arXiv subjects

Paola Caselli

Publications and source records attributed to Paola Caselli.

At least 91 records · Page 5Linked to original sources

arXiv2023

Infall of material onto the filaments in Barnard 5

Aims. We aim to study the structure and kinematics of the two filaments inside the subsonic core Barnard 5 in Perseus using high-resolution ($\approx$ 2400 au) NH3 data and a multi-component fit analysis. Methods. We used observations of NH3 (1,1) and (2,2) inversion transitions using the Very Large Array (VLA) and the Green Bank Telescope (GBT). We smoothed the data to a beam of 8'' to reliably fit multiple velocity components towards the two filamentary structures identified in B5. Results. Along with the core and cloud components, which dominate the flux in the line of sight, we detected two components towards the two filaments showing signs of infall. We also detected two additional components that can possibly trace new material falling into the subsonic core of B5. Conclusions. Following comparison with previous simulations of filament formation scenarios in planar geometry, we conclude that either the formation of the B5 filaments is likely to be rather cylindrically symmetrical or the filaments are magnetically supported. We also estimate infall rates of $1.6\times10^{-4}\,M_\odot\,yr^{-1}$ and $1.8\times10^{-4}\,M_\odot\,yr^{-1}$ (upper limits) for the material being accreted onto the two filaments. At these rates, the filament masses can change significantly during the core lifetime. We also estimate an upper limit of $3.5\times10^{-5}\,M_\odot\,yr^{-1}$ for the rate of possible infall onto the core itself. Accretion of new material onto cores indicates the need for a significant update to current core evolution models, where cores are assumed to evolve in isolation.

astro-ph.GA↗

arXiv2023

Rotational spectroscopic characterisation of the [D2,C,S] system: an update from the laboratory and theory

The synergy between high-resolution rotational spectroscopy and quantum-chemical calculations is essential for exploring future detection of molecules, especially when spectroscopy parameters are not available yet. By using highly correlated ab initio quartic force fields (QFFs) from explicitly correlated coupled cluster theory, a complete set of rotational constants and centrifugal distortion constants for D$_2$CS and cis/trans-DCSD isomers have been produced. Comparing our new ab initio results for D$_2$CS with new rotational spectroscopy laboratory data for the same species, the accuracy of the computed B and C rotational constants is within 0.1% while the A constant is only slightly higher. Additionally, quantum chemical vibrational frequencies are also provided, and these spectral reference data and new experimental rotational lines will provide additional references for potential observation of these deuterated sulfur species with either ground-based radio telescopes or space-based infrared observatories.

astro-ph.IM↗

arXiv2023

Nuclear spin ratios of deuterated ammonia in prestellar cores. LAsMA observations of H-MM1 and Oph D

We determine the ortho/para ratios of NH2D and NHD2 in two dense, starless cores, where their formation is supposed to be dominated by gas-phase reactions, which, in turn, is predicted to result in deviations from the statistical spin ratios. The Large APEX sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama Pathfinder EXperiment (APEX) telescope was used to observe the prestellar cores H-MM1 and Oph D in Ophiuchus in the ground-state lines of ortho and para NH2D and NHD2. The fractional abundances of these molecules were derived employing 3D radiative transfer modelling, using different assumptions about the abundance profiles as functions of density. We also ran gas-grain chemistry models with different scenarios concerning proton or deuteron exchanges and chemical desorption from grains to find out if one of these models can reproduce the observed spin ratios. The observationally deduced ortho/para ratios of NH2D and NHD2 are in both cores within 10% of their statistical values 3 and 2, respectively, and taking 3-sigma limits, deviations from these of about 20% are allowed. Of the chemistry models tested here, the model that assumes proton hop (as opposed to full scrambling) in reactions contributing to ammonia formation, and a constant efficiency of chemical desorption, comes nearest to the observed abundances and spin ratios. The nuclear spin ratios derived here are in contrast with spin-state chemistry models that assume full scrambling in proton donation and hydrogen abstraction reactions leading to deuterated ammonia. The efficiency of chemical desorption influences strongly the predicted abundances of NH3, NH2D, and NHD2, but has a lesser effect on their ortho/para ratios. For these the proton exchange scenario in the gas is decisive. We suggest that this is because of rapid re-processing of ammonia and related cations by gas-phase ion-molecule reactions.

