Chemical Feedbacks of Pebble Growth: Impacts on CO depletion and C/O ratios

Abstract

Observations of protoplanetary disks have revealed them to be complex and dynamic, with vertical and radial transport of gas and dust occurring simultaneously with chemistry and planet formation. Previous models of protoplanetary disks focused primarily on chemical evolution of gas and dust in a static disk, or dynamical evolution of solids in a chemically passive disk. In this paper, we present a new 1D method for modelling pebble growth and chemistry simultaneously. Gas and small dust particles are allowed to diffuse vertically, connecting chemistry at all elevations of the disk. Pebbles are assumed to form from the dust present around the midplane, inheriting the composition of ices at this location. We present the results of this model after 1 Myr of disk evolution around a 1$M_{\odot }$ star at various locations both inside and outside of the CO snowline. We find that for a turbulent disk ($\alpha =10^{-3}$), CO is depleted from the surface layers of the disk by roughly 1-2 orders of magnitude, consistent with observations of protoplanetary disks. This is achieved by a combination of ice sequestration and decreasing UV opacity, both driven by pebble growth. Further, we find the selective removal of ice species via pebble growth and sequestration can increase gas phase C/O ratios to values of approximately unity. However, our model is unable to produce C/O values of $\sim$1.5-2.0 inferred from protoplanetary disk observations, implying selective sequestration of ice is not sufficient to explain C/O ratios $>1$.

20 pages, 16 figures, 3 tables, accepted to ApJ

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• Chemical transformation of CO in evolving protoplanetary discs across stellar masses: a route to C-rich inner regions
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• Refractory carbon depletion by photolysis through dust collisions and vertical mixing
• PRODIGE -- Planet-forming disks in Taurus with NOEMA. I. Overview and first results for 12CO, 13CO, and C18O
• Multi-frequency analysis of the ALMA and VLA high resolution continuum observations of the substructured disc around CI Tau. Preference for sub-mm-sized low-porosity amorphous carbon grains
• Shaping the CO snowline in protoplanetary disks
• Dancing on the Grain: Variety of CO and its isotopologue fluxes as a result of surface chemistry and T Tauri disk properties
• SHAMPOO: A stochastic model for tracking dust particles under the influence of non-local disk processes
• HCN snowlines in protoplanetary disks: constraints from ice desorption experiments
• Protoplanetary Disk Chemistry