arXiv subjects

Ana López-Sepulcre

Publications and source records attributed to Ana López-Sepulcre.

At least 19 recordsLinked to original sources

arXiv2026

Chemical Complexity in the Early Stages of Star Formation in the SKAO Era

About 350 molecules have been identified in the interstellar medium (ISM), including complex molecules relevant to prebiotic chemistry. A remarkable level of molecular diversity has been observed from the earliest stages of star formation, providing the initial chemical inventory inherited by planetary systems. Radio observations have played a pivotal role in these discoveries, starting with the identification of the first polyatomic molecule, $\text{NH}_3$ (Cheung et al. 1968). (Sub-)millimeter observations have revealed complex organic molecules of prebiotic relevance, including formamide ($\text{NH}_2\text{CHO}$), glycolaldehyde ($\text{CH}_2\text{OHCHO}$), and even urea ($(\text{NH}_2)_2\text{CO}$), and hydroxylamine ($\text{NH}_2\text{OH}$), which are possible precursors of RNA nucleotides (Ceccarelli et al. 2023; Jiménez-Serra et al. 2020). However, in dense protostellar regions, dust opacity hampers the detection of molecular emission. Additionally, large molecules and those containing heavy atoms, which have rotational transitions at lower frequencies, often remain inaccessible to current instruments. The Square Kilometre Array Observatory (SKAO) will provide an unprecedented combination of sensitivity and angular resolution at radio wavelengths. This will allow for the detection of prebiotic species and offer new insights into the chemical pathways that shape emerging planetary systems (Jiménez-Serra et al. 2022). This chapter details the scientific questions and advancements that the SKAO, and more specifically, SKA-Mid equipped with the Band 5 receivers, will pursue in the field of astrochemistry, focusing on the chemical complexity in both high-mass and solar-type star-forming regions.

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arXiv2026

Unveiling Complex Chemistry in Planet-forming Disks with the SKAO

The chemical composition of planets is inherited from that of the natal protoplanetary disk at the time of planet formation. In recent years, we have made huge progress in characterizing disk chemistry. (Sub-)millimeter interferometers, such as ALMA, allowed us to detect emission lines from simple to complex organic molecules and to probe their radial and vertical distribution in disks. On the other hand, JWST has started to unveil the composition of disk ices, and line emission from the innermost disk regions. The advent of SKA will open new domains in the field, by observing emission lines from heavier molecules including heavy carbon chains and rings, and prebiotic molecules with peak emission in the cm range. Moreover, SKA will probe molecular emission from regions which are obscured by dust opacity at mm wavelengths, hence from the disk midplane, and often from the inner 30 au region. These observations will constrain the initial conditions for disk evolution and planet formation, allowing us to predict the chemical composition of the forming planets and their atmospheres. Comparison with forthcoming results on exoplanet atmospheres and on the chemistry of pristine bodies in the Solar System will provide new hints on the origin and evolution of planetary systems including our own.

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arXiv2025

FAUST XXIX. OCS line emission: a new method for measuring the luminosity of embedded protostars in binary systems

The luminosity of embedded protostars is commonly measured via observations of the dust continuum spectral energy distribution from millimetre to infrared wavelengths. However, this method cannot be applied to embedded protostars in binary or multiple systems, where their components are usually unresolved over this extended wavelength range. We propose a new method, based on the idea that a molecule formed (mainly) on the grain surfaces only emits lines in the region where it thermally sublimates from the grain mantles, heated by the photons emitted by the embedded source. In this respect, carbonyl sulfide (OCS) is an optimal molecule, because of its low binding energy and rotational lines in the millimetre. We apply the method to the protobinary system NGC1333 IRAS4A, using ALMA high-spatial resolution ($\sim$50 au) observations of the OCS(19-18) line as part of the ALMA Large Program FAUST. We also present new quantum mechanics calculations of the OCS binding energy distribution, essential for the application of the method. We found that the two binary components, A1 and A2, have a comparable luminosity within the error bars, 7.5$\pm$2.5 and 7$\pm$1 L$_\odot$, respectively. We discuss the reliability of the estimated luminosities and the potential of this new method for measuring the luminosity of embedded protostars in binary and multiple systems.

