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We investigate chemistry in the compression layer behind the interstellar shock waves, where molecular cloud formation starts. We perform three-dimensional magnetohydrodynamics simulations of converging flows of atomic gas with shock parameters of inclination between the interstellar magnetic field and the shock wave, pre-shock density, and shock velocity. Then we derive 1D mean-flow models, along which we calculate a detailed gas-grain chemical reaction network as a post process with various chemical parameters, i.e. cosmic-ray ionization rate, abundances of PAHs, and metals in the gas phase. While carbon chains reach their peak abundances when atomic carbon is dominant in the pseudo-time-dependent models of molecular clouds, such behavior is less significant in our models since the visual extinction of the compression layer is low ($\lesssim 1$ mag) when atomic carbon is abundant. Carbon chains, CN, and HCN increase at $A_V \gtrsim 1$ mag, where the gas-phase C/O ratio increases due to water ice formation. Shock parameters affect the physical structure and the evolutional timescale of the compression layer, and thus molecular evolution. Carbon chains are more abundant in models with higher post-shock density and slower gas accumulation. We calculate molecular column densities in the compression layer and compare them with the observations of diffuse and translucent clouds, which show reasonable agreement for water ice, carbon chains, and HCO$^+$. The observed variation of their column densities could be due to the difference in shock parameters and chemical parameters. The column density of CN is overestimated, for which we discuss possible reasons., Comment: Accepted in MNRAS. 20 pages, 14 figures

We present an investigation of Complex Organic Molecules (COMs) in the spatially resolved Keplerian disk around V883 Ori, an eruptive young star, based on a spectral survey carried out with ALMA in Band 6 (220.7$-$274.9 GHz). We identified about 3,700 molecular emission lines and discovered 23 COMs in the disk. We estimated the column densities of COMs detected through the iterative LTE line fitting method. According to our analyses, using only optically thin lines is critical to deriving the reliable column densities of COMs. Therefore, covering a large frequency range is important for the studies of COMs. The most distinct phenomenon found from the spectra of the V883 Ori disk is that nitrogen-bearing COMs other than CH$_{3}$CN are missing, whereas various oxygen-bearing COMs, except for the CH$_2$OH-bearing molecules, are detected. The missing CH$_2$OH-bearing COMs may indicate the warm water-ice dominant environment for forming COMs. We compared our results with various objects in different evolutionary stages, from Class 0 hot corinos to a Solar System comet 67P/Churyumov-Gerasimenko, to examine the effect of evolution on the COM compositions. In general, the COMs abundances relative to methanol in V883 Ori are higher than in the hot corinos and hot cores, while they are comparable to the cometary values. This may indicate the planet-forming material chemically evolves in the disk midplane after being accreted from the envelope. In addition, as found in the comet 67P/Churyumov-Gerasimenko, nitrogen might also be trapped as ammonium salt within the dust grains in the V883 Ori disk., Comment: Accepted for publication in ApJS

Molecular deuteration is a powerful diagnostic tool for probing the physical conditions and chemical processes in astrophysical environments. In this work, we focus on formaldehyde deuteration in the protobinary system NGC\,1333 IRAS\,4A, located in the Perseus molecular cloud. Using high-resolution ($\sim$\,100\,au) ALMA observations, we investigate the [D$_2$CO]/[HDCO] ratio along the cavity walls of the outflows emanating from IRAS\,4A1. Our analysis reveals a consistent decrease in the deuteration ratio (from $\sim$\,60-20\% to $\sim$\,10\%) with increasing distance from the protostar (from $\sim$\,2000\,au to $\sim$\,4000\,au). Given the large measured [D$_2$CO]/[HDCO], both HDCO and D$_2$CO are likely injected by the shocks along the cavity walls into the gas-phase from the dust mantles, formed in the previous prestellar phase. We propose that the observed [D$_2$CO]/[HDCO] decrease is due to the density profile of the prestellar core from which NGC\,1333 IRAS\,4A was born. When considering the chemical processes at the base of formaldehyde deuteration, the IRAS\,4A's prestellar precursor had a predominantly flat density profile within 3000\,au and a decrease of density beyond this radius.

