Search

Studying accretion-driven episodic outbursts in YSOs is key to understanding the later stages of star and planet formation. FU Orionis-type objects form a YSO subclass, distinguished by rapid, multi-magnitude increases in brightness at optical and near-infrared wavelengths. These outbursts may significantly impact the chemistry and molecular composition around eruptive stars. However, no comprehensive millimeter-wavelength line survey exists for more evolved (Class II) sources, unlike optical and near-infrared coverage. We conducted the first wideband millimeter spectral line survey of V1057 Cyg, a low-mass eruptive FUor with the highest observed peak accretion rate in its class. Using the IRAM 30-m telescope, we surveyed the 72-263 GHz range and complemented this with targeted spectra at 219, 227, 291, and 344 GHz with the APEX 12-m telescope. We conducted radiative transfer and population diagram analyses to get first estimates of the excitation temperatures and column densities. Several molecular species trace large-scale structures, and the position-velocity diagram of $^{12}$CO suggest episodic outburst activity, with outflow dynamical timescales on the order of tens of thousands of years. We identified simple molecules (C-, N-, O-, and S-bearing), deuterated species, molecular ions, and complex organic molecules. With over 30 molecular species (including isotopologues) detected, V1057 Cyg demonstrates rich chemistry for its evolutionary state, compared to other younger (Class 0/I) FUors. V1057 Cyg is a good candidate for future interferometric studies to resolve emission structures, to possibly constrain molecular freeze-out, and detect water and complex organic molecules. Our results highlight the importance of millimeter line surveys in complementing optical/near-infrared studies, improving statistics on molecular inventories in eruptive stars and their environments., Comment: 45 pages, 20 figures, Accepted for publication in Astronomy & Astrophysics (A&A). This work is dedicated to the memory of Karl M. Menten

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

Context. IRAS 16293E is a rare case of a prestellar core being subjected to the effects of at least one outflow.Aims. We want to disentangle the actual structure of the core from the outflow impact and evaluate the evolutionary stage of the core. Methods. Prestellar cores being cold and depleted, the best tracers of their central regions are the two isotopologues of trihydrogren cation which are observable from the ground, ortho-H$_2$D and para-D$_2$H . We used the Atacama Pathfinder EXperiment (APEX) telescope to map the para-D$_2$H$^+$ emission in IRAS 16293E and collected James Clerk Maxwell Telescope (JCMT) archival data of ortho-H$_2$D$^+$ . We compare their emission to that of other tracers, including dust emission, and analyse their abundance with the help of a 1D radiative transfer tool. The ratio of the abundances of ortho-H$_2$D$^+$ and para-D$_2$H$^+$ can be used to estimate the stage of the chemical evolution of the core.Results. We have obtained the first complete map of para-D$_2$H$^+$ emission in a prestellar core. We compare it to a map of ortho-H$_2$D$^+$ and show their partial anti-correlation. This reveals a strongly evolved core with a para-D$_2$H$^+$/ortho-H$_2$D$^+$ abundance ratio towards the centre for which we obtain a conservative lower limit from 3.9 (at 12 K) up to 8.3 (at 8 K) while the high extinction of the core is indicative of a central temperature below 10 K. This ratio is higher than predicted by the known chemical models found in the literature. Para-D$_2$H$^+$ (and indirectly ortho-H$_2$D$^+$) is the only species that reveals the true centre of this core, while the emission of other molecular tracers and dust are biased by the temperature structure that results from the impact of the outflow.Conclusions. This study invites to reconsider the analysis of previous observations of this source and possibly questions the validity of the deuteration chemical models or of the reaction and inelastic collisional rate coefficients of the H$^{+3}$ isotopologue family. This could impact the deuteration clock predictions for all sources.

Methanol is an abundant molecule in space. The column density of CH$_3^{18}$OH is in some star-forming regions so high that the search for CH$_3^{17}$OH is promising. But only very few transition frequencies of CH$_3^{17}$OH with a microwave accuracy have been published thus far. We recorded the rotational spectrum of CH$_3^{17}$OH between 38 and 1095 GHz employing a methanol sample enriched in $^{17}$O to 20\%. A torsion-rotation Hamiltonian model based on the rho-axis method was employed to fit the data, as in our previous studies. We searched for rotational transitions of CH$_3^{17}$OH in the imaging spectral line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming region Sgr B2(N). The observed spectra were modeled under the assumption of local thermodynamic equilibrium (LTE). The assignments cover $0 \le J \le 45$, $K_a \le 16$, and mainly the $v_ t = 0$ and 1 torsional states. The Hamiltonian model describes our data well. The model was applied to derive a line list for radio-astronomical observations. We report a tentative detection of CH$_3^{17}$OH along with secure detections of the more abundant isotopologs of methanol toward Sgr B2(N2b). The derived column densities yield isotopic ratios $^{12}$C/$^{13}$C = 25, $^{16}$O/$^{18}$O = 240, and $^{18}$O/$^{17}$O = 3.3, which are consistent with values found earlier for other molecules in Sgr B2. The agreement between the $^{18}$O/$^{17}$O isotopic ratio that we obtained for methanol and the $^{18}$O/$^{17}$O ratios reported in the past for other molecules in Sgr B2(N) strongly supports our tentative interstellar identification of CH$_3^{17}$OH. The accuracy of the derived line list is sufficient for further radio astronomical searches for this methanol isotopolog toward other star-forming regions., Comment: 16 pages, including tables, figures, references and appendices. Abstract slightly shortened. Astronomy and Astrophysics, accepted for publication

(abridged) We have mapped the prestellar core H-MM1 in Ophiuchus in rotational lines of ortho-H2D+ (oH2D+), N2H+, and DCO+ at the wavelength 0.8 mm with the Large APEX sub-Millimeter Array (LAsMA) multibeam receiver of the Atacama Pathfinder EXperiment (APEX) telescope. We also ran a series of chemistry models to predict the abundance distributions of the observed molecules, and to estimate the effect of the cosmic-ray ionisation rate on their abundances. The three line maps show different distributions. The oH2D+ map is extended and outlines the general structure of the core, while N2H+ mainly shows the density maxima, and the DCO+ emission peaks are shifted towards one edge of the core where a region of enhanced desorption has been found previously. According to the chemical simulation, the fractional oH2D+ abundance remains relatively high in the centre of the core, and its column density correlates strongly with the cosmic-ray ionisation rate. Simulated line maps constrain the cosmic-ray ionisation rate per hydrogen molecule to be low, between 5e-18/s and 1e-17/s in the H-MM1 core. This estimate agrees with the gas temperature measured in the core. Modelling line emission of oH2D+ provides a straightforward method of determining the cosmic-ray ionisation rate in dense clouds, where the primary ion, H3+, is not observable., Comment: accepted for publication in Astronomy & Astrophysics

Infrared emission features toward interstellar gas of the IC 348 star cluster in Perseus have been recently proposed to originate from the amino acid tryptophan. The assignment was based on laboratory infrared spectra of tryptophan pressed into pellets, a method which is known to cause large frequency shifts compared to the gas phase. We assess the validity of the assignment based on the original Spitzer data as well as new data from JWST. In addition, we report new spectra of tryptophan condensed in para-hydrogen matrices to compare with the observed spectra. The JWST MIRI data do not show evidence for tryptophan, despite deeper integration toward IC 348. In addition, we show that several of the lines attributed to tryptophan are likely due to instrumental artifacts. This, combined with the new laboratory data, allows us to conclude that there is no compelling evidence for the tryptophan assignment.

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

We want to investigate the influence of the powerful outflow driven by the hot core Sgr B2(N1) on the gas molecular inventory of the surrounding medium. We used the data taken as part of the 3 mm imaging spectral-line survey ReMoCA (Re-exploring Molecular Complexity with ALMA). Integrated intensity maps of SO and SiO emission reveal a bipolar structure with blue-shifted emission dominantly extending to the SE from the centre of the hot core and red-shifted emission to the NW. This is also prominently observed in emission of other S-bearing molecules and species that only contain N as a heavy element, including COMs, but also CH3OH, CH3CHO, HNCO, and NH2CHO. For a selection of COMs and simpler species, spectra were modelled under the assumption of LTE and population diagrams were derived at two positions, one in each outflow lobe. From this analysis, we obtained rotational temperatures, which are in a range of ~100-200K, and column densities. Abundances were subsequently compared to predictions of astrochemical models and to observations of L1157-B1, a position located in the well-studied outflow of the low-mass protostar L1157, and the source G+0.693-0.027, located in the Sgr B2 molecular cloud complex. Given the short distance of the analysed outflow positions to the centre of Sgr B2(N1), we propose a scenario in which a phase of hot-core chemistry (i.e. thermal desorption of ice species and high-temperature gas-phase chemistry) preceded a shock wave. The subsequent compression and further heating of the material resulted in the accelerated destruction of (mainly O-bearing) molecules. Gas-phase formation of cyanides seems to be able to compete with their destruction in the post-shock gas. Abundances of HCnN (n=3,5) are enhanced in the outflow component pointing to (additional) gas-phase formation. To confirm such a scenario, appropriate chemical shock models need to be run., Comment: Accepted for publication in A&A

