Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks

TL;DR

This study uses high-resolution ALMA observations to reveal complex chemical and dynamical structures in a massive proto-binary system, highlighting the presence of hot inner disks and potential counter-rotation, advancing understanding of massive star formation.

Contribution

First detection of alkali metal halide molecules in a massive protostellar disk, revealing dust destruction processes and hot inner disk chemistry at high resolution.

Findings

Detection of NaCl, SiO, SiS, and vibrationally-excited water lines in inner disks.

Evidence of dust destruction in the vicinity of protostars.

Possible counter-rotation of the twin disks.

Abstract

We report results of 0.05"-resolution observations toward the O-type proto-binary system IRAS 16547-4247 with the Atacama Large Millimeter/submillimeter Array (ALMA). We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outflows and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally-excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000-au scale. The H2O line tracing inner-disks has an upper-state energy of Eu/k>3000K, indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the protostars. We interpret that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest these "hot-disk" lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547-4247.