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Magnetic fields may play a crucial role in setting the initial conditions of massive star and star cluster formation. To investigate this, we report SOFIA-HAWC+ 214 μ m observations of polarized thermal dust emission and high-resolution GBT-Argus C ^18 O(1-0) observations toward the massive Infrared Dark Cloud (IRDC) G28.37+0.07. Considering the local dispersion of B -field orientations, we produce a map of the B -field strength of the IRDC, which exhibits values between ∼0.03 and 1 mG based on a refined Davis–Chandrasekhar–Fermi method proposed by Skalidis & Tassis. Comparing to a map of inferred density, the IRDC exhibits a B – n relation with a power-law index of 0.51 ± 0.02, which is consistent with a scenario of magnetically regulated anisotropic collapse. Consideration of the mass-to-flux ratio map indicates that magnetic fields are dynamically important in most regions of the IRDC. A virial analysis of a sample of massive, dense cores in the IRDC, including evaluation of magnetic and kinetic internal and surface terms, indicates consistency with virial equilibrium, sub-Alfvénic conditions, and a dominant role for B -fields in regulating collapse. A clear alignment of magnetic field morphology with the direction of the steepest column density gradient is also detected. However, there is no preferred orientation of protostellar outflow directions with the B -field. Overall, these results indicate that magnetic fields play a crucial role in regulating massive star and star cluster formation, and therefore they need to be accounted for in theoretical models of these processes.

Jets and disk winds arise from materials with excess angular momentum ejected from the accretion disks in forming stars. How these structures are launched and how they impact the gas within the innermost regions of these objects remains poorly understood. MWC349A is a massive star that has a circumstellar disk that rotates in accord with Kepler’s Law, with an ionized wind and a high-velocity jet launched from the disk surface. The strongly maser-amplified emission of hydrogen radio recombination lines (RRLs) observed toward this system provides a comprehensive picture of its ionized environment with exquisite detail. In this Letter, we present Atacama Large Millimeter/submillimeter Array observations of the H26 α RRL and continuum emission obtained with the highest angular resolution ever used toward this source (beam of ∼0.″02). The maser RRL emission is resolved for the first time and clearly delineates the ionized disk, wind, and jet. We analyzed the RRL data cubes with the 3D non-LTE radiative transfer model MORELI, confirming that the jet is poorly collimated. We found that the jet orientation is closer to the rotation axis of the system than derived from spatially unresolved data. This study confirms that hydrogen RRL masers are powerful probes of the physical structure and kinematics of the innermost ionized material around massive stars.

A compact source, G0.02467–0.0727, was detected in Atacama Large Millimeter/submillimeter Array 3 mm observations in continuum and very broad line emission. The continuum emission has a spectral index α ≈ 3.3, suggesting that the emission is from dust. The line emission is detected in several transitions of CS, SO, and SO _2 and exhibits a line width FWHM ≈ 160 km s ^−1 . The line profile appears Gaussian. The emission is weakly spatially resolved, coming from an area on the sky ≲1″ in diameter (≲10 ^4 au at the distance of the Galactic center, GC). The centroid velocity is v _LSR ≈ 40–50 km s ^−1 , which is consistent with a location in the GC. With multiple SO lines detected, and assuming local thermodynamic equilibrium (LTE) conditions, the gas temperature is T _LTE = 13 K, which is colder than seen in typical GC clouds, though we cannot rule out low-density, subthermally excited, warmer gas. Despite the high velocity dispersion, no emission is observed from SiO, suggesting that there are no strong (≳10 km s ^−1 ) shocks in the molecular gas. There are no detections at other wavelengths, including X-ray, infrared, and radio. We consider several explanations for the millimeter ultra-broad-line object (MUBLO), including protostellar outflow, explosive outflow, a collapsing cloud, an evolved star, a stellar merger, a high-velocity compact cloud, an intermediate-mass black hole, and a background galaxy. Most of these conceptual models are either inconsistent with the data or do not fully explain them. The MUBLO is, at present, an observationally unique object.

