arXiv subjects

J. E. Pineda

Publications and source records attributed to J. E. Pineda.

At least 19 recordsLinked to original sources

arXiv2026

Series of core collapse numerical simulations (SOLANUM) I: Modelling the early and late infall in a sun-like protostar

Magnetohydrodynamical simulations and interferometric observations toward young stellar objects reveal the accretion of gas that may alter the physical properties and chemical composition of protostellar disks. Our goal is to constrain the physical history and properties of late infalling gas, and assess its potential to change the physical and chemical properties of the disk. We carried out a core collapse simulation of 5 M$_{\odot}$ of gas endowed with tracer and sink particles during $\sim 3.6\times 10^{5}$ yr. We analyzed the properties of the rotationally supported disk, and the origin and physical history of the gas from which it is initially formed. We also selected the tracer particles that describe the late infall to analyze their origin and physical history, and compare them to the information obtained from the disk. The final mass of the sink reaches 1.02 M$_\odot$, while the mass of the disk stays fairly constant around 0.02 M$_\odot$. Throughout its evolution, the disk radius increases up to $\sim 40$ au and its density is reduced by a factor of $\sim 8$. Filaments that channel gas from the envelope to the disk and sink appear as a result of the magnetic interchange instability. Tracer particles can identify late infalling gas, whose physical properties resemble that of observed streamers and are only accreted in the final snapshots of the simulation. The origin and physical history of the late infalling gas are different from those of the gas that initially forms the disk. Core collapse simulations predict the appearance of filaments that connect the envelope to the disk. The late accretion of gas through these channels has properties similar to those of streamers and brings gas to the disk with a different physical history that could translate into a different chemical composition.

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arXiv2026

Corona Australis 151: an extremely young protostar

Context. Prestellar cores are the birthplace of stars and planetary systems, but they are short-lived objects, since the initial stages of dense core evolution, collapse, and the formation of a protostellar seed are fast. In an effort to build a catalogue of bona-fide prestellar cores in the Solar neighbourhood, we used APEX observations to identify dynamically evolved cores among dense cores observed with Herschel. One of them, Corona Australis 151, stood out because of its centrally peaked structure, with densities above 1e7cm-3 in the central 500-1000 au, and high deuteration levels (N2D+/N2H+~0.5), suggestive of an evolved, prestellar stage. Aims. Corona Australis 151 appears to be an evolved prestellar core, but the presence of broad wings in some of the detected lines and a tentative 70micron detection with Herschel partially challenges its prestellar stage. We intend to assess its evolutionary stage. Methods. We analyse new ALMA data of the continuum emission and of several line tracers (including typical outflow tracers) at a resolution of~150-200au, tracing the envelope. Results. We unveil the presence of a compact and young outflow (projected dynamical age:~500yr), traced by SiO, CO, and H2CO emission. The continuum emission traces an envelope structure of size~1000 au and mass 0.33M_sun(assuming Tdust=20 K). Conclusions. Corona Australis 151 is an extremely young protostar, possibly one of the youngest known in the Solar neighbourhood, and hence a new laboratory to study the chemical and dynamical evolution at the dawn of star formation.

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arXiv2026

End-to-end differentiable retrieval of molecular spectra using hydrodynamics, chemistry, and radiative transfer

We aim to reproduce observed molecular line emission using a pipeline that couples hydrodynamics, chemistry, and radiative transfer, capable of simultaneously optimizing all relevant physical and chemical parameters. We developed an end-to-end differentiable Jax pipeline consisting of a custom hydrodynamical code, a modified version of the differentiable chemical code Carbox, and a custom radiative transfer code. We tested the framework using controlled synthetic data. We demonstrate that the framework can recover the parameters of hydrodynamical shock models directly from molecular line spectra and optimize selected chemical reaction rate coefficients through gradient-based optimization. The differentiable formulation enables efficient optimization of the coupled physical and chemical model while preserving the full time-dependent evolution.