astro-ph.GA↗

arXiv2023

Exploring the dust grain size and polarization mechanism in the hot and massive Class 0 disk IRAS 16293-2422 B

Multiwavelength dust continuum and polarization observations arising from self-scattering have been used to investigate grain sizes in young disks. However, the polarization by self-scattering is low in face-on optically thick disks and puts some of the size constraints from polarization on hold, particularly for the younger and more massive disks. The 1.3 mm emission detected toward the hot ($\gtrsim$400 K) Class 0 disk IRAS 16293-2422 B has been attributed to self-scattering, predicting grain sizes between 200-2000 $μ$m. We investigate the effects of grain size in the resultant flux and polarization fractions from self-scattering using a hot and massive Class 0 disk model and compare with observations. We compared new and archival high-resolution observations between 1.3 and 18 mm to a set of synthetic models. We have developed a new public tool to automate this process called Synthesizer. This is an easy-to-use program to generate synthetic observations from numerical simulations. Optical depths are in the range of 130 to 2 from 1.3 to 18 mm, respectively. Predictions from significant grain growth populations, including millimetric grains are comparable to the observations at all wavelengths. The polarization fraction produced by self-scattering reaches a maximum of $\sim$0.1% at 1.3 mm for a maximum grain size of 100 $μ$m, being an order of magnitude lower than that observed with ALMA. From the comparison of Stokes I fluxes, we conclude that significant grain growth could be present in the young Class 0 disk IRAS 16293 B, particularly in the inner hot region ($<10$ au, $T>$ 300 K) where refractory organics evaporate. The polarization produced by self-scattering in our model is not high enough to explain the observations at 1.3 and 7 mm, and effects like dichroic extinction or polarization reversal of elongated aligned grains remain other possible but untested scenarios.

astro-ph.SR↗

arXiv2023

TRAO Survey of Nearby Filamentary Molecular clouds, the Universal Nursery of Stars (TRAO-FUNS). III. Filaments and dense cores in the NGC 2068 and NGC 2071 regions of Orion B

We present the results of molecular line observations performed toward the NGC 2068 and NGC 2071 regions of the Orion B cloud as the TRAO-FUNS project to study the roles of the filamentary structure in the formation of dense cores and stars in the clouds. Gaussian decomposition for the C$^{18}$O spectra with multiple velocity components and application of a Friends-of-Friends algorithm for the decomposed components allowed us to identify a few tens of velocity coherent filaments. We also identified 48 dense cores from the observations of N$_2$H$^{+}$ using a core finding tool, FellWalker. We made the virial analysis for these filaments and dense cores, finding that the filaments with N$_2$H$^{+}$ dense core are thermally supercritical, and the filaments with larger ratio between the line mass and the thermal critical line mass tend to have more dense cores. We investigated the contribution of the nonthermal motions in dense cores and filaments, showing the dense cores are mostly in transonic/subsonic motions while their natal filaments are mostly in supersonic motions. This may indicates that gas turbulent motions in the filaments have been dissipated at the core scale to form the dense cores there. The filaments with (dynamically evolved) dense cores in infalling motions or with NH$_2$D bright (or chemically evolved) dense cores are all found to be gravitationally critical. Therefore, the criticality of the filament is thought to provide a key condition for its fragmentation, the formation of dense cores, and their kinematical and chemical evolution.

astro-ph.GA↗

arXiv2023

FAUST X: Formaldehyde in the Protobinary System [BHB2007] 11: Small Scale Deuteration

