Recent discoveries of streamer-like structures around protostellar sources challenge the traditional picture of isolated, axisymmetric star formation. Here, we present new Atacama Large Millimeter/submillimeter Array observations of [BHB2007]-1, a flat-spectrum source connected to at least three such elongated structures. Two of these features are symmetrically located to the north and south of the disk, with velocities aligned with the disk on their respective sides. However, their unbound kinematics and curved morphology make it difficult to determine their origin. Possible explanations include outflows, interactions with the nearby [BHB2007]-2 system, and hyperbolic infall, but none fully account for all observed properties. In contrast, a newly identified collimated structure to the west shows clear evidence of gravitationally bound infall. Estimates of its mass, mass infall rate, and angular momentum suggest that this infalling streamer would roughly double the mass budget available to form planets and tilt the disk by a few tens of degrees. Furthermore, its misalignment with the midplane of the disk and the lack of diffuse envelope emission indicate that the streamer may have formed due to gravitational capture of cloud material unrelated to the source’s natal core. Together, these findings support a more dynamic picture of star formation, one where environmental interactions continue to shape the conditions for building planetary systems.

Context. Protoplanetary disk substructures are thought to play a crucial role in disk evolution and planet formation. Population studies of disks large-sample size surveys show that not only substructure, but also their rapid formation, are needed to reproduce the observed spectral indices. Moreover, they enable the simultaneous reproduction of the observed spectral index and size-luminosity distributions. Aims. This study is aimed at investigating the need for substructures and predicting their characteristics in reproducing the gas-to-dust size ratios observed in the Lupus star-forming region. Methods. We performed a population synthesis study of gas and dust evolution in disks using a two-population model (two-pop-py) and the DustPy code. We considered the effects of viscous evolution, dust growth, fragmentation, transport, and external photoevaporation. The simulated population distributions were obtained by post-processing the resulting disk profiles of surface density, maximum grain size, and disk temperature. Results. Although substructures do help in reducing the discrepancy between simulated and observed disk gas-to-dust size ratios, even when accounting for external photoevaporation, they do not fully resolve it. Only specific initial conditions in disks undergoing viscous evolution with external photoevaporation are able to reproduce the observations, highlighting a fine-tuning problem. Even in cases where substructured disks successfully reproduce the dust size and spectral index, they tend to overestimate gas radii. Conclusions. These results ultimately highlight the main challenge of simultaneously reproducing gas and dust sizes. One possible explanation is that the outermost substructure is linked to the disk truncation radius, which determines the gas radius. Alternatively, it might be the case that substructures are frequent enough to always be located near the outer radius of the gas.

A large fraction of planet-forming disks observed with ALMA show faint CO emission, often interpreted as strong CO depletion. However, faint emission may also arise from spatially unresolved disks, whose sizes are overestimated, making them appear intrinsically faint. The limited sensitivity of previous observations has prevented testing this scenario, hindering our understanding of disk evolution and planet formation. We present new ALMA Band 7 observations of 12CO (J=3-2) and 13CO (J=3-2) in 17 of the faintest disks in Lupus, aiming to assess whether compact disk structure can explain their weak CO emission. The data reach an angular resolution of 0.25arcsec (about 20 au at 160 pc) and are an order of magnitude deeper than archival observations. We apply line stacking to enhance sensitivity and compare the derived CO luminosities with physical-chemical models of compact and extended disks, also estimating gas and dust sizes. We detect both isotopologues in 10 disks, only 12CO in 4, and neither in 3. Several disks are consistent with being intrinsically compact and optically thick in both lines, providing an alternative to the CO depletion scenario. The inferred gas radii (Rco less than 40 au) support this interpretation and suggest that a significant fraction of disks may be born compact, in line with recent Class 0/I results. Gas-to-dust size ratios show no clear evidence for dust evolution, indicating these disks are not drift-dominated.

