| 1. |
- Taquet, V, et al.
(författare)
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Seeds of Life in Space (SOLIS) VI. Chemical evolution of sulfuretted species along the outflows driven by the low-mass protostellar binary NGC1333-IRAS4A
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 637
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Tidskriftsartikel (refereegranskat)abstract
- Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC1333-IRAS4A in the 1.3, 2, and 3mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east-south west direction. SO is detected at extremely high radial velocity up to +25 km s 1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm 3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2.
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| 2. |
- Motapon, O., et al.
(författare)
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Advances in the MQDT approach of electron/molecular cation reactive collisions : High precision extensive calculations for applications
- 2015
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Ingår i: DR2013. - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- Recent advances in the stepwise multichannel quantum defect theory approach of electron/molecular cation reactive collisions have been applied to perform computations of cross sections and rate coefficients for dissociative recombination and electron-impact rovibrational transitions of H-2(+), BeH+ and their deuterated isotopomers. At very low energy, rovibronic interactions play a significant role in the dynamics, whereas at high energy, the dissociative excitation strongly competes with all other reactive processes.
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| 3. |
- Mezei, J. Zs, et al.
(författare)
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Electronic and photonic reactive collisions in edge fusion plasma and interstellar space : application to H-2 and BeH systems
- 2015
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Ingår i: Light element atom, molecule and radical behaviour in the divertor and edge plasma regions. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- Reactive collisional and radiative elementary processes rate coefficients have been either computed using multichannel-quantum-defect theory methods, or measured in merged-beam (storage ring) and crossed-beam experiments. The reaction mechanisms are explained and output data are displayed in ready-to-be-used form, appropriate for the modeling of the kinetics of the edge fusion plasma and of the interstellar molecular clouds.
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| 4. |
- Wakelam, V., et al.
(författare)
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H2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations
- 2017
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Ingår i: Molecular Astrophysics. - : Elsevier BV. - 2405-6758. ; 9, s. 1-36
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Tidskriftsartikel (refereegranskat)abstract
- Molecular hydrogen is the most abundant molecule in the universe. It is the first one to form and survive photo-dissociation in tenuous environments. Its formation involves catalytic reactions on the surface of interstellar grains. The micro-physics of the formation process has been investigated intensively in the last 20 years, in parallel of new astrophysical observational and modeling progresses. In the perspectives of the probable revolution brought by the future satellite JWST, this article has been written to present what we think we know about the H2 formation in a variety of interstellar environments. © 2017 Elsevier B.V.
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| 5. |
- Senevirathne, Bethmini, 1982, et al.
(författare)
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Hydrogen atom mobility, kinetic isotope effects and tunneling on interstellar ices (I-h and ASW)
- 2017
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Ingår i: Molecular Astrophysics. - : Elsevier BV. - 2405-6758. ; 6, s. 59-69
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Tidskriftsartikel (refereegranskat)abstract
- Transitions of a single H atom between local minima on the surfaces of crystalline ice (I-h) and amorphous solid water (ASW) are studied theoretically in the temperature range 4-25 K. Binding energies, barrier heights, transition rate constants and the kinetic isotope effect (KIE) with and without tunneling are calculated. Harmonic transition state theory is used to obtain the transition rate constants and tunneling is treated with the Wigner tunneling correction, Eckart barrier correction and harmonic quantum transition state theory (HQTST). The classical binding energies are smaller on I-h (<47 meV) than on ASW (<89 meV). Also the classical barrier heights are smaller on I-h (<14 meV) than on ASW (<69 meV) and distributed over a range of energies, in line with previous experimental observations. Similarly the vibrationally adiabatic ground state (VAG) barrier heights are smaller on I-h (<7 meV) than on ASW (<54 meV). The surface morphology strongly influences the well depths. Tunneling increases some of the transition rate constants substantially but has a much smaller effect on others. The average KIE for I-h is higher than for ASW for the same range of barrier heights. (C) 2017 Elsevier B.V. All rights reserved.
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