Streamers feeding the SVS13-A protobinary system: astrochemistry reveals accretion shocks?
Abstract: We report ALMA high-angular resolution (∼ 50 au) observations of the binary system SVS13A. More specifically, we analyse deuterated water (HDO) and sulfur dioxide (SO2) emission. The molecular emission is...
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Cited by 5 publications
References 57 publications
Interstellar complex organic molecules (iCOMs) are species commonly found in the interstellar medium. They are believed to be crucial seed species for the build-up of chemical complexity in star forming regions as well as our own Solar System. Thus, understanding how their abundances evolve during the star formation process and whether it enriches the emerging planetary system is of paramount importance. We use data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disk and envelope system of solar protostars) to study the compact line emission towards the proto-binary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disk has previously been detected. More than 45 methyl formate ( lines are clearly detected with upper energies in the K range, as well as 8 dimethyl ether transitions ( in the K range, 1 ketene transition (H$_ $CCO) and 4 formic acid transitions (t-HCOOH). We compute the abundance ratios with respect to for $CCO, t-HCOOH (as well as an upper limit for CH$_ $CHO) through a radiative transfer analysis. We also report the upper limits on the column densities of nitrogen bearing iCOMs, $N$(C$_2$H$_5$CN) and $N$(C$_2$H$_3$CN). The emission from the detected iCOMs and their precursors is compact and encompasses both protostars, which are separated by only 0.2$^ prime $ (sim 28 au). The integrated intensities tend to align with the Southern filament, revealed by the high spatial resolution observations of the dust emission at 1.3 mm. A Position-Velocity and 2D analysis are performed on the strongest and uncontaminated transition and show three different spatial and velocity regions, two of them being close to 11B (Southern filament) and the third one near 11A. All our observations suggest that the detected methanol, as well as the other iCOMs, are generated by the shocked gas from the incoming filaments streaming towards BHB2007 11A and 11B, respectively, making this source one of the few where chemical enrichment of the gas caused by the streaming material is observed.
Interstellar complex organic molecules (iCOMs) are species commonly found in the interstellar medium. They are believed to be crucial seed species for the build-up of chemical complexity in star forming regions as well as our own Solar System. Thus, understanding how their abundances evolve during the star formation process and whether it enriches the emerging planetary system is of paramount importance. We use data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disk and envelope system of solar protostars) to study the compact line emission towards the proto-binary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disk has previously been detected. More than 45 methyl formate ( lines are clearly detected with upper energies in the K range, as well as 8 dimethyl ether transitions ( in the K range, 1 ketene transition (H$_ $CCO) and 4 formic acid transitions (t-HCOOH). We compute the abundance ratios with respect to for $CCO, t-HCOOH (as well as an upper limit for CH$_ $CHO) through a radiative transfer analysis. We also report the upper limits on the column densities of nitrogen bearing iCOMs, $N$(C$_2$H$_5$CN) and $N$(C$_2$H$_3$CN). The emission from the detected iCOMs and their precursors is compact and encompasses both protostars, which are separated by only 0.2$^ prime $ (sim 28 au). The integrated intensities tend to align with the Southern filament, revealed by the high spatial resolution observations of the dust emission at 1.3 mm. A Position-Velocity and 2D analysis are performed on the strongest and uncontaminated transition and show three different spatial and velocity regions, two of them being close to 11B (Southern filament) and the third one near 11A. All our observations suggest that the detected methanol, as well as the other iCOMs, are generated by the shocked gas from the incoming filaments streaming towards BHB2007 11A and 11B, respectively, making this source one of the few where chemical enrichment of the gas caused by the streaming material is observed.
Accuracy of ALMA estimates of young disk radii and masses
Protoplanetary disks, which are the natural consequence of the gravitational collapse of the dense molecular cloud cores, host the formation of the known planetary systems in our universe. Substantial efforts have been dedicated to investigating the properties of these disks in the more mature Class II stage, either via numerical simulations of disk evolution from a limited range of initial conditions or observations of their dust continuum and line emission from specific molecular tracers. The results coming from these two standpoints have been used to draw comparisons. However, few studies have investigated the main limitations at work when measuring the embedded Class 0/I disk properties from observations, especially in a statistical fashion. In this study, we provide a first attempt to compare the accuracy of some critical disk parameters in Class 0/I systems, as derived on real ALMA observational data, with the corresponding physical parameters that can be directly defined by theoreticians and modellers in numerical simulations. The approach we follow here is to provide full post-processing of the numerical simulations and apply it to the synthetic observations the same techniques used by observers to derive the physical parameters. We performed 3D Monte Carlo radiative transfer and mock interferometric observations of the disk populations formed in a magnetohydrodynamic (MHD) simulation model of disk formation through the collapse of massive clumps with the tools Radmc-3d and Casa respectively, to obtain their synthetic observations. With these observations, we re-employed the techniques commonly used in disk modelling from their continuum emissions to infer the properties that would most likely be obtained with real interferometers. We then demonstrated how these properties may vary with respect to the gas kinematics analyses and dust continuum modelling. Our modelling procedure, based on a two-component model for the disk and the envelope, shows that the disk sizes can be properly recovered from observations with sufficient angular resolutions, with an uncertainty of a factor $ 1.6-2.2$, whereas their masses cannot be accurately measured. Overall, the masses are predominantly underestimated for larger, more massive disks by a median factor of $ 2.5, $ and even up to $10$ in extreme cases, with the conversion from flux to dust mass under the optically thin assumption. We also find that the single Gaussian fittings are not a reliable modelling technique for young, embedded disks characterised by a strong presence of the envelopes. Thus, such an approach is to be used with caution. The radiative transfer post-processing and synthetic observations of MHD simulations offer genuine help in linking important observable properties of young planet-forming disks to their intrinsic values in simulations. Further extended investigations that tackle the caveats of this study, such as the lack of variation in the dust composition and distribution, dust-to-gas ratio, and other shortcomings in the numerical models, would be essential for setting constraints on our understanding of disk and planet formations.
Understanding the connection between outflows, winds, accretion, and discs in the inner protostellar regions is crucial for comprehending star and planet formation processes. We aim to we explore the inner 300 au of the protostar IRAS 4A2 as part of the ALMA FAUST Large Program. We analysed the kinematical structures of SiO and \ emission with 50 au resolution. 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 \ with respect to sys $, traced by methanol; (ii) an intermediate region (between 50 au and 150 au) traced by both SiO and CH$_3$OH, between 2 and 6 \ with respect to 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 with respect to sys $, and dominated by the outflow. In the intermediate region, we estimated a abundance ratio of about 120--400 and a SiO/H$_2$ abundance of $. We explored various possibilities to explain the origin of this region, such as, a rotating disc or inner envelope, a jet on the plane of the sky or precessing, and a wide-angle disc wind. We propose that \ and SiO in the inner 100 au probe the base of a wide-angle disc wind. The material accelerated in the wind crosses the plane of the sky, giving rise to the observed inverted velocity gradient, and sputtering the grain mantles and cores releasing CH$_3$OH and SiO. This is the first detection of a disc-wind candidate in SiO, and the second ever in
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