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arXiv2025

Glycolaldehyde and ethanol toward the L1157 outflow: resolved images and constraints on glycolaldehyde formation

Two main formation routes have been proposed for interstellar complex organic molecules (iCOMs): on dust grain surfaces and in the gas phase. Observing such molecules in protostellar outflow shock regions - provided that their ages are well-constrained - can help distinguish between these pathways by probing chemical evolution over time. This study focuses on the potential daughter-mother relationship of glycolaldehyde (CH$_2$OHCHO) and ethanol (C$_2$H$_5$OH), previously proposed in the literature. We test whether gas-phase reactions converting ethanol into glycolaldehyde derived in these works can explain the observed abundance of the latter in star-forming regions. We target the southern outflow of L1157, which hosts three shock regions, B0, B1 and B2, of increasing ages: about 900, 1500 and 2300 yr. We obtained high-resolution IRAM NOEMA maps of three lines of glycolaldehyde and one line of ethanol. We derived their abundances in the three shocks and used a pseudo time-dependent astrochemical model to simulate gas-phase and grain-surface formation scenarios for glycolaldehyde. Ethanol is assumed to form on grains and be released in the gas by shocks, where it is gradually converted into glycolaldehyde via the ethanol-tree reaction network. We present the first spatially resolved maps of glycolaldehyde and ethanol in the L1157 southern outflow, and more generally toward solar-like star forming regions. The abundance ratio [CH$_2$OHCHO]/[C$_2$H$_5$OH] increases from B1 to B2, consistent with model predictions. However, the model cannot reproduce all three shocked regions simultaneously, suggesting that one of the assumptions of our model, such as the same excitation temperature and grain composition in B0, B1 and B2, or gas temperature evolution, is wrong. Nonetheless, our modeling rules out the possibility that all the observed gaseous glycolaldehyde is a grain-surface product.

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arXiv2025

The evolution of CH in Planck Galactic Cold Clumps

Methylidyne (CH) has long been considered a reliable tracer of molecular gas in the low-to-intermediate extinction range. Although extended CH 3.3 GHz emission is commonly observed in diffuse and translucent clouds, observations in cold, dense clumps are rare. In this work, we conducted high-sensitivity CH observations toward 27 PGCCs with the Arecibo 305m telescope. Toward each source, the CH data were analyzed in conjunction with $^{13}$CO (1--0), HINSA, and H$_2$ column densities. Our results revealed ubiquitous subsonic velocity dispersions of CH, in contrast to $^{13}$CO, which is predominantly supersonic. The findings suggest that subsonic CH emissions may trace dense, low-turbulent gas structures in PGCCs. To investigate environmental effects, particularly the cosmic-ray ionization rate (CRIR), we estimated CRIR upper limits from HINSA, yielding values from $(8.1\pm4.7)\times10^{-18}$ to $(2.0\pm0.8)\times10^{-16}$ s$^{-1}$ ($N_{H_2}$ from $(1.7\pm0.2)\times10^{21}$ to $(3.6\pm0.4)\times10^{22}$~cm$^{-2}$). This result favors theoretical predictions of a cosmic-ray attenuation model, in which the interstellar spectra of low-energy CR protons and electrons match {\it Voyager} measurements, although alternative models cannot yet be ruled out. The abundance of CH decreases with increasing column density, while showing a positive dependence on the CRIR, which requires atomic oxygen not heavily depleted to dominate CH destruction in PGCCs. By fitting the abundance of CH with an analytic formula, we place constraints on atomic O abundance ($2.4\pm0.4\times10^{-4}$ with respect to total H) and C$^+$ abundance ($7.4\pm0.7\times10^{13}ζ_2/n_{\rm H_2}$). These findings indicate that CH formation is closely linked to the C$^+$ abundance, regulated by cosmic-ray ionization, while other processes, such as turbulent diffusive transport, might also contribute a non-negligible effect.

