arXiv subjects

H. S. P. Müller

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

At least 19 recordsLinked to original sources

arXiv2026

ATOMIUM: Inner circumstellar envelopes of oxygen-rich AGB stars as revealed by highly excited SiO lines

Silicon monoxide (SiO) traces the physical conditions and dynamics in the circumstellar envelopes (CSEs) of AGB stars. We present high-resolution ALMA Band 6 observations of highly excited SiO emission in 14 oxygen-rich AGB stars. We cover transitions from v = 0 to v = 8, including first detections of 28SiO v = 3, 4, 8, J = 6-5, 29SiO v = 6, J = 6-5, and 30SiO v = 4, 5, J = 6-5, some of which are masers. The v = 8 transition is the highest v-state observed in an AGB star yet. Masers in v = 0 are detected clearly in V PsA and IRC+10011 and tentatively in T Mic. R Hya exhibits the richest SiO spectrum. SiO J = 6-5 absorption is seen in R Aql, R Hya, S Pav, and T Mic, with features indicative of both infalls and outflows, and tentative detection of 28SiO v = 8, J = 6-5 absorption is found towards S Pav and R Aql. Highly excited SiO emission is often distributed in arcs or clumps with velocity gradients; components in R Hya and U Her align with predicted shock fronts. Detection rates show no significant difference between low and high mass-loss rate stars, although line overlap may affect some intensities. Maser detections appear uncorrelated with pulsation period or phase. The radius enclosing 90 per cent of compact SiO emission shows a tentative correlation with mass-loss rate. These results highlight the role of mass loss and CSE geometry in shaping high-excitation SiO emission.

astro-ph.SR↗

arXiv2025

A quest for sulfur-bearing refractory species. Identification of CaS in the interstellar medium

The recent detection of refractory molecules in massive star-forming regions provides a means of probing the innermost regions of disks around massive stars. These detections also make it possible to explore the chemical composition of refractories through gas-phase observations. In this regard, identifying refractory compounds containing sulfur could reveal potential connections between sulfur and refractories, as well as help determine the sulfur budget in these extreme environments. We find convincing evidence of a reliable detection of CaS, and tentative detections of KS and KSH in the disk G351.77-mm1. These are the first ever identifications of these species in the interstellar medium. The CaS, KS, and KSH column densities are about 3 orders of magnitude lower than those of the abundant sulfur compounds SO$_2$, CH$_3$SH and SiS, proving that these species are not the major reservoir of sulfur at the spatial scales probed by our observations. Higher angular resolution observations at different wavelengths are required to confirm these detections, which are of paramount importance to gain insights into the formation of gas-phase refractory molecules.

astro-ph.GA↗

arXiv2025

ATOMIUM: Continuum emission and evidence of dust enhancement from binary motion

Low- and intermediate-mass stars on the asymptotic giant branch (AGB) account for a significant portion of the dust and chemical enrichment in their host galaxy. Here we present ALMA observations of the continuum emission at 1.24 mm around a sample of 17 stars from the ATOMIUM survey. From our analysis of the stellar contributions to the continuum flux, we find that the semi-regular variables all have smaller physical radii and fainter monochromatic luminosities than the Mira variables. Comparing these properties with pulsation periods, we find a positive trend between stellar radius and period only for the Mira variables with periods above 300 days and a positive trend between the period and the monochromatic luminosity only for the red supergiants and the most extreme AGB stars with periods above 500 days. We find that the continuum emission at 1.2 mm can be classified into four groups. "Featureless" continuum emission is confined to the (unresolved) regions close to the star for five stars in our sample, relatively uniform extended flux is seen for four stars, tentative elongated features are seen for three stars, and the remaining five stars have unique or unusual morphological features in their continuum maps. These features can be explained by binary companions to 10 out of the 14 AGB stars in our sample. Based on our results we conclude that there are two modes of dust formation: well established pulsation-enhanced dust formation and our newly proposed companion-enhanced dust formation. If the companion is located close to the AGB star, in the wind acceleration region, then additional dust formed in the wake of the companion can increase the mass lost through the dust driven wind. This explains the different dust morphologies seen around our stars and partly accounts for a large scatter in literature mass-loss rates, especially among semiregular stars with small pulsation periods.