Characterizing the chemistry of complex organic molecules (COMs) at the epoch of planet formation provides insights into the chemical evolution of the interstellar medium (ISM) and the origin of organic materials in our Solar System. We report a detection of dimethyl ether (CH$_3$OCH$_3$) in the disk around the Herbig Ae star MWC 480 with the sensitive Atacama Large Millimeter/submillimeter Array observations. This is the first detection of CH$_3$OCH$_3$ in a non-transitional Class II disk. The spatially unresolved, compact (${\lesssim}$25 au in radius) nature, the broad line width ($\sim$30 km s$^{-1}$), and the high excitation temperature (${\sim}$200 K) indicate sublimation of COMs in the warm inner disk. Despite the detection of CH$_3$OCH$_3$, methanol (CH$_3$OH), the most abundant COM in the ISM, has not been detected, from which we constrain the column density ratio of CH$_3$OCH$_3$/CH$_3$OH ${\gtrsim}$7. This high ratio may indicate the reprocessing of COMs during the disk phase, as well as the effect of the physical structure in the inner disk. We also find that this ratio is higher than in COM-rich transition disks recently discovered. This may indicate that, in the full disk of MWC 480, COMs have experienced substantial chemical reprocessing in the innermost region, while the COM emission in the transition disks predominantly traces the inherited ice sublimating at the dust cavity edge located at larger radii (${\gtrsim}$20 au)., Comment: 16 pages, 6 figures, accepted for publication in ApJ

When the planet formation process begins in the disks surrounding young stars is still an open question. Annular substructures such as rings and gaps in disks are intertwined with planet formation, and thus their presence or absence is commonly used to investigate the onset of this process. Current observations show a limited number of disks surrounding protostars exhibiting annular substructures, all of them in the Class I stage. The lack of observed features in most of these sources may indicate a late emergence of substructures, but it could also be an artifact of these disks being optically thick. To mitigate the problem of optical depth, we investigate substructures within a very young Class 0 disk characterized by a low inclination using observations at longer wavelengths. We use 3 mm ALMA observations tracing dust emission at a resolution of 7 au to search for evidence of annular substructures in the disk around the deeply embedded Class 0 protostar Oph A SM1. The observations reveal a nearly face-on disk (i$\sim$16$^{\circ}$) extending up to 40 au. The radial intensity profile shows a clear deviation from a smooth profile near 30 au, which we interpret as the presence of either a gap at 28 au or a ring at 34 au with Gaussian widths of $\sigma=1.4^{+2.3}_{-1.2}$ au and $\sigma=3.9^{+2.0}_{-1.9}$ au, respectively. The 3 mm emission at the location of the possible gap or ring is determined to be optically thin, precluding the possibility that this feature in the intensity profile is due to the emission being optically thick. Annular substructures resembling those in the more evolved Class I and II disks could indeed be present in the Class 0 stage, earlier than previous observations suggested. Similar observations of embedded disks in which the high optical depth problem can be mitigated are clearly needed to better constrain the onset of substructures in the embedded stages., Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in A&A Letters

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the binary Class 0 protostellar system BHR 71 IRS1 and IRS2 as part of the Early Planet Formation in Embedded Disks (eDisk) ALMA Large Program. We describe the $^{12}$CO ($J$=2--1), $^{13}$CO ($J$=2--1), C$^{18}$O ($J$=2--1), H$_2$CO ($J=3_{2,1}$--$2_{2,0}$), and SiO ($J$=5--4) molecular lines along with the 1.3 mm continuum at high spatial resolution ($\sim$0.08" or $\sim$5 au). Dust continuum emission is detected toward BHR 71 IRS1 and IRS2, with a central compact component and extended continuum emission. The compact components are smooth and show no sign of substructures such as spirals, rings or gaps. However, there is a brightness asymmetry along the minor axis of the presumed disk in IRS1, possibly indicative of an inclined geometrically and optically thick disk-like component. Using a position-velocity diagram analysis of the C$^{18}$O line, clear Keplerian motions were not detected toward either source. If Keplerian rotationally-supported disks are present, they are likely deeply embedded in their envelope. However, we can set upper limits of the central protostellar mass of 0.46 M$_\odot$ and 0.26 M$_\odot$ for BHR 71 IRS1 and BHR 71 IRS2, respectively. Outflows traced by $^{12}$CO and SiO are detected in both sources. The outflows can be divided into two components, a wide-angle outflow and a jet. In IRS1, the jet exhibits a double helical structure, reflecting the removal of angular momentum from the system. In IRS2, the jet is very collimated and shows a chain of knots, suggesting episodic accretion events., Comment: 38 pages, 29 figures, accepted in ApJ

