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Tracing snowlines and C/O ratio in a planet-hosting disk

2023; EDP Sciences; Volume: 678; Linguagem: Inglês

10.1051/0004-6361/202346974

1432-0746

Alice S. Booth, Charles J. Law, Milou Temmink, Margot Leemker, Enrique Macías,

Atmospheric Ozone and Climate

The composition of a forming planet is set by the material it accretes from its parent protoplanetary disk. Therefore, it is crucial to map the chemical make-up of the gas in disks to understand the chemical environment of planet formation. This paper presents molecular line observations taken with the Atacama Large Millimeter/submillimeter Array of the planet-hosting disk around the young star HD 169142. We detect N 2 H + , CH 3 OH, [CI], DCN, CS, C 34 S, 13 CS, H 2 CS, H 2 CO, HC 3 N, and c–C 3 H 2 in this system for the first time. Combining these data with the recent detection of SO and previously published DCO + data, we estimated the location of H 2 O and CO snowlines and investigate radial variations in the gas phase C/O ratio. We find that the HD 169142 disk has a relatively low N 2 H + flux compared to the disks around Herbig stars HD 163296 and MWC 480, indicating less CO freeze-out, and place the CO snowline beyond the millimetre disk at ≈150 au. The detection of CH 3 OH from the inner disk is consistent with the H 2 O snowline being located at the edge of the central dust cavity at ≈20 au. The radially varying CS/SO ratio across the proposed H 2 O snowline location is consistent with this interpretation. Additionally, the detection of CH 3 OH in such a warm disk adds to the growing evidence supporting the inheritance of complex ices in disks from the earlier colder stages of star formation. Finally, we propose that the giant HD 169142 b located at 37 au is forming between the CO 2 and H 2 O snowlines where the local elemental make-up of the gas is expected to have C/O ≈ 1.0.