The chemistry of transient dense cores in interstellar clouds.

I model the chemical effects on dark clouds of their being composed of small (<0.1 pc), transient (order of 1 Myr), dense cores (which are only observed with high-resolution interferometry) within which most of the clouds' mass resides, surrounded by a diffuse background gas. I investigate the chemical evolution of the cores, and the resultant chemical enhancement of the background gas by cyclical processing through core formation and dissipation. I approximate the MHD mechanism of Falleh Hartquist (2002), by which large transient density inhomogeneities may be produced by slow-mode waves in a cold plasma, into a multi-point 1-D chemical code. Molecular freeze-out onto dust grains and subsequent re-injection into the gas phase are switched on or off according to the attainment of a critical visual extinction at individual points. I explore a grid of parameter space in five physical and chemical variables. Among a number of conclusions, I find firstly that multi-point chemical codes are highly necessary for modelling dark cloud regions, due to the large chemical variation over time and space. I find that the core chemistry is young at all times, in keeping with observations, and that the abundance and spatial extent of several important species is significantly enhanced by the cycling process. Further to this, I construct (non-interacting) assemblies of such cores, producing convolved maps mimicking observational constraints, and present evidence that such collections of transient dense cores may reproduce the morphologies observed in both low- and high-resolution molecular line studies of dark clouds. I further modify the convolution method in a number of ways, using this mapping procedure to test hypotheses derived from the chemical analysis. Hence I obtain observational diagnostics for the determination of physical and chemical conditions in dark clouds

Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions

Protostellar and cometary detections of organohalogens

Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes1. Consequently, they have been proposed as biomarkers in the search for life on exoplanets2. Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain3,4. Here we report the interstellar detection of two isotopologues of the organohalogen CH3Cl and put some constraints on CH3F in the gas surrounding the low-mass protostar IRAS 16293–2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH3Cl in the coma of comet 67P/Churyumov–Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets.Stars and planetary systemsInterstellar matter and star formatio

Modeling the production of highly-complex molecules in star-forming regions

Molecules of increasing complexity are being observed toward star-forming regions, including the recently detected iso-propyl cyanide, the first interstellar branched carbon-chain molecule. Modeling the formation of new complex organics requires new grain-surface production mechanisms, as well as gas-phase and grain-surface destruction processes. The method for constructing networks for new molecules is discussed, as well as the results of recent models of branched carbon-chain molecule chemistry. The formation of both simple and complex organics in cold regions is also discussed. New, exact kinetics models indicate that complex molecules may be formed efficiently at very low temperatures, if CO is abundant on the grain surfaces

Ice Age: chemodynamical modeling of Cha-MMS1 to predict new solid-phase species for detection with JWST

Stars and planetary system

Ice Age: chemodynamical modeling of Cha-MMS1 to predict new solid-phase species for detection with JWST

Stars and planetary system

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 ($sim 0.8$\,mm), it is generally more difficult to detect larger molecules than at longer wavelengths sim 3$\,mm) because of the increase in millimeter dust opacity, line confusion, and unfavorable partition function. We aim to search for large molecules (more than eight atoms) in the Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 spectrum of IRAS 16293-2422 B. In particular, the goal is to quantify the usability of ALMA Band 3 for molecular line surveys in comparison to similar studies at shorter wavelengths. We used deep ALMA Band 3 observations of IRAS 16293-2422 B to search for more than 70 molecules and identified as many lines as possible in the spectrum. The spectral settings were set to specifically target three-carbon species such as i- and n-propanol and glycerol, the next step after glycolaldehyde and ethylene glycol in the hydrogenation of CO. We then derived the column densities and excitation temperatures of the detected species and compared the ratios with respect to methanol between Band 3 ($ sim 3$\,mm) and Band 7 sim 1$\,mm, Protostellar Interferometric Line Survey) observations of this source to examine the effect of the dust optical depth. We identified lines of 31 molecules including many oxygen-bearing COMs such as CH$_3$OH, CH$_2$OHCHO, CH$_3$CH$_2$OH, and c-C$_2$H$_4$O and a few nitrogen- and sulfur-bearing ones such as HOCH$_2$CN and CH$_3$SH. The largest detected molecules are gGg-(CH$_2$OH)$_2$ and CH$_3$COCH$_3$. We did not detect glycerol or i- and n-propanol, but we do provide upper limits for them which are in line with previous laboratory and observational studies. The line density in Band 3 is only $sim 2.5$ times lower in frequency space than in Band 7. From the detected lines in Band 3 at a $level sim 25-30$ 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 $sim 2$) between Band 3 and Band 7. The effect of the 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 ($sim 3$\,mm) are not only crowded and complex, but they also take significantly longer integration times than shorter wavelength observations sim 0.8$\,mm) to reach the same sensitivity limit. The 3\,mm search has not yet resulted in the detection of larger and more complex molecules in warm sources. A full deep ALMA Band$2-3$(i.e. sim 3-4$\,mm wavelengths) survey is needed to assess whether low frequency data have the potential to reveal more complex molecules in warm sources

