If you like C/O variations, you should have put a ring on it

Abstract

The C/O-ratio as traced with C${}_2$H emission in protoplanetary disks is fundamental for constraining the formation mechanisms of exoplanets and our understanding of volatile depletion in disks, but current C${}_2$H observations show an apparent bimodal distribution which is not well understood, indicating that the C/O distribution is not described by a simple radial dependence. The transport of icy pebbles has been suggested to alter the local elemental abundances in protoplanetary disks, through settling, drift and trapping in pressure bumps resulting in a depletion of volatiles in the surface and an increase of the elemental C/O. We combine all disks with spatially resolved ALMA C${}_2$H observations with high-resolution continuum images and constraints on the CO snowline to determine if the C${}_2$H emission is indeed related to the location of the icy pebbles. We report a possible correlation between the presence of a significant CO-icy dust reservoir and high C${}_2$H emission, which is only found in disks with dust rings outside the CO snowline. In contrast, compact dust disks (without pressure bumps) and warm transition disks (with their dust ring inside the CO snowline) are not detected in C${}_2$H, suggesting that such disks may never have contained a significant CO ice reservoir. This correlation provides evidence for the regulation of the C/O profile by the complex interplay of CO snowline and pressure bump locations in the disk. These results demonstrate the importance of including dust transport in chemical disk models, for a proper interpretation of exoplanet atmospheric compositions, and a better understanding of volatile depletion in disks, in particular the use of CO isotopologues to determine gas surface densities.

Accepted by A&A Letters. 5 pages, 2 figures, plus appendix (5 pages, 4 figures)

References in corpus (19)

• Gas- and dust evolution in protoplanetary disks
• Ring shaped dust accumulation in transition disks
• Chemical enrichment of giant planets and discs due to pebble drift
• Direct mapping of the temperature and velocity gradients in discs. Imaging the vertical CO snow line around IM Lupi
• Lupus disks with faint CO isotopologues: low gas/dust or large carbon depletion?
• Hydrocarbon emission rings in protoplanetary disks induced by dust evolution
• Mass measurements in protoplanetary disks from hydrogen deuteride
• CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
• An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I
• Excess C/O and C/H in outer protoplanetary disk gas
• Robustness of N2H+ as tracer of the CO snowline
• A survey of C2H, HCN, and C18O in protoplanetary disks
• Methanol Along the Path from Envelope to Protoplanetary Disc
• Annular substructures in the transition disks around LkCa 15 and J1610
• An evolutionary study of volatile chemistry in protoplanetary disks
• Destruction of refractory carbon grains drives the final stage of proto-planetary disk chemistry
• Unlocking CO Depletion in Protoplanetary Disks II. Primordial C/H Predictions Inside the CO Snowline
• The dry and carbon poor inner disk of TW Hya: evidence for a massive icy dust trap
• Dust growth, fragmentation and self-induced dust traps in PHANTOM

Cited by in corpus (2)

• High-resolution atmospheric retrievals of WASP-121b transmission spectroscopy with ESPRESSO: Consistent relative abundance constraints across multiple epochs and instruments
• Global Modeling of Nebulae With Particle Growth, Drift, and Evaporation Fronts. III. Redistribution of Refractories and Volatiles