Protostellar Disks Research Articles

Characterization of Monosubstituted Benzene Ices

Aromatic structures are fundamental for key biological molecules such as RNA and metabolites and the abundances of aromatic molecules on young planets are therefore of high interest. Recent detections of benzonitrile and other aromatic compounds in interstellar clouds and comets have revealed a rich aromatic astrochemistry. In the cold phases of star and planet formation, most of these aromatic molecules are likely to reside in icy grain mantles, where they could be observed through IR spectroscopy. We present laboratory IR spectra of benzene and four monosubstituted benzene molecules—toluene, phenol, benzonitrile, and benzaldehyde—to determine their IR ice absorbances in undiluted aromatic ices, and in mixtures with water and CO. We also characterize the aromatic ice desorption rates, and extract binding energies and respective pre-exponential factors using temperature-programmed desorption experiments. We use these to predict at which protostellar and protoplanetary disk temperatures these molecules sublimate into the gas phase. We find that benzene and monosubstituted benzene derivatives are low-volatility with binding energies in the 5220–8390 K (43–70 kJ mol−1) range, which suggests that most of the chemistry of benzene and of functionalized aromatic molecules is to be expected to occur in the ice phase during star and planet formation.

CORINOS. II. JWST-MIRI Detection of Warm Molecular Gas from an Embedded, Disk-bearing Protostar

We present James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) observations of warm CO and H2O gas in emission toward the low-mass protostar IRAS 15398-3359, observed as part of the CORINOS program. The CO is detected via the rovibrational fundamental band and hot band near 5 μm, whereas the H2O is detected in the rovibrational bending mode at 6–8 μm. Rotational analysis indicates that the CO originates in a hot reservoir with an excitation temperature of 1598 ± 118 K, while the water is much cooler at 204 ± 7 K. Neither the CO nor the H2O line images are significantly spatially extended, constraining the emission to within ∼40 au of the protostar. The compactness and high temperature of the CO are consistent with an origin in the embedded protostellar disk, or in a compact disk wind. In contrast, the water must arise from a cooler region and requires a larger emitting area (compared to the CO) to produce the observed fluxes. The water may arise from a more extended part of the disk, or from the inner portion of the outflow cavity. Thus, the origin of the molecular emission observed with JWST remains ambiguous. Better constraints on the overall extinction, comparison with realistic disk models, and future kinematically resolved observations may all help to pinpoint the true emitting reservoirs.

The ALMA Legacy Survey of Class 0/I Disks in Corona australis, Aquila, chaMaeleon, oPhiuchus north, Ophiuchus, Serpens (CAMPOS). I. Evolution of Protostellar Disk Radii

We surveyed nearly all the embedded protostars in seven nearby clouds (Corona Australis, Aquila, Chamaeleon I and II, Ophiuchus North, Ophiuchus, Serpens) with the Atacama Large Millimeter/submillimeter Array at 1.3 mm observations with a resolution of 0.″1. This survey detected 184 protostellar disks, 90 of which were observed at a resolution of 14–18 au, making it one of the most comprehensive high-resolution disk samples across various protostellar evolutionary stages to date. Our key findings include the detection of new annular substructures in two Class I and two flat-spectrum sources, while 21 embedded protostars exhibit distinct asymmetries or substructures in their disks. We find that protostellar disks have a substantially large variability in their radii across all evolutionary classes. In particular, the fraction of large disks with sizes above 60 au decreases as the protostar evolves from Class 0 to Class I. Compiling the literature data, we discovered an increasing trend of the gas disk radii to dust disk radii ratio (R gas,Kep/R mm) with increasing bolometric temperature (T bol). Our results indicate that the dust and gas disk radii decouple during the early Class I stage. However, in the Class 0 stage, the dust and gas disk sizes are similar, which allows for a direct comparison between models and observational data at the earliest stages of protostellar evolution. We show that the distribution of radii in the 52 Class 0 disks in our sample is in high tension with various disk formation models, indicating that protostellar disk formation remains an unsolved question.

