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Owing to their similarities with giant exoplanets, brown dwarf companions of stars provide insights into the fundamental processes of planet formation and evolution. From their orbits, several brown dwarf companions are found to be more massive than theoretical predictions given their luminosities and the ages of their host stars (e.g. Brandt et al. 2021, Cheetham et al. 2018, Li et al. 2023). Either the theory is incomplete or these objects are not single entities. For example, they could be two brown dwarfs each with a lower mass and intrinsic luminosity (Brandt et al. 2021, Howe et al. 2024). The most problematic example is Gliese 229 B (Nakajima et al. 1995, Oppenheimer et al. 1995), which is at least 2-6 times less luminous than model predictions given its dynamical mass of $71.4\pm0.6$ Jupiter masses ($M_{\rm Jup}$) (Brandt et al. 2021). We observed Gliese 229 B with the GRAVITY interferometer and, separately, the CRIRES+ spectrograph at the Very Large Telescope. Both sets of observations independently resolve Gliese 229 B into two components, Gliese 229 Ba and Bb, settling the conflict between theory and observations. The two objects have a flux ratio of $0.47\pm0.03$ at a wavelength of 2 $\mu$m and masses of $38.1\pm1.0$ and $34.4\pm1.5$ $M_{\rm Jup}$, respectively. They orbit each other every 12.1 days with a semimajor axis of 0.042 astronomical units (AU). The discovery of Gliese 229 BaBb, each only a few times more massive than the most massive planets, and separated by 16 times the Earth-moon distance, raises new questions about the formation and prevalence of tight binary brown dwarfs around stars., Comment: Published in Nature. The Version of Record of this article is located at https://www.nature.com/articles/s41586-024-08064-x

(Abridged) We explore the chemistry of the most abundant C, O, S, and N bearing species in molecular clouds, in the context of the IRAM 30 m Large Programme Gas phase Elemental abundances in Molecular Clouds (GEMS). In this work, we aim to assess the limitations introduced in the observational works when a uniform density is assumed along the line of sight for fitting the observations, developing a very simple numerical model of a turbulent box. We perform a MHD simulation in order to reproduce the turbulent steady-state of a turbulent box with properties typical of a molecular filament before collapse. We post-process the results of the MHD simulation with a chemical code to predict molecular abundances, and then post-process this cube with a radiative transfer code to create synthetic emission maps for a series of rotational transitions observed during the GEMS project. From the chemical point of view, we find that turbulence produces variations on the predicted abundances, but they are more or less critical depending on the chosen transition and the chemical age. When compared to real observations, the results from the turbulent simulation provides a better fit than when assuming a uniform gas distribution along the line of sight. In the view of our results, we conclude that taking into account turbulence when fitting observations might significantly improve the agreement with model predictions. This is especially important for sulfur bearing species that are very sensitive to the variations of density produced by turbulence at early times (0.1 Myr). The abundance of CO is also quite sensitive to turbulence when considering the evolution beyond a few 0.1 Myr., Comment: Published in Astronomy and Astrophysics

The dust- and gas-rich protoplanetary disks around young stellar systems play a key role in star and planet formation. While considerable progress has recently been made in probing these disks on large scales of a few tens of astronomical units (au), the central au needs to be more investigated. We aim at unveiling the physical processes at play in the innermost regions of the strongly accreting T Tauri Star S CrA N by means of near-infrared interferometric observations. The K-band continuum emission is well reproduced with an azimuthally-modulated dusty ring. As the star alone cannot explain the size of this sublimation front, we propose that magnetospheric accretion is an important dust-heating mechanism leading to this continuum emission. The differential analysis of the Hydrogen Br$\gamma$ line is in agreement with radiative transfer models combining magnetospheric accretion and disk winds. Our observations support an origin of the Br$\gamma$ line from a combination of (variable) accretion-ejection processes in the inner disk region.