Protonated hydrogen cyanide, HCNH$^{+}$, plays a fundamental role in astrochemistry because it is an intermediary in gas-phase ion-neutral reactions within cold molecular clouds. However, the impact of the environment on the chemistry of HCNH$^{+}$ remains poorly understood. With the IRAM-30 m and APEX-12 m observations, we report the first robust distribution of HCNH$^{+}$ in the Serpens filament and in Serpens South. Our data suggest that HCNH$^{+}$ is abundant in cold and quiescent regions, but is deficit in active star-forming regions. The observed HCNH$^{+}$ fractional abundances relative to H$_{2}$ range from $3.1\times 10^{-11}$ in protostellar cores to $5.9\times 10^{-10}$ in prestellar cores, and the HCNH$^{+}$ abundance generally decreases with increasing H$_{2}$ column density, which suggests that HCNH$^{+}$ coevolves with cloud cores. Our observations and modeling results suggest that the abundance of HCNH$^{+}$ in cold molecular clouds is strongly dependent on the H$_{2}$ number density. The decrease in the abundance of HCNH$^{+}$ is caused by the fact that its main precursors (e.g., HCN and HNC) undergo freeze-out as the number density of H$_{2}$ increases. However, current chemical models cannot explain other observed trends, such as the fact that the abundance of HCNH$^{+}$ shows an anti-correlation with that of HCN and HNC, but a positive correlation with that of N$_{2}$H$^{+}$ in the southern part of the Serpens South northern clump. This indicates that additional chemical pathways have to be invoked for the formation of HCNH$^{+}$ via molecules like N$_{2}$ in regions in which HCN and HNC freeze out. Both the fact that HCNH$^{+}$ is most abundant in molecular cores prior to gravitational collapse and the fact that low-$J$ HCNH$^{+}$ transitions have very low H$_{2}$ critical densities make this molecular ion an excellent probe of pristine molecular gas., Comment: 25 pages, 26 figures, accepted for publication in A&A

Methylamine has been the only simple alkylamine detected in the interstellar medium for a long time. With the recent secure and tentative detections of vinylamine and ethylamine, respectively, dimethylamine has become a promising target for searches in space. Its rotational spectrum, however, has been known only up to 45 GHz until now. Here we investigate the rotation-tunneling spectrum of dimethylamine in selected regions between 76 and 1091 GHz using three different spectrometers in order to facilitate its detection in space. The quantum number range is extended to $J = 61$ and $K_a = 21$, yielding an extensive set of accurate spectroscopic parameters. To search for dimethylamine, we refer to the spectral line survey ReMoCA carried out with the Atacama Large Millimeter/submillimeter Array toward the high-mass star-forming region Sagittarius B2(N) and a spectral line survey of the molecular cloud G+0.693$-$0.027 employing the IRAM 30 m and Yebes 40 m radio telescopes. We report nondetections of dimethylamine toward the hot molecular cores Sgr B2(N1S) and Sgr B2(N2b) as well as G+0.693$-$0.027 which imply that dimethylamine is at least 14, 4.5 and 39 times less abundant than methylamine toward these sources, respectively. The observational results are compared to computational results from a gas-grain astrochemical model. The modeled methylamine to dimethylamine ratios are compatible with the observational lower limits. However, the model produces too much ethylamine compared with methylamine which could mean that the already fairly low levels of dimethylamine in the models may also be too high., Comment: Mon. Not. R. Astron. Soc., accepted. 33 pages including tables, figures, and appendix

FU Orionis (FUor) and EX Lupi (EXor) type objects are two groups of peculiar and rare pre-main sequence low-mass stars that are undergoing powerful accretion outbursts during their early stellar evolution. Water masers are widespread in star forming regions and are powerful probes of mass accretion and ejection, but little is known about the prevalence of them toward FUors/EXors. We perform the first systematic search for the 22.2 GHz water maser line in FUors/EXors to determine its overall incidence to perform follow-up high angular resolution observations. We used the Effelsberg 100-m radio telescope to observe the 22.2 GHz H2O maser toward a sample of 51 objects. We detect 5 water masers; 3 are associated with eruptive stars, resulting in a 6% detection rate for eruptive sources. These detections include one EXor, V512 Per (also known as SVS 13 or SVS 13A), and two FUors, Z CMa and HH 354 IRS. This is the first reported detection of water maser emission towards HH 354 IRS. We detect water maser emission in our pointing towards the FUor binary RNO 1B/1C, which most likely originates from the nearby deeply embedded source IRAS 00338+6312 (~4'', from RNO 1B/1C). Emission was also detected from H$_2$O(B) (also known as SVS 13C), a Class 0 source ~30'', from the EXor V512 Per. The peak flux density of H$_2$O(B) in our observations, 498.7 Jy, is the highest observed to date. In addition to the two non-eruptive Class 0 sources (IRAS 00338+6312 and H$_2$O(B) /SVS 13C), we detect maser emission towards one Class 0/I (HH 354 IRS) and two Class I (V512 Per and Z CMa) eruptive stars. We demonstrate the presence of 22.2 GHz water maser emission in FUor/EXor systems, opening the way to radio interferometric observations to study these eruptive stars on small scales. Comparing our data with historical observations suggest that multiple water maser flares have occurred in both V512 Per and H$_2$O(B)., Comment: 12 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

FU Orionis (FUor) and EX Lupi (EXor) type objects represent two small, but rather spectacular groups of low-mass, young eruptive stars. Outbursts of several magnitudes are observed, attributed to enhanced accretion from the circumstellar disk onto the central protostar. The host molecular environments of FUors/EXors are poorly explored due to the scarcity of systematic molecular line observations. We carried out the first dedicated survey of the molecular environments of a large sample of FUors/EXors, observing a total of 51 sources with the aim of studying the ammonia (NH$_3$) emission in their host environments. We observed the ammonia (J,K)=(1,1), (2,2), and (3,3) inversion transitions using the Effelsberg 100-m radio telescope. We derived H$_2$ column densities and dust temperatures using archival Herschel SPIRE data. We detected the (1,1) transition toward 28 sources and the (2,2) transition toward 12 sources, while the (3,3) transition was detected toward only two sources. We find kinetic temperatures between ~12 K and 21 K, ammonia column densities from $5.2\times10^{13}\,cm^{-2}$ to $3.2\times10^{15}\,cm^{-2}$, and fractional ammonia abundances with respect to H$_{2}$ from $4.7\times10^{-9}$ to $1.5\times10^{-7}$. The results are comparable to those found in infrared dark clouds (IRDCs). Kinetic analysis suggests that most of the eruptive stars in our sample reside in rather quiescent (sonic or transonic) host environments. Our NH$_3$ observations and analysis of the SPIRE dust-based H$_2$ column density maps confirm the presence of dense material toward 7 sources in our sample; additional sources might also harbour dense gas based on their NH$_2$ (2,2) detections, might indicate an earlier phase than originally classified. Based on our results, we suggest observations targeting additional molecular lines would help to refine the evolutionary classification of eruptive stars., Comment: 20 pages, 2 figures, accepted for publication in A&A

Up to date, only 6 imines have been detected in the interstellar medium. The 3-carbon imine, 2-propanimine ((CH$_3$)$_2$C=NH), is predicted to be the structural isomer with the lowest energy in the C$_3$H$_7$N group, and appears to be a good candidate for astronomical searches. Unexpectedly, no microwave or millimeter wave spectrum is available for 2-propanimine. In this work, we provide the first high resolution millimeter wave spectrum of 2-propanimine and its analysis. With the guide of this laboratory measurement, we aim to search for 2-propanimine in two molecule-rich sources Sgr B2(N) and IRAS 16293-2422 using observations from the Atacama Large Millimeter/submillimeter Array (ALMA). Starting from a synthesized sample, we measured the spectrum of 2-propanimine from 50 to 500 GHz, and the ground state lines are successfully assigned and fitted using XIAM and ERHAM programs with the aid of theoretical calculations. The barriers to internal rotation of the two CH$_3$ tops are determined to be 531.956(64) cm$^{-1}$ and 465.013(26) cm$^{-1}$. These data are able to provide reliable prediction of transition frequencies for astronomical search. Although a few line matches exist, no confirmed detection of 2-propanimine has been found in the hot molecular core Sgr B2(N1S) and the Class 0 protostar IRAS 16293B. Upper-limits of its column density have been derived, and indicate that 2-propanimine is at least 18 times less abundant than methanimine in Sgr B2(N1S), and is at most 50-83 % of methanimine in IRAS 16293B., Comment: 14 pages, 10 figures