Context. Deuterium in H-bearing species is enhanced during the early stages of star formation, however, only a small number of high spatial resolution deuteration studies exist towards protostellar objects, leaving the small-scale structures unrevealed and understudied. Aims. We aim to constrain the deuterium fractionation ratios in a Class 0/I protostellar object in formaldehyde (H2CO), which has abundant deuterated isotopologues in this environment. Methods. We observed the Class 0/I protobinary system [BHB2007] 11, whose emission components are embedded in circumstellar disks that have radii of 2-3 au, using ALMA within the context of the Large Program FAUST. The system is surrounded by a complex filamentary structure connecting to the larger circumbinary disk. In this work we present the first study of formaldehyde D-fractionation towards this source with detections of H2CO 3(0,3)-2(0,2), combined with HDCO 4(2,2)-3(2,1), HDCO 4(1,4)-3(1,3) and D2CO 4(0,4)-3(0,3). These observations enable multiple velocity components associated with the methanol hotspots also uncovered by FAUST data, as well as the external envelope, to be resolved. In addition, based on the kinematics seen in the observations of the H2CO emission, we propose the presence of a second large scale outflow. Results. HDCO and D2CO are only found in the central regions of the core while H2CO is found more ubiquitously. From radiative transfer modelling, the column densities ranges found for H2CO, HDCO and D2CO are (3-8)x10$^{14}$ cm$^{-2}$, (0.8-2.9)x10$^{13}$ cm$^{-2}$ and (2.6-4.3)x10$^{12}$ cm$^{-2}$, respectively, yielding an average D/H ratio of 0.01-0.04. Following the results of kinematic modelling, the second large scale feature is inconsistent with a streamer-like nature and we thus tentatively conclude that the feature is an asymmetric molecular outflow launched by a wide-angle disk wind.

astro-ph.GA↗

arXiv2023

Gas phase Elemental abundances in Molecular cloudS (GEMS). IX. Deuterated compounds of H2S in starless cores

H2S is thought to be the main sulphur reservoir in the ice, being therefore a key molecule to understand sulphur chemistry in the star formation process and to solve the missing sulphur problem. The H2S deuterium fraction can be used to constrain its formation pathways. We investigate for the first time the H2S deuteration in a large sample of starless cores (SC). We use observations of the GEMS IRAM 30m Large Program and complementary IRAM 30m observations. We consider a sample of 19 SC in Taurus, Perseus, and Orion, detecting HDS in 10 and D2S in five. The H2S single and double deuterium fractions are analysed with regard to their relation with the cloud physical parameters, their comparison with other interstellar sources, and their comparison with deuterium fractions in early stage star-forming sources of c-C3H2, H2CS, H2O, H2CO, and CH3OH. We obtain a range of X(HDS)/X(H2S)~0.025-0.2 and X(D2S)/X(HDS)~0.05-0.3. H2S single deuteration shows an inverse relation with the cloud kinetic temperature. H2S deuteration values in SC are similar to those observed in Class 0. Comparison with other molecules in other sources reveals a general trend of decreasing deuteration with increasing temperature. In SC and Class 0 objects H2CS and H2CO present higher deuteration fractions than c-C3H2, H2S, H2O, and CH3OH. H2O shows single and double deuteration values one order of magnitude lower than those of H2S and CH3OH. Differences between c-C3H2, H2CS and H2CO deuterium fractions and those of H2S, H2O, and CH3OH are related to deuteration processes produced in gas or solid phases, respectively. We interpret the differences between H2S and CH3OH deuterations and that of H2O as a consequence of differences on the formation routes in the solid phase, particularly in terms of the different occurrence of the D-H and H-D substitution reactions in the ice, together with the chemical desorption processes.

astro-ph.GA↗

arXiv2023

Initial conditions of star formation at $\lesssim$2000 au: physical structure and NH$_{3}$ depletion of three early-stage cores