We present the first detection in space of thionylimide (HNSO) toward the Galactic center molecular cloud G + 0.693-0.027, thanks to the superb sensitivity of an ultradeep molecular line survey carried out with the Yebes 40 m and IRAM 30 m telescopes. This molecule is the first species detected in the interstellar medium containing, simultaneously, N, S, and O. We have identified numerous K _a = 0, 1, and 2 transitions belonging to HNSO covering from J _up = 2 to J _up =10, including several completely unblended features. We derive a molecular column density of N = (8 ± 1)×10 ^13 cm ^−2 , yielding a fractional abundance relative to H _2 of ∼6 × 10 ^−10 , which is about ∼37 and ∼4.8 times less abundant than SO and SO _2 , respectively. Although there are still many unknowns in the interstellar chemistry of NSO-bearing molecules, we propose that HNSO is likely formed through the reaction of the NSO radical and atomic H on the surface of icy grains, with alternative routes also deserving exploration. Finally, HNSO appears as a promising link between N, S, and O interstellar chemistry, and its discovery paves the route to the detection of a new family of molecules in space.

This work aims to spectroscopically characterize and provide for the first time direct experimental frequencies of the ground vibrational state and two excited states of the simplest alkynyl thiocyanate (HCCSCN) for astrophysical use. Both microwave (8–16 GHz) and millimeter-wave regions (50–120 GHz) of the spectrum have been measured and analyzed in terms of Watson’s semirigid rotor Hamiltonian. A total of 314 transitions were assigned to the ground state of HCCSCN, and a first set of spectroscopic constants have been accurately determined. Spectral features of the molecule were then searched for in Sgr B2(N), NGC 6334I, G+0.693−0.027, and TMC-1 molecular clouds. Upper limits to the column density are provided.

We report the first detection of the metal-bearing molecules sodium sulfide and magnesium sulfide and the tentative detection of calcium monoxide in the interstellar medium toward the Galactic center molecular cloud G+0.693-0.027. The derived column densities are (5.0 ± 1.1) × 10 ^10 cm ^−2 , (6.0 ± 0.6) × 10 ^10 cm ^−2 , and (2.0 ± 0.5) × 10 ^10 cm ^−2 , respectively. This translates into fractional abundances with respect to H _2 of (3.7 ± 1.0) × 10 ^−13 , (4.4 ± 0.8) × 10 ^−13 , and (1.5 ± 0.4) × 10 ^−13 , respectively. We have also searched for other Na-, Mg-, and Ca-bearing species toward this source but none of them have been detected and thus we provide upper limits for their abundances. We discuss the possible chemical routes involved in the formation of these molecules containing metals under interstellar conditions. Finally, we compare the ratio between sulfur-bearing and oxygen-bearing molecules with and without metals, finding that metal-bearing sulfur molecules are much more abundant than metal-bearing oxygen ones, in contrast with the general trend found in the ratios between other nonmetal-oxygen- and sulfur-bearing molecules. This further strengthens the idea that sulfur may be a little depleted in G+0.693-0.027 as a result of the low-velocity shocks present in this source sputtering large amounts of material from dust grains.

We report the first detection in the interstellar medium of N -cyanomethanimine (H _2 CNCN), the stable dimer of HCN of highest energy and the most complex organic molecule identified in space containing the prebiotically relevant NCN backbone. We have identified a plethora of a -type rotational transitions with 3 ≤ J _up ≤ 11 and K _a ≤ 2 that belong to this species toward the Galactic center G+0.693-0.027 molecular cloud, the only interstellar source showing the three cyanomethanimine isomers (including the Z - and E -isomers of C -cyanomethanimine, HNCHCN). We have derived a total column density for H _2 CNCN of (2.9 ± 0.1) × 10 ^12 cm ^−2 , which translates into a total molecular abundance with respect to H _2 of (2.1 ± 0.3) × 10 ^−11 . We have also revisited the previous detection of E - and Z -HNCHCN and found a total C / N -cyanomethanimine abundance ratio of 31.8 ± 1.8 and a Z / E -HNCHCN ratio of 4.5 ± 0.2. While the latter can be explained on the basis of thermodynamic equilibrium, chemical kinetics are more likely responsible for the observed C / N -cyanomethanimine abundance ratio, where the gas-phase reaction between methanimine (CH _2 NH) and the cyanogen radical (CN) arises as the primary formation route.