We report the discovery of widespread maser emission in non-metastable inversion transitions of NH$_3$ toward various parts of the Sagittarius B2 molecular cloud/star forming region complex: We detect masers in the $J,K = $ (6,3), (7,4), (8,5), (9,6), and (10,7) transitions toward Sgr B2(M) and Sgr B2(N), an NH$_3$ (6,3) maser in Sgr B2(NS), and NH$_3$ (7,4), (9,6), and (10,7) masers in Sgr B2(S). With the high angular resolution data of the Karl G. Jansky Very Large Array (JVLA) in A-configuration we identify 18 maser spots. Nine maser spots arise from Sgr B2(N), one from Sgr B2(NS), five from Sgr B2(M), and three in Sgr B2(S). Compared to our Effelsberg single dish data, the JVLA data indicate no missing flux. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are $>$3000~K and reach up to several 10$^5$~K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or UCH{\scriptsize II} regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH{\scriptsize II} regions. Overall, Sgr B2 is unique in that it allows us to measure many NH$_3$ masers simultaneously, which may be essential to elucidate their so far poorly understood origin and excitation., Comment: 17 pages, 14 figures, 7 tables. Accepted for publication in A&A Letter

The molecule studied in this work, 2-hydroxyprop-2-enal, is among the candidates to be searched for in the interstellar medium (ISM), as it is a dehydration product of C3 sugars and contains structural motifs typical for some interstellar molecules. The aim of this work is to deepen knowledge about the millimetre-wave spectrum of 2-hydroxyprop-2-enal in the region enabling its search towards astronomical objects. We target the solar-type protostar IRAS16293-2422 and star-forming region Sagittarius (Sgr) B2(N). The rotational spectrum of 2-hydroxyprop-2-enal was measured and analysed in the frequency regions of 128-166 GHz and 285-329 GHz. The interstellar exploration towards IRAS16293-2422 was based on the Atacama Large Millimeter/submillimeter Array (ALMA) data of the Protostellar Interferometric Line Survey. We also used the imaging spectral line survey ReMoCA performed with ALMA toward Sgr B2(N). We modelled the astronomical spectra under the assumption of local thermodynamic equilibrium. We provide analysis of hundreds of rotational transitions of 2-hydroxyprop-2-enal in the ground state and the lowest lying excited vibrational state. We report its nondetection towards IRAS16293 B. The 2-hydroxyprop-2-enal/3-hydroxypropenal abundance ratio is estimated to be less-than or similar to 0.9-1.3 in agreement with the predicted value of 1.4. We also report the nondetection of 2-hydroxyprop-2-enal toward the hot molecular core Sgr B2(N1). We did not detect the related aldehydes 2-hydroxypropanal and 3-hydroxypropenal either. We find that these three molecules are at least 9, 4, and 10 times less abundant than acetaldehyde in this source, respectively. Despite the nondetections, the results of this work represent a significant improvement on previous investigations in the microwave region and meets the requirements for further searches of this molecule in the ISM., Comment: Accepted for publication in A&A

The interstellar detections of isocyanic acid, methyl isocyanate, and very recently also ethyl isocyanate, open the question of the possible detection of vinyl isocyanate in the interstellar medium. The aim of this study is to extend the laboratory rotational spectrum of vinyl isocyanate into the millimeter wave region and to undertake a check for its presence in the high-mass star forming region Sgr B2. The rotational spectrum of vinyl isocyanate was recorded in the frequency regions 127.5-218 and 285-330 GHz using the Prague millimeter wave spectrometer. The spectral analysis was supported by high-level quantum-chemical calculations. We assumed local thermodynamic equilibrium to compute synthetic spectra of vinyl isocyanate and to search for it in the ReMoCA survey performed with ALMA toward Sgr B2(N). We also searched for ethyl isocyanate in the same source. Accurate values for the rotational and centrifugal distortion constants are reported for the ground vibrational states of trans and cis vinyl isocyanate. We report nondetections of vinyl and ethyl isocyanate toward the main hot core of Sgr B2(N). We find that vinyl and ethyl isocyanate are at least 11 and 3 times less abundant than methyl isocyanate in this source, respectively. Although the precise formation mechanism of interstellar methyl isocyanate itself remains uncertain, we infer from existing astrochemical models that our observational upper limit for the CH3NCO:C2H5NCO ratio in Sgr B2(N) is consistent with ethyl isocyanate being formed on dust grains via the abstraction or photodissociation of an H atom from methyl isocyanate, followed by the addition of a methyl radical. The dominance of such a process for ethyl isocyanate production, combined with the absence of an analogous mechanism for vinyl isocyanate, would indicate that the ratio C2H3NCO:C2H5NCO should be rather less than unity., Comment: Accepted for publication in A&A

Using the high angular resolution provided by the ALMA interferometre we want to resolve the COM emission in the hot molecular core Sagittarius B2(N1) and thereby shed light on the desorption process of Complex Organic Molecules (COMs) in hot cores. We use data taken as part of the 3 mm spectral line survey Re-exploring Molecular Complexity with ALMA (ReMoCA) to investigate the morphology of COM emission in Sagittarius B2(N1). Spectra of ten COMs are modelled under the assumption of LTE and population diagrams are derived for positions at various distances to the south and west from the continuum peak. Based on this analysis, resolved COM rotation temperature and COM abundance profiles are derived. Based on the morphology, a rough separation into O- and N-bearing COMs can be done. Temperature profiles are in agreement with expectations of protostellar heating of an envelope with optically thick dust. Abundance profiles reflect a similar trend as seen in the morphology and, to a great extent, agree with results of astrochemical models that, besides the co-desorption with water, predict that O-bearing COMs are mainly formed on dust grain surfaces at low temperatures while at least some N-bearing COMs and CH$_3$CHO are substantially formed in the gas phase at higher temperatures. Our observational results, in comparison with model predictions, suggest that COMs that are exclusively or to a great extent formed on dust grains desorb thermally at ~100 K from the grain surface likely alongside water. Non-zero abundance values below ~100 K suggest that another desorption process is at work at these low temperatures: either non-thermal desorption or partial thermal desorption related to lower binding energies experienced by COMs in the outer, water-poor ice layers. In either case, this is the first time that the transition between two regimes of COM desorption has been resolved in a hot core., Comment: Accepted for publication in A&A

The primary alcohol $n$-propanol (i.e., $normal$-propanol or propan-1-ol; C$_3$H$_7$OH) occurs in five different conformers: $Ga$, $Gg$, $Gg'$, $Aa$, and $Ag$. All rotational spectra of the three conformers of the $G$ family are well described, making astronomical search of their spectroscopic signatures possible, as opposed to those of the $Aa$ and $Ag$ conformers. Our goal is to facilitate the astronomical detection of $Aa$ and $Ag$ conformers of $n$-propanol by characterizing their rotational spectra. We recorded the rotational spectra of $n$-propanol in the frequency domain of 18$-$505\,GHz.Additional double-modulation double-resonance (DM-DR) measurements were performed, more specifically with the goal to unambiguously assign weak transitions of the $Aa$ conformer and to verify assignments of the $Ag$ conformer. We derived a spectroscopic quantum mechanical model with experimental accuracy (with $J_\textrm{max}=70$ and $K_{a,\textrm{max}}=6$) for $Aa$ $n$-propanol. Furthermore, we unambiguously assigned transitions (with $J_\textrm{max}=69$ and $K_{a,\textrm{max}}=9$) of $Ag$ $n$-propanol; in doing so, we prove the existence of two tunneling states, $Ag^+$ and $Ag^-$. The astronomical search of all five conformers of $n$-propanol is now possible via their rotational signatures. These are applied in a companion article on the detection of $n$-propanol toward the hot molecular core Sgr B2(N2).

The detection of a branched alkyl molecule in the high-mass star forming protocluster Sgr B2(N) permitted by the advent of ALMA revealed a new dimension of interstellar chemistry. Astrochemical simulations subsequently predicted that beyond a certain degree of molecular complexity, branched molecules could even dominate over their straight-chain isomers. More generally, we aim at probing further the presence in the ISM of complex organic molecules with the capacity to exhibit both a normal and iso form, via the attachment of a functional group to either a primary or secondary carbon atom. We used the imaging spectral line survey survey ReMoCA performed with ALMA and the results of a recent spectroscopic study of propanol to search for the iso and normal isomers of this molecule in the hot molecular core Sgr B2(N2). We expanded the network of the astrochemical model MAGICKAL to explore the formation routes of propanol. We report the first interstellar detection of iso-propanol toward a position of Sgr B2(N2) that shows narrow linewidths. We also report the first secure detection of normal-propanol in a hot core. i-Propanol is found to be nearly as abundant as n-propanol, with an abundance ratio of 0.6 similar to the ratio of 0.4 that we obtained previously for i- and n-propyl cyanide in Sgr B2(N2). The results are in good agreement with the outcomes of our astrochemical models, which indicate that OH-radical addition to propylene in dust-grain ice mantles, driven by water photodissociation, can produce appropriate quantities of n- and i-propanol. The n-to-i ratio in Sgr B2(N2) may be a direct inheritance of the branching ratio of this reaction process. The detection of n- and i-propanol and their ratio indicate that the modest preference toward the normal form of propyl cyanide determined previously may be a more general feature among similarly sized interstellar molecules. [abridged], Comment: Accepted for publication in Astronomy and Astrophysics

