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Complex organic molecules (COMs) in protoplanetary disks are key to understanding the origin of volatiles in comets in our solar system, yet the chemistry of COMs in protoplanetary disks remains poorly understood. Here, we present Atacama Large Millimeter/submillimeter Array Band 3 observations of the disk around the young outbursting star V883 Ori, where the COMs sublimate from ices and are thus observable thanks to the warm condition of the disk. We have robustly identified ten oxygen-bearing COMs including 13C isotopologues in the disk-integrated spectra. The radial distributions of the COM emission, revealed by the detailed analyses of the line profiles, show the inner emission cavity, similar to the previous observations in Band 6 and Band 7. We found that the COMs abundance ratios with respect to methanol are significantly higher than those in the warm protostellar envelopes of IRAS 16293-2422 and similar to the ratios in the solar system comet 67P/Churyumov-Gerasimenko, suggesting the efficient (re)formation of COMs in protoplanetary disks. We also constrained the 12C/13C and D/H ratios of COMs in protoplanetary disks for the first time. The 12C/13C ratios of acetaldehyde, methyl formate, and dimethyl ether are consistently lower (∼20–30) than the canonical ratio in the interstellar medium (∼69), indicating the efficient 13C-fractionation of CO. The D/H ratios of methyl formate are slightly lower than the values in IRAS 16293-2422, possibly pointing to the destruction and reformation of COMs in disks. We also discuss the implications for nitrogen and sulfur chemistry in protoplanetary disks.

Observations of a protostellar envelope and disk (from which planets should form) in the relatively close star-forming region of the Taurus molecular cloud reveal unexpected chemistry in the gas between the envelope and the disk: the unsaturated hydrocarbon molecule cyclic-C 3 H 2 and sulphur monoxide. The chemistry of stellar disk formation The young protostar IRAS 04368+2557 in the constellation of Taurus is surrounded by an infalling and rotating protostellar envelope and an inner protostellar disk out of which a planetary system is expected to form. Nami Sakai et al . report the presence of cyclopropenylidene (cyclic-C 3 H 2 ) in the protostellar envelope, and enhanced sulphur monoxide (SO) at the centrifugal barrier, inward of which the disk is forming. The chemistry revealed at the transition from envelope to disk had not been predicted in models, and provides useful clues to understanding the mechanisms of disk evolution around stars. IRAS 04368+2557 is a solar-type (low-mass) protostar embedded in a protostellar core (L1527) in the Taurus molecular cloud 1 , 2 , which is only 140 parsecs away from Earth, making it the closest large star-forming region. The protostellar envelope has a flattened shape with a diameter of a thousand astronomical units (1  au is the distance from Earth to the Sun), and is infalling and rotating 3 , 4 , 5 . It also has a protostellar disk with a radius of 90  au (ref. 6 ), from which a planetary system is expected to form 7 , 8 . The interstellar gas, mainly consisting of hydrogen molecules, undergoes a change in density of about three orders of magnitude as it collapses from the envelope into the disk, while being heated from 10 kelvin to over 100 kelvin in the mid-plane, but it has hitherto not been possible to explore changes in chemical composition associated with this collapse. Here we report that the unsaturated hydrocarbon molecule cyclic-C 3 H 2 resides in the infalling rotating envelope, whereas sulphur monoxide (SO) is enhanced in the transition zone at the radius of the centrifugal barrier (100 ± 20  au ), which is the radius at which the kinetic energy of the infalling gas is converted to rotational energy. Such a drastic change in chemistry at the centrifugal barrier was not anticipated, but is probably caused by the discontinuous infalling motion at the centrifugal barrier and local heating processes there.

We performed synthetic observations of the Ulrich, Cassen, and Moosman (UCM) model to understand the relation between the physical structures of the infalling envelope around a protostar and their observational features in molecular lines, adopting L1527 as an example. We also compared the physical structure and synthetic position–velocity (P–V) diagrams of the UCM model and a simple ballistic (SB) model. There are multiple ways to compare synthetic data with observational data. We first calculated the correlation coefficient. The UCM model and the SB model show similarly good correlation with the observational data. While the correlation reflects the overall similarity between the cube datasets, we can alternatively compare specific local features, such as the centrifugal barrier in the SB model or the centrifugal radius in the UCM model. We evaluated systematic uncertainties in these methods. In the case of L1527, the stellar mass values estimated using these methods are all lower than the value derived from previous Keplerian analysis of the disk. This may indicate that the gas infall motion in the envelope is retarded by, e.g., magnetic fields. We also showed analytically that, in the UCM model, the spin-up feature of the P–V diagram is due to the infall velocity rather than the rotation. The line-of-sight velocity V is thus ∝x −0.5, where x is the offset. If the infall is retarded, rotational velocity should dominate so that V is proportional to x −1, as is often observed in the protostellar envelope.