IRAS04368+2557 in L1527 is a Class 0/I protostar with a clear disk-envelope system revealed by previous Atacama Large Millimeter/submillimeter Array (ALMA) observations. In this paper, we discuss the flared structure of this source with observed sulfur-bearing molecules included in the FAUST ALMA large program. The analyses of molecular distributions and kinematics have shown that CS, SO, and OCS trace different regions of the disk-envelope system. To evaluate the temperature across the disk, we derive rotation temperature with the two observed SO lines. The temperature profile shows a clear, flared “butterfly” structure with the higher temperature being ∼50 K and the central lower temperature region (

We present the first detection in space of O-protonated carbonyl sulfide (HOCS ^+ ), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the observation of all K _a = 0 transitions ranging from J _lo = 2 to J _lo = 13 of HOCS ^+ covered by our survey, we derive a column density of N = (9 ± 2) × 10 ^12 cm ^−2 , translating into a fractional abundance relative to H _2 of ∼7 × 10 ^−11 . Conversely, the S-protonated HSCO ^+ isomer remains undetected, and we derive an upper limit to its abundance with respect to H _2 of ≤3 × 10 ^−11 , a factor of ≥2.3 less abundant than HOCS ^+ . We obtain an HOCS ^+ /OCS ratio of ∼2.5 × 10 ^−3 , in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of HOCS ^+ is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionization rates (10 ^−15 –10 ^−14 s ^−1 ) are needed to reproduce the observed abundance of HOCS ^+ . In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find an HOCO ^+ /HOCS ^+ ratio of ∼31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value (∼37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains.

Phosphorus monoxide (PO) is a key brick of prebiotic chemistry since it is a potential precursor of phosphates, which are present in all living systems. Prompted by the lack of information on the different processes involved in the formation of PO, we have revisited and analyzed in detail the P( ^4 S ) + O _2 ( ^3 Σ ^− ) and P( ^4 S ) + O _2 ( ^1 Δ) reactions leading to PO. The former process has been widely studied from both experimental and theoretical points of view, however, with contradictory results. We have used high-level quantum-chemical calculations to accurately describe the reaction mechanisms. Next, rate constants have been computed using a master equation approach based on ab initio transition state theory. By incorporating the P( ^4 S ) + O _2 ( ^3 Σ ^− ) reaction in an astrochemical model, we have found that this reaction cannot be overlooked when aiming at a complete understanding of the PO abundance in regions dominated by shocks with speeds below 40 km s ^−1 .

We report the first detection in the interstellar medium (ISM) of a C _2 H _5 O _2 N isomer: syn -glycolamide (NH _2 C(O)CH _2 OH). The exquisite sensitivity at sub-mK levels of an ultradeep spectral survey carried out with the Yebes 40 m and IRAM 30 m telescopes toward the G+0.693–0.027 molecular cloud has allowed us to unambiguously identify multiple transitions of this species. We derived a column density of (7.4 ± 0.7) × 10 ^12 cm ^−2 , which implies a molecular abundance with respect to H _2 of 5.5 × 10 ^−11 . The other C _2 H _5 O _2 N isomers, including the higher-energy anti conformer of glycolamide and two conformers of glycine, were not detected. The upper limit derived for the abundance of glycine indicates that this amino acid is surely less abundant than its isomer glycolamide in the ISM. The abundances of the C _2 H _5 O _2 N isomers cannot be explained in terms of thermodynamic equilibrium; thus, chemical kinetics need to be invoked. While the low abundance of glycine might not be surprising, based on the relative low abundances of acids in the ISM compared to other compounds (e.g., alcohols, aldehydes, or amines), several chemical pathways can favor the formation of its isomer glycolamide. It can be formed through radical–radical reactions on the surface of dust grains. The abundances of these radicals can be significantly boosted in an environment affected by a strong ultraviolet field induced by cosmic rays, such as that expected in G+0.693–0.027. Therefore, as shown by several recent molecular detections toward this molecular cloud, it stands out as the best target to discover new species with carbon, oxygen, and nitrogen with increasing chemical complexity.