Pre-stellar cores represent a critical evolutionary phase in low-mass star formation. We aim to unveil the detailed thermal structure and density distribution of three early-stage cores, starless core L1517B, and prestellar core L694-2 and L429, with the high angular resolution observations of the NH$_{3}$ (1,1) and (2,2) inversion transitions obtained with VLA and GBT. In addition, we explore where/if NH$_{3}$ depletes in the central regions. Applying the mid-infrared extinction method to the $\textit{Spitzer}$ 8$~μ$m map we obtain a high angular resolution hydrogen column density map, and derive the gas density profile to assess the variation of NH$_{3}$ abundance as a function of gas volume density. The measured temperature profiles of L429 and L1517B show a minor decrease towards the core center, dropping from $\sim$9K to below 8K, and $\sim$11 K to 10 K, while L694-2 has a rather uniform temperature distribution around $\sim$9 K. Among the three cores, L429 has the highest central gas density, close to sonic velocity line-width, and largest localised velocity gradient, all indicative of an advanced evolutionary stage. We resolve that the abundance of NH$_{3}$ becomes two times lower in the central region of L429, occurring around a gas density of 4.4$\times$10$^{4}$$~cm^{-3}$. Compared to Ophiuchus/H-MM1 which shows an even stronger drop of the NH$_{3}$ abundance at 2$\times$10$^{5}$$~cm^{-3}$, the abundance variations of the three cores plus Ophiuchus/H-MM1 suggest a progressive NH$_{3}$ depletion with increasing central density of the core.

astro-ph.GA↗

arXiv2023

Gas phase Elemental abundances in Molecular cloudS (GEMS) VIII. Unlocking the CS chemistry: the CH + S$\rightarrow$ CS + H and C$_2$ + S$\rightarrow$ CS + C reactions

We revise the rates of reactions CH + S -> CS + H and C_2 + S -> CS + C, important CS formation routes in dark and diffuse warm gas. We performed ab initio calculations to characterize the main features of all the electronic states correlating to the open shell reactants. For CH+S we have calculated the full potential energy surfaces for the lowest doublet states and the reaction rate constant with a quasi-classical method. For C_2+S, the reaction can only take place through the three lower triplet states, which all present deep insertion wells. A detailed study of the long-range interactions for these triplet states allowed to apply a statistic adiabatic method to determine the rate constants. This study of the CH + S reaction shows that its rate is nearly independent on the temperature in a range of 10-500 K with an almost constant value of 5.5 10^{-11} cm^3/s at temperatures above 100~K. This is a factor \sim 2-3 lower than the value obtained with the capture model. The rate of the reaction C_2 + S depends on the temperature taking values close to 2.0 10^{-10} cm^3/s at low temperatures and increasing to 5. 10^{-10} cm^3/s for temperatures higher than 200~K. Our modeling provides a rate higher than the one currently used by factor of \sim 2. These reactions were selected for involving open-shell species with many degenerate electronic states, and the results obtained in the present detailed calculations provide values which differ a factor of \sim 2-3 from the simpler classical capture method. We have updated the sulphur network with these new rates and compare our results in the prototypical case of TMC1 (CP). We find a reasonable agreement between model predictions and observations with a sulphur depletion factor of 20 relative to the sulphur cosmic abundance, but it is not possible to fit all sulphur-bearing molecules better than a factor of 10 at the same chemical time.

astro-ph.GA↗

arXiv2023

Coagulation-Fragmentation Equilibrium for Charged Dust: Abundance of Submicron Grains Increases Dramatically in Protoplanetary Disks

Dust coagulation in protoplanetary disks is not straightforward and is subject to several slow-down mechanisms, such as bouncing, fragmentation and radial drift to the star. Furthermore, dust grains in UV-shielded disk regions are negatively charged due to collisions with the surrounding electrons and ions, which leads to their electrostatic repulsion. For typical disk conditions, the relative velocities between micron-size grains are small and their collisions are strongly affected by the repulsion. On the other hand, collisions between pebble-size grains can be too energetic, leading to grain fragmentation. The aim of the present paper is to study a combined effect of the electrostatic and fragmentation barriers on dust evolution. We numerically solve the Smoluchowski coagulation-fragmentation equation for grains whose charging occurs under conditions typical for the inner disk regions, where thermal ionization operates. We find that dust fragmentation efficiently resupplies the population of small grains under the electrostatic barrier. As a result, the equilibrium abundance of sub-micron grains is enhanced by several orders of magnitude compared to the case of neutral dust. For some conditions with fragmentation velocities $\sim 1$ m s$^{-1}$, macroscopic grains are completely destroyed.

