Explore the vast range of titles available.

Water is one of the central molecules for the formation and habitability of planets. In particular, the region where water freezes-out, the water snowline, could be a favorable location to form planets in protoplanetary disks. We use high resolution ALMA observations to spatially resolve H\\(_2\\)O, H\\(^{13}\\)CO\\(^+\\) and SO emission in the HL Tau disk. A rotational diagram analysis is used to characterize the water reservoir seen with ALMA and compare this to the reservoir visible at mid- and far-IR wavelengths. We find that the H\\(_2\\)O 183 GHz line has a compact central component and a diffuse component that is seen out to ~75 au. A radially resolved rotational diagram shows that the excitation temperature of the water is ~350 K independent of radius. The steep drop in the water brightness temperature outside the central beam of the observations where the emission is optically thick is consistent with the water snowline being located inside the central beam (\\(\\lesssim 6\\) au) at the height probed by the observations. Comparing the ALMA lines to those seen at shorter wavelengths shows that only 0.02%-2% of the water reservoir is visible at mid- and far-IR wavelengths, respectively, due to optically thick dust hiding the emission whereas 35-70% is visible with ALMA. An anti-correlation between the H\\(_2\\)O and H\\(^{13}\\)CO\\(^+\\) emission is found but this is likely caused by optically thick dust hiding the H\\(^{13}\\)CO\\(^+\\) emission in the disk center. Finally, we see SO emission tracing the disk and for the first time in SO a molecular outflow and the infalling streamer out to ~2\". The velocity structure hints at a possible connection between the SO and the H\\(_2\\)O emission. Spatially resolved observations of H\\(_2\\)O lines at (sub-)mm wavelengths provide valuable constraints on the location of the water snowline, while probing the bulk of the gas-phase reservoirs.

Element isotopic ratios are powerful tools to reconstruct the journey of planetary material, from the parental molecular cloud to protoplanetary disks, where planets form and accrete their atmosphere. Radial variations in isotopic ratios in protoplanetary disks reveal local pathways which can critically affect the degree of isotope fractionation of planetary material. In this work we present spatially-resolved profiles of the 14N/15N, 12C/13C, and D/H isotopic ratios of the HCN molecule in the PDS 70 disk, which hosts two actively-accreting giant planets. ALMA high spatial resolution observations of HCN, H13CN, HC15N, and DCN reveal radial variations of fractionation profiles. We extract the HCN/HC15N ratio out to ~120 au, which shows a decreasing trend outside the inner cavity wall of the PDS 70 disk located at ~50 au. We suggest that the radial variations observed in the HCN/HC15N ratio are linked to isotope selective photodissociation of N2. We leverage the spectrally resolved hyperfine component of the HCN line to extract the radial profile of the HCN/H13CN ratio between ~40 and 90 au, obtaining a value consistent with the ISM 12C/13C ratio. The deuteration profile is also mostly constant throughout the disk extent, with a DCN/HCN ratio ~0.02, in line with other disk-averaged values and radial profiles in disks around T Tauri stars. The extracted radial profiles of isotopologue ratios show how different fractionation processes dominate at different spatial scales in the planet-hosting disk of PDS 70.

The total disk gas mass and elemental C, N, O composition of protoplanetary disks are crucial ingredients for our understanding of planet formation. Measuring the gas mass is complicated, since H\\(_2\\) cannot be detected in the cold bulk of the disk and the elemental abundances with respect to hydrogen are degenerate with gas mass in all disk models. We present new NOEMA observations of CO, \\(^{13}\\)CO, C\\(^{18}\\)O and optically thin C\\(^{17}\\)O \\(J\\)=2-1 lines, and use additional high angular resolution Atacama Large Millimeter Array millimeter continuum and CO data to construct a representative model of LkCa 15. The transitions that constrain the gas mass and carbon abundance most are C\\(^{17}\\)O 2-1, N\\({_2}\\)H\\(^+\\) 3-2 and HD 1-0. Using these three molecules we find that the gas mass in the LkCa 15 disk is \\(M_\\mathrm{g}=0.01 ^{+0.01}_{-0.004} M_{\\odot}\\), a factor of six lower than estimated before. The carbon abundance is C/H = (\\(3 \\pm 1.5) \\times10^{-5}\\), implying a moderate depletion of elemental carbon by a factor of 3-9. All other analyzed transitions also agree with these numbers, within a modeling uncertainty of a factor of two. Using the resolved \\ce{C2H} image we find a C/O ratio of \\(\\sim\\)1, which is consistent with literature values of H\\(_2\\)O depletion in this disk. The lack of severe carbon depletion in the LkCa 15 disk is consistent with the young age of the disk, but contrasts with the higher depletions seen in older cold transition disks. Combining optically thin CO isotopologue lines with N\\(_2\\)H\\(^+\\) is promising to break the degeneracy between gas mass and CO abundance. The moderate level of depletion for this source with a cold, but young disk, suggests that long carbon transformation timescales contribute to the evolutionary trend seen in the level of carbon depletion among disk populations, rather than evolving temperature effects and presence of dust traps alone.

