Study of the high-mass star-forming region S255IR at various scales

The core of S255IR-SMA1 contains the protostar NIRS3 with a mass of about 20 $M_{\odot}$. A few years ago, the first burst of luminosity for massive protostars, caused by an episodic accretion event, was recorded here. We have been studying this object for a long time with various instruments, including ALMA. The general morphology and kinematics of this area have been investigated. Disk-shaped structures, jets and outflows have been identified and studied in detail. We have recently observed this object with ALMA at a resolution an order of magnitude higher than previously achieved―about 15 milliarcseconds, corresponding to about 25 AU. This paper presents new results from the analysis of these data together with observations in other bands. The new data show an inhomogeneous disk structure, an ionized region around the protostar, and the presence of a jet observed in the submillimeter continuum consisting of individual knots whose orientation differs markedly from that on large scales. The submillimeter emission from the jet most likely represents bremsstrahlung from ionized gas. Based on observations of the lines of some molecules, the kinematics and physical properties of this region are discussed. Methanol maser emission associated with the jet is observed.