Chemical Abundance Gradients of Organic Molecules within a Protostellar Disk

Observations of low-mass protostellar systems show evidence of rich, complex organic chemistry. Their low luminosity, however, makes determining abundance distributions of complex organic molecules within the water snowline challenging. However, the excitation conditions sampled by differing molecular distributions may produce substantive changes in the resulting emission. Thus, molecular excitation may recover spatial information from spatially unresolved data. By analyzing spatially unresolved NOrthern Extended Millimeter Array observations of CH3OH and CH3CN, we aim to determine if CH3OH and CH3CN are distributed differently in the protostellar disk around HOPS-370, a highly luminous intermediate-mass protostar. Rotational diagram analysis of CH3OH and CH3CN yields rotational temperatures of 198 ± 1.2 K and 448 ± 19 K, respectively, suggesting the two molecules have different spatial distributions. Source-specific 3D LTE radiative transfer models are used to constrain the spatial distribution of CH3OH and CH3CN within the disk. A uniform distribution with an abundance of 4 × 10−8 reproduces the CH3OH observations. In contrast, the spatial distribution of CH3CN needs to be either more compact (within ∼120 au versus ∼240 au for CH3OH) or exhibit a factor of ≳15 increase in abundance in the inner ∼55 au. A possible explanation for the difference in spatial abundance distributions of CH3OH and CH3CN is carbon-grain sublimation.

Early Signs of Structure in Protostellar Disks

Protostellar disks—rotating disks of gas and dust around pre-fusion ignition young stars—are divided into four main classes: Class 0: the youngest class, still deeply embedded in their parent molecular clouds and accumulating mass, with a lifespan on the order of 100k years. Class I: still embedded in molecular clouds, characterized by strong infrared and radio emissions generated by the heat from the collapsing central protostar, with a typical lifespan of a few hundred thousand years. Class II: more evolved with decreased accretion rates and active planet formation. Lifespan on the order of 2-3 million years. Class III: low accretion rate debris (mostly dust) disks. Remnants of planetary formation process. Typical lifespan of several million years. Focusing on the youngest disks, Classes 0 and I, we are investigating how early structure begins to show in the form of gaps and rings, indicating potential future planet formation. We use high resolution and high sensitivity (sub)millimeter wavelength observations from the ALMA (Atacama Large Millimeter/submillimeter Array) interferometer. Having identified approximately 10,700 potential Class 0 or I disks in the ALMA archive, we make use of several specialized code packages designed to fit or examine individual disks from their frequency space visibility data rather than from images to build a step-by-step process taking the initial ALMA data and providing the decision-making ability to categorize the disks into four primary categories: Smooth, Structured, Further Investigation, Not Usable. Having used the summer term to build, streamline, and document the needed process, we report building an initial catalog of usable Class 0 and Class I sources that contains 36 individual objects, with 7 categorized as Smooth, 8 as having Structure, and 6 needing Further Investigation.

Survey of complex organic molecules in starless and pre-stellar cores in the Perseus molecular cloud

ABSTRACT Cold ($\sim$10 K) and dense ($\sim 10^{5}$ cm$^{-3}$) cores of gas and dust within molecular clouds, known as starless and dynamically evolved pre-stellar cores, are the birthplaces of low-mass (M$\le$ few M$_\odot$) stars. As detections of interstellar complex organic molecules, or COMs, in starless cores has increased, abundance comparisons suggest that some COMs might be seeded early in the star formation process and inherited to later stages (i.e. protostellar discs and eventually comets). To date observations of COMs in starless cores have been limited, with most detections reported solely in the Taurus molecular cloud. It is therefore still a question whether different environments affect abundances. We have surveyed 35 starless and pre-stellar cores in the Perseus molecular cloud with the Arizona Radio Observatory (ARO) 12 m telescope detecting both methanol, CH$_3$OH, and acetaldehyde, CH$_3$CHO, in 100 per cent and 49 per cent of the sample, respectively. In the sub-sample of 15 cores where CH$_3$CHO was detected at $\gt 3\sigma$ ($\sim$18 mK) with the ARO 12 m, follow-up observations with the Yebes 40 m telescope were carried out. Detections of formic acid, t-HCOOH, ketene, H$_2$CCO, methyl cyanide, CH$_3$CN, vinyl cyanide, CH$_2$CHCN, methyl formate, HCOOCH$_3$, and dimethyl ether, CH$_3$OCH$_3$, are seen in at least 20 per cent of the cores. We discuss detection statistics, calculate column densities, and compare abundances across various stages of low-mass star formation. Our findings have more than doubled COM detection statistics in cold cores and show COMs are prevalent in the gas before star and planet formation in the Perseus molecular cloud.