We present measurements of key protoplanetary disk properties inferred from parametric models of ALMA 12 CO spectral line visibilities. We derived gas-disk radii, integrated fluxes, optically thick emission layers, and brightness temperature profiles for the disk population of the old (4–14 Myr) Upper Scorpius star-forming region. We measured CO emission sizes for 37 disks with bright CO J = 3–2 emission (S/N > 10 on the integrated flux; out of the 83 disks with CO detections), finding that the median radius containing 90% of the flux is ∼82 au, with radii spanning from 22 up to 247 au. We report a correlation between the 12 CO brightness temperatures and stellar luminosities, with a Pearson coefficient of 0.6, which we used to prove that the 12 CO optically thick emission layer primarily emanates from a region below the superheated dust, which is optically thin to the stellar irradiation. Moreover, we derive 33 CO emission-surface height profiles, finding a median aspect ratio of ⟨ z/r ⟩ ∼ 0.16 in a range from ∼0.01 up to ∼0.45 over the sample. Finally, we comment on the multiple systems in our sample, of which only some were already known. These results confirm that it is possible to derive bulk disk properties by modeling moderate-angular-resolution ALMA visibilities.

Stellar masses are a fundamental property to understand models of pre-main sequence evolution, but their values derived from Hertzsprung–Russell (HR) diagrams are strongly model dependent. We benchmark pre-main sequence stellar evolutionary tracks using stellar masses dynamically estimated by fitting a parametric model to ALMA observations of the 12CO (J = 3 − 2) line transition emitted by the disks orbiting 20 sources in the old (4 − 14 Myr) Upper Scorpius star forming region. We derive stellar masses from HR diagram fitting for ten different stellar evolutionary models, which we then compare with their stellar dynamical masses for comparison in the stellar mass range 0.1 − 1.3 M⊙. Models with a moderate-to-low fraction of cold stellar spots (f = 17%) most accurately reproduce the dynamical stellar masses (100% of the targets agree within ±1σ). While a higher spot coverage (f = 34%) provides similar stellar mass predictions similar to magnetic equipartition models, larger fractions (f ≥ 51%) significantly disagree with dynamical masses. Magnetic equipartition models overestimate stellar masses up to a factor ∼20%, whereas non-magnetic models underestimate them up to ∼12%. For some models, there is evidence that the stellar mass discrepancies are anticorrelated with dynamical stellar masses. When stellar dynamical mass priors are considered in HR diagram fitting, the median age of a single source can change up to ∼25%, while the median ages inferred across different tracks become consistent, with the age scatter decreasing by ≳77%. These results provide strong empirical constraints for testing and developing evolutionary models of pre-main sequence stars.

The inner Solar System is depleted in refractory carbon in comparison to the interstellar medium and the depletion likely took place in the protoplanetary disk phase of the Solar System. We study the effect of photolysis of refractory carbon in the upper layers of the protosolar disk and its interplay with dust collisional growth and vertical mixing. We make use of a 1D Monte Carlo model to simulate dust coagulation and vertical mixing. To model the FUV flux of the disk, we use a simple analytical prescription and benchmark it with data from a radiative transfer simulation. We study the effects of fragmentation and bouncing on dust distribution and the propagation of carbon depletion. We find that when bouncing is included, the size distribution is truncated at smaller sizes than fragmentation-limited size distributions but there is a loss of small grains as well. The population of small grains is reduced due to fewer fragmentation events and this reduces the effectiveness of photolysis. We find that dust collisional growth and vertical mixing increase the effectiveness of carbon depletion by efficiently replenishing carbon to the upper regions of the disk with higher FUV flux. It takes around 100-300 kyr to reach the measured carbon abundances at 1 au, depending on the strength of the turbulence in the disk. These timescales are faster than reported by previous studies. Collisional redistribution and turbulent mixing are important aspects of dust evolution that should be included when modeling dust chemistry as they can influence the efficiency of chemical processes. Photolysis, along with another process such as sublimation, most likely played a key role in refractory carbon depletion that we see around us in the inner Solar System.