MWC 349A is one of the rare stars known to have hydrogen radio recombination line (RRL) masers. The bright maser emission makes it possible to study the dynamics of the system at milliarcsecond (mas) precision. We present Atacama Large Millimeter/submillimeter Array observations of the 1.4 and 0.8 mm continuum emission of MWC 349A, as well as the H30 α and H26 α RRLs. Using the most extended array configuration of C43-10 with a maximum baseline of 16.2 km, we spatially resolved the H30 α line and 1.4 mm continuum emission for the first time. In addition to the known H30 α and H26 α maser emission from a Keplerian disk at LSR velocities from −12 to 28 km s ^−1 and from an ionized wind for velocities between −12 to −40 km s ^−1 and 28 to 60 km s ^−1 , we found evidence of a jet along the polar axis at V _LSR from −85 to −40 km s ^−1 and +60 to +100 km s ^−1 . These masers are found in a linear structure nearly aligned with the polar axis of the disk. If these masers lie close to the polar axis, their velocities could be as high as 575 km s ^−1 , which cannot be explained solely by a single expanding wind as proposed in Báez-Rubio et al. We suggest that they originate from a high-velocity jet, likely launched by a magnetohydrodynamic wind. The jet appears to rotate in the same direction as the rotation of the disk. A detailed radiative transfer modeling of these emissions will further elucidate the origin of these masers in the wind.

We performed a comprehensive investigation of methyl cyanoacetate (MCA) using high-resolution Fourier transform rotational spectroscopy. Two low energy conformers of MCA were observed in the vibrational ground state, in selected frequency regions from 2 to 110 GHz. We report accurately determined line lists, rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants for both conformers, as well as for several singly substituted heavy-atom isotopologues. One of the conformers was previously reported; however, the rotational transitions of the second conformer, which is newly described here, are observed to be generally more intense than the latter. The accurate predictions of rotational transitions into the millimeter-wave region can facilitate the detection of these conformers of MCA in the interstellar medium. Using the rotational spectroscopy data provided here, we searched for the two conformers of MCA in a deep and unbiased spectral survey of the molecular cloud G+0.693-0.027 located in the Galactic Center. None of the MCA conformers were detected. The upper limits for their abundances were derived with respect to the abundance of molecular hydrogen.

Nitriles play a key role as molecular precursors in prebiotic experiments based on the RNA-world scenario for the origin of life. These chemical compounds could have been partially delivered to the young Earth from extraterrestrial objects, stressing the importance of establishing the reservoir of nitriles in the interstellar medium. We report here the detection towards the molecular cloud G+0.693−0.027 of several nitriles, including cyanic acid (HOCN), and three C4H3N isomers (cyanoallene, CH2CCHCN; propargyl cyanide, HCCCH2CN; and cyanopropyne (CH3CCCN), and the tentative detections of cyanoformaldehyde (HCOCN), and glycolonitrile (HOCH2CN). We have also performed the first interstellar search of cyanoacetaldehyde (HCOCH2CN), which was not detected. Based on the derived molecular abundances of the different nitriles in G+0.693−0.027 and other interstellar sources, we have discussed their formation mechanisms in the ISM. We propose that the observed HOCN abundance in G+0.693−0.027 is mainly due to surface chemistry and subsequent shock-induced desorption, while HCOCN might be mainly formed through gas-phase chemistry. In the case of HOCH2CN, several grain-surface routes from abundant precursors could produce it. The derived abundances of the three C4H3N isomers in G+0.693−0.027 are very similar, and also similar to those previously reported in the dark cold cloud TMC-1. This suggests that the three isomers are likely formed through gas-phase chemistry from common precursors, possibly unsaturated hydrocarbons (CH3CCH and CH2CCH2) that react with the cyanide radical (CN). The rich nitrile feedstock found towards G+0.693−0.027 confirms that interstellar chemistry is able to synthesize in space molecular species that could drive the prebiotic chemistry of the RNA-world.

