The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO2 emission

TL;DR

This study uses ALMA observations of sulfur-bearing molecules to analyze the properties of the jet and disk in the HH 212 protostar, revealing details about jet composition, dynamics, and sulfur chemistry at unprecedented scales.

Contribution

First detailed ALMA imaging of sulfur molecules in HH 212's jet and disk, constraining their physical and chemical properties at very small scales.

Findings

The jet is fast (~100-200 km/s) and collimated (~90 AU), with a mass loss rate >0.2-2e-6 Msun/yr.

SO and SO2 effectively trace the inner molecular jet and disk, revealing velocity gradients and chemical abundances.

Sulfur in the jet is partly due to shocks and ambipolar diffusion, with SO abundance in the disk much higher than in evolved disks.

Abstract

To investigate the disk formation and jet launch in protostars is crucial to comprehend the earliest stages of star and planet formation. We aim to constrain the properties of the molecular jet and the disk of the HH 212 protostellar system at unprecedented angular scales through ALMA observations of sulfur-bearing molecules, SO 9(8)-8(7), SO 10(11)-10(10), SO2 8(2,6)-7(1,7). SO 9(8)-8(7) and SO2 8(2,6)-7(1,7) show broad velocity profiles. At systemic velocity they probe the circumstellar gas and the cavity walls. Going from low to high blue-/red-shifted velocities the emission traces the wide-angle outflow and the fast (~100-200 km/s) and collimated (~90 AU) molecular jet revealing the inner knots with timescales <50 years. The jet transports a mass loss rate >0.2-2e-6 Msun/yr, implying high ejection efficiency (>0.03-0.3). The SO and SO2 abundances in the jet are ~1e-7-1e-6. SO 10(11)-10(10) emission is compact and shows small-scale velocity gradients indicating that it originates partly from the rotating disk previously seen in HCO+ and C17O, and partly from the base of the jet. The disk mass is >0.002-0.013 Msun, and the SO abundance in the disk is ~1e-8-1e-7. SO and SO2 are effective tracers of the molecular jet in the inner few hundreds AU from the protostar. Their abundances indicate that 1% - 40% of sulfur is in SO and SO2 due to shocks in the jet/outflow and/or to ambipolar diffusion at the wind base. The SO abundance in the disk is 3-4 orders of magnitude larger than in evolved protoplanetary disks. This may be due to an SO enhancement in the accretion shock at the envelope-disk interface or in spiral shocks if the disk is partly gravitationally unstable.