In recent times, large organic molecules of exceptional complexity have been found in diverse regions of the interstellar medium. In this context, we aim to provide accurate frequencies of the ground vibrational state of two key aliphatic aldehydes, n-butanal and its branched-chain isomer, i-butanal, to enable their eventual detection in the interstellar medium. We employ a frequency modulation millimeter-wave absorption spectrometer to measure the rotational features of n- and i-butanal. We use the spectral line survey ReMoCA performed with the Atacama Large Millimeter/submillimeter Array to search for n- and i-butanal toward the star-forming region Sgr B2(N). We also search for both aldehydes toward the molecular cloud G+0.693-0.027 with IRAM 30 m and Yebes 40 m observations. Several thousand rotational transitions belonging to the lowest-energy conformers have been assigned in the laboratory spectra up to 325 GHz. A precise set of the relevant rotational spectroscopic constants has been determined for each structure. We report non-detections of n- and i-butanal toward both sources, Sgr B2(N1S) and G+0.693-0.027. We find that n- and i-butanal are at least 2-6 and 6-18 times less abundant than acetaldehyde toward Sgr B2(N1S), respectively, and that n-butanal is at least 63 times less abundant than acetaldehyde toward G+0.693-0.027. Comparison with astrochemical models indicates good agreement between observed and simulated abundances (where available). Grain-surface chemistry appears sufficient to reproduce aldehyde ratios in G+0.693-0.027; gas-phase production may play a more active role in Sgr B2(N1S). Our astronomical results indicate that the family of interstellar aldehydes in the Galactic center region is characterized by a drop of one order of magnitude in abundance at each incrementation in the level of molecular complexity.

During star formation, the dense gas undergoes significant chemical evolution leading to the emergence of a rich variety of molecules associated with hot cores and hot corinos. The physical and chemical conditions are poorly constrained; the early phases of emerging hot cores in particular represent an unexplored territory. We provide here a full molecular inventory of a massive protostellar core that is proposed to be a precursor of a hot core. We performed an unbiased spectral survey towards the hot core precursor associated with clump G328.2551-0.5321 between 159GHz and 374GHz. To identify the spectral lines, we used rotational diagrams and radiative transfer modelling assuming LTE. We detected 39 species and 26 isotopologues, and were able to distinguish a warm and compact inner region, a colder more extended envelope, and the kinematic signatures of the accretion shocks that have previously been observed with ALMA. We associate most of the emission of the small molecules with the cold gas, while the molecular emission of the warm gas is enriched by complex organic molecules (COMs). We find a high abundance of S-bearing molecules in the cold gas phase suggesting a low sulphur depletion, with a factor of > 1%. We identify nine COMs in the warm gas, four in the cold gas, and four towards the accretion shocks. The high abundances of S-bearing species originating from the undisturbed gas may suggest a contribution from shocked gas at the outflow cavity walls. The molecular composition of the warm gas is similar to that of both hot cores and hot corinos, but the molecular abundances are closer to the values found towards hot corinos than to values found towards hot cores. Considering the compactness of the warm region and its moderate temperature, we suggest that thermal desorption has not been completed towards this object yet, representing an early phase of the emergence of hot cores., Comment: 68 pages, 59 figures. Accepted by A&A after refereeing and language corrections. Abstract abbreviated

Thioacetamide (CH3CSNH2) is the sulfur analog to acetamide (CH3CONH2) and it is a viable candidate to search for in astronomical environments specifically toward regions where other S-bearing molecules have been found and, if possible, that also contain a detection of CH3CONH2. If detected, it would not only continue to expand the view of molecular complexity in astronomical environments, but also help to better elucidate the possible formation pathways of these types of species in these environments. The rotational spectrum of CH3CSNH2 was investigated up to 650 GHz. Using the newly refined spectrum of CH3CSNH2, as well as additional spectroscopic data on the chemically related species CH3CONH2, a variety of astronomical sources were searched including data from the following large surveys: The PRIMOS conducted with the Green Bank Telescope (GBT); Exploring molecular complexity with ALMA (EMoCA) conducted with ALMA; and Astrochemical Surveys at IRAM (ASAI) conducted with the Institut de Radioastronomie Millimetrique (IRAM) 30m Telescope. A total of 1428 transitions from the vt=0 state with maximum values J=47 and Ka=20 in the range up to 330 GHz, and J=95 and Ka=20 in the range from 400 - 660 GHz were assigned. We also assigned 321 transitions from the vt=1 state with the maximum values J=35 and Ka=9 up to 330 GHz. The final fit is based on the rho-axis-method (RAM) Hamiltonian model that includes 40 parameters. An astronomical search for CH3CSNH2 was conducted based on all the new spectroscopic data. No transitions of CH3CSNH2 were detected toward any of the sources contained in our survey. Using the appropriate telescope and physical parameters for each astronomical source, upper limits to the column densities were found for CH3CSNH2 toward each source., Comment: 16 pages, 8 figures, accepted for publication in Astronomy & Astrophysics

Numerous complex organic molecules have been detected in the universe among which amides are considered as models for species containing the peptide linkage. Acrylamide bears in its backbone not only the peptide bond, but also the vinyl functional group which is a common motif in many interstellar compounds. This makes acrylamide an interesting target for a search in space. In addition, a tentative detection of the related molecule propionamide has been recently claimed toward Sgr B2(N). We report accurate laboratory measurements and analyses of thousands rotational transitions for the syn and skew forms of acrylamide between 75 and 480 GHz. Tunneling through a low energy barrier between two symmetrically equivalent configurations has been revealed for the higher-energy skew species. We searched for emission of acrylamide in the imaging spectral line survey ReMoCA performed with ALMA toward Sgr B2(N). We also searched for propionamide in the same source. Neither acrylamide nor propionamide were detected toward the two main hot molecular cores of Sgr B2(N). We did not detect propionamide either toward a position located to the east of the main hot core, thereby not confirming the recent claim of its interstellar detection toward this position. We find that acrylamide and propionamide are at least 26 and 14 times, respectively, less abundant than acetamide toward the main hot core Sgr B2(N1S), and at least 6 and 3 times, respectively, less abundant than acetamide toward the secondary hot core Sgr B2(N2). A comparison with results of astrochemical kinetics model for related species suggests that acrylamide may be a few hundred times less abundant than acetamide, corresponding to a value at least an order of magnitude lower than the observational upper limits. Propionamide may be as little as only a factor of two less abundant than the upper limit derived toward Sgr B2(N1S)., Comment: Accepted for publication in A&A

Glycinamide is considered to be one of the possible precursors of the simplest amino acid glycine. Its only rotational spectrum reported so far has been in the cm-wave region. The aim of this work is to extend its laboratory spectrum into the mm wave region to support its searches in the ISM. Glycinamide was synthesised chemically and was studied with broadband rotational spectroscopy in the 90-329 GHz region. Tunneling across a low energy barrier between two symmetry equivalent configurations of the molecule resulted in splitting of each vibrational state and many perturbations in associated rotational energy levels, requiring careful coupled state fits for each vibrational doublet. We searched for emission of glycinamide in the imaging spectral line survey ReMoCA performed with ALMA toward Sgr B2(N). We report the first analysis of the mm-wave rotational spectrum of glycinamide, resulting in fitting to experimental measurement accuracy of over 1200 transition frequencies for the ground state tunneling doublet, of many lines for tunneling doublets for two singly excited vibrational states, and determination of precise vibrational separation in each doublet. We did not detect emission from glycinamide in the hot core Sgr B2(N1S). We found that glycinamide is at least seven times less abundant than aminoacetonitrile and 1.8 times less abundant than urea in this source. A comparison with results of astrochemical kinetics models for species related to glycinamide suggests that its abundance may be at least one order of magnitude below the upper limit obtained toward Sgr B2(N1S). This means that glycinamide emission in this source likely lies well below the spectral confusion limit in the frequency range covered by the ReMoCA survey. Targetting sources with a lower level of spectral confusion, such as the Galactic Center shocked region G+0.693-0.027, may be a promising avenue. [abridged], Comment: Accepted for publication in A&A

New and existing rotational spectra of methyl cyanide were analyzed to extend the global model of low-lying vibrational states and their interactions to $v_4=1$ at 920 cm$^{-1}$. The rotational spectra cover large portions of the 36$-$1439 GHz region and reach quantum numbers $J$ and $K$ of 79 and 16, respectively. Information on the $K$ level structure of CH$_3$CN is obtained from IR spectra. A spectrum of $2\nu_8$ around 717 cm$^{-1}$, analyzed in our previous study, covered also the $\nu_4$ band. The assignments in this band cover 880$-$952 cm$^{-1}$, attaining quantum numbers $J$ and $K$ of 61 and 13, respectively. The most important interaction of $v_4=1$ appears to be with $v_8=3$, $\Delta K=0$, $\Delta l=+3$, a previously characterized anharmonic resonance. We report new analyses of interactions with $\Delta K=-2$ and $\Delta l=+1$, with $\Delta K=-4$ and $\Delta l=-1$, and with $\Delta K=-6$ and $\Delta l=-3$; these four types of interactions connect all $l$ substates of $v_8=3$ in energy to $v_4=1$. A known $\Delta K=-2$, $\Delta l=+1$ interaction with $v_7=1$ was also analyzed, and investigations of the $\Delta K=+1$, $\Delta l=-2$ and $\Delta K=+3$, $\Delta l=0$ resonances with $v_8=2$ were improved, as were interactions between successive states with $v_8\le 3$, mainly through new $v_8\le 2$ rotational data. A preliminary single state analysis of the $v_4=v_8=1$ state was carried out based on rotational transition frequencies and on $\nu_4+\nu_8-\nu_8$ hot band data. A considerable fraction of the $K$ levels was reproduced within uncertainties in its entirety or in part, despite obvious widespread perturbations in $v_4=v_8=1$. We detect rotational transitions of methyl cyanide from within all vibrational states up to $v_4=1$ and $v_4=v_8=1$ tentatively toward the hot molecular core of Sagittarius B2(N) employing the Atacama Large Millimeter Array., Comment: 30 pages, J. Mol. Spectrosc., accepted