We report the first detection of the phosphorus monoxide ion (PO+) in the interstellar medium. Our unbiased and very sensitive spectral survey toward the G+0.693–0.027 molecular cloud covers four different rotational transitions of this molecule, two of which (J = 1–0 and J = 2–1) appear free of contamination from other species. The fit performed, assuming local thermodynamic equilibrium conditions, yields a column density of N=(6.0 ± 0.7) × 1011 cm−2. The resulting molecular abundance with respect to molecular hydrogen is 4.5 × 10–12. The column density of PO+ normalized by the cosmic abundance of P is larger than those of NO+ and SO+, normalized by N and S, by factors of 3.6 and 2.3, respectively. The N(PO+)/N(PO) ratio is 0.12 ± 0.03, more than one order of magnitude higher than that of N(SO+)/N(SO) and N(NO+)/N(NO). These results indicate that P is more efficiently ionized than N and S in the ISM. We have performed new chemical models that confirm that the PO+ abundance is strongly enhanced in shocked regions with high values of cosmic-ray ionization rates (10–15 − 10–14 s−1), as occurring in the G+0.693–0.027 molecular cloud. The shocks sputter the interstellar icy grain mantles, releasing into the gas phase most of their P content, mainly in the form of PH3, which is converted into atomic P, and then ionized efficiently by cosmic rays, forming P+. Further reactions with O2 and OH produces PO+. The cosmic-ray ionization of PO might also contribute significantly, which would explain the high N(PO+)/N(PO) ratio observed. The relatively high gas-phase abundance of PO+ with respect to other P-bearing species stresses the relevance of this species in the interstellar chemistry of P.

One of the theories for the origin of life proposes that a significant fraction of prebiotic material could have arrived to Earth from outer space between 4.1 and 3.8 billion years ago. This suggests that those prebiotic compounds could have originated in interstellar space, to be later on incorporated to small Solar-system bodies and planetesimals. The recent discovery of prebiotic molecules such as hydroxylamine and ethanolamine in the interstellar medium, strongly supports this hypothesis. However, some species such as sugars, key for the synthesis of ribonucleotides and for metabolic processes, remain to be discovered in space. The unmatched sensitivity of the Square Kilometre Array (SKA) at centimeter wavelengths will be able to detect even more complex and heavier prebiotic molecules than existing instrumentation. In this contribution, we illustrate the potential of the SKA to detect simple sugars with three and four carbon atoms, using a moderate investment of observing time.

The study of phosphorus chemistry in the interstellar medium has become a topic of growing interest in astrobiology because it is plausible that a wide range of P-bearing molecules were introduced in the early Earth by the impact of asteroids and comets on its surface, enriching prebiotic chemistry. Thanks to extensive searches in recent years, it has become clear that P mainly appears in the form of PO and PN in molecular clouds and star-forming regions. Interestingly, PO is systematically more abundant than PN by factors typically of ∼1.4–3, independently of the physical properties of the observed source. In order to unveil the formation routes of PO and PN, in this work we introduce a mathematical model for the time evolution of the chemistry of P in an interstellar molecular cloud and analyze its associated chemical network as a complex dynamical system. By making reasonable assumptions, we reduce the network to obtain explicit mathematical expressions that describe the abundance evolution of P-bearing species and study the dependences of the abundance of PO and PN on the system’s kinetic parameters with much faster computation times than available numerical methods. As a result, our model reveals that the formation of PO and PN is governed by just a few critical reactions, and fully explains the relationship between PO and PN abundances throughout the evolution of molecular clouds. Finally, the application of Bayesian methods constrains the real values of the most influential reaction rate coefficients making use of available observational data.