astro-ph.SR↗

arXiv2025

Reexploring Molecular Complexity with ALMA: Insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2)

We used ALMA to perform a line survey of the high-mass star forming region Sgr B2(N), called ReMoCA. We modeled under the assumption of LTE the spectra obtained toward the sources embedded in the secondary hot core Sgr B2(N2). We compared the chemical composition of these sources to that of sources from the literature and to predictions of the chemical kinetics model MAGICKAL. We detected up to 58 molecules toward Sgr B2(N2)'s hot cores, including up to 24 COMs, as well as many less abundant isotopologs. The compositions of some pairs of sources are well correlated, but differences also exist in particular for HNCO and NH2CHO. The abundances of series of homologous molecules drop by about one order of magnitude at each further step in complexity. The nondetection of radicals yields stringent constraints on the models. The comparison to the chemical models confirms previous evidence of a high cosmic-ray ionization rate in Sgr B2(N). The comparison to sources from the literature gives new insight into chemical differentiation. The composition of most hot cores of Sgr B2(N2) is tightly correlated to that of the hot core G31.41+0.31 and the hot corino IRAS 16293-2422B after normalizing the abundances by classes of molecules (O-, N-, O+N-, and S-bearing). There is no overall correlation between Sgr B2(N2) and the shocked region G+0.693-0.027 also located in Sgr B2, and even less with the cold starless core TMC-1. The class of N-bearing species reveals the largest variance among the four classes of molecules. The S-bearing class shows in contrast the smallest variance. These results imply that the class of N-bearing molecules reacts more sensitively to shocks, low-temperature gas phase chemistry after non-thermal desorption, or density. The abundance shifts observed between the N- and O-bearing molecules may indicate how violently and completely the ice mantles are desorbed. [abridged]

astro-ph.GA↗

arXiv2024

Chemical tracers of a highly eccentric AGB-main sequence star binary

Binary interactions have been proposed to explain a variety of circumstellar structures seen around evolved stars, including asymptotic giant branch (AGB) stars and planetary nebulae. Studies resolving the circumstellar envelopes of AGB stars have revealed spirals, discs and bipolar outflows, with shaping attributed to interactions with a companion. For the first time, we have used a combined chemical and dynamical analysis to reveal a highly eccentric and long-period orbit for W Aquilae, a binary system containing an AGB star and a main sequence companion. Our results are based on anisotropic SiN emission, the first detections of NS and SiC towards an S-type star, and density structures observed in the CO emission. These features are all interpreted as having formed during periastron interactions. Our astrochemistry-based method can yield stringent constraints on the orbital parameters of long-period binaries containing AGB stars, and will be applicable to other systems.

astro-ph.SR↗

arXiv2024

Rotational spectroscopy of CH$_3$OD with a reanalysis of CH$_3$OD toward IRAS 16293$-$2422

We have started a measurement campaign of numerous methanol isotopologs in low-lying torsional states in order to provide extensive line lists for radio astronomical observations from an adequate spectroscopic model and to investigate how the intricate vibration-torsion-rotation interactions manifest themselves in the spectra of different isotopic species. After CD$_3$OH and CD$_3$OD, we turn our focus to CH$_3$OD, which is an important species for studying deuteration in prestellar cores and envelopes that enshroud protostars. Notably, deuteration is frequently viewed as a diagnostic tool for star formation. The measurements used in this study were obtained in two spectroscopic laboratories and cover large fractions of the 34 GHz--1.35 THz range. As done in previous studies, we employed a torsion-rotation Hamiltonian model for our analysis that is based on the rho-axis method. The resulting model describes the ground and first excited torsional states of CH$_3$OD well up to quantum numbers $J \leqslant 51$ and $K_a \leqslant 18$. We derived a line list for radio astronomical observations from this model that is accurate up to at least 1.35~THz and should be sufficient for all types of radio astronomical searches for this methanol isotopolog in these two lowest torsional states. This line list was applied to a reinvestigation of CH$_3$OD in data from the Protostellar Interferometric Line Survey of IRAS 16293--2422 obtained with the Atacama Large Millimeter/submillimeter Array. The new accurately determined value for the column density of CH$_3$OD implies that the deuteration in methanol differs in its two functional groups by a factor of $\sim$7.5.

