Substructures in the Disk-Forming Region of the Class 0 Low-Mass
  Protostellar Source IRAS 16293-2422 Source A on a 10 au Scale
  We have observed the Class 0 protostellar source IRAS 16293-2422 A in the
C17O and H2CS lines as well as the 1.3 mm dust continuum with the Atacama Large
Millimeter/submillimeter Array at an angular resolution of ~0."1 (14 au). The
continuum emission of the binary component, Source A, reveals the substructure
consisting of 5 intensity peaks within 100 au from the protostar. The C17O
emission mainly traces the circummultiple structure on a 300 au scale centered
at the intensity centroid of the continuum, while it is very weak within the
radius of 50 au from the centroid. The H2CS emission, in contrast, traces the
rotating disk structure around one of the continuum peaks (A1). Thus, it seems
that the rotation centroid of the circummultiple structure is slightly
different from that of the disk around A1. We derive the rotation temperature
by using the multiple lines of H2CS. As approaching to the protostar A1, the
rotation temperature steeply rises up to 300 K or higher at the radius of 50 au
from the protostar. It is likely due to a local accretion shock and/or the
preferential protostellar heating of the transition zone from the
circummultiple structure to the disk around A1. This position corresponds to
the place where the organic molecular lines are reported to be enhanced. Since
the rise of the rotation temperature of H2CS most likely represents the rise of
the gas and dust temperatures, it would be related to the chemical
characteristics of this prototypical hot corino.