Using continuum and C^18O (2-1) line data obtained from the large ALMA program FAUST, we studied the structure of the protostellar binary system L1551 IRS5 at scales between 30 and 3,000 au to constrain its properties, from the circumstellar and circumbinary disks up to the envelope and outflow scales, which exhibits complex and entangled structures at the scales of its inner and outer envelopes, presumably caused by the influence of the central binary. Assuming a dust-to-gas ratio of 100, we calculated the dust+gas mass for the circumbinary disk and each circumstellar disk of the binary, obtaining 0.018 M_⊙, for the circumbinary disk, 0.004 M_⊙, and 0.002 M_⊙, for the northern and southern circumstellar disk respectively. From the line emission, we retrieved the gas masses for each structure component. With the C^18O (2-1) PV diagram along the circumbinary disk, we were able to constrain the centrifugal barrier, r_CB=55 au, update the specific angular momentum, j∼270 au km s^-1. We built an analytical model that can be used to predict the influence of the morphology of the outflow and a few dynamic features that can reproduce the system emission, allowing us to explain and discern the outflow contribution from the complex emission due to the binary. Additionally, we inferred the density power law index, α=1.7, and the envelope rotation velocity, v_c=2 km s^-1. Finally, the observations gave us the physical constraints to obtain a coherent outflow model for L1551 IRS5.

Using continuum and (CO)-O-18 (2-1) line data obtained from the large ALMA (Atacama Large Millimeter/submillimeter Array) programme FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar-like protostars), we studied the structure of the protostellar binary system L 1551 IRS 5 at scales between 30 and 3000 au to constrain its properties, from the circumstellar and circumbinary discs up to the envelope and outflow scales, which exhibits complex and entangled structures at the scales of its inner and outer envelopes, presumably caused by the influence of the central binary. Assuming a dust-to-gas ratio of 100, we calculated the dust + gas mass for the circumbinary disc and each circumstellar disc of the binary, obtaining 0.018 M-(R) for the circumbinary disc, 0.004 and 0.002 M-(R) for the northern and southern circumstellar disc, respectively. From the line emission, we retrieved the gas masses for each structure component. With the (CO)-O-18 (2-1) position-velocity diagram along the circumbinary disc, we were able to constrain the centrifugal barrier, r(CB) = 55 au, update the specific angular momentum, j similar to 270 au km s(-1). We built an analytical model that can be used to predict the influence of the morphology of the outflow and a few dynamic features that can reproduce the system emission, allowing us to explain and discern the outflow contribution from the complex emission due to the binary . Additionally , we inferred the density power-law index, alpha = 1 . 7 , and the envelope rotation velocity, v(c) = 2 km s(-1).Finally, the observations gave us the physical constraints to obtain a coherent outflow model for L 1551 IRS 5.

We have observed the late Class I protostellar source Elias 29 at a spatial resolution of 70 au with the Atacama Large Millimeter/submillimeter Array as part of the FAUST Large Program. We focus on the line emission of SO, while that of 34SO, C18O, CS, SiO, H13CO+, and DCO+ are used supplementarily. The spatial distribution of the SO rotational temperature (Trot(SO)) is evaluated by using the intensity ratio of its two rotational excitation lines. Besides in the vicinity of the protostar, two hot spots are found at a distance of 500 au from the protostar; Trot(SO) locally rises to 53 -15+25 K at the interaction point of the outflow and the southern ridge, and 72 -29+66 K within the southeastern outflow probably due to a jet-driven bow shock. However, the SiO emission is not detected at these hot spots. It is likely that active gas accretion through the disk-like structure and onto the protostar still continues even at this evolved protostellar stage, at least sporadically, considering the outflow/jet activities and the possible infall motion previously reported. Interestingly, Trot(SO) is as high as 20-30 K even within the quiescent part of the southern ridge apart from the protostar by 500-1000 au without clear kinematic indication of current outflow/jet interactions. Such a warm condition is also supported by the low deuterium fractionation ratio of HCO+ estimated by using the H13CO+ and DCO+ lines. The B-type star HD147889 similar to 0.5 pc away from Elias 29, previously suggested as a heating source for this region, is likely responsible for the warm condition of Elias 29.