astro-ph.GA↗

arXiv2024

The rotation-tunneling spectrum of 3-hydroxypropenal and confirmation of its detection toward IRAS 16293$-$2422 B

3-Hydroxypropenal (HOCHCHCHO) is the lower energy tautomer of malonaldehyde which displays a complex rotation-tunneling spectrum. It was detected tentatively toward the solar-type protostar IRAS 16293$-$2422 B with ALMA in the framework of the Protostellar Interferometric Line Survey (PILS). Several transitions, however, had large residuals, preventing not only their detection, but also the excitation temperature of the species from being determined unambiguously. We want to extend the existing rotational line list of 3-hydroxypropenal to shed more light on the recent observational results and to facilitate additional radio astronomical searches for this molecule. We analyzed the rotation-tunneling spectrum of 3-hydroxypropenal in the frequency regions between 150 and 330 GHz and between 400 and 660 GHz. Transitions were searched for in the PILS observations of IRAS 16293$-$2422. Local thermodynamic equilibrium (LTE) models were carried out and compared to the observations to constrain the excitation temperature. Additional transitions were searched for in other ALMA archival data of the same source to confirm the presence of 3-hydroxypropenal. More than 11500 transitions were assigned in the course of our investigation with quantum numbers $2 \le J \le 100$, $K_a \le 59$, and $K_c \le 97$, resulting in a greatly improved set of spectroscopic parameters. The comparison between the LTE models and the observations yields an excitation temperature of 125 K with a column density $N = 1.0 \times 10^{15}$ cm$^{-2}$ for this species. We identified seven additional lines of 3-hydroxypropenal that show a good agreement with the model in the ALMA archive data. The calculated rotation-tunneling spectrum of 3-hydroxypropenal has sufficient accuracy for radio astronomical searches. The detection of 3-hydroxypropenal toward IRAS 16293$-$2422 B is now secure.

astro-ph.GA↗

arXiv2024

A deep search for large complex organic species toward IRAS16293-2422 B at 3 mm with ALMA

Complex organic molecules (COMs) have been detected ubiquitously in protostellar systems. However, at shorter wavelengths (~0.8mm) it is more difficult to detect larger molecules than at longer wavelengths (~3mm) because of the increase of millimeter dust opacity, line confusion, and unfavorable partition function. We aim to search for large molecules (>8 atoms) in the ALMA Band 3 spectrum of IRAS 16293-2422 B. We search for more than 70 molecules and identify as many lines as possible in the spectrum. The spectral settings were set to specifically target three-carbon species such as propanol and glycerol. We identify lines of 31 molecules including many oxygen-bearing COMs such as CH3OH and c-C2H4O and a few nitrogen- and sulfur-bearing ones such as HOCH2CN and CH3SH. The largest detected molecules are gGg-(CH2OH)2 and CH3COCH3. We do not detect glycerol or propanol but provide upper limits for them which are in line with previous laboratory and observational studies. The line density in Band 3 is only ~2.5 times lower in frequency space than in Band 7. From the detected lines in Band 3 at a $\gtrsim 6σ$ level, ~25-30% of them could not be identified indicating the need for more laboratory data of rotational spectra. We find similar column densities and column density ratios of COMs (within a factor ~2) between Band 3 and Band 7. The effect of dust optical depth for IRAS 16293-2422 B at an off-source location on column densities and column density ratios is minimal. Moreover, for warm protostars, long wavelength spectra are not only crowded, but also take longer integration times to reach the same sensitivity limit. The 3mm search has not yet resulted in detection of larger and more complex molecules in warm sources. A full deep ALMA Band 2-3 (i.e., 3-4 mm) survey is needed to assess whether low frequency data have the potential to reveal more complex molecules in warm sources.