astro-ph.SR↗

arXiv2023

Measurements of rate coefficients of CN$^+$, HCN$^+$ and HNC$^+$ collisions with H$_2$ at cryogenic temperatures

The experimental determination of the reaction rate coefficients for production and destruction of $\text{HCN}^+$ and $\text{HNC}^+$ in collisions with $\text{H}_2$ is presented. A variable temperature 22 pole radio frequency ion trap was used to study the reactions in the temperature range of $17 - 250\;\text{K}$. The obtained rate coefficients for the reaction of $\text{CN}^+$ and of $\text{HCN}^+$ with $\text{H}_2$ are close to the collisional (Langevin) value, whereas that for the reaction of $\text{HNC}^+$ with $\text{H}_2$ is quickly decreasing with increasing temperature. The product branching ratios for the reaction of $\text{CN}^+$ with $\text{H}_2$ are also reported and show a notable decrease of $\text{HNC}^+$ product with respect to $\text{HCN}^+$ product with increasing temperature. These measurements have consequences for current astrochemical models of cyanide chemistry, in particular for the $\text{HCNH}^+$ cation.

astro-ph.GA↗

arXiv2023

Cold CAS Ion Trap -- 22 pole trap with ring electrodes for astrochemistry

The enhancement of a cryogenic radio frequency 22 pole trap instrument by the addition of ring electrodes is presented in detail. The ring electrodes tightly surround the poles and only a fraction of the applied electric potential penetrates to the trap axis, facilitating the fine control of slow cold ions. A precise computational model, describing the effective mechanical potential created by the applied static and rf fields, governing the ion behaviour, is employed to demonstrate and understand the operation of our setup. The use of ring electrodes for improved extraction of cold stored ions is shown. Variable trapping potentials, placed on one ring electrode, can be used to control the evaporation of only those $\text{H}^+$ ions from the trap, whose kinetic energy exceeds the barrier. This ring electrode trapping opens new possibilities to study processes of minimal kinetic energy release, e. g. spin exchange. We propose a robust modified method for the determination of temperature dependent ion molecule reaction rates, resistant to effects caused by neutral gas freezing and demonstrate it on the reaction of $\text{CO}^+$/$\text{CO}_2^+$ with $\text{H}_2$/$\text{D}_2$. Finally, the use of a supercontinuum laser for quick localisation of spectroscopic bands is examined on the $\text{N}_2^+$ Meinel system.

physics.chem-ph↗

arXiv2023

Nitrogen fractionation in ammonia and its insights on nitrogen chemistry

Context. Observations of $\rm ^{14}N/^{15}N$ in the interstellar medium are becoming more frequent thanks to the increased telescope capabilities. However, interpreting these data is still puzzling. In particular, measurements of $\rm ^{14}N/^{15}N$ in diazenylium revealed high levels of anti-fractionation in cold cores. Aims. Furuya & Aikawa (2018), using astrophysical simulations coupled with a gas-grain chemical code, concluded that the $^{15}$N-depletion in prestellar cores could be inherited from the initial stages, when $\rm ^{14}N^{15}N$ is selectively photodissociated and 15N atoms deplete onto the dust grain, forming ammonia ices. We aim to test this hypothesis. Methods. We targeted three sources (the prestellar core L1544, the protostellar envelope IRAS4A, and the shocked region L1157-B1) with distinct degrees of desorption or sputtering of the ammonia ices. We observed the NH3 isotopologues with the GBT, and we inferred the $\rm ^{14}N/^{15}N$ via a spectral fitting of the observed inversion transitions. Results. $^{15}$NH3(1,1) is detected in L1544 and IRAS4A, whilst only upper limits are deduced in L1157-B1. The NH3 isotopic ratio is significantly lower towards the protostar than at the centre of L1544, where it is consistent with the elemental value. We also present the first spatially resolved map of NH3 nitrogen isotopic ratio towards L1544. Conclusions. Our results are in agreement with the hypothesis that ammonia ices are enriched in $^{15}$N, leading to a decrease of the $\rm ^{14}N/^{15}N$ ratio when the ices are sublimated into the gas phase for instance due to the temperature rise in protostellar envelopes. The ammonia $\rm ^{14}N/^{15}N$ value at the centre of L1544 is a factor of 2 lower than that of N2H+, suggesting that the dominant formation pathway is hydrogenation of N atoms on dust grains, followed by non-thermal desorption.