Methane (CH4) is one of the major components of the icy mantle of cosmic dust prevalent in cold, dense regions of interstellar media, playing an important role in the synthesis of complex organic molecules and prebiotic molecules. Solid CH4 is considered to be formed via the successive hydrogenation of C atoms accreting onto dust: C + 4H -> CH4. However, most astrochemical models assume this reaction on the ice mantles of dust to be barrierless and efficient, without considering the states of adsorption. Recently, we found that C atoms exist in either the physisorbed or chemisorbed state on compact amorphous solid water, which is analogous to an interstellar ice mantle. These distinct adsorption states considerably affect the hydrogenation reactivity of the C atom. Herein, we elucidate the reactivities of physisorbed and chemisorbed C atoms with H atoms via sequential deposition and co-deposition processes. The results indicate that only physisorbed C atoms can produce CH4 on ice. Combining this finding with a previous estimate for the fraction of physisorbed C atoms on ice, we determined the upper limit for the conversion of C atoms into CH4 to be 30%., Comment: 24 pages, 4 figures, 1 table; accepted for publication in ApJ

The isomeric ratios of $^{198}$Au, $^{197}$Hg and $^{195}$Hg produced by $\alpha$-particle induced reactions on natural platinum were investigated experimentally up to 29 MeV by using the standard stacked foil activation technique and $\gamma$-ray spectrometry. The isomeric ratios of $^{197}$Hg and $^{195}$Hg determined by the conventional activation cross section formula showed strong cooling time dependence. The time dependence was resolved by adjusting the isomeric transition branching ratios for the two isotopes within a simultaneous decay curve analysis framework. Our analysis suggests 94.5$\pm$0.7% and 48.9$\pm$1.8% as the isomeric transition branching ratios of $^{197m}$Hg (24 h) and $^{195m}$Hg (42 h), respectively. The isomeric ratios and independent production cross sections of $^{198}$Au, $^{197}$Hg, $^{195}$Hg and some other Hg, Au and Pt isotopes were also measured down to 6 MeV with these corrected isomeric transition branching ratios, and compared with predictions of statistical and pre-equilibrium models by TALYS-2.0 to discuss spin cuto? parameter dependence. We found the measured isomeric ratios are better predicted if we reduce the spin cuto? parameter to half or less from that estimated with the rigid body moment of inertia., Comment: Submitted to European Physical Journal A

Recent observations suggest that planets formation starts early, in protostellar disks of $\le10^5$ yrs, which are characterized by strong interactions with the environment, e.g., through accretion streamers and molecular outflows. To investigate the impact of such phenomena on disk physical and chemical properties it is key to understand what chemistry planets inherit from their natal environment. In the context of the ALMA Large Program Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars (FAUST), we present observations on scales from ~1500 au to ~60 au of H$_2$CO, HDCO, and D$_2$CO towards the young planet-forming disk IRS~63. H$_2$CO probes the gas in the disk as well as in a large scale streamer (~1500 au) impacting onto the South-East (SE) disk side. We detect for the first time deuterated formaldehyde, HDCO and D$_2$CO, in a planet-forming disk, and HDCO in the streamer that is feeding it. This allows us to estimate the deuterium fractionation of H$_2$CO in the disk: [HDCO]/[H$_2$CO]$\sim0.1-0.3$ and [D$_2$CO]/[H$_2$CO]$\sim0.1$. Interestingly, while HDCO follows the H$_2$CO distribution in the disk and in the streamer, the distribution of D$_2$CO is highly asymmetric, with a peak of the emission (and [D]/[H] ratio) in the SE disk side, where the streamer crashes onto the disk. In addition, D$_2$CO is detected in two spots along the blue- and red-shifted outflow. This suggests that: (i) in the disk, HDCO formation is dominated by gas-phase reactions similarly to H$_2$CO, while (ii) D$_2$CO was mainly formed on the grain mantles during the prestellar phase and/or in the disk itself, and is at present released in the gas-phase in the shocks driven by the streamer and the outflow. These findings testify on the key role of streamers in the build-up of the disk both concerning the final mass available for planet formation and its chemical composition., Comment: 12 pages, 10 figures, accepted for publication on A&A

We investigate the chemical evolution of complex organic molecules (COMs) in turbulent disks using gas-ice chemical reaction network simulations. We trace trajectories of dust particles considering advection, turbulent diffusion, gas drag, and vertical settling, for 10$^6$ yrs in a protoplanetary disk. Then, we solve a gas-ice chemical reaction network along the trajectories and obtain the temporal evolution of molecular abundances. We find that the COM abundances in particles can differ by more than two orders of magnitude even when the UV fluence (i.e., the time integral of UV flux) received by the particles are similar, suggesting that not only the UV fluence but also the time variation of the UV flux does matter for the evolution of COMs in disks. The impact of UV fluence on molecular abundances differs between oxygen-bearing and nitrogen-bearing COMs. While higher UV fluence results in oxygen being locked into CO$_2$, leading to reduced abundances of oxygen-bearing COMs such as CH$_3$OCH$_3$, mild UV exposure can promote their formation by supplying the precursor radicals. On the other hand, nitrogen is not locked up into specific molecules, allowing the formation of nitrogen-bearing COMs, particularly CH$_3$NH$_2$, even for the particle that receives the higher UV fluence. We also find that the final COM abundances are mostly determined by the inherited abundances from the protostellar core when the UV fluence received by dust particles is less than a critical value, while they are set by both the inherited abundances and the chemistry inside the disk at higher UV fluence., Comment: 19 pages, to be published in MNRAS