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arXiv2026

A differentiable and optimizable 3D model for interpretation of observed spectral data cubes

Molecular spectral cubes of prestellar cores encode the information on the physical and chemical properties of these objects along the line of sight. To retrieve this information, we need an interpretable model that reproduces the observed spectra. We designed a differentiable 3D geometrical model that produces synthetic observations from the parameterized density and velocity fields, and that can be efficiently optimized to reproduce the real data cubes. The model has been applied to p-NH2D and N2D+ spectral cubes in the prestellar core L1544. The optimized model suggests that to reproduce the observed velocity difference between p-NH2D and N2D+ in L1544, an asymmetric structure in density and velocity is necessary.

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arXiv2026

PRODIGE - envelope to disk with NOEMA: VII. (Complex) organic molecules in the NGC1333 IRAS4B1 outflow: A new laboratory for shock chemistry

Shock chemistry is an excellent tool to shed light on the formation and destruction mechanisms of complex organic molecules (COMs). The L1157-mm outflow is the only low-mass protostellar outflow that has extensively been studied in this regard. Using the data taken as part of the PRODIGE (PROtostars & DIsks: Global Evolution) large program, we aim to map COM emission and derive the molecular composition of the protostellar outflow driven by the Class 0 protostar NGC1333 IRAS4B1 to introduce it as a new laboratory to study the impact of shocks on COM chemistry. In addition to typical outflow tracers such as SiO and CO, outflow emission is seen from H2CO, HNCO, and HC3N, as well as from the COMs CH3OH, CH3CN, and CH3CHO, and even from deuterated species such as DCN, D2CO, and CH2DOH. Maps of integrated intensity ratios between CH3OH and DCN, D2CO, and CH3CHO reveal gradients with distance from the protostar. Intensity ratio maps of HC3N and CH3CN with respect to CH3OH peak in the southern lobe where temperatures are highest. Rotational temperatures derived towards two positions, one in each lobe, are found in the range ~50-100 K. Abundances with respect to CH3OH are higher by factors of a few than for the L1157-B1. In conclusion, for the first time, we securely detected the COMs CH3CN, CH3CHO, and CH2DOH in the IRAS 4B1 outflow, serendipitously with limited sensitivity and bandwidth. Targeted observations will enable the discovery of new COMs and a more detailed analysis of their emission. Morphological differences between molecules in the IRAS 4B1 outflow lobes and their relative abundances provide first proof that this outflow is a promising new laboratory for shock chemistry, which will offer crucial information on COM formation and destruction as well as outflow structure and kinematics.

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arXiv2026

Projection effects in star-forming regions: I. Nearest-neighbour statistics and observational biases

Stars form as molecular clouds fragment into networks of dense cores, filaments, and subclusters. The characteristic spacing of these cores is a key observable imprint of fragmentation physics and is commonly measured using nearest-neighbour (NN) statistics. However, NN separations are derived from projected two-dimensional (2D) positions, while fragmentation occurs in three dimensions (3D). Using spherical and fractal toy models, we show that the standard geometric deprojection factor of $4/π\simeq1.27$ is inadequate because projection not only foreshortens separations but also rewires the NN network, while finite angular resolution merges close neighbours and inflates apparent spacings. We quantify these competing biases with Monte Carlo experiments spanning a wide range of morphologies, sample sizes, and effective resolutions. From these we derive an empirical correction factor that depends on both sample size and resolution: for small ($N\lesssim10$) or poorly resolved samples ($\lesssim$10 resolution elements across the field), intrinsic NN spacings exceed projected values by only 20 to 40%, whereas for well-sampled ($N\gtrsim100$), well-resolved data ($\gtrsim$30-50 resolution elements), true 3D separations are typically larger by a factor of $\sim$2. This calibration enables observers to convert measured 2D NN spacings into corresponding 3D estimates, with typical morphology-driven uncertainties of order 30 to 40%, and we demonstrate how it alters inferred fragmentation scales in observed and simulated core populations. [abridged]

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arXiv2025

FAUST. XXVIII. High-Resolution ALMA Observations of Class 0/I Disks: Structure, Optical Depths, and Temperatures