astro-ph.GA↗

arXiv2023

Investigation of the rotational spectrum of CD$_3$OD and an astronomical search toward IRAS 16293$-$2422

Solar-type prestellar cores and protostars display large amounts of deuterated organic molecules. Recent findings on CHD$_2$OH and CD$_3$OH toward IRAS 16293-2422 suggest that even fully deuterated methanol, CD$_3$OD, may be detectable as well. However, searches for CD$_3$OD are hampered in particular by the lack of intensity information from a spectroscopic model. The objective of the present investigation is to develop a spectroscopic model of CD$_3$OD in low-lying torsional states that is sufficiently accurate to facilitate searches for this isotopolog in space. We carried out a new measurement campaign for CD$_3$OD involving two spectroscopic laboratories that covers the 34 GHz-1.1 THz range. A torsion-rotation Hamiltonian model based on the rho-axis method was employed for our analysis. Our resulting model describes the ground and first excited torsional states of CD$_3$OD well up to quantum numbers $J \leq 51$ and $K_a \leq 23$. We derived a line list for radio-astronomical observations from this model that is accurate up to at least 1.1 THz and should be sufficient for all types of radio-astronomical searches for this methanol isotopolog. This line list was used to search for CD$_3$OD in data from the Protostellar Interferometric Line Survey of IRAS 16293$-$2422 obtained with the Atacama Large Millimeter/submillimeter Array. While we found several emission features that can be attributed largely to CD$_3$OD, their number is still not sufficiently high enough to establish a clear detection. Nevertheless, the estimate of 2$\times 10^{15}$ cm$^{-2}$ derived for the CD$_3$OD column density may be viewed as an upper limit that can be compared to column densities of CD$_3$OH, CH$_3$OD, and CH$_3$OH. The comparison indicates that the CD$_3$OD column density toward IRAS 16293-2422 is in line with the enhanced D/H ratios observed for multiply deuterated complex organic molecules.

astro-ph.SR↗

arXiv2023

Rotation-tunneling spectrum and astrochemical modeling of dimethylamine, CH$_3$NHCH$_3$, and searches for it in space

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.

astro-ph.GA↗

arXiv2023

The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview: Sample characterization through polarization analysis

Aims. Through the ATOMIUM project, based on an ALMA large program, we aim to present a consistent view of a sample of 17 nearby cool evolved stars (Aymptotic Giant Branch and red supergiant stars). Methods. Here we present VLT/SPHERE-ZIMPOL polarimetric maps obtained in the visible of 14 out of the 17 ATOMIUM sources. They were obtained contemporaneously with the ALMA high spatial resolution data. To help interpret the polarized signal, we produced synthetic maps of light scattering by dust, through 3D radiative transfer simulations with the RADMC3D code. Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads across several optical filters. We infer that it primarily probes dust located just outside of the point spread function, and in or near the plane of the sky, with a total optical depth close to unity in the line of sight, representing only a fraction of the total circumstellar dust. The maximum DoLP ranges from 0.03-0.38 depending on the source, fractions that can be reproduced by our 3D pilot models for grains composed of common dust species. The spatial structure of the DoLP shows a diverse set of shapes. Only for three sources do we note a correlation between the ALMA CO and SiO lines, which trace the gas density, and the DoLP, which traces the dust. Conclusion. The clumpiness of the DoLP and the lack of a consistent correlation between the gas and the dust location show that, in the inner circumstellar environment (CSE), dust formation occurs at very specific sites. This has potential consequences for the derived mass-loss rates and dust-to-gas ratio in the inner region of the CSE. Except for $π^1$~Gru and perhaps GY Aql, we do not detect interactions between the circumstellar wind and the hypothesized companions that shape the wind at larger scales. This suggests that the orbits of any other companions are tilted out of the plane of the sky.

astro-ph.SR↗

arXiv2022

Millimeter wave spectrum and search for vinyl isocyanate toward Sgr B2(N) with ALMA

