arXiv subjects

H. S. P. Müller

Publications and source records attributed to H. S. P. Müller.

At least 37 records · Page 2Linked to original sources

arXiv2021

ATOMIUM: Halide molecules around the S-type AGB star W Aquilae

S-type asymptotic giant branch (AGB) stars are thought to be intermediates in the evolution of oxygen- to carbon-rich AGB stars. The chemical compositions of their circumstellar envelopes are also intermediate, but have not been studied in as much detail as their carbon- and oxygen-rich counterparts. We aim to determine the abundances of AlCl and AlF from rotational lines, which have been observed for the first time towards an S-type AGB star, W Aql. In combination with models based on PACS observations, we aim to update our chemical kinetics network based on these results. We analyse ALMA observations towards W Aql of AlCl in the ground and first two vibrationally excited states and AlF in the ground vibrational state. Using radiative transfer models, we determine the abundances and spatial abundance distributions of Al$^{35}$Cl, Al$^{37}$Cl, and AlF. We also model HCl and HF emission and compare these models to PACS spectra to constrain the abundances of these species. AlCl is found in clumps very close to the star, with emission confined within 0.1$^{\prime\prime}$ of the star. AlF emission is more extended, with faint emission extending 0.2$^{\prime\prime}$ to 0.6$^{\prime\prime}$ from the continuum peak. We find peak abundances, relative to H$_2$, of $1.7\times 10^{-7}$ for Al$^{35}$Cl, $7\times 10^{-8}$ for Al$^{37}$Cl and $1\times 10^{-7}$ for AlF. From the PACS spectra, we find abundances of $9.7\times 10^{-8}$ and $\leq 10^{-8}$, relative to H$_2$, for HCl and HF, respectively. The AlF abundance exceeds the solar F abundance, indicating that fluorine synthesised in the AGB star has already been dredged up to the surface of the star and ejected into the circumstellar envelope. From our analysis of chemical reactions in the wind, we conclude that AlF may participate in the dust formation process, but we cannot fully explain the rapid depletion of AlCl seen in the wind.

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arXiv2021

Millimeter-wave spectroscopy of the $^{13}$CH$_3$OD isotopic species of methyl alcohol

The dramatic increase in sensitivity, spectral coverage and resolution of radio astronomical facilities in recent years has opened new possibilities for observation of chemical differentiation and isotopic fractionation in protostellar sources to shed light on their spatial and temporal evolution. In warm interstellar environments, methanol is an abundant species, hence spectral data for its isotopic forms are of special interest. In the present work, the millimeter-wave spectrum of the $^{13}$CH$_3$OD isotopologue has been investigated over the region from 150$-$510 GHz to provide a set of transition frequencies for potential astronomical application. The focus is on two types of prominent $^{13}$CH$_3$OD spectral groupings, namely the $a$-type $^qR$-branch multiplets and the $b$-type $Q$-branches. Line positions are reported for the $^qR(J)$ clusters for $J = 3$ to 10 for the $v_{\rm t} = 0$ and 1 torsional states, and for a number of $v_{\rm t} = 0$ and 1 $^rQ(J)$ or $^pQ(J)$ line series up to $J = 25$. The frequencies have been fitted to a multi-parameter torsion-rotation Hamiltonian, and upper level excitation energies have been calculated from the resulting molecular constants.

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arXiv2021

Rotational spectroscopic study and astronomical search for propiolamide in Sgr B2(N)

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.

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arXiv2020

(Sub)stellar companions shape the winds of evolved stars

Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe.

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arXiv2020

Millimeter- and submillimeter-wave spectroscopy of thioformamide and interstellar search toward Sgr B2(N)

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.