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arXiv2024

Full interferometric map of the L1157 southern outflow: Formamide (NH$_2$CHO) can form in the gas, after all

The formation mechanism of interstellar formamide (NH$_2$CHO), a key prebiotic precursor, is currently a matter of hot debate within the astrochemistry community, with both gas-phase and grain-surface chemical pathways having been proposed as its dominant formation route. The aim of the present study is to place firm observational constraints on the formation pathways leading to formamide thanks to new interferometric observations of the molecular outflow driven by the protostellar binary L1157. We employed the IRAM NOEMA interferometer to map the entire southern outflow of L1157, which contains three main shocked regions with increasing post-shock age: B0, B1, and B2. This allowed us to measure how the abundance of formamide, that of acetaldehyde (CH$_3$CHO), and the ratio of the two, vary with time in this region. In order to gain a greater understanding of the most likely formation routes of formamide, we ran a grid of astrochemical models and compared these to our observations. A comparison between observations and astrochemical modelling indicates that there are two possible scenarios: one in which the amount of formamide observed can be explained by gas-phase-only chemistry, and more specifically via the reaction H$_2$CO + NH$_2$ $\rightarrow$ NH$_2$CHO + H$_2$, and another in which part of the observed formamide originates from surface chemistry and part from gas-phase chemistry. Surface chemistry alone cannot account for the abundance of formamide that we measure. While grain-surface chemistry cannot be ruled out, the present study brings definitive proof that gas-phase chemistry does work in L1157-B and acts efficiently in the production of this molecular species.

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arXiv2024

FAUST XIX. D$_2$CO in the outflow cavities of NGC\,1333 IRAS\,4A: recovering the physical structure of its original prestellar core

Molecular deuteration is a powerful diagnostic tool for probing the physical conditions and chemical processes in astrophysical environments. In this work, we focus on formaldehyde deuteration in the protobinary system NGC\,1333 IRAS\,4A, located in the Perseus molecular cloud. Using high-resolution ($\sim$\,100\,au) ALMA observations, we investigate the [D$_2$CO]/[HDCO] ratio along the cavity walls of the outflows emanating from IRAS\,4A1. Our analysis reveals a consistent decrease in the deuteration ratio (from $\sim$\,60-20\% to $\sim$\,10\%) with increasing distance from the protostar (from $\sim$\,2000\,au to $\sim$\,4000\,au). Given the large measured [D$_2$CO]/[HDCO], both HDCO and D$_2$CO are likely injected by the shocks along the cavity walls into the gas-phase from the dust mantles, formed in the previous prestellar phase. We propose that the observed [D$_2$CO]/[HDCO] decrease is due to the density profile of the prestellar core from which NGC\,1333 IRAS\,4A was born. When considering the chemical processes at the base of formaldehyde deuteration, the IRAS\,4A's prestellar precursor had a predominantly flat density profile within 3000\,au and a decrease of density beyond this radius.

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arXiv2024

CH_3OH and Its Deuterated Species in the Disk/Envelope System of the Low-Mass Protostellar Source B335

Deuterium fractionation in the closest vicinity of a protostar is important in understanding its potential heritage to a planetary system. Here, we have detected the spectral line emission of CH3OH and its three deuterated species, CH2DOH, CHD2OH, and CH3OD, toward the low-mass protostellar source B335 at a resolution of 0.''03 (5 au) with Atacama Large Millimeter/submillimeter Array. They have a ring distribution within the radius of 24 au with the intensity depression at the continuum peak. We derive the column densities and abundance ratios of the above species at 6 positions in the disk/envelope system as well as the continuum peak. The D/H ratio of CH3OH is ~[0.03-0.13], which is derived by correcting the statistical weight of 3 for CH2DOH. The [CHD2OH]/[CH2DOH] ratio is derived to be higher ([0.14-0.29]). On the other hand, the [CH2DOH]/[CH3OD] ratio ([4.9-15]) is higher than the statistical ratio of 3, and is comparable to those reported for other low-mass sources. We study the physical structure on a few au scale in B335 by analyzing the CH3OH (183,15-182,16, A) and HCOOH (120,12-110,11) line emission. Velocity structures of these lines are reasonably explained as the infalling-rotating motion. The protostellar mass and the upper limit to centrifugal barrier are thus derived to be 0.03-0.07 M_{\odot} and <7 au, respectively, showing that B335 harbors a young protostar with a tiny disk structure. Such youth of the protostar may be related to the relatively high [CH2DOH]/[CH3OH] ratio.

