their formation2–4, although it is yet unclear whether water molecules are formed in situ or transported from the outer disk5,6. So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks7, similar to PDS 70, the first system with direct confirmation of protoplanet presence8,9. Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large (approximately 54 au) planet-carved gap separating an inner and outer disk10,11. Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H2 and/or OH, and survival through water self-shielding5. This is also supported by the presence of CO2 emission, another molecule sensitive to ultraviolet photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir12. Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry.

Accretion plays an important role in protoplanetary disk evolution, and it is thought that the accretion mechanism changes between low- and high-mass stars. Here we characterize accretion in intermediate-mass, pre-main-sequence Herbig Ae/Be (HAeBe) stars to search for correlations between accretion and system properties. We present new high-resolution, near-infrared spectra from the Immersion GRating INfrared Spectrograph for 102 HAeBes and analyze the accretion-tracing Brγ line at 2.166 μm. We also include the samples of Fairlamb et al. and Donehew & Brittain, for a total of 155 targets. We find a positive correlation between the Brγ and stellar luminosity, with a change in the slope between the Herbig Aes and Bes. We use L Brγ to determine the accretion luminosity and rate. We find that the accretion luminosity and rate depend on stellar mass and age; however, the trend disappears when normalizing the accretion luminosity by the stellar luminosity. We classify the objects into flared (group I) or flat (group II) disks and find that there is no trend with accretion luminosity or rate, indicating that the disk dust structure is not impacting accretion. We test for Brγ variability in objects that are common to our sample and previous studies. We find that the Brγ line equivalent width is largely consistent between the literature observations and those that we present here, except in a few cases where we may be seeing changes in the accretion rate.

We analyze Herschel Space Observatory observations of 104 young stellar objects with protoplanetary disks in the ∼1.5 Myr star-forming region Lynds 1641 (L1641) within the Orion A Molecular Cloud. We present spectral energy distributions from the optical to the far-infrared including new photometry from the Herschel Photodetector Array Camera and Spectrometer (PACS) at 70 µm. Our sample, taken as part of the Herschel Orion Protostar Survey, contains 24 transitional disks, eight of which we identify for the first time in this work. We analyze the full disks with irradiated accretion disk models to infer dust settling properties. Using forward modeling to reproduce the observed n K S −[70] index for the full disk sample, we find the observed disk indices are consistent with models that have depletion of dust in the upper layers of the disk relative to the midplane, indicating significant dust settling. We perform the same analysis on full disks in Taurus with Herschel data and find that Taurus is slightly more evolved, although both samples show signs of dust settling. These results add to the growing literature that significant dust evolution can occur in disks by ∼1.5 Myr.