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arXiv2020

The ALMA-PILS survey: First detection of the unsaturated 3-carbon molecules Propenal (C$_2$H$_3$CHO) and Propylene (C$_3$H$_6$) towards IRAS 16293$-$2422 B

Complex organic molecules with three carbon atoms are found in the earliest stages of star formation. In particular, propenal (C$_2$H$_3$CHO) is a species of interest due to its implication in the formation of more complex species and even biotic molecules. This study aims to search for the presence of C$_2$H$_3$CHO and other three-carbon species such as propylene (C$_3$H$_6$) in the hot corino region of the low-mass protostellar binary IRAS 16293--2422 to understand their formation pathways. We use ALMA observations in Band 6 and 7 from various surveys to search for the presence of C$_3$H$_6$ and C$_2$H$_3$CHO towards the protostar IRAS 16293--2422 B (IRAS 16293B). We report the detection of both C$_3$H$_6$ and C$_2$H$_3$CHO towards IRAS 16293B, however, no unblended lines were found towards the other component of the binary system, IRAS 16293A. We derive column density upper limits for C$_3$H$_8$, HCCCHO, n-C$_3$H$_7$OH, i-C$_3$H$_7$OH, C$_3$O, and cis-HC(O)CHO towards IRAS 16293B. We then use a three-phase chemical model to simulate the formation of these species in a typical prestellar environment followed by its hydrodynamical collapse until the birth of the central protostar. Different formation paths, such as successive hydrogenation and radical-radical additions on grain surfaces, are tested and compared to the observational results. The simulations reproduce the abundances within one order of magnitude from those observed towards IRAS 16293B, with the best agreement found for a rate of $10^{-12}$ cm$^3$ s$^{-1}$ for the gas-phase reaction C$_3$ + O $\rightarrow$ C$_2$ + CO. Successive hydrogenations of C$_3$, HC(O)CHO, and CH$_3$OCHO on grain surfaces are a major and crucial formation route of complex organics molecules, whereas both successive hydrogenation pathways and radical-radical addition reactions contribute to the formation of C$_2$H$_5$CHO.

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arXiv2020

Interstellar glycolamide: A comprehensive rotational study and an astronomical search in Sgr B2(N)

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.

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arXiv2020

Far-infrared laboratory spectroscopy of aminoacetonitrile and first interstellar detection of its vibrationally excited transitions

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$^{-2}$.

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arXiv2020

Complex organic molecules in low-mass protostars on solar system scales -- I. Oxygen-bearing species

Complex organic molecules (COMs) are thought to form on icy dust grains in the earliest phase of star formation. The evolution of these COMs from the youngest Class 0/I protostellar phases toward the more evolved Class II phase is still not fully understood. Since planet formation seems to start early, and mature disks are too cold for characteristic COM emission lines, studying the inventory of COMs on solar system scales in the Class 0/I stage is relevant. ALMA Band 3 (3 mm) and Band 6 (1 mm) observations are obtained of seven Class 0 protostars in the Perseus and Serpens star-forming regions. By modeling the inner protostellar region using 'LTE' models, the excitation temperature and column densities are determined for several O-bearing COMs. B1-c, B1-bS, and Serpens S68N show COM emission, i.e, three out of the seven sources. No clear correlation seems to exist between the occurrence of COMs and source luminosity. The abundances of several COMs with respect to CH3OH are remarkably similar for the three COM-rich sources, and to IRAS 16293-2422B and HH 212. For other COMs the abundances differ by up to an order of magnitude, indicating that local source conditions are case determining. B1-c hosts a cold ($T_{ex}\approx60$ K), more extended component of COM emission with a column density of typically a few % of the warm/hot ($T_{ex}\sim 200$ K), central component. A D/H ratio of 1-3 % is derived based on the CH2DOH/CH3OH ratio suggesting a temperature of $\sim$15~K during the formation of methanol. This ratio is consistent with other low-mass protostars. Future mid-infrared facilities such as JWST/MIRI will be essential to directly observe COM ices. Combining this with a larger sample of COM-rich sources with ALMA will allow for directly linking ice and gas-phase abundances in order to constrain the routes that produce and maintain chemical complexity during the star formation process.

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arXiv2020

Exploring molecular complexity with ALMA (EMoCA): Complex isocyanides in Sgr B2(N)

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 $ζ$ 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 $ζ$ than this model generally do not agree as well, nor do models with a constant $ζ$ 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.