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arXiv2024

Multiple chemical tracers finally unveil the intricate NGC\,1333 IRAS\,4A outflow system. FAUST XVI

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS\,4A protobinary system. This analysis is based on ALMA observations of SiO(5--4), H$_2$CO(3$_{0,3}$--2$_{0,3}$), and HDCO(4$_{1,4}$--3$_{1,3}$) with a spatial resolution of $\sim$150\,au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS\,4A1 and IRAS\,4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS\,4A1 exhibit extensions of 10$''$ and 13$''$ with position angles (PA) of 0$^{\circ}$ and -12$^{\circ}$, respectively, while those of IRAS\,4A2 are more extended, spanning 18$''$ and 25$''$ with PAs of 29$^{\circ}$ and 26$^{\circ}$. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

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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.

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arXiv2023

Streamers feeding the SVS13-A protobinary system: astrochemistry reveals accretion shocks?

We report ALMA high-angular resolution (~ 50 au) observations of the binary system SVS13-A. More specifically, we analyse deuterated water (HDO) and sulfur dioxide (SO2) emission. The molecular emission is associated with both the components of the binary system, VLA4A and VLA4B. The spatial distribution is compared to that of formamide (NH2CHO), previously analysed in the system. Deuterated water reveals an additional emitting component spatially coincident with the dust accretion streamer, at a distance larger than 120 au from the protostars, and at blue-shifted velocities (> 3 km/s from the systemic velocities). We investigate the origin of the molecular emission in the streamer, in light of thermal sublimation temperatures calculated using updated binding energies (BE) distributions. We propose that the observed emission is produced by an accretion shock at the interface between the accretion streamer and the disk of VLA4A. Thermal desorption is not completely excluded in case the source is actively experiencing an accretion burst.

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arXiv2022

Tracking the ice mantle history in the Solar-type Protostars of NGC 1333 IRAS 4

To understand the origin of the diversity observed in exoplanetary systems, it is crucial to characterize the early stages of their formation, represented by Solar-type protostars. Likely, the gaseous chemical content of these objects directly depends on the composition of the dust grain mantles formed before the collapse. Directly retrieving the ice mantle composition is challenging, but it can be done indirectly by observing the major components, such as NH3 and CH3OH at cm wavelengths, once they are released into the gas-phase during the warm protostellar stage. We observed several CH3OH and NH3 lines toward three Class 0 protostars in NGC1333 (IRAS 4A1, IRAS 4A2, and IRAS 4B), at high angular resolution (1"; ~300 au) with the VLA interferometer at 24-26 GHz. Using a non-LTE LVG analysis, we derived a similar NH3/CH3OH abundance ratio in the three protostars (<0.5, 0.015-0.5, and 0.003-0.3 for IRAS 4A1, 4A2, and 4B, respectively). Hence, we infer they were born from pre-collapse material with similar physical conditions. Comparing the observed abundance ratios with astrochemical model predictions, we constrained the dust temperature at the time of the mantle formation to be ~17 K, which coincides with the average temperature of the southern NGC 1333 diffuse cloud. We suggest that a brutal event started the collapse that eventually formed IRAS 4A1, 4A2 and 4B, which,therefore, did not experience the usual pre-stellar core phase. This event could be the clash of a bubble with NGC 1333 south, that has previously been evoked in the literature.

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arXiv2022

Chemical Differentiation and Temperature Distribution on a Few au Scale around the Protostellar Source B335

Resolving physical and chemical structures in the vicinity of a protostar is of fundamental importance for elucidating their evolution to a planetary system. In this context, we have conducted 1.2 mm observations toward the low-mass protostellar source B335 at a resolution of 0."03 with ALMA. More than 20 molecular species including HCOOH, NH2 CHO, HNCO, CH3 OH, CH2 DOH, CHD2 OH, and CH3 OD are detected within a few 10 au around the continuum peak. We find a systematic chemical differentiation between oxygen-bearing and nitrogen-bearing organic molecules by using the principal component analysis for the image cube data. The distributions of the nitrogen-bearing molecules are more compact than those of the oxygen-bearing ones except for HCOOH. The temperature distribution of the disk/envelope system is revealed by a multi-line analysis for each of HCOOH, NH2 CHO, CH3 OH, and CH2 DOH. The rotation temperatures at the radius of 0."06 along the envelope direction of CH3OH and CH2DOH are derived to be 150-165 K. On the other hand, those of HCOOH and NH2CHO, which have a smaller distribution, are 75-112 K, and are significantly lower than those for CH3OH and CH2DOH. This means that the outer envelope traced by CH3OH and CH2DOH is heated by additional mechanisms rather than the protostellar heating. We here propose the accretion shock as the heating mechanism. The chemical differentiation and the temperature structure on a few au scale provide us with key information to further understand chemical processes in protostellar sources.