Protostellar Disk Formation Regimes: Angular Momentum Conservation versus Magnetic Braking

Protostellar disks around young protostars exhibit diverse properties, with their radii ranging from less than ten to several hundred astronomical units. To investigate the mechanisms shaping this disk radius distribution, we compiled a sample of 27 Class 0 and I single protostars with resolved disks and dynamically determined protostellar masses from the literature. Additionally, we derived the radial profile of the rotational-to-gravitational-energy ratio in dense cores from the observed specific angular momentum profiles in the literature. Using these observed protostellar masses and rotational energy profile, we computed theoretical disk radii from the hydrodynamic and nonideal magnetohydrodynamic (MHD) models in Y.-N. Lee et al. and generated synthetic samples to compare with the observations. In our theoretical model, the disk radii are determined by hydrodynamics when the central protostar+disk mass is low. After the protostars and disks grow and exceed certain masses, the disk radii become regulated by magnetic braking and nonideal MHD effects. The synthetic disk radius distribution from this model matches well with the observations. This result suggests that hydrodynamics and nonideal MHD can be dominant in different mass regimes (or evolutionary stages), depending on the rotational energy and protostar+disk mass. This model naturally explains the rarity of large (>100 au) disks and the presence of very small (<10 au) disks. It also predicts that the majority of protostellar disks have radii of a few tens of astronomical units, as observed.

FORGE’d in FIRE III: The IMF in Quasar Accretion Disks from STARFORGE

Recently, we demonstrated self-consistent formation of strongly-magnetized quasar accretion disks (QADs) from cosmological radiation-magnetohydrodynamic-thermochemical galaxy-star formation simulations, including the full STARFORGE physics shown previously to produce a reasonable IMF under typical ISM conditions. Here we study star formation and the stellar IMF in QADs, on scales from 100 au to 10 pc from the SMBH. We show it is critical to include physics often previously neglected, including magnetic fields, radiation, and (proto)stellar feedback. Closer to the SMBH, star formation is suppressed, but the (rare) stars that do form exhibit top-heavy IMFs. Stars can form only in special locations (e.g. magnetic field switches) in the outer QAD. Protostars accrete their natal cores rapidly but then dynamically decouple from the gas and ‘wander,’ ceasing accretion on timescales ~100 yr. Their jets control initial core accretion, but the ejecta are ‘swept up’ into the larger-scale QAD flow without much dynamical effect. The strong tidal environment strongly suppresses common-core multiplicity. The IMF shape depends sensitively on un-resolved dynamics of protostellar disks (PSDs), as the global dynamical times can become incredibly short (&lt; yr) and tidal fields are incredibly strong, so whether PSDs can efficiently transport angular momentum or fragment catastrophically at &lt;10 au scales requires novel PSD simulations to properly address. Most analytic IMF models and analogies with planet formation in PSDs fail qualitatively to explain the simulation IMFs, though we discuss a couple of viable models.

Multiple Misaligned Outflows and Warped Accretion Flows in the Proto-multiple System Per-emb-8 and 55