Context. Large millimeter surveys of star-forming regions enable the study of entire populations of planet-forming disks and reveal correlations between their observable properties. The ever-increasing number of these surveys has led to a flourishing of population study, a valuable tool and approach that is spreading in ever more fields. Population studies of disks have shown that the correlation between disk size and millimeter flux could be explained either through disks with strong substructure, or alternatively by the effects of radial inward drift of growing dust particles. Aims. This study aims to constrain the parameters and initial conditions of planet-forming disks and address the question of the need for the presence of substructures in disks and, if needed, their predicted characteristics, based on the large samples of disk sizes, millimeter fluxes, and spectral indices available. Methods. We performed a population synthesis of the continuum emission of disks, exploiting a two-population model (two-pop-py), considering the influence of viscous evolution, dust growth, fragmentation, and transport, varying the initial conditions of the disk and substructure to find the best match with the observed distributions. Disks both with and without substructure have been examined. We obtained the simulated population distribution for the disk sizes, millimeter fluxes, and spectral indices by post-processing the resulting disk profiles (surface density, maximum grain size, and disk temperature). Results. We show that the observed distributions of spectral indices, sizes, and luminosities together can be best reproduced by disks with significant substructure; namely, a perturbation that is strong enough to be able to trap particles, that is formed early in the evolution of the disk, and that is within 0.4 Myr. Agreement is reached by relatively high initial disk masses (10(-2.3) M-star <= M-disk <= 10(-0.5) M-star) and moderate levels of turbulence (10(-3.5) <= alpha <= 10(-2.5)). Other disk parameters play a weaker role. Only opacities with a high absorption efficiency can reproduce the observed spectral indices. Conclusions. Disk population synthesis is a precious tool for investigating and constraining the parameters and initial conditions of planet-forming disks. The generally low observed spectral indices call for significant substructure, like that which planets in the mass range of Saturn to a few Jupiters would induce, to already be present before 0.4 Myr. Our results indicate that substructure, which so far has only been assessed in individual disks, is likely ubiquitous and extends to the whole population, and imply that most "smooth" disks hide unresolved substructure.

In the Orion Nebula Cluster (ONC), protoplanetary disks exhibit ionized gas clouds in the form of a striking teardrop shape as massive stars irradiate the disk material. We present the first spatially and spectrally resolved observations of 12 proplyds, using Integral Field Spectroscopy observations performed with the MUSE instrument in Narrow Field Mode (NFM) on the VLT. We present the morphology of the proplyds in seven emission lines and measure the radius of the ionization front (I-front) of the targets in four tracers, covering transitions of different ionization states for the same element. We also derive stellar masses for the targets. The measurements follow a consistent trend of increasing I-front radius for a decreasing strength of the far-UV radiation as expected from photoevaporation models. By analyzing the ratios of the I-front radii as measured in the emission lines of Ha, [OI] 6300, [OII] 7330, and [OIII] 5007, we observe the ionization stratification, that is, the most ionized part of the flow being the furthest from the disk (and closest to the UV source). The ratios of I-front radii scale in the same way for all proplyds in our sample regardless of the incident radiation. We show that the stratification can help constrain the densities near the I-front by using a 1D photoionization model. We derive the upper limits of photoevaporative mass-loss rates by assuming ionization equilibrium, and estimate values decreasing towards lower impinging radiation. We do not find a correlation between Mloss and stellar mass. The highest mass-loss rate is for the proplyd 244-440. These values of Mloss, combined with estimates of the disk mass with ALMA, confirm previous estimates of the short lifetime of these proplyds. This work demonstrates the potential of this dataset and offers a new set of observables to be used to test current and future models of external photoevaporation.