Recent exoplanet studies have revealed that the orbital planes of planets are not always aligned with one another or with the equatorial plane of the central star. The misalignment has been ascribed to gravitational scattering by giant planets and/or companion stars 1 – 3 or to fly-bys in stellar cluster environments 4 . Alternatively, the misalignment could be natal: that is, such planets were born in a warped protostellar disk 5 , 6 . Warped disk structures have been reported in some transition disks and protoplanetary disks 7 , 8 , but not in the earlier stages of protostar evolution, although such a possibility is suggested by outflow morphology 9 , 10 . Here we report millimetre-wavelength dust continuum observations of the young embedded protostar IRAS 04368+2557 in the protostellar core L1527 at a distance 11 of 137 parsecs; the protostar’s disk is almost edge-on 12 – 16 . The inner and outer parts of the disk have slightly different orbital planes, connected at 40 to 60 astronomical units from the star, but the disk has point symmetry with respect to the position of the protostar. We interpret it as a warped disk that is rotationally supported. Because there is no evidence for a companion source 17 , 18 , the warped structure must be due to either anisotropic accretion of gas with different rotational axes, or misalignment of the rotation axis of the disk with the magnetic field direction. Observations at millimetre wavelengths reveal a young protostar surrounded by a disk with two differently tilted regions.

The origin of complex organic molecules (COMs) in young Class 0 protostars has been one of the major questions in astrochemistry and star formation. While COMs are thought to form on icy dust grains via gas-grain chemistry, observational constraints on their formation pathways have been limited to gas-phase detection. Sensitive mid-infrared spectroscopy with JWST enables unprecedented investigation of COM formation by measuring their ice absorption features. Mid-infrared emission from disks and outflows provide complementary constraints on the protostellar systems. We present an overview of JWST/Mid-Infrared Instrument (MIRI) Medium Resolution Spectroscopy (MRS) and imaging of a young Class 0 protostar, IRAS 15398−3359, and identify several major solid-state absorption features in the 4.9–28 μm wavelength range. These can be attributed to common ice species, such as H2O, CH3OH, NH3, and CH4, and may have contributions from more complex organic species, such as C2H5OH and CH3CHO. In addition to ice features, the MRS spectra show many weaker emission lines at 6–8 μm, which are due to warm CO gas and water vapor, possibly from a young embedded disk previously unseen. Finally, we detect emission lines from [Fe ii], [Ne ii], [S i], and H2, tracing a bipolar jet and outflow cavities. MIRI imaging serendipitously covers the southwestern (blueshifted) outflow lobe of IRAS 15398−3359, showing four shell-like structures similar to the outflows traced by molecular emission at submillimeter wavelengths. This overview analysis highlights the vast potential of JWST/MIRI observations and previews scientific discoveries in the coming years.

Deuterium fractionation in molecules is known as one of the most powerful tools to study chemical processes during star and planet formation. Among various interstellar molecules, methanol often shows very high deuterium fractionation. It is the most abundant saturated organic molecule and is known as a parent species to form more complex organic molecules. However, deriving the abundance of deuterated methanol suffers from the uncertainty in the intrinsic line intensities (S μ 2) of CH3OH isotopologues. Due to their floppy nature, theoretical evaluation of the S μ 2 values is not straightforward, particularly for asymmetric-top asymmetric-frame isotopologues such as CH2DOH. In this study, we have measured the line frequencies and their intensities for CH2DOH in the millimeter-wave region from 216 to 264 GHz by using an emission-type millimeter and submillimeter-wave spectrometer. For the a-type J = 5 − 4 transition, the derived S μ 2 values are 13%–27% larger than those theoretically calculated, except for the transitions of K a = 2 for e 0 and K a = 1 for e 1 affected by avoided level crossing. For b-type transitions, significant systematic differences are found between theoretical and experimental S μ 2 values. The results of the present study enable us to accurately derive from observations the CH2DOH abundances, which are essential for understanding deuterium fractionation in various sources.

