Volume 643, November 2020
|Number of page(s)||13|
|Section||Interstellar and circumstellar matter|
|Published online||10 November 2020|
Sustained oscillations in interstellar chemistry models
LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université,
e-mail: Evelyne.Roueff@obspm.fr; email@example.com
2 Université de Paris, Paris, France
Accepted: 29 September 2020
Context. Nonlinear behavior in interstellar chemical models has been recognized for 25 years now. Different mechanisms account for the possibility of multiple fixed-points at steady-state, characterized by the ionization degree of the gas.
Aims. Chemical oscillations are also a natural behavior of nonlinear chemical models. We study under which conditions spontaneous sustained chemical oscillations are possible, and what kind of bifurcations lead to, or quench, the occurrence of such oscillations.
Methods. The well-known ordinary differential equations (ODE) integrator VODE was used to explore initial conditions and parameter space in a gas phase chemical model of a dark interstellar cloud.
Results. We recall that the time evolution of the various chemical abundances under fixed temperature conditions depends on the density over cosmic ionization rate nH∕ζ ratio. We also report the occurrence of naturally sustained oscillations for a limited but well-defined range of control parameters. The period of oscillations is within the range of characteristic timescales of interstellar processes and could lead to spectacular resonances in time-dependent models. Reservoir species (C, CO, NH3, ...) oscillation amplitudes are generally less than a factor two. However, these amplitudes reach a factor ten to thousand for low abundance species, e.g. HCN, ND3, that may play a key role for diagnostic purposes. The mechanism responsible for oscillations is tightly linked to the chemistry of nitrogen, and requires long chains of reactions such as found in multi-deuteration processes.
Key words: astrochemistry / instabilities / methods: numerical / ISM: abundances / evolution / molecular processes
© E. Roueff and J. Le Bourlot 2020
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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