We present high-resolution (~7.5 au) ALMA observations at 1.3 and 3 mm of 16 disks around Class 0/I protostars across multiple star-forming regions and a variety of multiplicities, showing a range of disk sizes (~2-100 au) and including circumbinary disks (CBDs) in binaries with separations <100 au. The disk properties show similarities to Class II disks, including (a) low spectral index (SI) values (alpha=2.1) that increase with disk radius, (b) 3 mm disk sizes only marginally smaller than at 1.3 mm (<10%), and (c) radial intensity profiles well described by modified self-similar profiles. We also find key differences: (i) SI values increasing with radius, but exceeding 2 only at the disk edge (ii) higher brightness temperatures Tb, in some cases higher than the predicted temperatures due to irradiation, and (iii) ~10x higher luminosity at a given size compared to the Class II disks. These results confirm significant optical depth in the observed Class 0/I disks, at both 1.3 and 3 mm, helping to explain their higher luminosities, but higher temperatures are also required for the most compact (< 40 au) disks, suggesting additional viscous heating. Considering optical depth, most disk dust masses are estimated in the range 30-900 Mearth (0.01-0.3 Msun in gas), resulting in some disks reaching marginal gravitational instability. The median location of the water iceline is ~3 au, but it can extend beyond 10-20 au for the hottest disks. CBDs exhibit lower optical depths at both wavelengths and hence higher SI values (alpha=3.0), dust masses of 100 Mearth, and beta~1.5 (2 Class 0 CBDs) and beta~1 (1 Class I CBD), suggesting substantial grain growth only in the more evolved CBD. The inferred high optical depths provide a compelling explanation for the apparent scarcity of dust substructures in the younger disks at ~ 1 mm, despite mounting evidence for early planet formation (ABRIDGED).

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arXiv2025

First results from ALPPS: a sub-Alfvénic streamer in SVS13A

We present the first results from the ALMA Perseus Polarization Survey (ALPPS), focusing on the magnetic field in the SVS13A circumbinary disk. The dataset includes full-Stokes dust continuum observations at $\sim0\farcs3$ and 870 $μ$m, as well as molecular line emission from C$^{17}$O$(J=3 \rightarrow 2)$ at $\sim0\farcs3$, C$^{18}$O$(J=2 \rightarrow 1)$ at $\sim0\farcs2$, and DCN$(J=3 \rightarrow 2)$ at $\sim0\farcs1$ angular resolution. Our observations resolve both a previously identified dust spiral and an infalling streamer, capturing their spatial and kinematic structures. The streamer is traced from scales $>300$ au down to the circumbinary disk. Using alignment measure (AM) maps and histograms that compare the orientations of the plane-of-sky magnetic field with local intensity and velocity gradients, we find that the AM distribution peaks at a value of 1. This AM peak strongly suggests alignment between the field and the dust total intensity emission, as well as between the field and the gas velocity, which in turn suggests grain alignment by magnetic fields. From our data, we derive a magnetic field strength, B$_{\mathrm{pos}} \sim 1.1 \pm 0.6$\, mG, and a kinetic to magnetic energy ratio of $0.5 \pm 0.4$, suggesting magnetic dominance. We also produced a map of the Alfvénic Mach number, finding $\mathcal{M}_{\rm A} < 1$ along the streamer, consistent with sub-Alfvénic infalling motions. Therefore, the field is likely facilitating the inflow of material from the envelope onto the disk by constraining movement across the field lines. This represents the first detection of a magnetically sub-Alfvénic infalling streamer in a protostellar system.

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arXiv2025

Hunting pre-stellar cores with APEX: overview

[Abridged] $Context.$ Pre-stellar cores are centrally concentrated starless cores on the verge of star formation and they represent the initial conditions for star and planet formation. Pre-stellar cores host an active organic chemistry and isotopic fractionation, kept stored into thick icy mantles, which can be inherited by the future protoplanetary disks and planetesimals. So far, only a few have been studied in detail, with special attention being paid to L1544 in the Taurus Molecular Cloud. $Aims.$ The aim is to identify nearby ($<$200 pc) pre-stellar cores in an unbiased way, to build a sample that can then be studied in detail. $Methods.$ We first used the Herschel Gould Belt Survey archival data, selecting all those starless cores with central H$_2$ number densities higher than or equal to 3$\times$10$^5$ cm$^{-3}$, the density of L1544 within the Herschel beam. The selected 40 (out of 1746) cores have then been observed in N$_2$H$^+$(3-2) and N$_2$D$^+$(4-3) using the APEX antenna. $Results.$ A total of 17 bona-fide (i.e., with a deuterium fraction larger than 10%) pre-stellar cores have been identified. Other 16 objects can also be considered pre-stellar, as they are dynamically evolved starless cores, but their deuterium fraction is relatively low ($<$10%). The remaining 7 objects have been found associated with very young stellar objects. $Conclusions.$ Dust continuum emission, together with spectroscopic observations of N$_2$H$^+$(3-2) and N$_2$D$^+$(4-3), is a powerful tool to identify pre-stellar cores in molecular clouds. Detailed modeling of the physical structure of the objects is now required for reconstructing the chemical composition as a function of radius. This work has provided a statistically significant sample of 33 pre-stellar cores, a crucial step in the understanding of the process of star and planet formation.

