Abstract
Abstract We report results of -resolution observations toward the O-type proto-binary system IRAS 16547–4247 with the Atacama Large Millimeter/submillimeter Array. 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 , 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 posit 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 that 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.
Highlights
Massive stars are important sources of ultraviolet (UV) radiation, turbulent energy, and heavy elements in galaxies
In this Letter, we mainly present the detection of sodium chloride, silicon compounds, and water lines as probes of the individual circumstellar disks
We report the dynamical and chemical structures of the massive proto-binary system IRAS 16547–4247 using 0. 05resolution Atacama Large Millimeter/Submillimeter Array (ALMA) observations at 3, 1.3, and 0.85 mm
Summary
Massive stars are important sources of ultraviolet (UV) radiation, turbulent energy, and heavy elements in galaxies. An essential question is whether or not massive protostars accrete through disks, as in low-mass star formation. Zapata et al (2015, 2019) reported a binary system seen as compact dusty objects with an apparent separation of 300 au, surrounded by a circumbinary disk, using ALMA observations. In this Letter, we mainly present the detection of sodium chloride, silicon compounds, and water lines as probes of the individual circumstellar disks. We propose that these inner-disk tracers may be common around massive protostars at the scale of 100 au, and valuable in understanding the disk properties in massive star formation
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