For all the amides detected in the interstellar medium (ISM), the corresponding nitriles or isonitriles have also been detected in the ISM, some of which have relatively high abundances. Among the abundant nitriles for which the corresponding amide has not yet been detected is cyanoacetylene (HCCCN), whose amide counterpart is propiolamide (HCCC(O)NH$_2$). With the aim of supporting searches for this amide in the ISM, we provide a complete rotational study of propiolamide from 6 GHz to 440 GHz using rotational spectroscopic techniques in the frequency and time domain. We identified and measured more than 5500 distinct frequency lines of propiolamide and obtained accurate sets of spectroscopic parameters for the ground state and the three low-lying excited vibrational states. We used the ReMoCA spectral line survey performed with the Atacama Large Millimeter/submillimeter Array toward the star-forming region Sgr B2(N) to search for propiolamide. We report the nondetection of propiolamide toward the hot cores Sgr B2(N1S) and Sgr B2(N2). We find that propiolamide is at least 50 and 13 times less abundant than acetamide in Sgr B2(N1S) and Sgr B2(N2), respectively, indicating that the abundance difference between both amides is more pronounced by at least a factor of 8 and 2, respectively, than for their corresponding nitriles. Although propiolamide has yet to be included in astrochemical modeling networks, the observed upper limit to the ratio of propiolamide to acetamide seems consistent with the ratios of related species as determined from past simulations., Comment: The article will be published as a regular paper in Astronomy and Astrophysics

As a part of the CALYPSO large programme, we constrain the properties of protostellar jets and outflows in a sample of 21 Class 0 protostars with internal luminosities, Lint, from 0.035 to 47 Lsun. We analyse high angular resolution (~0.5"-1") IRAM PdBI observations in CO (2-1), SO ($5_6-4_5$), and SiO (5-4). CO (2-1), which probes outflowing gas, is detected in all the sources (for the first time in SerpS-MM22 and SerpS-MM18b). Collimated high-velocity jets in SiO (5-4) are detected in 67% of the sources (for the first time in IRAS4B2, IRAS4B1, L1448-NB, SerpS-MM18a), and 77% of these also show jet/outflow emission in SO ($5_6-4_5$). In 5 sources (24% of the sample) SO ($5_6-4_5$) probes the inner envelope and/or the disk. The CALYPSO survey shows that the outflow phenomenon is ubiquitous and that the detection rate of high-velocity jets increases with protostellar accretion, with at least 80% of the sources with Lint>1 Lsun driving a jet. The protostellar flows exhibit an onion-like structure, where the SiO jet (opening angle ~10$^o$) is nested into a wider angle SO (~15$^o$) and CO (~25$^o$) outflow. On scales >300 au the SiO jets are less collimated than atomic jets from Class II sources (~3$^o$). Velocity asymmetry between the two jet lobes are detected in one third of the sources, similarly to Class II atomic jets, suggesting that the same launching mechanism is at work. Most of the jets are SiO rich (SiO/H2 from >2.4e-7 to >5e-6), which indicates efficient release of >1%-10% of silicon in gas phase likely in dust-free winds, launched from inside the dust sublimation radius. The mass-loss rates (from ~7e-8 to ~3e-6 Msun/yr) are larger than what was measured for Class II jets. Similarly to Class II sources, the mass-loss rates are ~1%-50% of the mass accretion rates suggesting that the correlation between ejection and accretion in young stars holds from 1e4 yr up to a few Myr., Comment: Accepted for publication by A&A, 40 pages, 7 figures + appendixes

The Serpens filament, a prominent elongated structure in a relatively nearby molecular cloud, is believed to be at an early evolutionary stage, so studying its physical and chemical properties can shed light on filament formation and early evolution. The main goal is to address the physical and chemical properties as well as the dynamical state of the Serpens filament at a spatial resolution of $\sim$0.07 pc and a spectral resolution of $\lesssim$0.1~km~s$^{-1}$. We performed $^{13}$CO (1--0), C$^{18}$O (1--0), C$^{17}$O (1--0), $^{13}$CO (2--1), C$^{18}$O (2--1), and C$^{17}$O (2--1) imaging observations toward the Serpens filament with the Institut de Radioastronomie Millim{\'e}trique 30-m (IRAM-30 m) and Atacama Pathfinder EXperiment (APEX) telescopes. Widespread narrow $^{13}$CO (2--1) self-absorption is observed in this filament, causing the $^{13}$CO morphology to be different from the filamentary structure traced by C$^{18}$O and C$^{17}$O. Our excitation analysis suggests that the opacities of C$^{18}$O transitions become higher than unity in most regions, and this analysis confirms the presence of widespread CO depletion. Further we show that the local velocity gradients have a tendency to be perpendicular to the filament's long axis in the outskirts and parallel to the large-scale magnetic field direction. The magnitudes of the local velocity gradients decrease toward the filament's crest. The observed velocity structure can be a result of gravity-driven accretion flows. The isochronic evolutionary track of the C$^{18}$O freeze-out process indicates the filament is young with an age of $\lesssim$2 Myr. We propose that the Serpens filament is a newly-formed slightly-supercritical structure which appears to be actively accreting material from its ambient gas., Comment: 26 pages, 24 figures, 2 tables, accepted for publication in A&A; A 3D view of the C18O(2-1) cube can be found in https://gongyan2444.github.io/gallery.html

Context. The process of mass accretion in the earliest phases of star formation is still not fully understood: Does the accretion rate smoothly decline with the age of the protostar or are there short, intermittent accretion bursts? Aims. We aim to explore whether or not the observed C$^{18}$O and N$_2$H$^+$ emission pattern towards the VeLLO IRAM 04191+1522 can be understood in the framework of a scenario where the emission is chemically tracing a past accretion burst. Methods.We used high-angular-resolution Plateau de Bure Interferometer (PdBI) observations of C$^{18}$O and N$_2$H$^+$ towards IRAM 04191+1522 that were obtained as part of the CALYPSO IRAM Large Program. We model these observations using a chemical code with a time-dependent physical structure coupled with a radiative transfer module, where we allow for variations in the source luminosity. Results. We find that the N$_2$H$^+$ line emission shows a central hole, while the C$^{18}$O emission is compact. The morphology of these two lines cannot be reproduced with a constant luminosity model based on the present-day internal luminosity (0.08 L$_{sun}$). However, the N$_2$H$^+$ peaks are consistent with a constant-luminosity model of 12 L$_{sun}$. Using a model with time-dependent temperature and density profiles, we show that the observed N$_2$H$^+$ peak emission could indeed be caused by a past accretion burst. Such a burst should have occurred a couple of hundred years ago. Conclusions. We suggest that an accretion burst occurred in IRAM 04191+1522 in the recent past. If such bursts are common and sufficiently long in VeLLOs, they could lead to higher accretion onto the central object than their luminosity suggests. For IRAM 04191 in particular, our results yield an estimated final mass of 0.2 - 0.25 M$_{sun}$ by the end of the Class 0 phase, which would make this object a low-mass star rather than a brown dwarf., Comment: 13 pages, 12 figures, Accepted for publication in A&A, (this version with corrected list of authors in metadata)

Thioformamide NH2CHS is a sulfur-bearing analog of formamide NH2CHO. The latter was detected in the interstellar medium back in the 1970s. Most of the sulfur-containing molecules detected in the interstellar medium are analogs of corresponding oxygen-containing compounds. Therefore, thioformamide is an interesting candidate for a search in the interstellar medium. The rotational spectrum of thioformamide was measured and analyzed in the frequency range 150 to 660 GHz using the Lille spectrometer. We searched for thioformamide toward the high-mass star-forming region Sagittarius (Sgr) B2(N) using the ReMoCA spectral line survey carried out with the Atacama Large Millimeter/submillimeter Array (ALMA). Accurate rotational constants were obtained from the analysis of the ground state of parent, 34S, 13C, and 15N singly substituted isotopic species of thioformamide. For the parent isotopolog, the lowest two excited vibrational states, v12 = 1 and v9 = 1, were analyzed using a model that takes Coriolis coupling into account. Thioformamide was not detected toward the hot cores Sgr B2(N1S) and Sgr B2(N2). The sensitive upper limits indicate that thioformamide is nearly three orders of magnitude at least less abundant than formamide. This is markedly different from methanethiol, which is only about two orders of magnitude less abundant than methanol in both sources. The different behavior shown by methanethiol versus thioformamide may be caused by the preferential formation of the latter (on grains) at late times and low temperatures, when CS abundances are depressed. This reduces the thioformamide-to-formamide ratio, because the HCS radical is not as readily available under these conditions.