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arXiv2025

Cosmic-ray ionisation rate in low-mass cores: the role of the environment

Context: Cosmic rays drive several key processes for the chemistry and dynamical evolution of star-forming regions. Their effect is quantified mainly by means of the cosmic-ray ionisation rate $ζ_2$. Aims: We aim to obtain a sample of $ζ_2$ measurements in 20 low-mass starless cores embedded in different parental clouds, to assess the average level of ionisation in this kind of sources and to investigate the role of the environment in this context. The warmest clouds in our sample are Ophiuchus and Corona Australis, where star formation activity is higher than in the Taurus cloud and the other isolated cores we targeted. Methods: We compute $ζ_2$ using an analytical method based on the {column density} of ortho-$\rm H_2D^+$, the CO abundance, and the deuteration level of HCO$^+$. To estimate these quantities, we analysed new, high-sensitivity molecular line observations obtained with the Atacama Pathfinder EXperiment (APEX) single-dish telescope and archival continuum data from Herschel. Results: We report $ζ_2$ estimates in 17 cores in our sample and provide upper limits on the three remaining sources. The values span almost two orders of magnitude, from $1.3 \times 10^{-18}\, \rm s^{-1}$ to $8.5 \times 10^{-17}\, \rm s^{-1}$. Conclusions: We find no significant correlation between $ζ_2$ and the core's column densities $N\rm (H_2)$. On the contrary, we find a positive correlation between $ζ_2$ and the cores' temperature, estimated via Herschel data: cores embedded in warmer environments present higher ionisation levels. The warmest clouds in our sample are Ophiuchus and Corona Australis, where star formation activity is higher than in the other clouds we targeted. The higher ionisation rates in these regions support the scenario that low-mass protostars in the vicinity of our targeted cores contribute to the re-acceleration of local cosmic rays.

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arXiv2025

ANTIHEROES-PRODIGE: Quantifying the connection from envelope to disk with the IRAM 30m telescope and NOEMA I. Attack of the streamers: L1448N's fight for order in the chaos

Star formation is a hierarchical process ranging from molecular clouds down to individual protostars. In particular how infalling asymmetric structures, called streamers, delivering new material onto protostellar systems, are connected to the surrounding envelope is not understood. We investigate the connection between the cloud material at 10000 au scales down to 300 au scales towards L1448N in the Perseus star-forming region hosting three young Class 0/I protostellar systems. Sensitive molecular line observations taken with the IRAM 30m telescope and NOEMA at 1.4 mm are used to study the kinematic properties in the region traced by the molecular lines. Several infalling streamers are associated with the protostellar systems, some of them traced by C18O and DCN, while one of them is bright in SO and SO2. The kinematic properties of the former streamers are consistent with the velocities observed at large envelope scales of 10000 au, while the latter case show different kinematics. The masses and infall rates of the streamers are 0.01 Msun and 0.01-0.1 Msun and 10^-6 Msun/yr and 5-18x10^-6 Msun/yr for IRS3A and IRS3C, respectively. The envelope mass in the L1448N region is ~16Msun, thus the mass of a single streamer is low compared to the envelope mass (<1%). However, compared to the estimated mass of the protostellar systems a single streamer could deliver up to 1% and 8-17% of mass towards IRS3A (M*~1.2 Msun) and IRS3C (M*~1 Msun), respectively. The rotational signatures of structures in L1448N are all connected - from the large-scale envelope, infalling streamers, down to the rotation of all three disks. Two of the three Class 0/I protostellar systems are still fed by this surrounding material, which can be associated to the remnant envelope. However, we also find a streamer that is bright in SO and SO2 towards IRS3C that could be connected to a nearby sulfur reservoir.