Recent observations suggest that planet formation starts early, in protostellar disks of $ yrs, which are characterized by strong interactions with the environment, such as through accretion streamers and molecular outflows. To investigate the impact of such phenomena on the physical and chemical properties of a disk, 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 sim 1500 au to sim 60 au of H$_2$CO, HDCO, and D$_2$CO toward the young planet-forming disk IRS 63. The H$_2$CO probes the gas in the disk as well as in a large scale streamer ($ 1500$ au) impacting onto the southeast disk side. We detected 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. These detections allowed us to estimate the deuterium fractionation of H$_2$CO in the disk: HDCO H$_2$CO 0.1-0.3$ and D$_2$CO H$_2$CO 0.1$. Interestingly, while HDCO follows the H$_2$CO distribution in the disk and in the streamer, the distribution of D$_2$CO is highly asymmetric, with a peak of the emission (and D H ratio) in the southeast disk side, where the streamer crashes onto the disk. In addition, D$_2$CO was detected in two spots along the blue- and redshifted outflow. This suggests that (i) in the disk, HDCO formation is dominated by gas-phase reactions in a manner similar to H$_2$CO, while (ii) D$_2$CO is 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 to the key role of streamers in the buildup of the disk concerning both the final mass available for planet formation and its chemical composition.

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. Elongated trails of infalling gas, often referred to as "streamers," have recently been observed around young stellar objects (YSOs) at different evolutionary stages. This asymmetric infall of material can significantly alter star and planet formation processes, especially in the more evolved YSOs. Aims. In order to ascertain the infalling nature of observed streamer-like structures and then systematically characterize their dynamics, we developed the code TIPSY (Trajectory of Infalling Particles in Streamers around Young stars). Methods. Using TIPSY, the streamer molecular line emission is first isolated from the disk emission. Then the streamer emission, which is effectively a point cloud in three-dimensional (3D) position-position-velocity space, is simplified to a curve-like representation. The observed streamer curve is then compared to the theoretical trajectories of infalling material. The best-fit trajectories are used to constrain streamer features, such as the specific energy, the specific angular momenta, the infall timescale, and the 3D morphology. Results. We used TIPSY to fit molecular-line ALMA observations of streamers around a Class II binary system, S CrA, and a Class I/II protostar, HL Tau. Our results indicate that both of the streamers are consistent with infalling motion. TIPSY results and mass estimates suggest that S CrA and HL Tau are accreting material at a rate of $\gtrsim27$ M$_{jupiter}$ Myr$^{-1}$ and $\gtrsim5$ M$_{jupiter}$ Myr$^{-1}$, respectively, which can significantly increase the mass budget available to form planets. Conclusions. TIPSY can be used to assess whether the morphology and kinematics of observed streamers are consistent with infalling motion and to characterize their dynamics, which is crucial for quantifying their impact on the protostellar systems.

Context. Understanding the connection between outflows, winds, accretion, and discs in the inner protostellar regions is crucial for comprehending star and planet formation processes. 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 CH3OH 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 +/- 1.5 km s(-1) with respect to v(sys), traced by methanol; (ii) an intermediate region (between 50 au and 150 au) traced by both SiO and CH3OH, between 2 and 6 km s(-1) with respect to v(sys), 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 CH3OH/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, a rotating disc or inner envelope, a jet on the plane of the sky or precessing, and a wide-angle disc wind. Conclusions. We propose that CH3OH and SiO in the inner 100 au probe the base of a wide-angle disc 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 CH3OH and SiO. This is the first detection of a disc-wind candidate in SiO, and the second ever in CH3OH.

Constraining turbulence in disks is key towards understanding their evolution through the transport of angular momentum. Until now measurements of high turbulence have remained elusive and methods for estimating turbulence relay mostly on complex radiative transfer models of the data. Using the disk emission from IM Lup, a source proposed to be undergoing Magneto-Rotational Instabilities (MRI) and possibly have high turbulence values in the upper disk layers, we present a new way of directly measuring turbulence without need of radiative transfer or thermochemical models. Through the characterization of the CN and C$_2$H emission in IM Lup, we aim to connect the information on the vertical and thermal structure of a particular disk region to derive turbulence at that location. By using an optically thin tracer it is possible to directly measure turbulence from the non-thermal broadening of the line. The vertical layers of the CN and C$_2$H emission are traced directly from the channel maps using ALFAHOR. By comparing their position to that of optically thick CO observations we are able to characterize the kinetic temperature of the emitting region. Using a simple parametric model of the line intensity with DISCMINER we accurately measure the emission linewidth and separate the thermal and non-thermal components. Assuming that the non-thermal component is fully turbulent, we are able to directly estimate the turbulent motions at the studied radial and vertical location of CN emission. IM Lup shows high turbulence of Mach 0.4-0.6 at $z/r \sim$ 0.25. Considering previous estimates of low turbulence near the midplane, this may indicate a vertical gradient in the disk turbulence, which is a key prediction of MRI studies. CN and C$_2$H are both emitting from a localized upper disk region at $z/r =$0.2-0.3, in agreement with thermochemical models.