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.

astro-ph.GA↗

arXiv2022

Rotational spectroscopy $n$-propanol: $Aa$ and $Ag$ conformers

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).

physics.chem-ph↗

arXiv2022

Interstellar detection and chemical modeling of iso-propanol and its normal isomer

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]

astro-ph.GA↗

arXiv2022

The ALMA-PILS survey: First tentative detection of 3-hydroxypropenal (HOCHCHCHO) in the interstellar medium and chemical modeling of the C$_3$H$_4$O$_2$ isomers

Characterizing the molecular composition of solar-type protostars is useful for improving our understanding of the physico-chemical conditions under which the Sun and its planets formed. In this work, we analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) data of the Protostellar Interferometric Line Survey (PILS), an unbiased spectral survey of the solar-type protostar IRAS~16293--2422, and we tentatively detected 3-hydroxypropenal (HOCHCHCHO) for the first time in the interstellar medium towards source B. Based on the observed line intensities and assuming local thermodynamic equilibrium, its column density is constrained to be $\sim$10$^{15}$ cm$^{-2}$, corresponding to an abundance of 10$^{-4}$ relative to methanol, CH$_3$OH. Additional spectroscopic studies are needed to constrain the excitation temperature of this molecule. We included HOCHCHCHO and five of its isomers in the chemical network presented in Manigand et al. (2021) and we predicted their chemical evolution with the Nautilus code. The model reproduces the abundance of HOCHCHCHO within the uncertainties. This species is mainly formed through the grain surface reaction CH$_2$CHO + HCO $\rightarrow$ HCOCH$_2$CHO, followed by the tautomerization of HCOCH$_2$CHO into HOCHCHCHO. Two isomers, CH$_3$COCHO and CH$_2$COHCHO, are predicted to be even more abundant than HOCHCHCHO. Spectroscopic studies of these molecules are essential in searching for them in IRAS~16293--2422 and other astrophysical sources.

astro-ph.GA↗

arXiv2021

Laboratory rotational spectroscopy of acrylamide and search for acrylamide and propionamide toward Sgr B2(N) with ALMA

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).

astro-ph.GA↗

arXiv2021

Rotational and rovibrational spectroscopy of CD$_3$OH with an account of CD$_3$OH toward IRAS 16293$-$2422

Solar-type protostars harbor highly deuterated complex organics. While this degree of deuteration may provide important clues in studying the formation of these species, spectroscopic information on multiply deuterated isotopologs is often insufficient. In particular, searches for triply deuterated methanol, CD$_3$OH, are hampered by the lack of intensity information from a spectroscopic model. The aim of the present study is to develop such a model of CD$_3$OH in low-lying torsional states that is sufficiently accurate to facilitate further searches for CD$_3$OH in space. We performed a new measurement campaign for CD$_3$OH involving three spectroscopic laboratories that covers the 34 GHz-1.1 THz and the 20-900 cm$^{-1}$ ranges. The analysis was performed using the torsion-rotation Hamiltonian model based on the rho-axis method. We determined a model that describes the ground and first excited torsional states of CD$_3$OH, up to quantum numbers $J \leqslant 55$ and $K_a \leqslant 23$, and we derived a line list for radio-astronomical observations. This list is accurate up to at least 1.1 THz and should be sufficient for all types of radio-astronomical searches for this methanol isotopolog. It was used to search for CD$_3$OH in data from the Protostellar Interferometric Line Survey of IRAS 16293-2422 using ALMA. CD$_3$OH is securely detected in the data, with a large number of clearly separated and well-reproduced lines. We detected lines belonging to the ground and the first excited torsional states. The derived abundance of CD$_3$OH relative to non-deuterated isotopolog confirm the significant enhancement of this multiply deuterated variant. This finding is in line with other observations of multiply deuterated complex organic molecules and may serve as an important constraint on their formation models.

astro-ph.GA↗

arXiv2021

Millimetre-wave laboratory study of glycinamide and search for it with ALMA toward Sagittarius B2(N)

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]

astro-ph.GA↗