We aim to determine the $^{14}$N/$^{15}$N and $^{12}$C/$^{13}$C ratios for HCN in six starless and prestellar cores and compare the results between the direct method using radiative transfer modeling and the indirect double isotope method assuming a fixed $^{12}$C/$^{13}$C ratio. We present IRAM 30m observations of the HCN 1-0, HCN 3-2, HC15N 1-0 and H13CN 1-0 transitions toward six embedded cores. The ${}^{14}$N/${}^{15}$N ratio was derived using both the indirect double isotope method and directly through non-local thermodynamic equilibrium (NLTE) 1D radiative transfer modeling of the HCN emission. The latter also provides the ${}^{12}$C/${}^{13}$C ratio, which we compared to the local interstellar value. The derived ${}^{14}$N/${}^{15}$N ratios using the indirect method are generally in the range of 300-550. This result could suggest an evolutionary trend in the nitrogen fractionation of HCN between starless cores and later stages of the star formation process. However, the direct method reveals lower fractionation ratios of around $\sim$250, mainly resulting from a lower ${}^{12}$C/${}^{13}$C ratio in the range $\sim$20-40, as compared to the local interstellar medium value of 68. This study reveals a significant difference between the nitrogen fractionation ratio in HCN derived using direct and indirect methods. This can influence the interpretation of the chemical evolution and reveal the pitfalls of the indirect double isotope method for fractionation studies. However, the direct method is challenging, as it requires well-constrained source models to produce accurate results. No trend in the nitrogen fractionation of HCN between earlier and later stages of the star formation process is evident when the results of the direct method are considered., Comment: Accepted for publication in A&A

Within the project Evolution of Chemistry in the envelope of HOt corinoS (ECHOS), we present a study of sulphur chemistry in the envelope of the Class 0 source B335 through observations in the spectral range 7, 3, and 2 mm. We have modelled observations assuming LTE and LVG approximation. We have also used the code Nautilus to study the time evolution of sulphur species. We have detected 20 sulphur species with a total gas-phase S abundance similar to that found in the envelopes of other Class 0 objects, but with significant differences in the abundances between sulphur carbon chains and sulphur molecules containing oxygen and nitrogen. Our results highlight the nature of B335 as a source especially rich in sulphur carbon chains unlike other Class 0 sources. The low presence or absence of some molecules, such as SO and SO+, suggests a chemistry not particularly influenced by shocks. We, however, detect a large presence of HCS+ that, together with the low rotational temperatures obtained for all the S species (<15 K), reveals the moderate or low density of the envelope of B335. We also find that observations are better reproduced by models with a sulphur depletion factor of 10 with respect to the sulphur cosmic elemental abundance. The comparison between our model and observational results for B335 reveals an age of 10$^4$$<$t$<$10$^5$ yr, which highlights the particularly early evolutionary stage of this source. B335 presents a different chemistry compared to other young protostars that have formed in dense molecular clouds, which could be the result of accretion of surrounding material from the diffuse cloud onto the protostellar envelope of B335. In addition, the analysis of the SO2/C2S, SO/CS, and HCS+/CS ratios within a sample of prestellar cores and Class 0 objects show that they could be used as good chemical evolutionary indicators of the prestellar to protostellar transition.

Complex organic molecules (COMs) have been observed to be abundant in the gas phase toward protostars. Deep line surveys have been carried out only for a limited number of well-known high-mass star forming regions using the Atacama Large Millimeter/submillimeter Array (ALMA), which has unprecedented resolution and sensitivity. Statistical studies on oxygen-bearing COMs (O-COMs) in high-mass protostars using ALMA are still lacking. With the recent CoCCoA survey, we are able to determine the column density ratios of six O-COMs with respect to methanol (CH$_3$OH) in a sample of 14 high-mass protostellar sources to investigate their origin through ice and/or gas-phase chemistry. The selected species are: acetaldehyde (CH$_3$CHO), ethanol (C$_2$H$_5$OH), dimethyl ether (DME, CH$_3$OCH$_3$), methyl formate (MF, CH$_3$OCHO), glycolaldehyde (GA, CH$_2$OHCHO), and ethylene glycol (EG, (CH$_2$OH)$_2$). DME and MF have the highest and most constant ratios within one order of magnitude, while the other four species have lower ratios and exhibit larger scatter by 1-2 orders of magnitude. We compare the O-COM ratios of high-mass CoCCoA sources with those of 5 low-mass protostars available from the literature, along with the results from experiments and simulations. We find that the O-COM ratios with respect to methanol are on the same level in both the high- and low-mass samples, which suggests that these species are mainly formed in similar environments during star formation, probably in ice mantles on dust grains during early pre-stellar stages. Current simulations and experiments can reproduce most observational trends with a few exceptions, and hypotheses exist to explain the differences between observations and simulations/experiments, such as the involvement of gas-phase chemistry and different emitting areas of molecules., Comment: Accepted for publication in Astronomy & Astrophysics. 17 pages and 7 figures in the main body, 15 pages and 8 figures in the appendix

