C/O AND SNOWLINE LOCATIONS IN PROTOPLANETARY DISKS: THE EFFECT OF RADIAL DRIFT AND VISCOUS GAS ACCRETION

The C/O ratio is a defining feature of both gas giant atmospheric and protoplanetary disk chemistry. In disks, the C/O ratio is regulated by the presence of snowlines of major volatiles at different distances from the central star. We explore the effect of the radial drift of solids and viscous gas accretion onto the central star on the snowline locations of the main C and 0 carriers in a protoplanetary disk, H2O, CO2, and CO, and their consequences for the C/O ratio in gas and dust throughout the disk. We determine the snowline locations for a range of fixed initial particle sizes and disk types. For our fiducial disk model, we find that grains with sizes similar to 0.5 cm less than or similar to s less than or similar to 7 m for an irradiated disk and similar to 0.001 cm less than or similar to s less than or similar to 7 m for an evolving and viscous disk desorb at a size-dependent location in the disk, which is independent of the particle's initial position. The snowline radius decreases for larger particles, up to sizes of 7 m. Compared to a static disk, we find that radial drift and gas accretion in a viscous disk move the H20 snowline inwards by up to 40%, the CO2 snowline by up to 60%, and the CO snowline by up to 50%. We thus determine an inner limit on the snowline locations when radial drift and gas accretion are accounted for.