MWC 349A is a massive star with a well-known circumstellar disk rotating following a Keplerian law, and an ionized wind launched from the disk surface. Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) carried out toward this system, however, have revealed an additional high-velocity component in the strong, maser emission of hydrogen radio recombination lines (RRLs), suggesting the presence of a high-velocity ionized jet. In this work, we present 3D non-LTE radiative transfer modeling of the emission of the H30 α and H26 α maser lines, and of their associated radio continuum emission, toward MWC 349A. By using the MORELI code, we reproduce the spatial distribution and kinematics of the high-velocity emission of the H30 α and H26 α maser lines with a high-velocity ionized jet expanding at a velocity of ∼250 km s ^−1 , surrounded by MWC 349A’s wide-angle ionized wind. The bipolar jet, which is launched from MWC 349A’s disk, is poorly collimated and slightly misaligned with respect to the disk rotation axis. Thanks to the unprecedented sensitivity and spatial accuracy provided by ALMA, we also find that the already known, wide-angle ionized wind decelerates as it expands radially from the ionized disk. We briefly discuss the implications of our findings for understanding the formation and evolution of massive stars. Our results show the huge potential of RRL masers as powerful probes of the innermost ionized regions around massive stars and of their high-velocity jets.

A quarter century after the detection of the last interstellar carboxylic acid, acetic acid (CH _3 COOH), we report the discovery of a new one, the cis-trans form of carbonic acid (HOCOOH), toward the Galactic center molecular cloud G+0.693–0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also directly identified several pairs of unblended lines in the astronomical data (between 75 and 120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for cis-trans HOCOOH of N = (6.4 ± 0.4) × 10 ^12 cm ^−2 , which yields an abundance with respect to molecular H _2 of 4.7 × 10 ^−11 . Meanwhile, the extremely low dipole moment (about 15 times lower) of the lower-energy conformer, cis-cis HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H _2 of ≤1.2 × 10 ^−9 , which suggests that cis-cis HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a cis-cis / cis-trans ratio of ≤25, consistent with the smaller energy difference between both conformers compared with the relative stability of trans- and cis -formic acid. Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the solar system, which could be inherited during the star formation process.

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 ${119}_{-26}^{+20}$ K and ${3.2}_{-1.0}^{+2.5}\times {10}^{18}$ cm ^−2 , respectively. The beam filling factor is derived to be ${0.018}_{-0.003}^{+0.005}$ , 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 (∼10 au) and warm carbon-chain chemistry rich in carbon-chain species on large scales (∼100–1000 au). A possible implication of the small emitting region is further discussed in relation to the origin of the hot corino activity.

IRAM 30 m Observations toward eight protostellar outflow sources were taken in the 96–176 GHz range. Transitions of CH3OH and CH3CHO were detected in seven of them. The integrated emissions of the transitions of each species that fell into the observed frequency range were measured and fit using RADEX and LTE models. Column densities and gas properties inferred from this fitting are presented. The ratio of the A and E-type isomers of CH3OH indicates that the methanol observed in these outflows was formed on the grain surface. Both species demonstrate a reduction of terminal velocity in their line profiles in faster outflows, indicating destruction in the post-shock gas phase. This destruction, and a near constant ratio of the CH3OH and CH3CHO column densities, imply it is most likely that CH3CHO also forms on the grain surface. [ABSTRACT FROM AUTHOR]

The main carrier of sulfur in dense clouds, where it is depleted from the gas phase, remains a mystery. Shock waves in young molecular outflows disrupt the ice mantles and allow us to directly probe the material that is ejected into the gas phase. A comprehensive study of sulfur-bearing species toward L1157-B1, a shocked region along a protostellar outflow, has been carried out as part of the IRAM-30 m large program ASAI. The data set contains over 100 lines of CCS, H2CS, OCS, SO, SO2, and isotopologues. The results of these observations are presented, complementing previous studies of sulfur-bearing species in the region. The column densities and fractional abundances of these species are measured and together these species account for 10% of the cosmic sulfur abundance in the region. The gas properties derived from the observations are also presented, demonstrating that sulfur bearing species trace a wide range of different gas conditions in the region. [ABSTRACT FROM AUTHOR]