Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-12-09
Astronomy and Astrophysics
Astrophysics
Accepted for publication in A&A letters. Language edited
Scientific paper
10.1051/0004-6361:200811082
Aims. We attempt to understand the presence of gas phase CO below its freezing temperature in circumstellar disks. We study two promising mechanisms to explain this phenomenon: turbulent mixing and photodesorption. Methods. We compute the chemical evolution of circumstellar disks including grain surface reactions with and without turbulent mixing and CO photodesorption. Results. We show that photodesorption significantly enhances the gas phase CO abundance, by extracting CO from the grains when the visual extinction remains below about 5 magnitudes. However the resulting dependence of column density on radial distance is not consistent with observations so far. We propose that this inconsistency could be the result of grain growth. On the other hand, the influence of turbulent mixing is not found to be straightforward. The efficiency of turbulent mixing depends upon a variety of parameters, including the disk structure. For the set of parameters we chose, turbulent mixing is not found to have any significant influence on the CO column density.
Dutrey Anne
Guilloteau Stéphane
Herbst Eric
Hersant Franck
Wakelam Valentine
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