We investigate the role of carbon monoxide ice in the chemical evolution of prestellar cores using astrochemical rate equation models. We constrain the ratios of the binding energies on CO ice and H$_{2}$O ice for a series of adsorbates deemed important in diffusive chemistry on H$_{2}$O ices. We later include these ratios in our chemical reaction network model, where the binding and diffusion energies of icy species vary as a function of the surface composition. When the surface coverage of CO increases, the model shows an enhancement of O-bearing complex organic molecules, especially those formed from the intermediate products of CO hydrogenation (e.g. HCO) and CH$_{3}$/CH$_{2}$. Because the binding energy of CH$_{3}$/CH$_{2}$ is in the right range, its diffusion rate increases significantly with CO coverage. At $T>$14 K and with less influence, enhanced diffusion of HCO also contributes to the increase of the abundances of COM. We find, however, that chemistry is not always enhanced on CO ice and that the temperature and cosmic ray ionization rate of each astronomical object is crucial for this particular chemistry, revealing a highly non-trivial behavior that needs to be addressed on a per-case basis. Our results are highly relevant in the context of interstellar ice observations with JWST., Comment: Accepted for publication in Astronomy and Astrophysics

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS\,4A protobinary system. This analysis is based on ALMA observations of SiO(5--4), H$_2$CO(3$_{0,3}$--2$_{0,3}$), and HDCO(4$_{1,4}$--3$_{1,3}$) with a spatial resolution of $\sim$150\,au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS\,4A1 and IRAS\,4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS\,4A1 exhibit extensions of 10$''$ and 13$''$ with position angles (PA) of 0$^{\circ}$ and -12$^{\circ}$, respectively, while those of IRAS\,4A2 are more extended, spanning 18$''$ and 25$''$ with PAs of 29$^{\circ}$ and 26$^{\circ}$. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

Context. Understanding the connection between outflows, winds, accretion and disks in the inner protostellar regions is crucial for comprehending star and planet formation process. Aims. We aim to we explore the inner 300 au of the protostar IRAS 4A2 as part of the ALMA FAUST Large Program. Methods. We analysed the kinematical structures of SiO and CH$_3$OH emission with 50 au resolution. Results. The emission arises from three zones: i) a very compact and unresolved region ($<$50 au) dominated by the ice sublimation zone, at $\pm$1.5 km s$^{-1}$ with respect to vsys, traced by methanol; ii) an intermediate region (between 50 au and 150 au) traced by both SiO and CH$_3$OH, between 2 and 6 km s$^{-1}$ with respect to vsys, with an inverted velocity gradient (with respect to the large scale emission), whose origin is not clear; iii) an extended region ($>$150 au) traced by SiO, above 7 km s$^{-1}$ with respect to vsys, and dominated by the outflow. In the intermediate region we estimated a CH$_3$OH/SiO abundance ratio of about 120-400 and a SiO/H$_2$ abundance of 10$^{-8}$. We explored various possibilities to explain the origin of this region such as, rotating disk/inner envelope, jet on the plane of the sky/precessing, wide angle disk wind. Conclusions. We propose that CH$_3$OH and SiO in the inner 100 au probe the base of a wide-angle disk wind. The material accelerated in the wind crosses the plane of the sky, giving rise to the observed inverted velocity gradient, and sputtering the grain mantles and cores releasing CH$_3$OH and SiO. This is the first detection of a disk wind candidate in SiO, and the second ever in CH$_3$OH., Comment: Accepted in A&A Letters

The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH$_3$OH, H$_2$CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Methanol emission reveals an arc-like structure at $\sim$1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H$_2$CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H$_2$ column density of $\sim$7$\times$10$^{21}$ cm$^{-2}$, a mass of $\sim$9$\times$10$^{-3}$ M$_\odot$, and a lower limit on the dust spectral index of $1.4$. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues., Comment: 12 pages, 8 figures, 3 tables. Accepted Letter in Astronomy & Astrophysics