Observations of interstellar material infalling onto star- and planet-forming systems have become increasingly common thanks to recent advancements in radio interferometry. These structures replenish disks with fresh material, have the potential to significantly alter their dynamics, trigger the formation of substructures, induce shocks, and modify their physical and chemical properties. In this study, we combine new ALMA band 3 and archival band 6 observations to characterize the dust content and mass infall rate of a 4,000 au arc-like structure infalling onto M512, a class I young stellar object located in the Lynds 1641 region of the Orion A molecular cloud. We measure for the first time spectral index maps and derive a dust opacity index profile along a streamer, constraining grain properties and its dust mass. We measure a spectral index $\alpha \sim$ 3.2 across the entire structure, and a dust opacity index $\beta \sim$ 1.6. Given grain properties consistent with the measured $\beta$, the structure can host up to 245 M$_{\oplus}$ of dust, being comparable or even exceeding the mass of the inner, unresolved 600 au, which contains the protoplanetary disk of M512. Such a massive streamer can strongly affect the evolution of the star- and planet-forming inner system. Assuming typical ISM dust-to-gas ratio of 1%, free-fall timescales (50 kyr) imply total mass infall rates up to 1.5 $\cdot$ 10$^{-6}$ M$_{\odot}$/yr. M512 has been classified as an outbursting source with multi-epoch photometry, thus representing an interesting case study to explore the possible connection between infalling streamers and accretion outbursts.

Complex organic molecules in protoplanetary disksProtoplanetary disks are considered a material reservoir for planetary assembly. Hence, resolving the spatial distribution of complex organic molecules (COMs) in protoplanetary disks is crucial in estimating the potential habitability of other worlds. Unfortunately, under typical cold disk conditions, a significant portion of the complex organic inventory is thought to be locked on the surface of dust grains. Even methanol (CH3OH), one of the simplest COMs and a cornerstone for making more complex O-bearing molecules, has been barely glimpsed in disks with few detections associated with warm conditions generated by dust cavities or stellar outbursts. Nevertheless, smaller but brighter tracers like formaldehyde (H2CO) could be used in the typical colder disks. Formaldehyde: a potential alternative for tracing the frozen organic content in disksH2CO is a small organic molecule considered a precursor of CH3OH on the icy surfaces of dust grains, with the difference that the former can be more easily released into the gas phase than the latter due to lower desorption energies. However, gas-phase reactions can also form efficiently H2CO. Since the specific contribution of each mechanism is poorly constrained, determining the dominant formation pathway of H2CO is necessary for setting up its potential as a tracer of the cold reservoir in protoplanetary disks. Within this context, we present spectrally and spatially resolved ALMA observations of several H2CO lines toward the bright Herbig Ae protoplanetary disk HD 163296. We determined the excitation conditions of H2CO as a function of disk radius and put constraints on the height of H2CO emission to get clues about its formation. We discuss our findings in the context of previous results in T Tauri and Herbig Ae/Be sources, emphasizing the case of the closest protoplanetary disk, TW Hya, where H2CO was studied with a similar level of analysis that we did for HD 163296.Disentangling H2CO origins in disks: gas-phase or dust-grain surface chemistry?We find that H2CO likely forms from a combination of gas-phase and grain-surface chemistry in HD 163296. This is in contrast to the case of TW Hya, the only T Tauri source with known CH3OH detections and where the cold gas-phase chemistry is expected to predominate in the formation of H2CO. To understand these differences, we compare our observational results with predictions from the physicochemical code DALI by using fiducial models of the physical structure of each disk previously reported in the literature. However, we note that HD163296 and TW Hya do not represent the entire population of protoplanetary disks. To better understand how H2CO forms in more typical disks, we are currently analyzing observations from the DECO ALMA large program. DECO consists of a survey of 80 protoplanetary disks around low-mass stars (the most common exoplanet hosts), targeting multiple molecular lines of several species, including multiple transitions of H2CO.

