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Cosmic ray induced desorption in prestellar cores
Aurore Bacmann IPAG, Grenoble, FR | |
| Molecular depletion has long been predicted and observed in the dense interstellar medium. It has also been long noted that without desorption, all molecules, including CO and CH3OH should have completely frozen out on to the dust grains within the typical lifetime of prestellar cores. However, this is not supported by observations, which show that significant amounts of molecules are still detected despite an abundance drop of ~2 orders of magnitude in the densest regions. While several desorption mechanisms have been invoked to account for the partial return of ices into the gas phase, for example UV photodesorption or cosmic ray sputtering, their efficiencies remain poorly constrained. These are however crucial for chemical models, in order to understand observed abundances in depletion-dominated environments. Recent photodesorption experiments have shown UV photons are several orders of magnitude less efficient at desorbing methanol than previously believed. While this illustrates the need for laboratory experiments to quantify desorption processes, it also raises the question as to which processes allow methanol ices to sublimate. Cosmic rays sputtering is another likely process returning frozen-out molecules back into the gas phase, yet its treatment in chemical models is not based on experimental results. Here we present the results of swift-ion irradiation of interstellar ice analogues carried out at the GANIL ion accelerator facility. We determine a sputtering yield, i.e. the number of desorbed molecules per incident ion. Introduced into a chemical model, the data show that cosmic rays are efficient enough to account for the desorption of methanol in ice mixtures and to reproduce observed abundances in prestellar cores. | |
| Collaborators: A. Faure, IPAG, FR E. Quirico, IPAG, FR P. Boduch, CIMAP, FR H. Rothard, CIMAP, FR E. Dartois, ISMO, FR M. Chabot, ISN, FR |
Suggested Session:
Chemistry |