Measuring isotopic ratios is a sensitive technique used to obtain information on stellar nucleosynthesis and chemical evolution. We present measurements of the carbon and sulphur abundances in the interstellar medium of the central region of our Galaxy. The selected targets are the +50km/s Cloud and several l.o.s. clouds towards Sgr B2(N). Towards the +50km/s Cloud, we observed the J=2-1 rotational transitions of CS, C34S, 13CS, C33S, and 13C34S, and the J=3-2 transitions of CS and C34S with the IRAM-30m telescope, as well as the J=6-5 transitions of C34S and 13CS with the APEX 12m telescope, all in emission. The J=2-1 rotational transitions of CS, C34S, 13CS, and 13C34S were observed with ALMA in the envelope of Sgr B2(N), with those of CS and C34S also observed in the l.o.s. clouds towards Sgr B2(N), all in absorption. In the +50km/s Cloud we derive a 12C13C isotopic ratio of ~22.1, that leads, with the measured 13CS/C34S line intensity ratio, to a 32S/34S ratio of 16.3+3.0-2.4. We also derive the 32S/34S isotopic ratio more directly from the two isotopologues 13CS and 13C34S, which leads to an independent 32S/34S estimation of 16.3+2.1-1.7 and 17.9+-5.0 for the +50km/s Cloud and Sgr B2(N), respectively. We also obtain a 34S/33S ratio of ~4.3 in the +50 km/s Cloud. Previous studies observed a decreasing trend in the 32S/34S isotopic ratios when approaching the Galactic centre. Our result indicates a termination of this tendency at least at a galactocentric distance of 130-30+60 pc. This is at variance with findings based on 12C/13C, 14N/15N and 18O/17O isotope ratios, where the above-mentioned trend is observed to continue right to the central molecular zone. This can indicate a drop in the production of massive stars at the Galactic centre, in the same line as recent metallicity gradient studies, and opens the work towards a comparison with Galactic and stellar evolution models., Comment: 16 pages, 7 figures, accepted for publication by A&A

Aminoacetonitrile, a molecule detected in the interstellar medium only towards the star-forming region Sagittarius B2 (Sgr B2) thus far, is considered an important prebiotic species. To date, observations were limited to ground state emission lines, whereas transitions from within vibrationally excited states remained undetected. We wanted to accurately determine the energies of the low-lying vibrational states of aminoacetonitrile, which are expected to be populated in Sgr B2(N1), the main hot core of Sgr B2(N). This step is fundamental in order to properly evaluate the vibration-rotation partition function of aminoacetonitrile as well as the line strengths of the rotational transitions of its vibrationally excited states. This is necessary to derive accurate column densities and secure the identification of these transitions in astronomical spectra. The far-infrared ro-vibrational spectrum of aminoacetonitrile has been recorded in absorption against a synchrotron source of continuum emission. Three bands, corresponding to the lowest vibrational modes of aminoacetonitrile, were observed in the frequency region below 500 cm$^{-1}$. The combined analysis of ro-vibrational and pure rotational data allowed us to prepare new spectral line catalogs for all the states under investigation. We used the imaging spectral line survey ReMoCA performed with ALMA to search for vibrationally excited aminoacetonitrile toward Sgr B2(N1). On the basis of these spectroscopic predictions, we report the interstellar detection of aminoacetonitrile in its $v_{11}=1$ and $v_{18}=1$ vibrational states toward Sgr B2(N1) in addition to emission in its vibrational ground state. The intensities of the identified $v_{11}=1$ and $v_{18}=1$ lines are consistent with the detected $v=0$ lines under LTE at a temperature of 200 K for an aminoacetonitrile column density of $1.1 \times 10^{17}$ cm$^{-2}$., Comment: 14 pages, 7 figures, 5 tables, accepted for publication in A&A

Glycolamide is a glycine isomer and also one of the simplest derivatives of acetamide (e.g., one hydrogen atom is replaced with a hydroxyl group), which is a known interstellar molecule. Using a battery of state of the art rotational spectroscopic techniques in the frequency and time domain, around 1500 transitions have been newly assigned. Based on the reliable frequency predictions, we report a radioastronomical search for glycolamide in the well known high-mass star forming region Sgr B2(N) using the ALMA imaging spectral line survey ReMoCA. We also searched for glycolamide toward Sgr B2(N) with the Effelsberg radio telescope. We report the nondetection of glycolamide toward this source with an abundance at least six and five times lower than that of acetamide and glycolaldehyde, respectively. Our astrochemical model suggests that glycolamide may be present in this source at a level just below the upper limit, which was derived from the EMoCA survey. We could also not detect the molecule in the region's extended molecular envelope, which was probed with the Effelsberg telescope. We find an upper limit to its column density that is similar to the column densities obtained earlier for acetamide and glycolaldehyde with the Green Bank Telescope., Comment: The article will be published as a regular paper in Astronomy and Astrophysics (Forthcoming article since 19 May 2020)

CK Vul erupted in 1670 and is considered a stellar-merger candidate. Its remnant contains a molecular component of surprisingly rich composition. We present interferometric line surveys with subarcsec resolution with ALMA and SMA. The observations provide interferometric maps of molecular line emission at frequencies between 88 and 243 GHz that allow imaging spectroscopy of more than 180 transitions of 26 species. We present, classify, and analyze the different morphologies of the emission regions displayed by the molecules. We also perform a non-LTE radiative-transfer analysis of emission of most of the observed species, deriving temperatures and column densities in five parts of the nebula. Non-LTE effects are clearly seen in complex species including methanol absorption against the CMB. The temperatures are 17 K in the inner remnant and 14 K in the extended lobes. We find total (hydrogen plus helium) densities in the range of $10^4-10^6$ cm$^{-3}$. The column densities provide relative abundance patterns in the remnant which currently are not understood. Attempts to derive elemental abundances within the assumption of a chemical equilibrium give only loose constraints on the CNO elements. That the formation of many of the observed molecules requires a major involvement of circumstellar shocks remains the preferred possibility. The molecular gas could have formed 350 yr ago or more recently. The molecules are well shielded from the interstellar radiation field by the circumstellar dust. Their presence alone indicates that the unobservable central star cannot be a hot object such as a white dwarf. This excludes some of the proposed scenarios on the nature of CK Vul. The general characteristics of the molecular environment of CK Vul derived in this study resemble quite well those of some pre-planetary nebulae and AGB stars, most notably that of OH231.8., Comment: submitted to A&A; comments welcome

Star-forming regions show a rich and varied chemistry, including the presence of complex organic molecules - both in the cold gas distributed on large scales, and in the hot regions close to young stars where protoplanetary disks arise. Recent advances in observational techniques have opened new possibilities for studying this chemistry. In particular, the Atacama Large Millimeter/submillimeter Array (ALMA) has made it possible to study astrochemistry down to Solar System size scales, while also revealing molecules of increasing variety and complexity. In this review, we discuss recent observations of the chemistry of star-forming environments, with a particular focus on complex organic molecules, taking context from the laboratory experiments and chemical models that they have stimulated. The key takeaway points are: The physical evolution of individual sources plays a crucial role in their inferred chemical signatures, and remains an important area for observations and models to elucidate. Comparisons of the abundances measured toward different star-forming environments (high-mass versus low-mass, Galactic center versus Galactic disk) reveal a remarkable similarity, an indication that the underlying chemistry is relatively independent of variations in their physical conditions. Studies of molecular isotopologs in star-forming regions provide a link with measurements in our own Solar System, and thus may shed light on the chemical similarities and differences expected in other planetary systems., Comment: Invited review to be published in Annual Reviews of Astronomy and Astrophysics; 55 pages, 10 figures

We used the EMoCA survey data to search for isocyanides in Sgr B2(N2) and their corresponding cyanide analogs. We then used the coupled three-phase chemical kinetics code MAGICKAL to simulate their chemistry. Several new species, and over 100 new reactions have been added to the network. In addition, a new single-stage simultaneous collapse/warm-up model has been implemented, thus eliminating the need for the previous two-stage models. A variable, visual extinction-dependent $\zeta$ was also incorporated into the model and tested. We report the tentative detection of CH$_3$NC and HCCNC in Sgr B2(N2), which represents the first detection of both species in a hot core of Sgr B2. Our updated chemical models can reproduce most observed NC:CN ratios reasonably well depending on the physical parameters chosen. The model that performs best has an extinction-dependent cosmic-ray ionization rate that varies from ~2 $\times$ 10$^{-15}$ s$^{-1}$ at the edge of the cloud to ~1 $\times$ 10$^{-16}$ s$^{-1}$ in the center. Models with higher extinction-dependent $\zeta$ than this model generally do not agree as well, nor do models with a constant $\zeta$ greater than the canonical value of 1.3 $\times$ 10$^{-17}$ s$^{-1}$ throughout the source. Radiative transfer models are run using results of the best-fit chemical model. Column densities produced by the radiative transfer models are significantly lower than those determined observationally. Inaccuracy in the observationally determined density and temperature profiles is a possible explanation. Excitation temperatures are well reproduced for the true ``hot core'' molecules, but are more variable for other molecules such as HC$_3$N, for which fewer lines exist in ALMA Band 3., Comment: 29 pages, 24 figures, accepted for publication in Astronomy & Astrophysics