To investigate the formation process of multiple systems, we have analyzed the Atacama Large Millimeter/submillimeter Array archival data of the 1.3 mm continuum, 12CO (2-1) and C18O (2-1) emission in a proto-multiple system consisting of a Class 0 protostar Per-emb-8 and a Class I protobinary Per-emb-55 A and B. The 1.3 mm continuum emission is likely to primarily trace their protostellar disks, and the Keplerian disk rotation is observed in Per-emb-8 and Per-emb-55 A in the emission lines. In Per-emb-8, we identify two arm-like structures with a length of ∼1000 au connecting the eastern and western of its disk in the continuum and C18O emission. Our analysis suggests that these arm-like structures are most likely infalling flows. In the 12CO emission, we discover a second bipolar outflow associated with Per-emb-8. The two bipolar outflows in Per-emb-8 are possibly launched along the normal axes of the misaligned inner and outer parts of its warped protostellar disk. In Per-emb-55, we find that the red- and blueshifted lobes of its bipolar outflow are misaligned by 90°. The presence of the warped disk, multiple misaligned outflows, and asymmetric infalling flows suggest complex dynamics in proto-multiple systems, and these could be related to the tidal interactions between the companions and/or the turbulent environments forming this proto-multiple system.

Fragmentation in Gravitationally Unstable Collapsar Disks and Subsolar Neutron Star Mergers

Although stable neutron stars (NSs) can in principle exist down to masses M ns ≈ 0.1 M ⊙, standard models of stellar core-collapse predict a robust lower limit M ns ≳ 1.2 M ⊙, roughly commensurate with the Chandrasekhar mass M Ch of the progenitor’s iron core (electron fraction Y e ≈ 0.5). However, this limit may be circumvented in sufficiently dense neutron-rich environments (Y e < 0.5) for which MCh∝Ye2 is reduced to ≲1 M ⊙. Such physical conditions could arise in the black hole accretion disks formed from the collapse of rapidly rotating stars (“collapsars”), as a result of gravitational instabilities and cooling-induced fragmentation, similar to models for planet formation in protostellar disks. We confirm that the conditions to form subsolar-mass NS (ssNS) may be marginally satisfied in the outer regions of massive neutrino-cooled collapsar disks. If the disk fragments into multiple ssNSs, their subsequent coalescence offers a channel for precipitating subsolar mass LIGO/Virgo gravitational-wave mergers that does not implicate primordial black holes. The model makes several additional predictions: (1) ∼Hz frequency Doppler modulation of the ssNS-merger gravitational-wave signals due to the binary’s orbital motion in the disk; (2) at least one additional gravitational-wave event (coincident within ≲hours), from the coalescence of the ssNS-merger remnant(s) with the central black hole; (3) an associated gamma-ray burst and supernova counterpart, the latter boosted in energy and enriched with r-process elements from the NS merger(s) embedded within the exploding stellar envelope (“kilonovae inside a supernova”).

Polarization Substructure in the Spiral-dominated HH 111 Disk: Evidence for Grain Growth

The HH 111 protostellar disk has recently been found to host a pair of spiral arms. Here we report the dust polarization results in the disk as well as the inner envelope around it, obtained with the Atacama Large Millimeter/submillimeter Array in continuum at λ ∼ 870 μm and ∼0.″05 resolution. In the inner envelope, polarization is detected with a polarization degree of ∼6% and an orientation almost everywhere parallel to the minor axis of the disk and thus likely to be due to the dust grains magnetically aligned mainly by toroidal fields. In the disk, the polarization orientation is roughly azimuthal on the far side and becomes parallel to the minor axis on the near side, with a polarization gap in between on the far side near the central protostar. The disk polarization degree is ∼2%. The polarized intensity is higher on the near side than the far side, showing a near–far side asymmetry. More importantly, the polarized intensity and thus polarization degree are lower in the spiral arms but higher in between the arms, showing an anticorrelation of the polarized intensity with the spiral arms. Our modeling results indicate that this anticorrelation is useful for constraining the polarization mechanism and is consistent with the dust self-scattering by the grains that have grown to a size of ∼150 μm. The interarms are sandwiched and illuminated by two brighter spiral arms and thus have higher polarized intensity. Our dust self-scattering model can also reproduce the observed polarization orientation parallel to the minor axis on the near side and the observed azimuthal polarization orientation at the two disk edges in the major axis. Further modeling work is needed to study how to reproduce the observed near–far side asymmetry in the polarized intensity and the observed azimuthal polarization orientation on the far side.