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arXiv2025

PRODIGE VI -- Envelope to Disk with NOEMA: VI. The Missing Sulfur Problem

Determining the amount of sulfur in volatiles and refractories in the ISM remains one of the main problems in astrochemistry. The detection of H$_2$S ices, which are thought to be one of the main sulfur reservoirs, has not been achieved yet, and the only S-bearing species detected in the ices to date is OCS. PRODIGE large survey observations with NOEMA of several Class 0/I protostars in the Perseus Molecular Cloud provide a perfect opportunity to study the H$_2$S and OCS composition of the ices through the volatiles sublimated in the warm inner core (T$>$100K, n $\sim10^6$cm$^{-3}$) of these protostars. Our aim is to determine the H$_2$S/OCS ratio in the warm inner core of 24 protostars in order to study how it is affected by different factors during its evolution. We used the NOEMA millimeter observations from the PRODIGE program of H$_2$S, H$_2^{33}$S, OCS, OC$^{33}$S and OC$^{34}$S to estimate the H$_2$S and OCS column densities in the warm inner cores. We used SO and SO$_2$ data from the ALMA archive to give a rough estimate of the total sulfur abundance. We explore the chemistry of H$_2$S and OCS in the warm cores using chemical and dynamical simulations of the collapse of a dense core to form a protostar. The estimated H$_2$S/OCS ratio reveals a segregation of the sources into ``OCS-poor'' and ``OCS-rich'' protostars, where the OCS-poor protostars present higher H$_2$S/OCS ratios than the OCS-rich ones. Total sulfur abundance is always dominated by either H$_2$S or OCS, grows with evolution during the Class 0 phase up to $D_S<8$, and decreases again in the Class I. Simulations show that temperature changes in the pre-stellar phase and during the collapse can produce substantial differences in the H$_2$S and OCS abundances and in the H$_2$S/OCS ratio. Our analysis shows that the H$_2$S/OCS ratio is strongly influenced by the environment and the initial conditions of the cloud.

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arXiv2025

PRODIGE - envelope to disk with NOEMA: V. Low 12C/13C ratios for CH3OH and CH3CN in hot corinos

The 12C/13C isotope ratio has been derived towards numerous cold clouds (20-50 K) and a couple protoplanetary disks and exoplanet atmospheres. However, direct measurements of this ratio in the warm gas (>100 K) around young low-mass protostars remain scarce, but are required to study its evolution during star and planet formation. We derived 12C/13C ratios from the isotopologues of the complex organic molecules (COMs) CH3OH and CH3CN in the warm gas towards seven Class 0/I protostellar systems to improve our understanding of the evolution of the 12C/13C ratios during star and planet formation. We used the data that were taken as part of the PRODIGE large program with the NOEMA at 1mm. The emission of CH3OH and CH3CN is spatially unresolved in the PRODIGE data (300au scale). Derived rotational temperatures exceed 100K, telling us that they trace the gas of the hot corino, where CH3CN probes hotter regions than CH3OH on average (290 K versus 180 K). The column density ratios between the 12C and 13C isotopologues, derived from LTE analysis, range from 4 to 30, thus, are significantly lower than the expected local ISM isotope ratio of about 68. Assuming that CH3CN and CH3OH may inherit the 12C/13C ratio from their precursor species, astrochemical models were conducted for the latter and compared with our observational results. We conclude that an enrichment in 13C in COMs at the earliest protostellar stages is likely inherited from the COMs' precursor species, whose 12C/13C ratios are set during the prestellar stage via isotopic exchange reactions. This also implies that low 12C/13C ratios observed at later evolutionary stages could at least partially be inherited. A final conclusion on 12C/13C ratios in protostellar environments requires improved observations to tackle current observational limitations and additional modelling efforts.

