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arXiv · 1503.02659

Evidence for DCO+ as a probe of ionization in the warm disk surface

Cécile Favre·Edwin A. Bergin·L. Ilsedore Cleeves·Franck Hersant·Chunhua Qi·Yuri Aikawa
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Abstract

In this Letter we model the chemistry of DCO$^{+}$ in protoplanetary disks. We find that the overall distribution of the DCO$^{+}$ abundance is qualitatively similar to that of CO but is dominated by thin layer located at the inner disk surface. To understand its distribution, we investigate the different key gas-phase deuteration pathways that can lead to the formation of DCO$^{+}$. Our analysis shows that the recent update in the exothermicity of the reaction involving CH$_2$D$^{+}$ as a parent molecule of DCO$^{+}$ favors deuterium fractionation in warmer conditions. As a result the formation of DCO$^{+}$ is enhanced in the inner warm surface layers of the disk where X-ray ionization occurs. Our analysis points out that DCO$^{+}$ is not a reliable tracer of the CO snow line as previously suggested. We thus predict that DCO$^{+}$ is a tracer of active deuterium and in particular X-ray ionization of the inner disk.

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Cécile Favre, Edwin A. Bergin, L. Ilsedore Cleeves, Franck Hersant, Chunhua Qi, Yuri Aikawa. 2015-03-09. Evidence for DCO+ as a probe of ionization in the warm disk surface. https://doi.org/10.1088/2041-8205/802/2/l23

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