High-resolution observations show that typically both the dust and the gas in nearby extended protoplanetary disks are structured, possibly related to radial and azimuthal variations in the disk density and/or chemistry. The aim of this work is to identify the expected location and intensity of rings seen in molecular line emission of HCN, CN, C\\(_2\\)H, NO, [CI], and HCO\\(^+\\) in gapped disks while exploring a range of physical conditions across the gap. In particular, we model HD 100546 disk where molecular rings are co-spatial with the dust rings at \\(\\)20 and \\(\\)200 au, in contrast to most other gapped disks. The fiducial model of a gapped disk with a 15 au gas cavity, a 20 au dust cavity, and a shallow (a factor of \\(10\\)) gas and deep dust gap at 40-175 au provides a good fit to the continuum, CO isotopologues, HCN, and HCO\\(^+\\) in the HD 100546 disk. However, the predictions for [CI], CN, C\\(_2\\)H and NO do not match the intensity nor the morphology of the observations. An exploration of the parameter space shows that in general the molecular emission rings are only co-spatial with the dust rings if the gas gap between the dust rings is depleted by at least four orders of magnitude in gas or if the C/O ratio of the gas is varying as a function of radius. For shallower gaps the decrease in the UV field roughly balances the effect of a higher gas density for UV tracers such as CN, C\\(_2\\)H, and NO. Therefore, these radicals are not good tracers of the gas gap depth. The C/O ratio primarily effects the intensity of the lines without changing the morphology much. The co-spatial rings observed in the HD 100546 disk could be indicative of a radially varying C/O ratio in the HD 100546 disk with a C/O above 1 in a narrow region across the dust rings, together with a shallow gas gap that is depleted by a factor of \\(\\)10 in gas, and a reduced background UV field.

We present the first results of a pilot program to conduct an Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (211-275 GHz) spectral line study of young stellar objects (YSO) that are undergoing rapid accretion episodes, i.e. FU Ori objects (FUors). Here, we report on molecular emission line observations of the FUor system, V883 Ori. In order to image the FUor object with full coverage from ~0.5 arcsec to the map size of ~30 arcsec, i.e. from disc to outflow scales, we combine the ALMA main array (the 12-m array) with the Atacama Compact Array (7-m array) and the total power (TP) array. We detect HCN, HCO\\(^{+}\\), CH\\(_{3}\\)OH, SO, DCN, and H\\(_{2}\\)CO emissions with most of these lines displaying complex kinematics. From PV diagrams, the detected molecules HCN, HCO\\(^{+}\\), CH\\(_{3}\\)OH, DCN, SO, and H\\(_{2}\\)CO probe a Keplerian rotating disc in a direction perpendicular to the large-scale outflow detected previously with the \\(^{12}\\)CO and \\(^{13}\\)CO lines. Additionally, HCN and HCO\\(^{+}\\) reveal kinematic signatures of infall motion. The north outflow is seen in HCO\\(^{+}\\), H\\(_{2}\\)CO, and SO emissions. Interestingly, HCO\\(^{+}\\) emission reveals a pronounced inner depression or \"hole\" with a size comparable to the radial extension estimated for the CH\\(_{3}\\)OH and 230 GHz continuum. The inner depression in the integrated HCO\\(^{+}\\) intensity distribution of V883 Ori is most likely the result of optical depth effects, wherein the optically thick nature of the HCO\\(^{+}\\) and continuum emission towards the innermost parts of V883 Ori can result in a continuum subtraction artifact in the final HCO\\(^{+}\\) flux level.

