Deuterium Fractionation in Protoplanetary Disks
First Author:
Chunhua Qi
Email: cqi AT cfa.harvard.edu
Harvard-Smithsonian CfA
60 Garden Street, MS 42
Cambridge, MA 02138, USA
Coauthors:
Wilner, David, Harvard-Smithsonian CfA
Aikawa, Yuri, Kobe University
Blake, Geoffrey, Caltech
Hogerheijde, Michiel, Leiden University
Abstract
Revised abstract:
Deuterated molecule chemistry is sensitive to the temperature history of interstellar and circumstellar gas, and observations of deuterated species can constrain the origin of primitive solar system bodies such as comets and other icy planetesimals.We present Submillimeter Array observations of the HCO+, DCO+, HCN and DCN J=3-2 lines in the disks around the K8V star TW Hya and the A1V star HD 163296 at arcsecond scales. We constrain the radial and vertical distributions of various species using a model where the molecular emission from an irradiated accretion disk is sampled with a 2D Monte Carlo radiative transfer code. We find enhanced molecular D/H ratios in both disks, and we attribute these enhancements to different processes. In the cold disk of TW Hya, the DCO+/HCO+ ratio increases with increasing radius due to low temperatures far from the star, as expected from low-temperature gas-phase deuterium fractionation processes. In the warm disk of HD 163296, these processes should be prohibited. The detailed processes leading to such high abundance of DCO+ is still unknown.
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