Chemical and Physical Picture of IRAS 16293-2422 Source B at a
  Sub-arcsecond Scale Studied with ALMA
  We have analyzed the OCS, H$_2$CS, CH$_3$OH, and HCOOCH$_3$ data observed
toward the low-mass protostar IRAS 16293--2422 Source B at a sub-arcsecond
resolution with ALMA. A clear chemical differentiation is seen in their
distributions; OCS and H$_2$CS are extended with a slight rotation signature,
while CH$_3$OH and HCOOCH$_3$ are concentrated near the protostar. Such a
chemical change in the vicinity of the protostar is similar to the companion
(Source A) case. The extended component is interpreted by the
infalling-rotating envelope model with a nearly face-on configuration. The
radius of the centrifugal barrier of the infalling-rotating envelope is roughly
evaluated to be ($30-50$) au. The observed lines show the inverse P-Cygni
profile, indicating the infall motion with in a few 10 au from the protostar.
The nearly pole-on geometry of the outflow lobes is inferred from the SiO
distribution, and thus, the infalling and outflowing motions should coexist
along the line-of-sight to the protostar. This implies that the infalling gas
is localized near the protostar and the current launching points of the outflow
have an offset from the protostar. A possible mechanism for this configuration
is discussed.