astro-ph.GA↗

arXiv2023

Implementation of chemistry in the Athena++ code

Chemistry plays a key role in many aspects of astrophysical fluids. Atoms and molecules are agents for heating and cooling, determine the ionization fraction, serve as observational tracers, and build the molecular foundation of life. We present the implementation of a chemistry module in the publicly available magneto-hydrodynamic code Athena++. We implement several chemical networks and heating and cooling processes suitable for simulating the interstellar medium (ISM). A general chemical network framework in the KIDA format is also included, allowing the user to easily implement their own chemistry. Radiation transfer and cosmic-ray ionization are coupled with chemistry and solved with the simple six-ray approximation. The chemical and thermal processes are evolved as a system of coupled ODEs with an implicit solver from the CVODE library. We perform and present a series of tests to ensure the numerical accuracy and convergence of the code. Many tests combine chemistry with gas dynamics, including comparisons with analytic solutions, 1D problems of the photo-dissociation regions and shocks, and realistic 3D simulations of the turbulent ISM. We release the code with the new public version of Athena++, aiming to provide a robust and flexible code for the astrochemical simulation community.

astro-ph.GA↗

arXiv2023

Chemical Differentiation around Five Massive Protostars Revealed by ALMA -Carbon-Chain Species, Oxygen-/Nitrogen-Bearing Complex Organic Molecules-

We present Atacama Large Millimeter/submillimeter Array Band 3 data toward five massive young stellar objects (MYSOs), and investigate relationships between unsaturated carbon-chain species and saturated complex organic molecules (COMs). An HC$_{5}$N ($J=35-34$) line has been detected from three MYSOs, where nitrogen(N)-bearing COMs (CH$_{2}$CHCN and CH$_{3}$CH$_{2}$CN) have been detected. The HC$_{5}$N spatial distributions show compact features and match with a methanol (CH$_{3}$OH) line with an upper-state energy around 300 K, which should trace hot cores. The hot regions are more extended around the MYSOs where N-bearing COMs and HC$_{5}$N have been detected compared to two MYSOs without these molecular lines, while there are no clear differences in the bolometric luminosity and temperature. We run chemical simulations of hot-core models with a warm-up stage, and compare with the observational results. The observed abundances of HC$_{5}$N and COMs show good agreements with the model at the hot-core stage with temperatures above 160 K. These results indicate that carbon-chain chemistry around the MYSOs cannot be reproduced by warm carbon-chain chemistry, and a new type of carbon-chain chemistry occurs in hot regions around MYSOs.

astro-ph.GA↗

arXiv2023

3D Radiative Transfer Modelling and Virial Analysis of Starless Cores in the B10 Region of the Taurus Molecular Cloud

