Modelling line emission of deuterated H_3^+ from prestellar cores

Context: The depletion of heavy elements in cold cores of interstellar molecular clouds can lead to a situation where deuterated forms of H_3^+ are the most useful spectroscopic probes of the physical conditions. Aims: The aim is to predict the observability of the rotational lines of H_2D^+ and D_2H^+ from prestellar cores. Methods: Recently derived rate coefficients for the H_3^+ + H_2 isotopic system were applied to the "complete depletion" reaction scheme to calculate abundance profiles in hydrostatic core models. The ground-state lines of H_2D^+(o) (372 GHz) and D_2H^+(p) (692 GHz) arising from these cores were simulated. The excitation of the rotational levels of these molecules was approximated by using the state-to-state coefficients for collisions with H_2. We also predicted line profiles from cores with a power-law density distribution advocated in some previous studies. Results: The new rate coefficients introduce some changes to the complete depletion model, but do not alter the general tendencies. One of the modifications with respect to the previous results is the increase of the D_3^+ abundance at the cost of other isotopologues. Furthermore, the present model predicts a lower H_2D^+ (o/p) ratio, and a slightly higher D_2H^+ (p/o) ratio in very cold, dense cores, as compared with previous modelling results. These nuclear spin ratios affect the detectability of the submm lines of H_2D^+(o) and D_2H^+(p). The previously detected H_2D^+ and D_2H^+ lines towards the core I16293E, and the H_2D^+ line observed towards Oph D can be reproduced using the present excitation model and the physical models suggested in the original papers.Comment: 10 pages, 11 Figures; ver2: updated some of the Figures, added some references, added an entry to acknowledgement

Dimethyl ether in its ground state, v=0, and lowest two torsionally excited states, v11=1 and v15=1, in the high-mass star-forming region G327.3-0.6

The goal of this paper is to determine the respective importance of solid state vs. gas phase reactions for the formation of dimethyl ether. This is done by a detailed analysis of the excitation properties of the ground state and the torsionally excited states, v11=1 and v15=1, toward the high-mass star-forming region G327.3-0.6. With the Atacama Pathfinder EXperiment 12 m submillimeter telescope, we performed a spectral line survey. The observed spectrum is modeled assuming local thermal equilibrium. CH3OCH3 has been detected in the ground state, and in the torsionally excited states v11=1 and v15=1, for which lines have been detected here for the first time. The emission is modeled with an isothermal source structure as well as with a non-uniform spherical structure. For non-uniform source models one abundance jump for dimethyl ether is sufficient to fit the emission, but two components are needed for the isothermal models. This suggests that dimethyl ether is present in an extended region of the envelope and traces a non-uniform density and temperature structure. Both types of models furthermore suggest that most dimethyl ether is present in gas that is warmer than 100 K, but a smaller fraction of 5%-28% is present at temperatures between 70 and 100 K. The dimethyl ether present in this cooler gas is likely formed in the solid state, while gas phase formation probably is dominant above 100 K. Finally, the v11=1 and v15=1 torsionally excited states are easily excited under the density and temperature conditions in G327.3-0.6 and will thus very likely be detectable in other hot cores as well.Comment: 12 pages (excluding appendices), 8 figures, A&A in pres

Infrared spectroscopy of solid CO-CO2 mixtures and layers

The spectra of pure, mixed and layered CO and CO2 ices have been studied systematically under laboratory conditions using infrared spectroscopy. This work provides improved resolution spectra (0.5 cm-1) of the CO2 bending and asymmetric stretching mode, as well as the CO stretching mode, extending the existing Leiden database of laboratory spectra to match the spectral resolution reached by modern telescopes and to support the interpretation of the most recent data from Spitzer. It is shown that mixed and layered CO and CO2 ices exhibit very different spectral characteristics, which depend critically on thermal annealing and can be used to distinguish between mixed, layered and thermally annealed CO-CO2 ices. CO only affects the CO2 bending mode spectra in mixed ices below 50K under the current experimental conditions, where it exhibits a single asymmetric band profile in intimate mixtures. In all other ice morphologies the CO2 bending mode shows a double peaked profile, similar to that observed for pure solid CO2. Conversely, CO2 induces a blue-shift in the peak-position of the CO stretching vibration, to a maximum of 2142 cm-1 in mixed ices, and 2140-2146 cm-1 in layered ices. As such, the CO2 bending mode puts clear constraints on the ice morphology below 50K, whereas beyond this temperature the CO2 stretching vibration can distinguish between initially mixed and layered ices. This is illustrated for the low-mass YSO HH46, where the laboratory spectra are used to analyse the observed CO and CO2 band profiles and try to constrain the formation scenarios of CO2.Comment: Accepted in A&

On the equivalence of two deformation schemes in quantum field theory

Two recent deformation schemes for quantum field theories on the two-dimensional Minkowski space, making use of deformed field operators and Longo-Witten endomorphisms, respectively, are shown to be equivalent.Comment: 14 pages, no figure. The final version is available under Open Access. CC-B

Laboratory experiments on interstellar ice analogs: The sticking and desorption of small physisorbed molecules

Molecular oxygen and nitrogen are difficult to observe since they are infrared inactive and radio quiet. The low O2 abundances found so far combined with general considerations of dense cloud conditions suggest molecular oxygen is frozen out at low temperatures (< 20 K) in the shielded inner regions of cloud cores. In solid form O2 and N2 can only be observed as adjuncts within other ice constituents, like CO. In this work we focus on fundamental properties of N2 and O2 in CO ice-gas systems, e.g. desorption characteristics and sticking probabilities at low temperatures for different ice morphologies