Investigating the asymmetric chemistry in the disk around the young star HD 142527

Abstract

The atmospheric composition of planets is determined by the chemistry of the disks in which they form. Studying the gas-phase molecular composition of disks thus allows us to infer what the atmospheric composition of forming planets might be. Recent observations of the IRS 48 disk have shown that (asymmetric) dust traps can directly impact the observable chemistry through (radial and vertical) transport and the sublimation of ices. The asymmetric HD 142527 disk provides another good opportunity to investigate the role of dust traps in setting the disk’s chemical composition. In this work we use archival ALMA observations of the HD 142527 disk to obtain a molecular inventory that is as large as possible in order to investigate the possible influence of the asymmetric dust trap on the disk’s chemistry. We present the first ALMA detections of [C I], 13C18O, DCO+, H2CO, and additional transitions of HCO+ and CS in this disk. In addition, we present upper limits for non-detected species such as SO and CH3OH. For the majority of the observed molecules, a decrement in the emission at the location of the dust trap is found. For the main CO isotopologues, continuum oversubtraction is the likely cause of the observed asymmetry, while for CS and HCN we propose that the observed asymmetries are likely due to shadows cast by the misaligned inner disk. As the emission of the observed molecules is not co-spatial with the dust trap, and no SO or CH3OH is found, thermal sublimation of icy mantles does not appear to play a major role in changing the gas-phase composition of the outer disk in HD 142527 disk. Using our observations of 13C18O and DCO+ and a RADMC-3D model, we determine the CO snowline to be located beyond the dust traps, favouring cold gas-phase formation of H2CO rather than the hydrogenation of CO-ice and subsequent sublimation.