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arXiv2020

The ALMA-PILS survey: Inventory of complex organic molecules towards IRAS 16293-2422 A

Complex organic molecules (COM) are detected in many sources in the warm inner regions of envelopes surrounding deeply embedded protostars. Exactly how these COM form remains an open question. This study aims to constrain the formation of complex organic molecules through comparisons of their abundances towards the Class 0 protostellar binary IRAS 16293-2422 (IRAS16293). We utilised observations from the ALMA Protostellar Interferometric Line Survey of IRAS16293. The species identification and the rotational temperature and column density estimation were derived by fitting the extracted spectra towards IRAS16293 A and IRAS16293 B with synthetic spectra. The majority of the work in this paper pertains to the analysis of IRAS16293 A for a comparison with the results from the other binary component, which have already been published. We detect 15 different COM, as well as 16 isotopologues towards the most luminous companion protostar IRAS16293 A. Tentative detections of an additional 11 isotopologues are reported. We also searched for and report on the first detections of CH3OCH2OH and t-C2H5OCH3 towards IRAS16293 B and the follow-up detection of CH2DCHO and CH3CDO. Twenty-four lines of CHD2OH are also identified. The comparison between the two protostars of the binary system shows significant differences in abundance for some of the species, which are partially correlated to their spatial distribution. The spatial distribution is consistent with the sublimation temperature of the species; those with higher expected sublimation temperatures are located in the most compact region of the hot corino towards IRAS16293 A. This spatial differentiation is not resolved in IRAS16293 B and will require observations at a higher angular resolution. In parallel, the list of identified CHD2OH lines shows the need of accurate spectroscopic data including their line strength.

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arXiv2019

Rotational spectrum of isotopic methyl mercaptan, (13)CH3SH, in the laboratory and towards Sagittarius B2(N2)

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.

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arXiv2019

The ALMA-PILS survey: propyne (CH$_3$CCH) in IRAS 16293$-$2422

Context. Propyne (CH$_3$CCH) has been detected in a variety of environments, from Galactic star-forming regions to extragalactic sources. Such molecules are excellent tracers of the physical conditions in star-forming regions. Aims. This study explores the emission of CH$_3$CCH in the low-mass protostellar binary, IRAS 16293$-$2422, examining the spatial scales traced by this molecule, as well as its formation and destruction pathways. Methods. ALMA observations from the Protostellar Interferometric Line Survey (PILS) are used to determine the abundances and excitation temperatures of CH$_3$CCH towards both protostars, exploring spatial scales from 70 to 2400 au. The three-phase chemical kinetics model MAGICKAL is also used, to explore the chemical reactions of this molecule. Results. CH$_3$CCH is detected towards both IRAS 16293A and IRAS 16293B and is found to trace the hot corino component around each source in the PILS dataset. Eighteen transitions above 3$σ$ are detected, enabling robust excitation temperatures and column densities to be determined in each source. In IRAS 16293A, an excitation temperature of 90 K and a column density of 7.8$\times$10$^{15}$ cm$^{-2}$ best fits the spectra. In IRAS 16293B, an excitation temperature of 100 K and 6.8$\times$10$^{15}$ cm$^{-2}$ best fits the spectra. The chemical modelling finds that in order to reproduce the observed abundances, both gas-phase and grain-surface reactions are needed. Conclusions. CH$_3$CCH is a molecule whose brightness and abundance in many different regions can be utilised to provide a benchmark of molecular variation with the physical properties of star-forming regions. It is essential when making such comparisons, that the abundances are determined with a good understanding of the spatial scale of the emitting region, to ensure that accurate abundances are derived.

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arXiv2019

Rotational spectroscopy of methyl mercaptan CH$_3$$^{32}$SH at millimeter and submillimeter wavelengths

We present a new global study of the millimeter (mm) wave, submillimeter (sub-mm) wave, and terahertz (THz) spectra of the lowest three torsional states of methyl mercaptan (CH$_3$SH). New measurements have been carried out between 50 and 510 GHz using the Kharkiv mm wave and the Cologne sub-mm wave spectrometers whereas THz spectra records were used from our previous study. The new data, involving torsion-rotation transitions with $J$ up to 61 and $K_a$ up to 18, were combined with previously published measurements and fit using the rho-axis-method torsion-rotation Hamiltonian. The final fit used 124 parameters to give an overall weighted root-mean-square deviation of 0.72 for the dataset consisting of 6965 microwave (MW) and 16345 far-infrared line frequencies sampling transitions within and between the ground, first, and second excited torsional states. This investigation presents a two-fold expansion in the $J$ quantum numbers and a significant improvement in the fit quality, especially for the MW part of the data, thus allowing us to provide more reliable predictions to support astronomical observations.