In the centre of pre-stellar cores, deuterium fractionation is enhanced due to the low temperatures and high densities. Therefore, the chemistry of deuterated molecules can be used to study the earliest stages of star formation. We analyse the deuterium fractionation of simple molecules, comparing the level of deuteration in the envelopes of the pre-stellar core L1544 in Taurus and the protostellar core HH211 in Perseus. We used single-dish observations of CCH, HCN, HNC, HCO$^+$, and their $^{13}$C-, $^{18}$O- and D-bearing isotopologues, detected with the Onsala 20m telescope. We derived the column densities and the deuterium fractions of the molecules. Additionally, we used radiative transfer simulations and results from chemical modelling to reproduce the observed molecular lines. We used new collisional rate coefficients for HNC, HN$^{13}$C, DNC, and DCN that consider the hyperfine structure of these molecules. We find high levels of deuteration for CCH (10%) in both sources, consistent with other carbon chains, and moderate levels for HCN (5-7%) and HNC (8%). The deuterium fraction of HCO$^+$ is enhanced towards HH211, most likely caused by isotope-selective photodissociation of C$^{18}$O. Similar levels of deuteration show that the process is likely equally efficient towards both cores, suggesting that the protostellar envelope still retains the chemical composition of the original pre-stellar core. The fact that the two cores are embedded in different molecular clouds also suggests that environmental conditions do not have a significant effect on the deuteration within dense cores. Radiative transfer modelling shows that it is necessary to include the outer layers of the cores to consider the effects of extended structures. Besides HCO$^+$ observations, HCN observations towards L1544 also require the presence of an outer diffuse layer where the molecules are relatively abundant., Comment: 27 pages, 17 figures, accepted for publication in A&A

Pre-stellar cores represent the earliest stage of the star- and planet-formation process. By characterizing the physical and chemical structure of these cores we can establish the initial conditions for star and planet formation and determine to what degree the chemical composition of pre-stellar cores is inherited to the later stages. A 3D MHD model of a pre-stellar core embedded in a dynamic star-forming cloud is post-processed using sequentially continuum radiative transfer, a gas-grain chemical model, and a line-radiative transfer model. Results are analyzed and compared to observations of CH$_3$OH and $c$-C$_3$H$_2$ in L1544. Nine different chemical models are compared to the observations to determine which initial conditions are compatible with the observed chemical segregation in the prototypical pre-stellar core L1544. The model is able to reproduce several aspects of the observed chemical differentiation in L1544. Extended methanol emission is shifted towards colder and more shielded regions of the core envelope while $c$-C$_3$H$_2$ emission overlaps with the dust continuum, consistent with the observed chemical structure. Increasing the strength of the interstellar radiation field or the cosmic-ray ionization rate with respect to the typical values assumed in nearby star-forming regions leads to synthetic maps that are inconsistent with the observed chemical structure. Our model shows that the observed chemical dichotomy in L1544 can arise as a result of uneven illumination due to the asymmetrical structure of the 3D core and the environment within which the core has formed. This highlights the importance of the 3D structure at the core-cloud transition on the chemistry of pre-stellar cores., Comment: Accepted for publication in A&A