Gas-phase sulphur bearing volatiles appear to be severely depleted in protoplanetary disks. The detection of CS and non-detections of SO and SO2 in many disks have shown that the gas in the warm molecular layer, where giant planets accrete their atmospheres, has a high C/O ratio. In this letter, we report the detection of SO and SO2 in the Oph-IRS 48 disk using ALMA. This is the first case of prominent SO2 emission detected from a protoplanetary disk. The molecular emissions of both molecules is spatially correlated with the asymmetric dust trap. We propose that this is due to the sublimation of ices at the edge of the dust cavity and that the bulk of the ice reservoir is coincident with the millimetre dust grains. Depending on the partition of elemental sulphur between refractory and volatile materials the observed molecules can account for 15-100% of the total sulphur budget in the disk. In strong contrast to previous results, we constrain the C/O ratio from the CS/SO ratio to be < 1 and potentially solar. This has important implications for the elemental composition of planets forming within the cavities of warm transition disks.

The chemistry of planet-forming disks sets the exoplanet atmosphere composition and the prebiotic molecular content. Dust traps are of particular importance as pebble growth and transport are crucial for setting the chemistry where giant planets are forming. The asymmetric Oph~IRS~48 dust trap located at 60 au radius provides a unique laboratory for studying chemistry in pebble-concentrated environments in warm Herbig disks with low gas-to-dust ratios down to 0.01. We use deep ALMA Band~7 line observations to search the IRS~48 disk for H\\(_2\\)CO and CH\\(_3\\)OH line emission, the first steps of complex organic chemistry. We report the detection of 7 H\\(_2\\)CO and 6 CH\\(_3\\)OH lines with energy levels between 17 and 260 K. The line emission shows a crescent morphology, similar to the dust continuum, suggesting that the icy pebbles play an important role in the delivery of these molecules. Rotational diagrams and line ratios indicate that both molecules originate from warm molecular regions in the disk with temperatures \\(>\\)100 K and column densities \\(\\sim10^{14}\\) cm\\(^{-2}\\) or a fractional abundance of \\(\\sim10^{-8}\\) and with H\\(_2\\)CO/CH\\(_3\\)OH\\(\\sim\\)0.2, indicative of ice chemistry. Based on arguments from a physical-chemical model with low gas-to-dust ratios, we propose a scenario where the dust trap provides a huge icy grain reservoir in the disk midplane or an `ice trap', which can result in high gas-phase abundances of warm COMs through efficient vertical mixing. This is the first time that complex organic molecules have been clearly linked to the presence of a dust trap. These results demonstrate the importance of including dust evolution and vertical transport in chemical disk models, as icy dust concentrations provide important reservoirs for complex organic chemistry in disks.

With two directly detected protoplanets, the PDS 70 system is a unique source in which to study the complex interplay between forming planets and their natal environment. The large dust cavity carved by the two giant planets can affect the disk chemistry, and therefore the molecular emission morphology. On the other hand, chemical properties of the gas component of the disk are expected to leave an imprint on the planetary atmospheres. In this work, we reconstruct the emission morphology of a rich inventory of molecular tracers in the PDS 70 disk, and we look for possible chemical signatures of the two actively accreting protoplanets, PDS b and c. We leverage Atacama Large Millimeter/submillimeter Array (ALMA) band 6 high-angular-resolution and deep-sensitivity line emission observations, together with image and \\(uv\\)-plane techniques, to boost the detection of faint lines. We robustly detect ring-shaped emission from \\(^{12}\\)CO, \\(^{13}\\)CO, C\\(^{18}\\)O, H\\(^{13}\\)CN, HC\\(^{15}\\)N, DCN, H\\(_2\\)CO, CS, C\\(_2\\)H, and H\\(^{13}\\)CO\\(^{+}\\) lines in unprecedented detail. Most of the molecular tracers show a peak of the emission inside the millimeter dust peak. We interpret this as the direct impact of the effective irradiation of the cavity wall, as a result of the planet formation process. Moreover, we have found evidence of an O-poor gas reservoir in the outer disk, which is supported by the observations of bright C-rich molecules, the non-detection of SO, and a lower limit on the \\(\\mathrm{CS/SO}\\) ratio of \\(\\sim1\\). Eventually, we provide the first detection of the c-C\\(_3\\)H\\(_2\\) transitions at 218.73 GHz, and the marginal detection of an azimuthal asymmetry in the higher-energy H\\(_2\\)CO (3\\(_{2,1}\\)-2\\(_{2,0}\\)) line, which could be due to accretion heating near PDS 70b.