FAUST XVII: Super deuteration in the planet-forming system IRS 63 where the streamer strikes the disk

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 Stagger Code for Accurate and Efficient, Radiation-coupled Magnetohydrodynamic Simulations

We describe the Stagger code for simulations of magnetohydrodynamic (MHD) systems. This is a modular code with a variety of physics modules that will let the user run simulations of deep stellar atmospheres, sunspot formation, stellar chromospheres and coronae, proto-stellar disks, star formation from giant molecular clouds, and even galaxy formation. The Stagger code is efficiently and highly parallelizable, enabling such simulations with large ranges of both spatial and temporal scales. We describe the methodology of the code and present the most important of the physics modules, as well as its input and output variables. We show results of a number of standard MHD tests to enable comparison with other, similar codes. In addition, we provide an overview of tests that have been carried out against solar observations, ranging from spectral line shapes, spectral flux distribution, limb darkening, intensity and velocity distributions of granulation, to seismic power spectra and the excitation of p-modes. The Stagger code has proven to be a high-fidelity code with a large range of uses.

Early Planet Formation in Embedded Disks (eDisk). XV. Influence of Magnetic Field Morphology in Dense Cores on Sizes of Protostellar Disks

The magnetic field of a molecular cloud core may play a role in the formation of circumstellar disks in the core. We present magnetic field morphologies in protostellar cores of 16 targets in the Atacama Large Millimeter/submillimeter Array large program “Early Planet Formation in Embedded Disks (eDisk),” which resolved their disks with 7 au resolutions. The 0.1 pc scale magnetic field morphologies were inferred from the James Clerk Maxwell Telescope POL-2 observations. The mean orientations and angular dispersions of the magnetic fields in the dense cores are measured and compared with the radii of the 1.3 mm continuum disks and the dynamically determined protostellar masses from the eDisk program. We observe a significant correlation between the disk radii and the stellar masses. We do not find any statistically significant dependence of the disk radii on the projected misalignment angles between the rotational axes of the disks and the magnetic fields in the dense cores, nor on the angular dispersions of the magnetic fields within these cores. However, when considering the projection effect, we cannot rule out a positive correlation between disk radii and misalignment angles in three-dimensional space. Our results suggest that the morphologies of magnetic fields in dense cores do not play a dominant role in the disk formation process. Instead, the sizes of protostellar disks may be more strongly affected by the amount of mass that has been accreted onto star+disk systems, and possibly other parameters, for example, magnetic field strength, core rotation, and magnetic diffusivity.

Probing the physics of star formation (ProPStar)

Context. The detections of narrow channels of accretion toward protostellar disks, known as streamers, have increased in number in the last few years. However, it is unclear whether streamers are a common feature around protostars that were previously missed, or if they are a rare phenomenon. Aims. Our goals are to obtain the incidence of streamers toward a region of clustered star formation and to trace the origins of their gas to determine whether they originate within the filamentary structure of molecular clouds or from beyond. Methods. We used combined observations of the nearby NGC 1333 star-forming region, carried out with the NOEMA interferometer and the IRAM 30m single dish. Our observations cover the area between the systems IRAS 4 and SVS 13. We traced the chemically fresh gas within NGC 1333 with HC3N molecular gas emission and the structure of the fibers in this region with N2H+ emission. We fit multiple velocity components in both maps and used clustering algorithms to recover velocity-coherent structures. Results. We find streamer candidates toward 7 out of 16 young stellar objects within our field of view. This represents an incidence of approximately 40% of young stellar objects with streamer candidates in a clustered star-forming region. The incidence increases to about 60% when we only considered embedded protostars. All streamers are found in HC3N emission. Conclusions. Given the different velocities between HC3N and N2H+ emission, and because by construction, N2H+ traces the fiber structure, we suggest that the gas that forms the streamers comes from outside the fibers. This implies that streamers can connect cloud material that falls onto the filaments with protostellar disk scales.