Complex organic molecules (COMs) have been detected in a few Class 0 protostars but their origin is not well understood. Going beyond studies of individual objects, we want to investigate the origin of COMs in young protostars on a statistical basis. We use the CALYPSO survey performed with the IRAM PdBI to search for COMs at high angular resolution in a sample of 26 solar-type protostars, including 22 Class 0 and four Class I objects. Methanol is detected in 12 sources and tentatively in one source, which represents half of the sample. Eight sources (30%) have detections of at least three COMs. We find a strong chemical differentiation in multiple systems with five systems having one component with at least three COMs detected but the other component devoid of COM emission. The internal luminosity is found to be the source parameter impacting the most the COM chemical composition of the sources, while there is no obvious correlation between the detection of COM emission and that of a disk-like structure. A canonical hot-corino origin may explain the COM emission in four sources, an accretion-shock origin in two or possibly three sources, and an outflow origin in three sources. The CALYPSO sources with COM detections can be classified into three groups on the basis of the abundances of oxygen-bearing molecules, cyanides, and CHO-bearing molecules. These chemical groups correlate neither with the COM origin scenarii, nor with the evolutionary status of the sources if we take the ratio of envelope mass to internal luminosity as an evolutionary tracer. We find strong correlations between molecules that are a priori not related chemically (for instance methanol and methyl cyanide), implying that the existence of a correlation does not imply a chemical link. [abridged], Comment: Accepted for publication in Astronomy and Astrophysics

[abridged] Understanding how the infalling gas redistribute most of its initial angular momentum inherited from prestellar cores before reaching the stellar embryo is a key question. Disk formation has been naturally considered as a possible solution to this "angular momentum problem". However, how the initial angular momentum of protostellar cores is distributed and evolves during the main accretion phase and the beginning of disk formation has largely remained unconstrained up to now. In the framework of the IRAM CALYPSO survey, we used high dynamic range C$^{18}$O (2-1) and N$_2$H$^+$ (1-0) observations to quantify the distribution of specific angular momentum along the equatorial axis in a sample of 12 Class 0 protostellar envelopes from scales ~50 to 10000 au. The radial distributions of specific angular momentum in the CALYPSO sample suggest two distinct regimes within protostellar envelopes: the specific angular momentum decreases as $j \propto r^{1.6 \pm 0.2}$ down to ~1600 au and then tends to become relatively constant around 6 $\times$ 10$^{-4}$ km s$^{-1}$ pc down to ~50 au. The values of specific angular momentum measured in the inner Class 0 envelopes, namely that of the material directly involved in the star formation process ($<$1600 au), is on the same order of magnitude as what is inferred in small T-Tauri disks. Thus, disk formation appears to be a direct consequence of angular momentum conservation during the collapse. Our analysis reveals a dispersion of the directions of velocity gradients at envelope scales $>$1600 au, suggesting that they may not be related to rotational motions of the envelopes. We conclude that the specific angular momentum observed at these scales could find its origin in core-forming motions (infall, turbulence) or trace an imprint of the initial conditions for the formation of protostellar cores., Comment: 62 pages, 66 figures

The formation of protoplanetary disks is not well understood. To understand how and when these disks are formed, it is crucial to characterize the kinematics of the youngest protostars at a high angular resolution. Here we study a sample of 16 Class 0 protostars to measure their rotation profile at scales from 50 to 500~au and search for Keplerian rotation. We used high-angular-resolution line observations obtained with the Plateau de Bure Interferometer as part of the CALYPSO large program. From $\mathrm{^{13}CO}$ ($J=2-1$), $\mathrm{C^{18}O}$ ($J=2-1$) and SO ($N_{j}=5_{6}-4_{5}$) moment maps, we find that seven sources show rotation about the jet axis at a few hundred au scales: SerpS-MM18, L1448-C, L1448-NB, L1527, NGC1333- IRAS2A, NGC1333-IRAS4B, and SVS13-B. We analyzed the kinematics of these sources in the $uv$ plane to derive the rotation profiles down to 50~au scales. We find evidence for Keplerian rotation in only two sources, L1527 and L1448-C. Overall, this suggests that Keplerian disks larger than 50 au are uncommon around Class 0 protostars. However, in some of the sources, the line emission could be optically thick and dominated by the envelope emission. Due to the optical thickness of these envelopes, some of the disks could have remained undetected in our observations., Comment: Accepted for publication in Astronomy & Astrophysics

On the basis of its low luminosity, its chemical composition, and the absence of a large-scale outflow, the dense core Cha-MMS1 located in the Chamaeleon I molecular cloud was proposed as a first hydrostatic core (FHSC) candidate a decade ago. Our goal is to test this hypothesis by searching for a slow, compact outflow driven by Cha-MMS1 that would match the predictions of MHD simulations for this short phase of star formation. We use the Atacama Large Millimetre/submillimetre Array (ALMA) to map Cha-MMS1 at high angular resolution in CO 3-2 and 13CO 3-2 as well as in continuum emission. We report the detection of a bipolar outflow emanating from the central core, along a (projected) direction roughly parallel to the filament in which Cha-MMS1 is embedded and perpendicular to the large-scale magnetic field. The morphology of the outflow indicates that its axis lies close to the plane of the sky. We measure velocities corrected for inclination of more than 90km/s which is clearly incompatible with the expected properties of a FHSC outflow. Several properties of the outflow are determined and compared to previous studies of Class 0 and Class I protostars. The outflow of Cha-MMS1 has a much smaller momentum force than the outflows of other Class 0 protostars. In addition, we find a dynamical age of 200-3000yr indicating that Cha-MMS1 might be one of the youngest ever observed Class 0 protostars. While the existence of the outflow suggests the presence of a disk, no disk is detected in continuum emission and we derive an upper limit of 55au to its radius. We conclude that Cha-MMS1 has already gone through the FHSC phase and is a young Class 0 protostar, but it has not brought its outflow to full power yet., Comment: Accepted for publication in A&A

Classical hot cores are rich in molecular emission, and they show a high abundance of complex organic molecules (COMs). The emergence of molecular complexity is poorly constrained in the early evolution of hot cores. Using the Atacama Large Millimeter Array we put observational constraints on the physical location of COMs in a high-mass protostellar envelope associated with the G328.2551-0.5321 clump. The protostar is single down to ~400au scales and we resolve the emission region of COMs. Using thermodynamic equilibrium modelling of the available 7.5 GHz bandwidth around ~345 GHz, we detect emission from 10 COMs, and identify a line of deuterated water (HDO). The most extended emission originates from methanol, methyl formate and formamide. Together with HDO, these molecules are found to be associated with both the accretion shocks and the inner envelope, for which we estimate a moderate temperature of $T_{\rm kin}\sim$110 K. Our findings reveal a significant difference in the distribution of COMs. O-bearing COMs, such as ethanol, acetone, and ethylene glycol are almost exclusively found and show a higher abundance towards the accretion shocks with $T_{\rm kin}\sim$180 K. Whereas N-bearing COMs with a CN group, such as vinyl and ethyl cyanide peak on the central position, thus the protostar and the accretion disk. This is the first observational evidence for a large column density of COMs seen towards accretion shocks at the centrifugal barrier at the inner envelope. Since the molecular composition is dominated by that of the accretion shocks and the radiatively heated hot inner region is very compact, we propose this source to be a precursor to a classical, radiatively heated hot core., Comment: Accepted for publication in A&A (17 pages, 9 figures). The abstract is abbreviated

Analyzing the properties of dust and its evolution in the early phases of star formation is crucial to put constraints on the collapse and accretion processes as well as on the pristine properties of planet-forming seeds. We analyze PdBI observations at 1.3 and 3.2 mm for 12 Class 0 protostars obtained as part of the CALYPSO survey and derive dust emissivity index (beta) profiles as a function of the envelope radius at 200-2000 au scales. Most of the protostellar envelopes show low dust emissivity indices decreasing toward the central regions. The decreasing trend remains after correction of the (potentially optically-thick) central region emission, with surprisingly low beta (lower than 1) values across most of the envelope radii of NGC1333-IRAS4A, NGC1333-IRAS4B, SVS13B, and Serpens-SMM4. We discuss the various processes that could explain such low and varying dust emissivity indices at envelope radii 200-2000 au. Our observations of extremely low dust emissivity indices could trace the presence of large (mm-size) grains in Class 0 envelopes and a radial increase of the dust grain size toward the inner envelope regions. While it is expected that large grains in young protostellar envelopes could be built via grain growth and coagulation, we stress that the typical timescales required to build mm grains in current coagulation models are at odds with the youth of our Class 0 protostars. Additional variations in the dust composition could also partly contribute to the low beta we observe. The steepness of the beta radial gradient depends strongly on the envelope mass, which might favor a scenario where large grains are built in high density protostellar disks and transported to the intermediate envelope radii, for example with the help of outflows and winds., Comment: 17 pages, 11 figures, accepted for publication in A&A