Young protostellar binary systems, with expected ages less than $\sim$10$^5$ years, are little modified since birth, providing key clues to binary formation and evolution. We present a first look at the young, Class 0 binary protostellar system R CrA IRAS 32 from the Early Planet Formation in Embedded Disks (eDisk) ALMA large program, which observed the system in the 1.3 mm continuum emission, $^{12}$CO (2-1), $^{13}$CO (2-1), C$^{18}$O (2-1), SO (6$_5$-5$_4$), and nine other molecular lines that trace disk, envelope, shocks, and outflows. With a continuum resolution of $\sim$0.03$^{\prime\prime}$ ($\sim$5 au, at a distance of 150 pc), we characterize the newly discovered binary system with a separation of 207 au, their circumstellar disks, and a circumbinary disk-like structure. The circumstellar disk radii are 26.9$\pm$0.3 and 22.8$\pm$0.3 au for sources A and B, respectively, and their circumstellar disk dust masses are estimated as 22.5$\pm$1.1 and 12.4$\pm$0.6 M$_{\Earth}$. The circumstellar disks and the circumbinary structure have well aligned position angles and inclinations, indicating formation in a smooth, ordered process such as disk fragmentation. In addition, the circumstellar disks have a near/far-side asymmetry in the continuum emission suggesting that the dust has yet to settle into a thin layer near the midplane. Spectral analysis of CO isotopologues reveals outflows that originate from both of the sources and possibly from the circumbinary disk-like structure. Furthermore, we detect Keplerian rotation in the $^{13}$CO isotopologues toward both circumstellar disks and likely Keplerian rotation in the circumbinary structure; the latter suggests that it is probably a circumbinary disk., Comment: 33 pages, 29 figures, 6 tables

An unbiased spectral survey of V883 Ori, an eruptive young star, was carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 6. The detected line emission from various molecules reveals morphological/kinematical features in both the Keplerian disk and the infalling envelope. A direct infall signature, red-shifted absorption against continuum, has been detected in CO, HCO$^+$, HCN, HNC, and H$_2$CO. HCO$^+$ and SO show large arm-like structures that probably connect from an infalling envelope to the disk. HCN and H$_2$CO reveal a distinct boundary between the inner and outer disk and reveal tentative spiral structures connecting the outer disk to the inner disk. HNC shows a large central emission hole (r $\sim$0.3\arcsec) due to its chemical conversion to HCN at high temperatures. The HDO emission, a direct tracer of the water sublimation region, has been detected in the disk. Molecular emission from complex organic molecules (COMs) is confined within the HDO emission boundary, and HCO$^+$ has an emission hole in its distribution due to its destruction by water. Together, these features suggest that the current episode of eruption in V883 Ori may be triggered by the infall from the envelope to the outer disk, generating a spiral wave, which propagates inward and greatly enhances the accretion onto the central star., Comment: Accepted for publication in ApJ

We present MIRI MRS observations of the large, multi-gapped protoplanetary disk around the T-Tauri star AS 209. The observations reveal hundreds of water vapor lines from 4.9 to 25.5 $\mu$m towards the inner $\sim1$ au in the disk, including the first detection of ro-vibrational water emission in this disk. The spectrum is dominated by hot ($\sim800$ K) water vapor and OH gas, with only marginal detections of CO$_2$, HCN, and a possible colder water vapor component. Using slab models with a detailed treatment of opacities and line overlap, we retrieve the column density, emitting area, and excitation temperature of water vapor and OH, and provide upper limits for the observable mass of other molecules. Compared to MIRI spectra of other T-Tauri disks, the inner disk of AS 209 does not appear to be atypically depleted in CO$_2$ nor HCN. Based on \textit{Spitzer IRS} observations, we further find evidence for molecular emission variability over a 10-year baseline. Water, OH, and CO$_2$ line luminosities have decreased by factors 2-4 in the new MIRI epoch, yet there are minimal continuum emission variations. The origin of this variability is yet to be understood., Comment: Accepted for publication in ApJ

We present the outflows detected in HOPS 373SW, a protostar undergoing a modest $30\%$ brightness increase at 850 $\mu$m. Atacama Large Millimeter/submillimeter Array (ALMA) observations of shock tracers, including SiO 8--7, CH$_3$OH 7$_{\rm k}$--6$_{\rm k}$, and $^{12}$CO 3--2 emission, reveal several outflow features around HOPS 373SW. The knots in the extremely high-velocity SiO emission reveal the wiggle of the jet, for which a simple model derives a 37$^\circ$ inclination angle of the jet to the plane of the sky, a jet velocity of 90 km s$^{-1}$, and a period of 50 years. The slow SiO and CH$_3$OH emission traces U-shaped bow shocks surrounding the two CO outflows. One outflow is associated with the high-velocity jets, while the other is observed to be close to the plane of the sky. The misaligned outflows imply that previous episodic accretion events have either reoriented HOPS 373SW or that it is an unresolved protostellar binary system with misaligned outflows., Comment: Accepted for publication in ApJ