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arXiv2022

CH$_3$CN deuteration in the SVS13-A Class I hot-corino. SOLIS XV

We studied the line emission from CH3CN and its deuterated isotopologue CH$_2$DCN towards the prototypical Class I object SVS13-A, where the deuteration of a large number of species has already been reported. Our goal is to measure the CH$_3$CN deuteration in a Class I protostar, for the first time, in order to constrain the CH$_3$CN formation pathways and the chemical evolution from the early prestellar core and Class 0 to the evolved Class I stages. We imaged CH2DCN towards SVS13-A using the IRAM NOEMA interferometer at 3mm in the context of the Large Program SOLIS (with a spatial resolution of 1.8"x1.2"). The NOEMA images have been complemented by the CH$_3$CN and CH$_2$DCN spectra collected by the IRAM-30m Large Program ASAI, that provided an unbiased spectral survey at 3mm, 2mm, and 1.3mm. The observed line emission has been analysed using LTE and non-LTE LVG approaches. The NOEMA/SOLIS images of CH2DCN show that this species emits in an unresolved area centered towards the SVS13-A continuum emission peak, suggesting that methyl cyanide and its isotopologues are associated with the hot corino of SVS13-A, previously imaged via other iCOMs. In addition, we detected 41 and 11 ASAI transitions of CH$_3$CN and CH2DCN, respectively, which cover upper level energies (Eup) from 13 to 442 K and from 18 K to 200 K, respectively. The derived [CH2DCN]/[CH3CN] ratio is $\sim$9\%. This value is consistent with those measured towards prestellar cores and a factor 2-3 higher than those measured in Class 0 protostars. Contrarily to what expected for other molecular species, the CH3CN deuteration does not show a decrease in SVS13-A with respect to measurements in younger prestellar cores and Class 0 protostars. Finally, we discuss why our new results suggest that CH3CN was likely synthesised via gas-phase reactions and frozen onto the dust grain mantles during the cold prestellar phase.

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arXiv2022

The two hot corinos of the SVS13-A protostellar binary system: counterposed siblings

We present ALMA high-angular resolution ($\sim$ 50 au) observations of the Class I binary system SVS13-A. We report images of SVS13-A in numerous interstellar complex organic molecules: CH$_{\rm 3}$OH, $^{13}$CH$_{\rm 3}$OH, CH$_{\rm 3}$CHO, CH$_{\rm 3}$OCH$_{\rm 3}$, and NH$_{\rm 2}$CHO. Two hot corinos at different velocities are imaged in VLA4A (V$_{sys}$= +7.7 km s$^{-1}$) and VLA4B (V$_{sys}$= +8.5 km s$^{-1}$). From a non-LTE analysis of methanol lines we derive a gas density of 3 $\times$ 10$^8$ cm$^{-3}$, and gas temperatures of 140 K and 170 K for VLA4A and VLA4B, respectively. For the other species the column densities are derived from a LTE analysis. Formamide, which is the only N-bearing species detected in our observations, is more prominent around VLA4A, while dimethyl ether, methanol and acetaldehyde are associated with both VLA4A and VLA4B. We derive in the two hot corinos abundance ratios of $\sim$ 1 for CH$_{\rm 3}$OH, $^{13}$CH$_{\rm 3}$OH, and CH$_{\rm 3}$OCH$_{\rm 3}$, $\sim$ 2 for CH$_{\rm 3}$CHO, and $\sim$ 4 for NH$_{\rm 2}$CHO. The present dataset supports a chemical segregation between the different species inside the binary system. The emerging picture is that of an onion-like structure of the two SVS13-A hot corinos, caused by the different binding energies of the species, also supported by ad hoc quantum chemistry calculations. In addition, the comparison between molecular and dust maps suggests that the interstellar complex organic molecules emission originates from slow shocks produced by accretion streamers impacting the VLA4A and VLA4B disks and enriching the gas-phase component.

