Physical and Chemical Structure of Protoplanetary Disks with Grain Growth

We calculate the physical structure of protoplanetary disks by evaluating the gas density and temperature self-consistently and solving separately for the dust temperature. The effect of grain growth is taken into account by assuming a power-law size distribution and varying the maximum radius of grains a max . In our fiducial model with a max = 10 μm, the gas is warmer than the dust in the surface layer of the disk, while the gas and dust have the same temperature in deeper layers. In the models with larger a max , the gas temperature in the surface layer is lower than in the fiducial model because of reduced photoelectric heating rates from small grains, while the deeper penetration of stellar radiation warms the gas at intermediate height. A detailed chemical reaction network is solved at outer radii ( r ≥ 50 AU). Vertical distributions of some molecular species at different radii are similar when plotted as a function of hydrogen column density Σ H from the disk surface. Consequently, molecular column densities do not much depend on disk radius. In the models with larger a max , the lower temperature in the surface layer makes the geometrical thickness of the disk smaller, and the gaseous molecules are confined to smaller heights. However, if we plot the vertical distributions of molecules as a function of Σ H , they do not significantly depend on a max . The dependence of the molecular column densities on a max is not significant either. Notable exceptions are HCO + , H , and H 2 D + , which have smaller column densities in the models with larger a max .