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

International audienceGlycinamide (NHCHC(O)NH) 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 centimetre-wave region on a laser-ablation generated supersonic expansion sample. Aims. The aim of this work is to extend the laboratory spectrum of glycinamide to the millimetre (mm) wave region to support searches for this molecule in the interstellar medium and to perform the first check for its presence in the high-mass star forming region Sagittarius B2(N). Methods. Glycinamide was synthesised chemically and was studied with broadband rotational spectroscopy in the 90-329 GHz region with the sample in slow flow at 50°C. Tunnelling 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 the Atacama Large Millimetre/submillimetre Array towards Sgr B2(N). The astronomical spectra were analysed under the assumption of local thermodynamic equilibrium. Results. We report the first analysis of the mm-wave rotational spectrum of glycinamide, resulting in fitting - to experimental measurement accuracy - of over 1200 assigned and measured transition frequencies for the ground-state tunnelling doublet and of many lines for tunnelling doublets for two singly excited vibrational states. We also determine the precise vibrational separation in each doublet. We did not detect emission from glycinamide in the hot molecular core Sgr B2(N1S). We derived a column density upper limit of 1.5 × 1016 cm-2, which implies 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 towards 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. Conclusions. Thanks to the spectroscopic data provided by this study, the search for glycinamide in the interstellar medium can continue on a firm basis. 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. © ESO 2022

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

International audienceContext. The interstellar detections of isocyanic acid (HNCO), methyl isocyanate (CH3NCO), and very recently also ethyl isocyanate (C2H5NCO) invite the question of whether or not vinyl isocyanate (C2H3NCO) can be detected in the interstellar medium. There are only low-frequency spectroscopic data (&lt;40 GHz) available for this species in the literature, which makes predictions at higher frequencies rather uncertain, which in turn hampers searches for this molecule in space using millimeter (mm) wave astronomy. Aims. The aim of the present study is on one hand to extend the laboratory rotational spectrum of vinyl isocyanate to the mm wave region and on the other to search, for the first time, for its presence in the high-mass star-forming region Sgr B2, where other isocyanates and a plethora of complex organic molecules are observed. Methods. We recorded the pure rotational spectrum of vinyl isocyanate in the frequency regions 127.5-218 and 285-330 GHz using the Prague mm wave spectrometer. The spectral analysis was supported by high-level quantum-chemical calculations. On the astronomy side, we assumed local thermodynamic equilibrium to compute synthetic spectra of vinyl isocyanate and to search for it in the ReMoCA survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star-forming protocluster Sgr B2(N). Additionally, we searched for the related molecule ethyl isocyanate in the same source. Results. Accurate values for the rotational and centrifugal distortion constants are reported for the ground vibrational states of trans and cis vinyl isocyanate from the analysis of more than 1000 transitions. 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. Conclusions. 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 less than unity. Even though vinyl isocyanate was not detected toward Sgr B2(N), the results of this work represent a significant improvement on previous low-frequency studies and will help the astronomical community to continue searching for this species in the Universe

Impact of Antipsychotic Review and Nonpharmacological InterventiononAntipsychotic Use, Neuropsychiatric Symptoms, and Mortality in People With Dementia Living in Nursing Homes: A Factorial Cluster-Randomized Controlled Trial by the Well-Being and Health for People With Dementia (WHELD) Program

This study evaluated the impact of antipsychotic review, social interaction, and exercise, in conjunction with person-centered care, on antipsychotic use, agitation, and depression in people with dementia living in nursing homes