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arXiv2025

The Galactic-Centre Arms inferred from ACES (ALMA CMZ Exploration Survey)

Analyzing longitude-velocity diagrams (LVDs) in the CS(J=2-1) and H13CN(J=1-0) molecular lines from the internal release data of the ALMA Central-Molecular-Zone Exploration Survey (ACES) and in the 13CO (J=1-0) line from the Nobeyama Galactic-Centre (GC) survey, we identify six GC Arms as prominent straight LV ridges. In addition to the currently known Arms I to IV, we identify a new inner arm, Arm V, and further highlight the circum-nuclear disc (CND) as Arm VI. Integrated intensity maps of the Arms on the sky suggest that most of the Arms compose ring-like structures inclined from the Galactic plane. We determine the radii (curvatures) of the Arms using the velocity-gradient ($dv/dl$) method, assuming that the arms are rotating on circular orbits at a constant velocity of $\sim 150$ km/s. We show that Arms I and II compose the main ring structure of the CMZ with radii $\sim 100$--120 pc; Arm III is a dense arm 42 pc from the GC; Arm IV is a clear and narrow arm 20 pc from the GC; and Arm V is a faint, long arm of 8.2 pc radius. We show that the circum-nuclear disc (CND) composes the sixth arm, Arm VI, of radius $\sim 2.3$ pc associated with bifurcated spiral fins. We also discuss the association of the 20- and 50-km/s clouds with these Arms. The radii of the arms fall on an empirical relation $R\sim 630 (2/5)^N$ for $N=1$ (Arm I) to 6 (VI), suggesting either discrete rings or a logarithmic spiral with pitch angle $\sim 22^\circ$. The vertical full extent of the arm increases with radius and is represented by $z\sim 0.7 (R/1 {\rm pc})^{0.7}$ pc. The tilt angle of the arms from the Galactic plane, or the warping, increases rapidly toward the GC.

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arXiv2025

FAUST XXV. A potential new molecular outflow in [BHB2007] 11

During the early stages of star formation, accretion processes such as infall from the envelope and molecular streamers, and ejection of matter through winds and jets take place simultaneously. The Class 0/I binary [BHB2007] 11 shows evidence for accretion and ejection at the scales of the circumbinary disk and the inner close binary. Recent H$_2$CO observations showed two elongated structures with hints of outflowing motion almost perpendicular to the main CO outflow, which is launched from the circumbinary disk. With the aim of verifying the nature of these elongated structures, we analyze the line emission of H$^{13}$CO$^+$, CCH, c-C$_3$H$_2$ and SiO observed with ALMA within the Large Program FAUST. These molecules trace material moving at velocities close to the ambient cloud velocity. The images of H$^{13}$CO$^+$, CCH, c-C$_3$H$_2$ show the elongated structures, whose gas kinematics are consistent with outflowing motions and with rotation in the opposite sense to the main CO outflow. The derived mass loss rate from these large-scale structures is $(1.8\pm0.5)\times10^{-6}M_{\odot}\textrm{ yr}^{-1}$, in agreement with those measured in outflows driven by Class 0/I protostars. The SiO image reveals compact emission close to the binary system, with a slight elongation aligned with the larger-scale structures. This suggests that SiO is released from the sputtering of dust grains in the shocked material at the base of the potential new outflow, with a relative abundance of $\geq(0.11-2.0)\times10^{-9}$. However, higher angular and spectral resolution observations are needed to accurately estimate the outflow launching radius and its powering source. Given the location and the abundance of the SiO emission, we propose that the second outflow may be launched from inside the circumbinary disk, likely by the less massive companion, which is actively accreting material from its surroundings.

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arXiv2025

Hunting pre-stellar cores with APEX: Corona Australis 151, the densest pre-stellar core or the youngest protostar?

Context. Pre-stellar cores are the birthplaces of Sun-like stars and represent the initial conditions for the assembly of protoplanetary systems. Due to their short lifespans, they are rare. In recent efforts to increase the number of such sources identified in the Solar neighbourhood, we have selected a sample of 40 starless cores from the publicly available core catalogs of the Herschel Gould Belt survey. In this work, we focus on one of the sources that stands out for its high central density: Corona Australis 151. Aims. We use molecular lines that trace dense gas (n>=10^6 cm-3) to confirm the exceptionally high density of this object, to study its physical structure, and to understand its evolutionary stage. Methods. We detected the N2H+ 3-2 and 5-4 transitions, and the N2D+ 3-2, 4-3, and 6-5 lines with the APEX telescope. We use the Herschel continuum data to infer a spherically symmetric model of the core's density and temperature. This is used as input to perform non-local-thermodynamic-equilibrium radiative transfer to fit the observed five lines. Results. Our analysis confirms that this core is characterised by very high densities (a few x 10^7 cm-3 at the centre) and cold temperatures. We infer a high deuteration level of N2D+/N2H+=0.50, indicative of an advanced evolutionary stage. In the large bandwidth covered by the APEX data, we detect several other deuterated species, including CHD2OH, D2CO, and ND3. We also detect multiple sulphurated species that present broader lines with signs of high-velocity wings. Conclusions. The observation of high-velocity wings and the fact that the linewidths of N2H+ and N2D+ become larger with increasing frequency can be interpreted either as an indication of supersonic infall motions developing in the central parts of a very evolved pre-stellar core or as the signature of outflows from a very low luminosity object (VeLLO). *SHORTENED*