IRAS 15398−3359, a Class 0 protostar in the Lupus I star-forming region, is associated with three generations of outflows. The primary outflow, i.e., the most recent one, shows an internal structure named the “shell structure” in the near-infrared emission map. The shell structure is also seen in the emission lines of CO, H2CO, and other species. We find a similar structure in an underexpanded jet produced in aerodynamics and other engineering applications. A high-pressure gas ejected through a nozzle expands to form a supersonic flow. When the pressure of the ejected gas becomes lower than that of the ambient gas, the jet is compressed to form a shock wave. The shock-heated gas expands again to form substructures along the jet. We examine the similarity between the primary outflow of IRAS 15398−3359 and the industrial underexpanded jet and the possibility that the shell structure of the former is due to repeated expansion and compression in the direction perpendicular to the jet propagation.

Methanol is one of the most abundant complex organic molecules in interstellar environments. Molecular lines of its rare isotopologues 12CH317OH and 12CH318OH therefore play a crucial role in examining the column density of 12CH316OH, which serves as a reference for organic molecular chemistry in interstellar clouds. In this study, we have recorded the spectroscopic emission spectrum of 12CH317OH in the frequency range between 216 and 264 GHz by making use of an emission-type millimeter and submillimeter spectrometer. We have specifically paid attention to the Q-branch transitions, which are the strongest line series in this frequency region. Among the stable oxygen isotopes, 16O, 17O, and 18O of methanol, only 12CH317OH obviously shows line profiles having double and/or triple peaks in low-J transitions, due to the nuclear quadrupole interaction. The newly obtained 12CH317OH data will play an important role in facilitating a deeper understanding of the organic chemistry related to star and planet formation. The 12CH317OH line data allow us to trace and constrain the isotopic ratio 17O/18O in methanol, which is efficient to investigate the galactic-scale evolution of elements. In addition, we also assigned some transitions of 13CH317OH in the recorded spectrum.

Characterizing the physical properties of dust grains in a protoplanetary disk is critical to comprehending the planet formation process. Our study presents Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution observations of the young protoplanetary disk around DG Tau at a 1.3 mm dust continuum. The observations, with a spatial resolution of ≈0.″04, or ≈5 au, revealed a geometrically thin and smooth disk without substantial substructures, suggesting that the disk retains the initial conditions of the planet formation. To further analyze the distributions of dust surface density, temperature, and grain size, we conducted a multiband analysis with several dust models, incorporating ALMA archival data of the 0.87 and 3.1 mm dust polarization. The results showed that the Toomre Q parameter is ≲2 at a 20 au radius, assuming a dust-to-gas mass ratio of 0.01. This implies that a higher dust-to-gas mass ratio is necessary to stabilize the disk. The grain sizes depend on the dust models, and for the DSHARP compact dust, they were found to be smaller than ∼400 μm in the inner region (r ≲ 20 au) while exceeding larger than 3 mm in the outer part. Radiative transfer calculations show that the dust scale height is lower than at least one-third of the gas scale height. These distributions of dust enrichment, grain sizes, and weak turbulence strength may have significant implications for the formation of planetesimals through mechanisms such as streaming instability. We also discuss the CO snowline effect and collisional fragmentation in dust coagulation for the origin of the dust size distribution.

Understanding the chemical past of our Sun and how life appeared on Earth is no mean feat. The best strategy we can adopt is to study newborn stars located in an environment similar to the one in which our Sun was born and assess their chemical content. In particular, hot corinos are prime targets because recent studies have shown correlations between interstellar complex organic molecules abundances from hot corinos and comets. The ORion ALMA New GEneration Survey aims to assess the number of hot corinos in the closest and best analog to our Sun’s birth environment, the OMC-2/3 filament. In this context, we investigated the chemical nature of 19 solar-mass protostars and found that 26% of our sample sources show warm methanol emission indicative of hot corinos. Compared to the Perseus low-mass star-forming region, where the PErseus ALMA CHEmistry Survey detected hot corinos in ∼60% of the sources, the hot corinos seem to be relatively scarce in the OMC-2/3 filament. While this suggests that the chemical nature of protostars in Orion and Perseus is different, improved statistics is needed in order to consolidate this result. If the two regions are truly different, this would indicate that the environment is likely playing a role in shaping the chemical composition of protostars.