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 $\propto x^{-0.5}$, 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., Comment: 17 pages, 12 figures, published in ApJ, 2024 January 11

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 (ALMA) 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 $^{13}$C-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 $^{12}$C/$^{13}$C and D/H ratios of COMs in protoplanetary disks for the first time. The $^{12}$C/$^{13}$C ratios of acetaldehyde, methyl formate, and dimethyl ether are consistently lower ($\sim$ 20-30) than the canonical ratio in the interstellar medium ($\sim$ 69), indicating the efficient $^{13}$C-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., Comment: 38 pages, 22 figures, Accepted for publication in AJ

While most debris disks consist of dust with little or no gas, a fraction has significant amounts of gas detected via emission lines of CO, ionized carbon, and/or atomic oxygen. Almost all such gaseous debris disks known are around A-type stars with ages up to 50 Myr. We show, using semi-analytic disk evolution modeling, that this can be understood if the gaseous debris disks are remnant protoplanetary disks that have become depleted of small grains compared to the interstellar medium. Photoelectric heating by the A-stars' FUV radiation is then inefficient, while the stars' EUV and X-ray emissions are weak owing to a lack of surface convective zones capable of driving magnetic activity. In this picture, stars outside the range of spectral types from A through early B are relatively hard to have such long-lived gas disks. Less-massive stars have stronger magnetic activity in the chromosphere, transition region, and corona with resulting EUV and X-ray emission, while more-massive stars have photospheres hot enough to produce strong EUV radiation. In both cases, primordial disk gas is likely to photoevaporate well before 50 Myr. These results come from 0D disk evolution models where we incorporate internal accretion stresses, MHD winds, and photoevaporation by EUV and X-ray photons with luminosities that are functions of the stellar mass and age. A key issue this work leaves open is how some disks become depleted in small dust so that FUV photoevaporation slows. Candidates include grains' growth, settling, radial drift, radiation force, and incorporation into planetary systems., Comment: Submitted to ApJL

We present ALMA observations of the Class I source Oph IRS63 in the context of the Early Planet Formation in Embedded Disks (eDisk) large program. Our ALMA observations of Oph IRS63 show a myriad of protostellar features, such as a shell-like bipolar outflow (in $^{12}$CO), an extended rotating envelope structure (in $^{13}$CO), a streamer connecting the envelope to the disk (in C$^{18}$O), and several small-scale spiral structures seen towards the edge of the dust continuum (in SO). By analyzing the velocity pattern of $^{13}$CO and C$^{18}$O, we measure a protostellar mass of $\rm M_\star = 0.5 \pm 0.2 $~$\rm M_\odot$ and confirm the presence of a disk rotating at almost Keplerian velocity that extends up to $\sim260$ au. These calculations also show that the gaseous disk is about four times larger than the dust disk, which could indicate dust evolution and radial drift. Furthermore, we model the C$^{18}$O streamer and SO spiral structures as features originating from an infalling rotating structure that continuously feeds the young protostellar disk. We compute an envelope-to-disk mass infall rate of $\sim 10^{-6}$~$\rm M_\odot \, yr^{-1}$ and compare it to the disk-to-star mass accretion rate of $\sim 10^{-8}$~$\rm M_\odot \, yr^{-1}$, from which we infer that the protostellar disk is in a mass build-up phase. At the current mass infall rate, we speculate that soon the disk will become too massive to be gravitationally stable., Comment: 26 pages and 17 figures

Carbon-enhanced metal-poor (CEMP) stars in the Galactic halo have a wide range of neutron-capture element abundance patterns. To identify their origin, we investigated three modes of $s$-process nucleosynthesis that have been proposed to operate in extremely metal-poor (EMP) Asymptotic Giant Branch (AGB) stars: the convective 13C burning, which occurs when hydrogen is engulfed by the helium flash convection in low-mass AGB stars, the convective 22Ne burning, which occurs in the helium flash convection of intermediate-mass AGB stars, and the radiative 13C burning, which occurs in the $^{13}$C pocket that is formed during the inter-pulse periods. We show that the production of $s$-process elements per iron seed ($s$-process efficiency) does not depend on metallicity below $[{\rm Fe}/{\rm H}]=-2$, because 16O in the helium zone dominates the neutron poison. The convective 13C mode can produce a variety of $s$-process efficiencies for Sr, Ba and Pb, including the maxima observed among CEMP stars. The 22Ne mode only produce the lowest end of $s$-process efficiencies among CEMP models. We show that the combination of these two modes can explain the full range of observed enrichment of $s$-process elements in CEMP stars. In contrast, the 13C pocket mode can hardly explain the high level of enrichment observed in some CEMP stars, even if considering star-to-star variations of the mass of the 13C pocket. These results provide a basis for discussing the binary mass transfer origin of CEMP stars and their subgroups., Comment: 22 pages, 13 figures, 1 table. Accepted for publication in Publications of the Astronomical Society of Japan