astro-ph.SR↗

arXiv2025

Resolved Gas Temperatures and 12C/13C ratios in SVS13A from ALMA Observations of CH3CN and CH3-13-CN

Context. Multiple systems are common in field stars, and the frequency is found to be higher in early evolutionary stages. Thus, the study of young multiple systems during the embedded stages is key to have a comprehensive understanding of star formation. In particular, how material accretes from the large-scale envelope into the inner region and how this flow interacts with the system physically and chemically has not yet been well characterized observationally. Aims. We aim to provide a snapshot of the forming protobinary system SVS13A, consisting of VLA4A and VLA4B. This includes clear pictures of its kinematic structures, physical conditions, and chemical properties. Methods. We conducted ALMA observations toward SVS13A targeting CH3CN and CH3-13CN J=12-11 K-ladder line emission with a high spatial resolution of ~30 au at a spectral resolution of ~0.08 km s-1 Results. We perform LTE radiative transfer models to fit the spectral features of the line emission. We find the two-layer LTE radiative model including dust absorption is essential to interpret the CH3CN and CH3-13-CN line emission. We identify two major and four small kinematic components, and derive their physical and chemical properties. Conclusions. We find a possible infalling signature toward the bursting secondary source VLA4A, which may be fed by an infalling streamer from the large-scale envelope. The mechanical heating in the binary system, as well as the infalling shocked gas, likely play a role in the thermal structure of the protobinary system. By accumulating mass from the streamer, the system might have experienced a gravitationally unstable phase before the accretion outburst. Finally, the derived CH3CN/CH3-13-CN ratio is lower than the canonical ratio in the ISM and is different between VLA4A and VLA4B.

astro-ph.GA↗

arXiv2024

Hunting pre-stellar cores with APEX: IRAS16293E (Oph464)

Pre-stellar cores are the first steps in the process of star and planet formation. However, the dynamical and chemical evolution of pre-stellar cores is still not well understood. We aim at estimating the central density of the pre-stellar core IRAS16293E and at carrying out an inventory of molecular species towards the density peak of the core. We observed high-$J$ rotational transitions of N$_2$H$^+$ and N$_2$D$^+$, and several other molecular lines towards the dust emission peak using the Atacama Pathfinder EXperiment (APEX) telescope, and derived the density and temperature profiles of the core using far-infrared surface brightness maps from $Herschel$. The N$_2$H$^+$ and N$_2$D$^+$ lines were analysed by non-LTE radiative transfer modelling. Our best-fit core model consists in a static inner region, embedded in an infalling envelope with an inner radius of approximately 3000 au (21" at 141 pc). The observed high-J lines of N$_2$H$^+$ and N$_2$D$^+$ (with critical densities greater than 10$^6$ cm$^{-3}$) turn out to be very sensitive to depletion; the present single-dish observations are best explained with no depletion of N$_2$H$^+$ and N$_2$D$^+$ in the inner core. The N$_2$D$^+$/N$_2$H$^+$ ratio that best reproduces our observations is 0.44, one of the largest observed to date in pre-stellar cores. Additionally, half of the molecules that we observed are deuterated isotopologues, confirming the high-level of deuteration towards this source. Non-LTE radiative transfer modelling of N$_2$H$^+$ and N$_2$D$^+$ lines proved to be an excellent diagnostic of the chemical structure and dynamics of a pre-stellar core. Probing the physical conditions immediately before the protostellar collapse is a necessary reference for theoretical studies and simulations with the aim of understanding the earliest stages of star and planet formation and the time scale of this process.

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