Context. Constraining turbulence in disks is key to understanding their evolution via the transport of angular momentum. Measurements of high turbulence remain elusive, and methods for estimating turbulence mostly rely on complex radiative transfer models of the data. Using the disk emission from IM Lup, a source proposed to be undergoing magneto-rotational instabilities (MRIs) and to possibly have high turbulence values in the upper disk layers, we present a new way of directly measuring turbulence without the need of radiative transfer or thermochemical models. Aims. Through the characterization of the CN and C2H emission in IM Lup, we aim to connect the information on the vertical and thermal structure of a particular disk region to derive the turbulence at that location. By using an optically thin tracer, it is possible to directly measure turbulence from the nonthermal broadening of the line. Methods. The vertical layers of the CN and C2H emission were traced directly from the channel maps using ALFAHOR. By comparing their position to that of optically thick CO observations, we were able to characterize the kinetic temperature of the emitting region. Using a simple parametric model of the line intensity with DISCMINER, we accurately measured the emission linewidth and separated the thermal and nonthermal components. Assuming that the nonthermal component is fully turbulent, we were able to directly estimate the turbulent motions at the studied radial and vertical location of CN emission. Results. IM Lup shows a high turbulence of Mach 0.4–0.6 at z/r ~ 0.25. Considering previous estimates of low turbulence near the midplane, this may indicate a vertical gradient in the disk turbulence, which is a key prediction in MRI studies. CN and C2H are both emitting from a localized upper disk region at z/r = 0.2–0.3, in agreement with thermochemical models.

The evolution of protoplanetary disks in regions with massive OB stars is influenced by externally driven winds that deplete the outer parts of these disks. The winds have previously been studied via forbidden oxygen emission lines, which also arise in isolated disks in low-mass star-forming regions (SFRs) with weak external UV fields in photoevaporative or magnetic (internal) disk winds. It is crucial to determine how to disentangle external winds from internal ones. Here, we report a proxy for unambiguously identifying externally driven winds with a forbidden line of neutral atomic carbon, [C I] 8727 & Aring;. We compare for the first time the spatial location of the emission in the [O I] 5577 & Aring;, [O I] 6300 & Aring;, and [C I] 8727 & Aring; lines traced by VLT/MUSE-NFM with the ALMA Band 7 continuum disk emission in a sample of 12 proplyds in the Orion Nebula Cluster (ONC). We confirm that the [O I] 5577 & Aring; emission is co-spatial with the disk emission, whereas that of [O I] 6300 & Aring; is emitted both on the disk surface and on the ionization front of the proplyds. We show for the first time that the [C I] 8727 & Aring; line is also co-spatial with the disk surface in proplyds, as seen in the MUSE and ALMA data comparison. The peak emission is compatible with the stellar location in all cases, apart from one target with high relative inclination with respect to the ionizing radiation, where the peak emission is located at the disk edge in the direction of the ionizing radiation. To verify whether the [C I] 8727 & Aring; line is detected in regions where external photoevaporation is not expected, we examined VLT/X-Shooter spectra for young stars in low-mass SFRs. Although the [O I] 5577 & Aring; and 6300 & Aring; lines are well detected in all these targets, the total detection rate is << 10% in the case of the [C I] 8727 & Aring; line. This number increases substantially to a similar to 40% detection rate in sigma-Orionis, a region with higher UV radiation than in low-mass SFRs, but lower than in the ONC. The spatial location of the [C I] 8727 & Aring; line emission and the lack of its detection in isolated disks in low-mass SFRs strongly suggest that this line is a tell-tale tracer of externally driven photoevaporative winds, which agrees with recent excitation models.