The abundances of deuterated molecules with respect to their main isotopologue counterparts have been determined to be orders of magnitude higher than expected from the cosmic abundance of deuterium relative to hydrogen. The increasing number of singly and multi-deuterated species detections helps us to constrain the interplay between gas-phase and solid-state chemistry and to understand better deuterium fractionation in the early stages of star formation. Acetaldehyde is one of the most abundant complex organic molecules (COMs) in star-forming regions and its singly deuterated isotopologues have already been observed towards protostars. A spectroscopic catalogue for astrophysical purposes is built for doubly deuterated acetaldehyde CHD2CHO from measurements in the laboratory. Submillimetre wave transitions were measured for the non-rigid doubly deuterated acetaldehyde CHD2CHO displaying hindered internal rotation of its asymmetrical CHD2 methyl group. A line position analysis is carried out allowing us to reproduce 853 transition frequencies with a weighted root mean square standard deviation of 1.7, varying 40 spectroscopic constants. A spectroscopic catalogue for astrophysical purposes is built from the analysis results. Using this catalogue we were able to detect for the first time CHD2CHO towards the low-mass protostellar system IRAS 16293-2422 utilizing data from the ALMA Protostellar Interferometric Line Survey. The first detection of the CHD2CHO species allows for the derivation of its column density with a value of 1.3x10^15 cm^-2 and an uncertainty of 10-20%. The resulting D2/D ratio of ~20% is found to be coincident with D2/D ratios derived for other complex organic molecules towards IRAS~16293-2422, pointing at a common formation environment with enhanced deuterium fractionation.

Gas phase Elemental abundances in molecular CloudS (GEMS) is an IRAM 30m large program aimed at determining the elemental abundances of carbon (C), oxygen (O), nitrogen (N), and sulfur (S) in a selected set of prototypical star-forming filaments. In particular, the elemental abundance of S remains uncertain by several orders of magnitude and its determination is one of the most challenging goals of this program. We have carried out an extensive chemical modeling of the fractional abundances of CO, HCO$^+$, HCN, HNC, CS, SO, H$_2$S, OCS, and HCS$^+$ to determine the sulfur depletion toward the 244 positions in the GEMS database. These positions sample visual extinctions from A$_V$ $\sim$ 3 mag to $>$50 mag, molecular hydrogen densities ranging from a few 10$^3$~cm$^{-3}$ to 3$\times$10$^6$~cm$^{-3}$, and T$_k$ $\sim$ 10$-$35 K. Most of the positions in Taurus and Perseus are best fitted assuming early-time chemistry, t=0.1 Myr, $\zeta_{H_2}$$\sim$ (0.5$-$1)$\times$10$^{-16}$ s$^{-1}$, and [S/H]$\sim$1.5$\times$10$^{-6}$. On the contrary, most of the positions in Orion are fitted with t=1~Myr and $\zeta_{H_2}$$\sim$ 10$^{-17}$ s$^{-1}$. Moreover, $\sim$40% of the positions in Orion are best fitted assuming the undepleted sulfur abundance, [S/H]$\sim$1.5$\times$10$^{-5}$. Our results suggest that sulfur depletion depends on the environment. While the abundances of sulfur-bearing species are consistent with undepleted sulfur in Orion, a depletion factor of $\sim$20 is required to explain those observed in Taurus and Perseus. We propose that differences in the grain charge distribution in the envelopes of the studied clouds might explain these variations. The shocks associated with past and ongoing star formation could also contribute to enhance [S/H] in Orion., Comment: 22 pages, 15 figures, Astronomy and Astrophysics, in press

