2020ApJ...889...43Z

We investigate at a high angular resolution the spatial and kinematic structure of the S255IR high-mass star-forming region, which demonstrated recently the first disk-mediated accretion burst in the massive young stellar object. The observations were performed with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 7 at an angular resolution of ∼ 0.''1, which corresponds to ∼180 au. The 0.9 mm continuum, C³⁴S(7-6) and CCH N = 4 - 3 data show a presence of very narrow (∼1000 au), very dense (n ∼ 10⁷ cm^–3), and warm filamentary structures in this area. At least some of them represent apparently dense walls around the high velocity molecular outflow with a wide opening angle from the S255IR-SMA1 core, which is associated with the NIRS3 YSO. This wide-angle outflow surrounds a narrow jet. At the ends of the molecular outflow there are shocks, traced in the SiO(8-7) emission. The SiO abundance there is enhanced by at least 3 orders of magnitude. The CO(3-2) and SiO(8-7) data show a collimated and extended high velocity outflow from another dense core in this area, SMA2. The outflow is bent and consists of a chain of knots, which may indicate periodic ejections possibly arising from a binary system consisting of low- or intermediate-mass protostars. The C³⁴S emission shows evidence of rotation of the parent core. Finally, we detected two new low-mass compact cores in this area (designated as SMM1 and SMM2), which may represent prestellar objects.