Molecules with ALMA at Planet-forming Scales (MAPS) VIII: CO Gap in AS 209--Gas Depletion or Chemical Processing?

Abstract

Emission substructures in gas and dust are common in protoplanetary disks. Such substructures can be linked to planet formation or planets themselves. We explore the observed gas substructures in AS 209 using thermochemical modeling with RAC2D and high-spatial resolution data from the Molecules with ALMA at Planet-forming Scales(MAPS) program. The observations of C${}^{18}$O J=2-1 emission exhibit a strong depression at 88 au overlapping with the positions of multiple gaps in millimeter dust continuum emission. We find that the observed CO column density is consistent with either gas surface-density perturbations or chemical processing, while C${}_2$H column density traces changes in the C/O ratio rather than the H${}_2$ gas surface density. However, the presence of a massive planet (> 0.2 M${}_{Jup}$) would be required to account for this level of gas depression, which conflicts with constraints set by the dust emission and the pressure profile measured by gas kinematics. Based on our models, we infer that a local decrease of CO abundance is required to explain the observed structure in CO, dominating over a possible gap-carving planet present and its effect on the H${}_2$ surface density. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement Series.

21 pages, 18 figures

References in corpus (33)

• Gas- and dust evolution in protoplanetary disks
• Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
• Ring shaped dust accumulation in transition disks
• Molecules with ALMA at Planet-forming Scales (MAPS) I: Program Overview and Highlights
• Protoplanetary disk masses from CO isotopologues line emission
• Multiple Disk Gaps and Rings Generated by a Single Super-Earth
• Hydrocarbon emission rings in protoplanetary disks induced by dust evolution
• Molecules with ALMA at Planet-forming Scales (MAPS) V: CO gas distributions
• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• Molecules with ALMA at Planet-forming Scales (MAPS) IV: Emission Surfaces and Vertical Distribution of Molecules
• CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
• On the formation of multiple concentric rings and gaps in protoplanetary disks
• Water vapor distribution in protoplanetary disks
• A survey of C2H, HCN, and C18O in protoplanetary disks
• Bright C2H emission in protoplanetary disks in Lupus: high volatile C/O>1 ratios
• The efficiency of dust trapping in ringed proto-planetary discs
• Molecules with ALMA at Planet-forming Scales (MAPS). VII. Sub-stellar O/H and C/H and super-stellar C/O in planet feeding gas
• Exploring the Origins of Carbon in Terrestrial Worlds
• Chemistry in Protoplanetary Disks: the gas-phase CO/H2 ratio and the Carbon reservoir
• Molecules with ALMA at Planet-forming Scales (MAPS) VI: Distribution of the small organics HCN, C2H, and H2CO
• Destruction of Refractory Carbon in Protoplanetary Disks
• The spatial distribution of carbon dust in the early solar nebula and the carbon content of planetesimals
• The TW Hya Rosetta Stone Project III: Resolving the Gaseous Thermal Profile of the Disk
• An evolutionary study of volatile chemistry in protoplanetary disks
• Unbiased mm-wave Line Surveys of TW Hya and V4046 Sgr: The Enhanced C2H and CN Abundances of Evolved Protoplanetary Disks
• Gas mass tracers in protoplanetary disks: CO is still the best
• Molecules with ALMA at Planet-forming Scales (MAPS) XIII: HCO${}^{+}$ and disk ionization structure
• A Ring of C2H in the Molecular Disk Orbiting TW Hya
• Interpreting high spatial resolution line observations of planet-forming disks with gaps and rings -- The case of HD 163296
• 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
• Chemical Evolution in a Protoplanetary Disk within Planet Carved Gaps and Dust Rings
• Using HCO${}^{+}$ isotopologues as tracers of gas depletion in protoplanetary disk gaps

Cited by in corpus (3)

• Molecules with ALMA at Planet-forming Scales (MAPS) I: Program Overview and Highlights
• Molecules with ALMA at Planet-forming Scales (MAPS) V: CO gas distributions
• Molecules with ALMA at Planet-forming Scales (MAPS). VII. Sub-stellar O/H and C/H and super-stellar C/O in planet feeding gas