Aims: We aim to spatially and spectrally resolve the Br-gamma hydrogen emission line with the methods of interferometry in order to examine the kinematics of the hydrogen gas emission region in the inner accretion disk of a sample of solar-like young stellar objects. The goal is to identify trends and categories among the sources of our sample and to discuss whether or not they can be tied to different origin mechanisms associated with Br-gamma emission in T Tauri stars, chiefly and most prominently magnetospheric accretion. Methods: We observed a sample of seven T Tauri stars for the first time with VLTI GRAVITY, recording spectra and spectrally dispersed interferometric quantities across the Br-gamma line in the NIR K-band. We use them to extract the size of the Br-gamma emission region and the photocenter shifts. To assist in the interpretation, we also make use of radiative transfer models of magnetospheric accretion to establish a baseline of expected interferometric signatures if accretion is the primary driver of Br-gamma emission. Results: From among our sample, we find that five of the seven T~Tauri stars show an emission region with a half-flux radius in the range broadly expected for magnetospheric truncation. Two of the five objects also show Br-gamma emission primarily originating from within the corotation radius, while two other objects exhibit extended emission on a scale beyond 10 R$_*$, one of them even beyond the K~band continuum half-flux radius of 11.3 R$_*$. Conclusions: We find strong evidence to suggest that for the two weakest accretors in the sample, magnetospheric accretion is the primary driver of Br-gamma radiation. The results for the remaining sources imply either partial or strong contributions coming from spatially extended emission components in the form of outflows, such as stellar or disk winds., Comment: Version corresponds to the one in A&A production. The author list has been amended with "GRAVITY Collaboration" as first entry in keeping with the convention established for papers published by the GRAVITY consortium in recent years

Prestellar cores, the birthplace of Sun-like stars, form from the fragmentation of the filamentary structure that composes molecular clouds, from which they must inherit at least partially the kinematics. Furthermore, when they are on the verge of gravitational collapse, they show signs of subsonic infall motions. How extended these motions are, which depends on how the collapse occurs, remains largely unknown. We want to investigate the kinematics of the envelope that surrounds the prototypical prestellar core L1544, studying the cloud-core connection. To our aims, we observed the $\rm HCO^+$(1-0) transition in a large map. \hcop is expected to be abundant in the envelope, making it an ideal probe of the large-scale kinematics in the source. We modelled the spectrum at the dust peak by means of a non local-thermodynamical-equilibrium radiative transfer. In order to reproduce the spectrum at the dust peak, a large ($\sim 1\, \rm pc$) envelope is needed, with low density (tens of $\rm cm^{-3}$ at most) and contraction motions, with an inward velocity of $\approx 0.05\,\rm km \, s^{-1}$. We fitted the data cube using the Hill5 model, which implements a simple model {for the optical depth and excitation temperature profiles along the line-of-sight,} in order to obtain a map of the infall velocity. This shows that the infall motions are extended, with typical values in the range $0.1-0.2\,\rm km \, s^{-1}$. Our results suggest that the contraction motions extend in the diffuse envelope surrounding the core, which is consistent with recent magnetic field measurements in the source, which showed that the envelope is magnetically supercritical., Comment: Accepted for publication on ApJ, 24 Oct. 2022

We aim to quantify the effect of chemistry on the infall velocity in the prestellar core L1544. Previous observational studies have found evidence for double-peaked line profiles for the rotational transitions of several molecules, which cannot be accounted for with the models presently available for the physical structure of the source, without ad hoc up-scaling of the infall velocity. We ran one-dimensional hydrodynamical simulations of the collapse of a core with L1544-like properties (in terms of mass and outer radius), using a state-of-the-art chemical model with a very large chemical network combined with an extensive description of molecular line cooling, determined via radiative transfer simulations, with the aim of determining whether these expansions of the simulation setup (as compared to previous models) can lead to a higher infall velocity. After running a series of simulations where the simulation was sequentially simplified, we found that the infall velocity is almost independent of the size of the chemical network or the approach to line cooling. We conclude that chemical evolution does not have a large impact on the infall velocity, and that the higher infall velocities that are implied by observations may be the result of the core being more dynamically evolved than what is now thought, or alternatively the average density in the simulated core is too low. However, chemistry does have a large influence on the lifetime of the core, which varies by about a factor of two across the simulations and grows longer when the chemical network is simplified. Therefore, although the model is subject to several sources of uncertainties, the present results clearly indicate that the use of a small chemical network leads to an incorrect estimate of the core lifetime, which is naturally a critical parameter for the development of chemical complexity in the precollapse phase., Comment: 12 pages incl. Appendix; 8 figures; accepted to A&A; replacement to reflect the change of the title of the paper post-acceptance