JWST Observations of Young protoStars (JOYS)

Context. Accretion and ejection dictate the outcomes of star and planet formation processes. The mid-infrared (MIR) wavelength range offers key tracers of processes that have been difficult to detect and spatially resolve in protostars until now. Aims. We aim to characterize the interplay between accretion and ejection in the low-mass Class I protobinary system TMC1, comprising two young stellar objects: TMC1-W and TMC1-E at a 85 au separation. Methods. Using the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) observations in 5–28 μm range, we measured the intensities of emission lines of H2, atoms, and ions, for instance, the [Fe II] and [Ne II], and HI recombination lines. We analyzed the spatial distribution of the different species using the MIRI Medium Resolution Spectrometer (MRS) capabilities to spatially resolve emission at 0″​​.2–0″​​.7 scales. we compared these results with the corresponding Atacama Large Millimeter/submillimeter Array (ALMA) maps tracing cold gas and dust. Results. We detected H2 outflow coming from TMC1-E, with no significant H2 emission from TMC1-W. The H2 emission from TMC1-E outflow appears narrow and extends to wider opening angles with decreasing Eup from S(8) to S(1) rotational transitions, indicating the disk wind as its origin. The outflow from TMC1-E protostar shows spatially extended emission lines of [Ne II], [Ne III], [Ar II], and [Ar III], with their line ratios consistent with UV radiation as a source of ionization. With ALMA, we detected an accretion streamer infalling from &gt; 1000 au scales onto the TMC1-E component. The TMC1-W protostar powers a collimated jet, detected with [Fe II] and [Ni II], making it consistent with energetic flow. A much weaker ionized jet is observed from TMC1-E, and both jets appear strikingly parallel to each other, indicating that the disks are co-planar. TMC1-W is associated with strong emission from hydrogen recombination lines, tracing the accretion onto the young star. Conclusions. MIRI-MRS observations provide an unprecedented view of protostellar accretion and ejection processes on 20 au scales. Observations of a binary Class I protostellar system show that the two processes are clearly intertwined, with accretion from the envelope onto the disk influencing a wide-angle wind ejected on disk scales. Finally, the accretion from the protostellar disk onto the protostar is associated with the source launching a collimated high-velocity jet within the innermost regions of the disk.

A laboratory infrared model of astrophysical pyrimidines

ABSTRACT Nucleobases are essential molecules for life, forming integral parts of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in all terrestrial life forms. Despite evidence of their abiotic synthesis in meteorites and laboratory simulations of interstellar medium (ISM) conditions, nucleobases have not been detected in the ISM. This study investigates the infrared spectra of uracil, cytosine, and thymine – pyrimidine nucleobases – embedded in an ice mixture simulating common volatiles found in protostellar discs. Our objective was to explore the feasibility of identifying unique infrared bands of pyrimidines in the ISM, despite significant overlapping absorption features from simpler, more abundant interstellar species such as H2O, CO, CH3OH, and NH3. Laboratory results revealed that although two common bands (1240 and 760 cm−1 in uracil; 1236 and 763 cm−1 in cytosine; and 1249 and 760 cm−1 in thymine) were identified, the detection of these bands in space is challenged by overlapping absorption features. Recent observations with the JWST have shown that interstellar organic species exhibit infrared signals within similar ranges, making it impossible to distinguish pyrimidine bands from these organics. Thus, detecting pyrimidines with current telescopes is infeasible, not due to sensitivity limitations or the need for more powerful instrumentation, but because of the intrinsic overlap in spectral features. This study complements previous research on purines by examining pyrimidines and including the impact of common ISM volatiles in the ice composition. The results highlight the significant challenges in detecting complex molecules in the ISM, underscoring the importance of understanding the spectral complexities and interactions to interpret astronomical observations accurately.

The First Estimation of the Ambipolar Diffusivity Coefficient from Multi-scale Observations of the Class 0/I Protostar, HOPS-370

