Exploring the 100 au Scale Structure of the Protobinary System NGC 2264
  CMM3 with ALMA
  We have observed the young protostellar system NGC 2264 CMM3 in the 1.3 mm
and 2.0 mm bands at a resolution of about 0.1$"$ (70 au) with ALMA. The
structures of two distinct components, CMM3A and CMM3B, are resolved in the
continuum images of both bands. CMM3A has an elliptical structure extending
along the direction almost perpendicular to the known outflow, while CMM3B
reveals a round shape. We have fitted two 2D-Gaussian components to the
elliptical structure of CMM3A and CMM3B, and have separated the disk and
envelope components for each source. The spectral index $\alpha$ between 2.0 mm
and 0.8 mm is derived to be 2.4-2.7 and 2.4-2.6 for CMM3A and CMM3B,
respectively, indicating the optically thick dust emission and/or the grain
growth. A velocity gradient in the disk/envelope direction is detected for
CMM3A in the CH$_3$CN, CH$_3$OH, and $^{13}$CH$_3$OH lines detected in the 1.3
mm band, which can be interpreted as the rotation of the disk/envelope system.
From this result, the protostellar mass of CMM3A is roughly evaluated to be
$0.1- 0.5$ $M_\odot$ by assuming Keplerian rotation. The mass accretion rate is
thus estimated to be $5\times10^{-5}$ - 4 $\times$ $10^{-3}$ $M_\odot$
yr$^{-1}$, which is higher than typical mass accretion rate of low-mass
protostars. The OCS emission line shows a velocity gradient in both outflow
direction and disk/envelope direction. A hint of outflow rotation is found, and
the specific angular momentum of the outflow is estimated to be comparable to
that of the disk. These results provide us with novel information on the
initial stage of a binary/multiple system.