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arXiv2022

A train of shocks at 3000 au scale? Exploring the clash of an expanding bubble into the NGC 1333 IRAS 4 region. SOLIS XIV

There is evidence that the star formation process is linked to the intricate net of filaments in molecular clouds, which may be also due to gas compression from external triggers. We studied the southern region of the Perseus NGC 1333 molecular cloud, known to be heavily shaped by similar external triggers, to shed light on the process that perturbed the filament where the Class 0 IRAS4 protostars lie. We use new IRAM-NOEMA observations of SiO and CH3OH, both known to trace violent events as shocks, toward IRAS 4A as part of the Large Program Seeds Of Life in Space (SOLIS). We detected three parallel elongated ($>$6000 au) structures, called fingers, with narrow line profiles (~1.5 $km s^{-1}$) peaked at the cloud systemic velocity, tracing gas with high density (5-20 $10^5 cm^{-3}$) and high temperature (80-160 K). They are chemically different, with the northern finger traced by both SiO and CH3OH ([CH3OH]/[SiO]~160-300), while the other two only by SiO ([CH3OH]/[SiO]$<$ 40). Among various possibilities, a train of three shocks, distanced by $>$5000 yr, would be consistent with the observations if a substantial fraction of silicon, frozen onto the grain mantles, is released by the shocks.We suggest that the shock train is due to an expanding gas bubble, coming behind NGC 1333 from the southwest and clashing against the filament, where IRAS 4A lies. Finally, we propose a solution to the two-decades long debate on the nature and origin of the widespread narrow SiO emission observed in the south part of NGC 1333, namely that it is due to unresolved trains of shocks.

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arXiv2022

FAUST III. Misaligned rotations of the envelope, outflow, and disks in the multiple protostellar system of VLA 1623$-$2417

We report a study of the low-mass Class-0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H$^{13}$CO$^+$ ($J=3-2$), CS ($J=5-4$), and CCH ($N=3-2$) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circum-binary VLA 1623A disk as well as the VLA 1623B disk. We found that the minor axis of the circum-binary disk of VLA 1623A is misaligned by about 12 degrees with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circum-binary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be $5-16$ au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circum-binary disk. The origin of its opposite gradient is also discussed.

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arXiv2022

Seeds of Life in Space (SOLIS). XIII. Nitrogen fractionation towards the protocluster OMC-2 FIR4

Isotopic fractionation is an important tool to investigate the chemical history of our Solar System (SS). In particular, the isotopic fraction of nitrogen (14N/15N) is lower in comets and other pristine SS bodies with respect to the value measured for the protosolar nebula, suggesting a local chemical enrichment of 15N during the SS formation. Therefore, interferometric studies of nitrogen fractionation in SS precursors are imperative for us to obtain clues about our astrochemical origins. In this work, we investigated the variation of the 14N/15N ratio in one of the closest analogues of the environment in which the SS was born: the protocluster OMC-2 FIR4. We present the first comparison at high angular resolution between HCN and N2H+ using interferometric data. We analysed observations of the HCN isotopologues H13CN and HC15N in the OMC-2 FIR4 protocluster, specifically the transitions H13CN (1-0) and HC15N (1-0), from NOEMA within the context of the IRAM Seeds Of Life In Space Large Program. We combined our results with analysis of archival data obtained with ALMA of N2H+ and its 15N isotopologues. Our results show a small regional variation in the ratio for HCN from ~250 to 500. The ratios in the central regions of FIR4, where the candidate protostars are located, are largely consistent (~300). They also show little variation from the part of the protocluster known to harbour a high cosmic-ray ionisation rate, to the portion with lower rate. We also found a small variation in the ratio of N2H+ across different regions from ~200 to ~400. These results suggest that local changes in the physical parameters occurring on small linear scales probed by our observations do not seem to affect the 14N/15N ratio in either HCN or N2H+ and hence that this is independent of the molecule used. Moreover, the high level of irradiation due to cosmic rays does not affect the N-fractionation either.

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