Spectral line profiles of several molecules observed towards the pre-stellar core L1544 appear double-peaked. For abundant molecular species this line morphology has been linked to self-absorption. However, the physical process behind the double-peaked morphology for less abundant species is still under debate. In order to understand the cause behind the double-peaked spectra of optically thin transitions and their link to the physical structure of pre-stellar cores, we present high-sensitivity and high-spectral resolution HC$^{17}$O$^+$ $J =$1-0 observations towards the dust peak in L1544. We observed the HC$^{17}$O$^+$ (1-0) spectrum with the Institut de Radioastronomie Millim\'etrique (IRAM) 30m telescope. By using new state-of-the-art collisional rate coefficients, a physical model for the core and the fractional abundance profile of HC$^{17}$O$^+$, the hyperfine structure of this molecular ion is modelled for the first time with the radiative transfer code LOC applied to the predicted chemical structure of a contracting pre-stellar core. We applied the same analysis to the chemically related C$^{17}$O molecule. The observed HC$^{17}$O$^+$(1-0) and C$^{17}$O(1-0) lines have been successfully reproduced with a non-local thermal equilibrium (LTE) radiative transfer model applied to chemical model predictions for a contracting pre-stellar core. An upscaled velocity profile (by 30%) is needed to reproduce the HC$^{17}$O$^+$(1-0) observations. The double peaks observed in the HC$^{17}$O$^+$(1-0) hyperfine components are due to the contraction motions at densities close to the critical density of the transition ($\sim$10$^{5}$ cm$^{-3}$) and to the fact that the HCO$^{+}$ fractional abundance decreases toward the centre.

Context: In the centre of pre-stellar cores, the deuterium fractionation is enhanced due to the cold temperatures and high densities. Therefore, the chemistry of deuterated molecules can be used to probe the evolution and the kinematics in the earliest stages of star formation. Aims: We analyse emission maps of cyclopropenylidene, c-C$_3$H$_2$, to study the distribution of the deuteration throughout the prototypical pre-stellar core L1544. Methods: We use single-dish observations of c-C$_3$H$_2$, c-H$^{13}$CC$_2$H, c-C$_3$HD, and c-C$_3$D$_2$ towards the pre-stellar core L1544, performed at the IRAM 30m telescope. We derive the column density and deuterium fraction maps, and compare these observations with non-LTE radiative transfer simulations. Results: The highest deuterium fractions are found close to the dust peak at the centre of L1544, where the increased abundance of H$_2$D$^+$ ions drives the deuteration process. The peak values are N(c-C$_3$HD)/N(c-C$_3$H$_2)=0.17\pm0.01$, N(c-C$_3$D$_2$)/N(c-C$_3$H$_2)=0.025\pm0.003$ and N(c-C$_3$D$_2$)/N(c-C$_3$HD$)=0.16\pm0.03$, which is consistent with previous single point observations. The distributions of c-C$_3$HD and c-C$_3$D$_2$ indicate that the deuterated forms of c-C$_3$H$_2$ in fact trace the dust peak and not the c-C$_3$H$_2$ peak. Conclusions: The N(c-C$_3$D$_2$)/N(c-C$_3$HD) map confirms that the process of deuteration is more efficient towards the centre of the core and demonstrates that carbon-chain molecules are still present at high densities. This is likely caused by an increased abundance of He$^+$ ions destroying CO, which increases the amount of carbon atoms in the gas phase., Comment: 13 pages, 9 figures

In the context of the IRAM 30m Large Program GEMS, we present a study of thioformaldehyde in several starless cores located in star-forming filaments of Taurus, Perseus, and Orion. We investigate the influence of the environmental conditions on the abundances of these molecules in the cores, and the effect of time evolution. We have modelled the observed lines of H2CS, HDCS, and D2CS using the radiative transfer code RADEX. We have also used the chemical code Nautilus to model the evolution of these species depending on the characteristics of the starless cores. We derive column densities and abundances for all the cores. We also derive deuterium fractionation ratios, Dfrac, to determine and compare the evolutionary stage between different parts of each star-forming region. Our results indicate that the north region of the B213 filament in Taurus is more evolved than the south, while the north-eastern part of Perseus presents an earlier evolutionary stage than the south-western zone. Model results also show that Dfrac decreases with the cosmic-ray ionisation rate, while it increases with density and with the degree of sulphur depletion. In particular, we only reproduce the observations when the initial sulphur abundance in the starless cores is at least one order of magnitude lower than the solar elemental sulphur abundance. The progressive increase in HDCS/H2CS and D2CS/H2CS with time makes these ratios powerful tools for deriving the chemical evolutionary stage of starless cores. However, they cannot be used to derive the temperature of these regions, since both ratios present a similar evolution at two different temperature ranges (7-11 K and 15-19 K). Regarding chemistry, (deuterated) thioformaldehyde is mainly formed through gas-phase reactions (double-replacement and neutral-neutral displacement reactions), while surface chemistry plays an important role as a destruction mechanism., Comment: 31 pages, 26 figures