[Abridged] Most disks observed at high angular resolution show substructures. Knowledge about the gas surface density and temperature is essential to understand these. The aim of this work is to constrain the gas temperature and surface density in two transition disks: LkCa15 and HD 169142. We use new ALMA observations of the \\(^{13}\\)CO \\(J=6-5\\) transition together with archival \\(J=2-1\\) data of \\(^{12}\\)CO, \\(^{13}\\)CO and C\\(^{18}\\)O to observationally constrain the gas temperature and surface density. Furthermore, we use the thermochemical code DALI to model the temperature and density structure of a typical transition disk. The \\(6-5/2-1\\) line ratio in LkCa15 constrains the gas temperature in the emitting layers inside the dust cavity to be up to 65 K, warmer than in the outer disk at 20-30 K. For the HD 169142, the peak brightness temperature constrains the gas in the dust cavity of HD 169142 to be 170 K, whereas that in the outer disk is only 100 K. Models also show that a more luminous central star, a lower abundance of PAHs and the absence of a dusty inner disk increase the temperature of the emitting layers and hence the line ratio in the gas cavity. The gas column density in the LkCa15 dust cavity drops by a factor >2 compared to the outer disk, with an additional drop of an order of magnitude inside the gas cavity at 10 AU. In the case of HD 169142, the gas column density drops by a factor of 200\\(-\\)500 inside the gas cavity, which could be due to a massive companion of several M\\(_{\\mathrm{J}}\\). The broad dust-depleted gas region from 10-68 AU for LkCa15 may imply several lower mass planets. This work demonstrates that knowledge of the gas temperature is important to determine the gas surface density and thus whether planets, and if so what kind of planets, are the most likely carving the dust cavities.

[Abridged] Planet formation is expected to be enhanced around snowlines in protoplanetary disks, in particular around the water snowline. However, the close proximity of the water snowline to the host star and water in the Earth's atmosphere makes a direct detection of the water snowline in protoplanetary disks challenging. Following earlier work on protostellar envelopes, the aim of this research is to investigate the validity of HCO\\(^+\\) and H\\(^{13}\\)CO\\(^+\\), as tracers of the water snowline in protoplanetary disks, as HCO\\(^+\\) is destroyed by gas-phase water. Two small chemical networks are used to predict the HCO\\(^+\\) abundance in a typical Herbig Ae disk. Subsequently, the corresponding emission profiles are modelled for H\\(^{13}\\)CO\\(^+\\) and HCO\\(^+\\) \\(J=2-1\\), which provides the best balance between brightness and optical depth effects of the continuum emission. The HCO\\(^+\\) abundance jumps by two orders of magnitude just outside the water snowline at 4.5 AU. We find that the emission of H\\(^{13}\\)CO\\(^+\\) and HCO\\(^+\\) is ring-shaped due to three effects: destruction of HCO\\(^+\\) by gas-phase water, continuum optical depth, and molecular excitation effects. The presence of gas-phase water causes an additional drop of only \\(\\sim\\)13% and 24% in the center of the disk, for H\\(^{13}\\)CO\\(^+\\) and HCO\\(^+\\), respectively. For the much more luminous outbursting source V883Ori, our models predict that the effect of dust and excitation are not limiting if the snowline is located outside \\(\\sim\\)40 AU. Our analysis of ALMA observations of HCO\\(^+\\) \\(J=3-2\\) is consistent with the water snowline located around 100 AU. The HCO\\(^+\\) abundance drops steeply around the water snowline, but dust and excitation can conceal the drop in HCO\\(^+\\) emission due to the water snowline. Therefore, locating the water snowline with HCO\\(^+\\) in Herbig disks is very difficult, but it is possible for outbursting sources like V883Ori.