Protostars are born in magnetized environments. As a consequence, the formation of protostellar disks can be suppressed by the magnetic field, efficiently removing the angular momentum of the infalling material. Nonideal MHD effects are proposed as one way to allow protostellar disks to form. Thus, it is important to understand their contributions to observations of protostellar systems. We derive an analytical equation to estimate the ambipolar diffusivity coefficient at the edge of the protostellar disk in the Class 0/I protostar, HOPS-370, for the first time, under the assumption that the disk radius is set by ambipolar diffusion. Using previous results of the protostellar mass, disk mass, disk radius, density and temperature profiles, and magnetic field strength, we estimate the ambipolar diffusivity coefficient to be 1.7−1.4+1.5×1019cm2s−1 . We quantify the contribution of ambipolar diffusion by estimating its dimensionless Elsässer number to be ∼1.7−1.0+1.0 , indicating its dynamical importance in this region. We compare our results to those of the chemical calculations of the ambipolar diffusivity coefficient using the Non-Ideal Magnetohydrodynamics Coefficients and Ionization Library, which are consistent with our results. In addition, we compare our derived ambipolar diffusivity coefficient to the diffusivity coefficients for ohmic dissipation and the Hall effect, and find ambipolar diffusion is dominant in our density regime. These results demonstrate a new methodology to understand nonideal MHD effects in observations of protostellar disks. More detailed modeling of the magnetic field, envelope, and microphysics, along with a larger sample of protostellar systems, is needed to further understand the contributions of nonideal MHD.

Probing the eccentricity in protostellar discs: Modelling kinematics and morphologies

Context. Protostellar discs are mostly modelled as circular structures of gas and dust orbiting a protostar. However, a number of physical mechanisms, for example, the presence of a (sub)stellar companion or initial axial asymmetry, can cause the gas and dust orbital motion to become eccentric. Theoretical studies have revealed that, when present, disc eccentricity is expected to occur with predictable profiles that can be long-lasting and potentially observable in protostellar systems. Aims. We construct an analytical model predicting the typical features of the kinematics and morphology of eccentric protostellar discs, with the final goal of characterising the observational appearance of eccentricity in discs. Methods. We validate the model using a numerical simulation of a circumbinary disc (where the binary makes the disc eccentric). We finally post-process the simulation with Monte Carlo radiative transfer to study how eccentric features would appear through the ‘eyes’ of ALMA. Results. Besides the motion of the material on eccentric Keplerian orbits in the disc orbital plane, the most characteristic eccentric feature emerging from the analytical model is strong vertical motion with a typical anti-symmetric pattern (with respect to the disc line of pericentres). A circumbinary disc with a ≈ 40 au eccentric cavity (ecav = 0.2), carved by an abin = 15 au binary, placed at a distance d = 130 pc, is expected to host in its upper emission surface vertical oscillations up to vz ~ 400 m s−1 close to the cavity edge, that is to say, well within ALMA spectral and spatial resolution capabilities. A residual spiral pattern in the vertical velocity Δvz ~ 150 m s−1 of the simulation cannot be captured by the theoretical model, we speculate it to be possibly linked to the presence of a companion in the system.

ALMA view of the L1448-mm protostellar system on disk scales: CH3OH and H13CN as new disk wind tracers

Protostellar disks are known to accrete; however, the exact mechanism that extracts the angular momentum and drives accretion in the low-ionization “dead” region of the disk is under debate. In recent years, magnetohydrodynamic (MHD) disk winds have become a popular solution. Even so, observations of these winds require both high spatial resolution (~10 s au) and high sensitivity, which has resulted in only a handful of MHD disk wind candidates to date. In this work we present high angular resolution (~30 au) ALMA observations of the emblematic L1448-mm protostellar system and find suggestive evidence for an MHD disk wind. The disk seen in dust continuum (~0.9 mm) has a radius of ~23 au. Rotating infall signatures in H13CO+ indicate a central mass of 0.4 ± 0.1 M⊙ and a centrifugal radius similar to the dust disk radius. Above the disk, we identify rotation signatures in the outflow traced by H13CN, CH3OH, and SO lines and find a kinematical structure consistent with theoretical predictions for MHD disk winds. This is the first detection of an MHD disk wind candidate in H13CN and CH3OH. The wind launching region estimated from cold MHD wind theory extends out to the disk edge. The magnetic lever arm parameter would be λϕ ≃ 1.7, in line with recent non-ideal MHD disk models. The estimated mass-loss rate is approximately four times the protostellar accretion rate (Ṁacc ≃ 2 × 10−6M⊙ yr−1) and suggests that the rotating wind could carry enough angular momentum to drive disk accretion.