Methyl mercaptan (CH3SH) is a known interstellar molecule with abundances high enough that the detection of some of its minor isotopologues is promising. The present study aims at providing accurate spectroscopic parameters for the (13)CH3SH isotopologue to facilitate its identification in the interstellar medium at millimetre and submillimetre wavelengths. Through careful analysis of recent CH3SH spectra from 49-510 GHz and 1.1-1.5 THz recorded at natural isotopic composition, extensive assignments were possible not only for the ground torsional state of (13)CH3SH, but also in the first and second excited states. The torsion-rotation spectrum displays complex structure due to the large-amplitude internal rotation of the (13)CH3 group, similar to the main and other minor isotopic species of methyl mercaptan. The assigned transition frequencies have been fitted to within experimental error with a 52-parameter model employing the RAM36 programme. With predictions based on this fit, (13)CH3SH was searched for in spectra from the Atacama Large Millimetre/submillimetre Array (ALMA) towards the Galactic centre source Sgr B2(N2). Several transitions were expected to be observable, but all of them turned out to be severely blended with emission from other species, which prevents us from identifying (13)CH3SH in this source., Comment: 20 pages (with figures and tables); Can. J. Phys. (https://www.nrcresearchpress.com/journal/cjp), accepted

Episodic accretion has been used to explain the wide range of protostellar luminosities, but its origin and influence on the star forming process are not yet fully understood. We present an ALMA survey of N$_2$H$^+$ ($1-0$) and HCO$^+$ ($3-2$) toward 39 Class 0 and Class I sources in the Perseus molecular cloud. N$_2$H$^+$ and HCO$^+$ are destroyed via gas-phase reactions with CO and H$_2$O, respectively, thus tracing the CO and H$_2$O snowline locations. A snowline location at a much larger radius than that expected from the current luminosity suggests that an accretion burst has occurred in the past which has shifted the snowline outward. We identified 18/18 Class 0 and 9/10 Class I post-burst sources from N$_2$H$^+$, and 7/17 Class 0 and 1/8 Class I post-burst sources from HCO$^+$.The accretion luminosities during the past bursts are found to be $\sim10-100~L_\odot$. This result can be interpreted as either evolution of burst frequency or disk evolution. In the former case, assuming that refreeze-out timescales are 1000 yr for \ce{H2O} and 10,000 yr for CO, we found that the intervals between bursts increases from 2400 yr in the Class 0 to 8000 yr in the Class I stage. This decrease in the burst frequency may reflect that fragmentation is more likely to occur at an earlier evolutionary stage when the young stellar object is more prone to instability., Comment: 22 pages, 15 figures, accepted to ApJ

We want to study the rotational spectra of CH$_3^{13}$C(O)CH$_3$ and $^{13}$CH$_3$C(O)CH$_3$ and search for them in Sagittarius B2(N2). We investigated the laboratory rotational spectrum of isotopically enriched CH$_3^{13}$C(O)CH$_3$ between 40 GHz and 910 GHz and of acetone between 36 GHz and 910 GHz in order to study $^{13}$CH$_3$C(O)CH$_3$ in natural isotopic composition. In addition, we searched for emission lines produced by these species in a molecular line survey of Sagittarius B2(N) carried out with ALMA. Discrepancies between predictions of the main isotopic species and the ALMA spectrum prompted us to revisit the rotational spectrum of this isotopolog. We assigned 9711 new transitions of CH$_3^{13}$C(O)CH$_3$ and 63 new transitions of $^{13}$CH$_3$C(O)CH$_3$ in the laboratory spectra. More than 1000 additional lines were assigned for the main isotopic species. We modeled the ground state data of all three isotopologs satisfactorily with the ERHAM program. We find that models of the torsionally excited states $v _{12} = 1$ and $v _{17} = 1$ of CH$_3$C(O)CH$_3$ improve only marginally. No transition of CH$_3^{13}$C(O)CH$_3$ is clearly detected toward the hot molecular core Sgr B2(N2). However, we report a tentative detection of $^{13}$CH$_3$C(O)CH$_3$ with a $^{12}$C/$^{13}$C isotopic ratio of 27 that is consistent with the ratio previously measured for alcohols in this source. Several dozens of transitions of both torsional states of the main isotopolog are detected as well. Our predictions of CH$_3^{13}$C(O)CH$_3$ and CH$_3$C(O)CH$_3$ are reliable into the terahertz region. The spectrum of $^{13}$CH$_3$C(O)CH$_3$ should be revisited in the laboratory with an enriched sample. Transitions pertaining to the torsionally excited states $v _{12} = 1$ and $v _{17} = 1$ of CH$_3$C(O)CH$_3$ could be identified unambiguously in Sagittarius B2(N2)., Comment: A&A in press; Abstract abbreviated; 37 pages: 12 pages + 25 pages Appendix

The search for complex organic molecules in the interstellar medium (ISM) has revealed species of ever greater complexity. This search relies on the progress made in the laboratory to characterize their rotational spectra. Our understanding of the processes that lead to molecular complexity in the ISM builds on numerical simulations that use chemical networks fed by laboratory and theoretical studies. The advent of ALMA and NOEMA has opened a new door to explore molecular complexity in the ISM. Their high angular resolution reduces the spectral confusion of star-forming cores and their increased sensitivity allows the detection of low-abundance molecules that could not be probed before. The complexity of the recently-detected molecules manifests itself not only in terms of number of atoms but also in their molecular structure. We discuss these developments and report on ReMoCA, a new spectral line survey performed with ALMA toward the high-mass star-forming region Sgr B2(N)., Comment: to appear in the proceedings of the IAU Symposium No. 350 on Laboratory Astrophysics: from Observations to Interpretation

As the number of complex organic molecules (COMs) detected in the interstellar medium increases, it becomes important to place meaningful constraints on the formation pathways of these species. The molecular cloud SgrB2(N) is host to several hot molecular cores in the early stage of star formation, where a great variety of COMs are detected in the gas phase. Because of its exposure to the extreme conditions of the the Galactic center region, SgrB2(N) is one of the best targets to study the impact of environmental conditions on the production of COMs. Our main goal is to characterize the physico-chemical evolution of SgrB2(N)'s sources in order to explain their chemical differences and constrain their environmental conditions. The chemical composition of SgrB2(N)'s hot cores, N2, N3, N4, and N5 is derived by modeling their 3mm emission spectra extracted from the EMoCA imaging spectral line survey performed with ALMA. We derive the density distribution in the envelope of the sources based on the masses computed from the ALMA dust continuum emission maps. We use the radiative transfer code RADMC-3D to compute temperature profiles based on the COM rotational temperatures derived from population diagrams. We use published results of 3D RMHD simulations of high-mass star formation to estimate the time evolution of the sources properties. We employ the chemical code MAGICKAL to compute time-dependent chemical abundances in the sources and investigate how physical properties and environmental conditions influence the production of COMs. We find that chemical models with a cosmic-ray ionization rate of 7e-16s-1 best reproduce the abundances with respect to methanol of ten COMs observed toward SgrB2(N2-N5). We also show that COMs still form efficiently on dust grains with minimum dust temperatures in the prestellar phase as high as 15K, but that minimum temperatures higher than 25K are excluded.

Urea, NH2C(O)NH2, is a molecule of great importance in organic chemistry and biology. Two searches for urea in the interstellar medium were reported in the past, but neither were conclusive. We want to take advantage of the increased sensitivity and angular resolution provided by ALMA to search for urea toward the hot cores embedded in the high-mass star forming region Sgr B2(N). We use the new spectral line survey ReMoCA performed toward Sgr B2(N) with ALMA in its observing cycle 4. The spectra are analyzed under the LTE approximation. We construct a full synthetic spectrum that includes all the molecules identified so far. We use new spectroscopic predictions for urea in its vibrational ground state and first vibrationally excited state to search for this complex organic molecule in the ReMoCA data set. We employ the gas-grain chemical kinetics model MAGICKAL to interpret the astronomical observations. We report the secure detection of urea toward the hot core Sgr B2(N1) at a position called N1S slightly offset from the continuum peak, which avoids obscuration by the dust.. We derive a column density of 2.7x10^16 cm-2 for urea, two orders of magnitude lower than formamide, and one order of magnitude below methyl isocyanate, acetamide, and N-methylformamide. The latter molecule is reliably identified toward N1S with 60 clearly detected lines, confirming an earlier claim of its tentative interstellar detection. We report the first interstellar detections of NH2CH18O and 15NH2CHO. We also report the nondetection of urea toward the secondary hot core Sgr B2(N2) with an abundance relative to the other four species at least one order of magnitude lower than toward the main hot core. Our chemical model roughly reproduces the relative abundances of formamide, methyl isocyanate, acetamide, and N-methylformamide, but it overproduces urea by at least one order of magnitude., Comment: Accepted for publication in A&A. The abstract has been shortened to comply with the size limit set by arXiv. A few minor corrections were applied to version 2