Protostellar disks are a ubiquitous part of the star formation process and the future sites of planet formation. As part of the Early Planet Formation in Embedded Disks (eDisk) large program, we present high-angular resolution dust continuum ($\sim40\,$mas) and molecular line ($\sim150\,$mas) observations of the Class 0 protostar, IRAS 15398-3359. The dust continuum is small, compact, and centrally peaked, while more extended dust structures are found in the outflow directions. We perform a 2D Gaussian fitting to find the deconvolved size and $2\sigma$ radius of the dust disk to be $4.5\times2.8\,\mathrm{au}$ and $3.8\,\mathrm{au}$, respectively. We estimate the gas+dust disk mass assuming optically thin continuum emission to be $0.6-1.8\,M_\mathrm{jup}$, indicating a very low-mass disk. The CO isotopologues trace components of the outflows and inner envelope, while SO traces a compact, rotating disk-like component. Using several rotation curve fittings on the PV diagram of the SO emission, the lower limits of the protostellar mass and gas disk radius are $0.022\,M_\odot$ and $31.2\,\mathrm{au}$ from our Modified 2 single power-law fitting. A conservative upper limit of the protostellar mass is inferred to be $0.1\,M_\odot$. The protostellar mass-accretion rate and the specific angular momentum at the protostellar disk edge are found to be between $1.3-6.1\times10^{-6}\,M_\odot\,\mathrm{yr^{-1}}$ and $1.2-3.8\times10^{-4}\,\mathrm{km\,s^{-1}\,pc}$, respectively, with an age estimated between $0.4-7.5\times10^{4}\,$yr. At this young age with no clear substructures in the disk, planet formation would likely not yet have started. This study highlights the importance of high-resolution observations and systematic fitting procedures when deriving dynamical properties of deeply embedded Class 0 protostars., Comment: 28 pages, 16 figures. Accepted for publication in ApJ as one of the first-look papers of the eDisk ALMA Large Program

As evidenced by recent survey results, majority of asteroids are slow rotators (P>12 h), but lack spin and shape models due to selection bias. This bias is skewing our overall understanding of the spins, shapes, and sizes of asteroids, as well as of their other properties. Also, diameter determinations for large (>60km) and medium-sized asteroids (between 30 and 60 km) often vary by over 30% for multiple reasons. Our long-term project is focused on a few tens of slow rotators with periods of up to 60 hours. We aim to obtain their full light curves and reconstruct their spins and shapes. We also precisely scale the models, typically with an accuracy of a few percent. We used wide sets of dense light curves for spin and shape reconstructions via light-curve inversion. Precisely scaling them with thermal data was not possible here because of poor infrared data: large bodies are too bright for WISE mission. Therefore, we recently launched a campaign among stellar occultation observers, to scale these models and to verify the shape solutions, often allowing us to break the mirror pole ambiguity. The presented scheme resulted in shape models for 16 slow rotators, most of them for the first time. Fitting them to stellar occultations resolved previous inconsistencies in size determinations. For around half of the targets, this fitting also allowed us to identify a clearly preferred pole solution, thus removing the ambiguity inherent to light-curve inversion. We also address the influence of the uncertainty of the shape models on the derived diameters. Overall, our project has already provided reliable models for around 50 slow rotators. Such well-determined and scaled asteroid shapes will, e.g. constitute a solid basis for density determinations when coupled with mass information. Spin and shape models continue to fill the gaps caused by various biases., Comment: Accepted to Astronomy & Astrophysics. 12 pages + appendices

