Chemistry in Disks. IX. Observations and modeling of HCO+ and DCO+ in DM Tau

الأصل · EN

We present resolved Plateau de Bure Array observations of DM Tau in lines of HCO+ (3-2), (1-0) and DCO+ (3-2). A power-law fitting approach allowed a derivation of column densities of these two molecules. A chemical inner hole of 50 AU was found in both HCO+ and DCO+ with DCO+ emission extending to only 450 AU. An isotopic ratio of RD = N(DCO+) / N(HCO+) was found to range from 0.1 at 50 AU and 0.2 at 450 AU. Chemical modeling allowed an exploration of the sensitivity of these molecular abundances to physical parameters out with temperature, finding that X-rays were the domination ionization source in the HCO+ molecular region and that RD also is sensitive to the CO depletion. The ionization fraction, assuming a steady state system, was found to be x(e-) 10⁻⁷. Modeling suggests that HCO+ is the dominant charged molecule in the disk but its contribution to ionization fraction is dwarfed by atmoic ions such as C+, S+ and H+.