Low-mass stars like our Sun begin their evolution within cold (10 K) and dense ($\sim 10^5$ cm$^{-3}$) cores of gas and dust. The physical structure of starless cores is best probed by thermal emission of dust grains. We present a high resolution dust continuum study of the starless cores in the B10 region of the Taurus Molecular Cloud. New observations at 1.2mm and 2.0mm ($12^{"}$ and $18^{"}$ resolution) with the NIKA2 instrument on the IRAM 30m have probed the inner regions of 14 low-mass starless cores. We perform sophisticated 3D radiative transfer modelling for each of these cores through the radiative transfer framework $\textit{pandora}$, which utilizes RADMC-3D. Model best-fits constrain each cores' central density, density slope, aspect ratio, opacity, and interstellar radiation field strength. These `typical' cores in B10 span central densities from $5 \times 10^4 - 1 \times 10^6$ cm$^{-3}$, with a mean value of $2.6 \times 10^5$ cm$^{-3}$. We find the dust opacity laws assumed in the 3D modelling, as well as the estimates from $\textit{Herschel}$, have dust emissivity indices, $β$'s, on the lower end of the distribution constrained directly from the NIKA2 maps, which averages to $β= 2.01\pm0.48$. From our 3D density structures and archival NH$_3$ data, we perform a self-consistent virial analysis to assess each core's stability. Ignoring magnetic field contributions, we find 9 out of the 14 cores ($64\%$) are either in virial equilibrium or are bound by gravity and external pressure. To push the bounded cores back to equilibrium, an effective magnetic field difference of only $\sim 15 μ$G is needed.

astro-ph.GA↗

arXiv2023

FAUST VII. Detection of A Hot Corino in the Prototypical Warm Carbon-Chain Chemistry Source IRAS 15398-3359

We have observed the low-mass protostellar source, IRAS 15398$-$3359, at a resolution of 0.$''$2-0.$''$3, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST, to examine the presence of a hot corino in the vicinity of the protostar. We detect nine CH$_3$OH lines including the high excitation lines with upper state energies up to 500 K. The CH$_3$OH rotational temperature and the column density are derived to be 119$^{+20}_{-26}$ K and 3.2$^{+2.5}_{-1.0}\times$10$^{18}$ cm$^{-2}$, respectively. The beam filling factor is derived to be 0.018$^{+0.005}_{-0.003}$, indicating that the emitting region of CH$_3$OH is much smaller than the synthesized beam size and is not resolved. The emitting region of three high excitation lines, 18$_{3,15}-18_{2,16}$, A ($E_u=$447 K), 19$_{3,16}-19_{2,17}$, A ($E_u=$491 K), and 20$_{3,17}-20_{2,18}$, A ($E_u=$537 K), is located within the 50 au area around the protostar, and seems to have a slight extension toward the northwest. Toward the continuum peak, we also detect one emission line from CH$_2$DOH and two features of multiple CH$_3$OCHO lines. These results, in combination with previous reports, indicate that IRAS 15398$-$3359 is a source with hybrid properties showing both hot corino chemistry rich in complex organic molecules on small scales $\sim$10 au) and warm carbon-chain chemistry (WCCC) rich in carbon-chain species on large scales ($\sim$100-1000 au). A possible implication of the small emitting region is further discussed in relation to the origin of the hot corino activity.

astro-ph.SR↗

arXiv2023

The kinematics of the magnetised protostellar core IRAS15398-3359

Observations of protostellar envelopes are essential to understand better the process of gravitational collapse toward star and planet formation. From a theoretical perspective, magnetic fields are considered an important factor during the early stages of star formation, especially during the main accretion phase. We aim to study the relation between kinematics and magnetic fields at a very early stage of the star formation process by using data from the Atacama Pathfinder EXperiment (APEX) single dish antenna with the angular resolution of 28". We observed the two molecular lines C18O(2-1) and DCO+(3-2), toward the Class 0 young stellar object IRAS15398-3359. We implement a multi-component Gaussian fitting on the molecular data to study the kinematics. Also, we use previous polarization observations on this source to predict the influence of the magnetic field on the core. The velocity gradient along the central object can be explained as an ongoing outflow motion. We report flowing of material from the filament toward the central object, and of the merging of two velocity components in the C18O (2-1) emission around the protostar position, probably due to the merging of filamentary clouds. Our analysis shows that the large-scale magnetic field line observed previously is preferentially aligned to the rotation axis of the core.

astro-ph.GA↗