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arXiv2019

The Physical and chemical structure of Sagittarius B2 -- IV. Converging filaments in the high-mass cluster forming region Sgr B2(N)

We have used an unbiased, spectral line-survey that covers the frequency range from 211 to 275 GHz and was obtained with ALMA (angular resolution of 0.4 arcsec) to study the small-scale structure of the dense gas in Sagittarius B2 (north). Eight filaments are found converging to the central hub and extending for about 0.1 pc. The spatial structure, together with the presence of the massive central region, suggest that these filaments may be associated with accretion processes. In order to derive the kinematic properties of the gas in a chemically line-rich source like Sgr B2(N), we have developed a new tool that stacks all the detected transition lines of any molecular species. This permits to increase the signal-to-noise ratio of our observations and average out line blending effects, which are a common problem in line-rich regions. We derive velocity gradients along the filaments of about 20-100 km s$^{-1}$ pc$^{-1}$, which are 10-100 times larger than those typically found on larger scales (1 pc) in other star-forming regions. The mass accretion rates of individual filaments are about 0.05 M$_\odot$ yr$^{-1}$, which result in a total accretion rate of 0.16 M$_\odot$ yr$^{-1}$. Some filaments harbor dense cores that are likely forming stars and stellar clusters. The stellar content of these dense cores is on the order of 50% of the total mass. We conclude that the cores may merge in the center when already forming stellar clusters but still containing a significant amount of gas, resulting in a "damp" merger. The high density and mass of the central region, combined with the presence of converging filaments with high mass, high accretion rates and embedded dense cores already forming stars, suggest that Sgr B2(N) may have the potential to evolve into a super stellar cluster.

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arXiv2019

Re-exploring Molecular Complexity with ALMA (ReMoCA): Interstellar detection of urea

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.

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arXiv2019

The complex chemistry of hot cores in Sagittarius B2(N): Influence of cosmic-ray ionization and thermal history

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.

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arXiv2019

The ALMA-PILS survey: Gas dynamics in IRAS 16293$-$2422 and the connection between its two protostars

[Abridged] The majority of stars form in binary or higher order systems. The Class 0 protostellar system IRAS16293-2422 contains two protostars, 'A' and 'B', separated by ~600 au and embedded in a single, 10^4 au scale envelope. Their relative evolutionary stages have been debated. We aim to study the relation and interplay between the two protostars A and B at spatial scales of 60 to ~1000 au. We selected molecular gas line transitions of CO, H2CO, HCN, CS, SiO, and CCH from the ALMA-PILS spectral imaging survey (329-363 GHz) and used them as tracers of kinematics, density, and temperature in the IRAS16293-2422 system. The angular resolution of the PILS data set allows us to study these quantities at a resolution of 0.5 arcsec (60 au [..]). Line-of-sight velocity maps of both optically thick and optically thin molecular lines reveal: (i) new manifestations of previously known outflows emanating from protostar A; (ii) a kinematically quiescent bridge of dust and gas spanning between the two protostars, with an inferred density between 4 10^4 and 3 10^7 cm^-3; and (iii) a separate, straight filament seemingly connected to protostar B seen only in CCH, with a flat kinematic signature. Signs of various outflows, all emanating from source A, are evidence of high-density and warmer gas; none of them coincide spatially and kinematically with the bridge. We hypothesize that the bridge arc is a remnant of filamentary substructure in the protostellar envelope material from which protostellar sources A and B have formed. One particular morphological structure appears to be due to outflowing gas impacting the quiescent bridge material. The continuing lack of clear outflow signatures unambiguously associated to protostar B and the vertically extended shape derived for its disk-like structure lead us to conclude that source B may be in an earlier evolutionary stage than source A.

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