A major asymmetric ice trap in a planet-forming disk: II. prominent SO and SO2 pointing to C/O < 1

TL;DR

This study reports the first detection of SO2 in a protoplanetary disk, revealing a C/O ratio less than 1, which impacts our understanding of planetary composition and sulfur chemistry in planet-forming regions.

Contribution

It presents the first observation of prominent SO2 emission in a disk and links molecular emissions to dust traps, suggesting ice sublimation at dust cavity edges influences sulfur chemistry.

Findings

SO and SO2 detected in the Oph-IRS 48 disk

C/O ratio constrained to be less than 1, possibly solar

Sulfur reservoir accounts for 15-100% of total sulfur in the disk

Abstract

Gas-phase sulphur bearing volatiles appear to be severely depleted in protoplanetary disks. The detection of CS and non-detections of SO and SO2 in many disks have shown that the gas in the warm molecular layer, where giant planets accrete their atmospheres, has a high C/O ratio. In this letter, we report the detection of SO and SO2 in the Oph-IRS 48 disk using ALMA. This is the first case of prominent SO2 emission detected from a protoplanetary disk. The molecular emissions of both molecules is spatially correlated with the asymmetric dust trap. We propose that this is due to the sublimation of ices at the edge of the dust cavity and that the bulk of the ice reservoir is coincident with the millimetre dust grains. Depending on the partition of elemental sulphur between refractory and volatile materials the observed molecules can account for 15-100% of the total sulphur budget in the disk. In strong contrast to previous results, we constrain the C/O ratio from the CS/SO ratio to be < 1 and potentially solar. This has important implications for the elemental composition of planets forming within the cavities of warm transition disks.