Precise estimates of protostellar masses are crucial to characterize the formation of stars of low masses down to brown-dwarfs (BDs; M* < 0.08 Msun). The most accurate estimation of protostellar mass uses the Keplerian rotation in the circumstellar disk around the protostar. To apply the Keplerian rotation method to a protostar at the low-mass end, we have observed the Class 0 protostar IRAS 16253-2429 using the Atacama Large Millimeter/submillimeter Array (ALMA) in the 1.3 mm continuum at an angular resolution of 0.07" (10 au), and in the 12CO, C18O, 13CO (J=2-1), and SO (J_N = 6_5-5_4) molecular lines, as part of the ALMA Large Program Early Planet Formation in Embedded Disks (eDisk). The continuum emission traces a non-axisymmetric, disk-like structure perpendicular to the associated 12CO outflow. The position-velocity (PV) diagrams in the C18O and 13CO lines can be interpreted as infalling and rotating motions. In contrast, the PV diagram along the major axis of the disk-like structure in the 12CO line allows us to identify Keplerian rotation. The central stellar mass and the disk radius are estimated to be ~0.12-0.17 Msun and ~13-19 au, respectively. The SO line suggests the existence of an accretion shock at a ring (r~28 au) surrounding the disk and a streamer from the eastern side of the envelope. IRAS 16253-2429 is not a proto-BD but has a central stellar mass close to the BD mass regime, and our results provide a typical picture of such very low-mass protostars., Comment: 41 pages, 14 figures

We present high-resolution, high-sensitivity observations of the Class 0 protostar RCrA IRS5N as part of the Atacama Large Milimeter/submilimeter Array (ALMA) large program Early Planet Formation in Embedded Disks (eDisk). The 1.3 mm continuum emission reveals a flattened continuum structure around IRS5N, consistent with a protostellar disk in the early phases of evolution. The continuum emission appears smooth and shows no substructures. However, a brightness asymmetry is observed along the minor axis of the disk, suggesting the disk is optically and geometrically thick. We estimate the disk mass to be between 0.007 and 0.02 M$_{\odot}$. Furthermore, molecular emission has been detected from various species, including C$^{18}$O (2$-$1), $^{12}$CO (2$-$1), $^{13}$CO (2$-$1), and H$_2$CO (3$_{0,3}-2_{0,2}$, 3$_{2,1}-2_{2,0}$, and 3$_{2,2}-2_{2,1}$). By conducting a position-velocity analysis of the C$^{18}$O (2$-$1) emission, we find that the disk of IRS5N exhibits characteristics consistent with Keplerian rotation around a central protostar with a mass of approximately 0.3 M$_{\odot}$. Additionally, we observe dust continuum emission from the nearby binary source, IRS5a/b. The emission in $^{12}$CO toward IRS5a/b seems to emanate from IRS5b and flow into IRS5a, suggesting material transport between their mutual orbits. The lack of a detected outflow and large-scale negatives in \tlvco~observed toward IRS5N suggests that much of the flux from IRS5N is being resolved out. Due to this substantial surrounding envelope, the central IRS5N protostar is expected to be significantly more massive in the future., Comment: 25 pages, 24 figures. Accepted for publication in ApJ

Theoretical models and observations suggest that the abundances of molecular ions in protoplanetary disks should be highly sensitive to the variable ionization conditions set by the young central star. We present a search for temporal flux variability of HCO+ J=1-0, which was observed as a part of the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program. We split out and imaged the line and continuum data for each individual day the five sources were observed (HD 163296, AS 209, GM Aur, MWC 480, and IM Lup, with between 3 to 6 unique visits per source). Significant enhancement (>3\sigma) was not observed, but we find variations in the spectral profiles in all five disks. Variations in AS 209, GM Aur, and HD 163296 are tentatively attributed to variations in HCO+ flux, while variations in IM Lup and MWC 480 are most likely introduced by differences in the \textit{uv} coverage, which impact the amount of recovered flux during imaging. The tentative detections and low degree of variability are consistent with expectations of X-ray flare driven HCO+ variability, which requires relatively large flares to enhance the HCO+ rotational emission at significant (>20%) levels. These findings also demonstrate the need for dedicated monitoring campaigns with high signal to noise ratios to fully characterize X-ray flare driven chemistry., Comment: Accepted for publication in ApJ, 18 pages, 9 figures

We report the detection of the millimeter CH$_3$OH masers including a new detection of class I (11$_{0,11}$-10$_{1,10}$A) and class II (6$_{1,5}$-5$_{2,4}$E) maser transitions toward the high-mass protostar S255IR NIRS3 in post-burst phase. The CH$_3$OH emissions were detected as a mixture of maser and thermal characteristics. We examine the detected transitions using an excitation diagram and LTE model spectra and compare the observed properties with those of thermal lines. Class II CH$_3$OH maser transitions showed distinctive intensity and velocity distributions from those of thermal transitions. Bright distinct emission components in addition to the fragmented and arc-shaped emissions are only detected in class I CH$_3$OH maser transitions toward southern and western directions from the protostellar position, implying the presence of the slow outflow shocks., Comment: 9 pages, 4 Figures, 1 Table, Accepted for publication in ApJL