Protostellar jets are an important agent of star formation feedback, tightly connected with the mass-accretion process. The history of jet formation and mass-ejection provides constraints on the mass accretion history and the nature of the driving source. We want to characterize the time-variability of the mass-ejection phenomena at work in the Class 0 protostellar phase, in order to better understand the dynamics of the outflowing gas and bring more constraints on the origin of the jet chemical composition and the mass-accretion history. We have observed the emission of the CO 2-1 and SO N_J=5_4-4_3 rotational transitions with NOEMA, towards the intermediate-mass Class 0 protostellar system Cep E. The CO high-velocity jet emission reveals a central component associated with high-velocity molecular knots, also detected in SO, surrounded by a collimated layer of entrained gas. The gas layer appears to accelerate along the main axis over a length scale delta_0 ~700 au, while its diameter gradually increases up to several 1000au at 2000au from the protostar. The jet is fragmented into 18 knots of mass ~10^-3 Msun, unevenly distributed between the northern and southern lobes, with velocity variations up to 15 km/s close to the protostar, well below the jet terminal velocities. The knot interval distribution is approximately bimodal with a scale of ~50-80yr close to the protostar and ~150-200yr at larger distances >12". The mass-loss rates derived from knot masses are overall steady, with values of 2.7x10^-5 Msun/yr (8.9x10^-6 Msun/yr) in the northern (southern) lobe. The interaction of the ambient protostellar material with high-velocity knots drives the formation of a molecular layer around the jet, which accounts for the higher mass-loss rate in the north. The jet dynamics are well accounted for by a simple precession model with a period of 2000yr and a mass-ejection period of 55yr., Comment: 13 pages, 9 figures, 3 table. Accepted in A&A

Deuteration is a crucial tool to understand the complexity of interstellar chemical processes, especially when they involve the interplay of gas-phase and grain-surface chemistry. In the case of multiple deuteration, comparing observation with the results of chemical modelling is particularly effective to study how molecules are inherited in the different stages within the process of star and planet formation. We aim to study the the D/ H ratio in H2CS across the prototypical pre-stellar core L1544. This study allows us to test current gas-dust chemical models involving sulfur in dense cores. We present here single-dish observations of H2CS, HDCS and D2CS with the IRAM 30m telescope. We analyse their column densities and distributions, and compare these observations with gas-grain chemical models. The deuteration maps of H2CS in L1544 are compared with the deuteration maps of methanol, H2CO, N2H+ and HCO+ towards the same source. Furthermore, the single and double deuteration of H2CS towards the dust peak of L1544 is compared with H2CO and c-C3H2. The difference between the deuteration of these molecules in L1544 is discussed and compared with the prediction of chemical models. The maximum deuterium fractionation for the first deuteration of H2CS is N(HDCS)/N(H2CS)$\sim$30$\%$ and is located towards the north-east at a distance of about 10000 AU from the dust peak. While for c-C3H2 the first and second deuteration have a similar efficiency, for H2CS and H2CO the second deuteration is more efficient, leading to D2CX/HDCX$\sim$100$\%$ (with X= O or S). Our results imply that the large deuteration of H2CO and H2CS observed in protostellar cores as well as in comets is likely inherited from the pre-stellar phase. However, the comparison with state-of-the-art chemical models suggests that the reaction network for the formation of the doubly deuterated H2CS and H2CO it is not complete yet., Comment: Accepted for publication in A&A