A Change of Rotation Profile in the Envelope in the HH 111 Protostellar
  System: A Transition to a Disk?
  The HH 111 protostellar system consists of two Class I sources (VLA 1 and 2)
with putative disks deeply embedded in a flattened envelope at a distance of
400 pc. Here is a follow-up study of this system in C18O (J=2-1), SO (N_J =
5_6-4_5), and 1.33 mm continuum at ~ 1" (400 AU) resolution, and it may show
for the first time how a rotationally supported disk can be formed inside an
infalling envelope. The 1.33 mm continuum emission is seen arisen from both
sources, likely tracing the dusty putative disks around them. In particular,
the emission around the VLA 1 source is elongated in the equatorial plane with
a radius of ~ 300 AU. The envelope is well seen in C18O, extending to ~ 7000 AU
out from the VLA 1 source, with the innermost part overlapping with the dusty
disk. It has a differential rotation, with the outer part (~ 2000-7000 AU)
better described by a rotation that has constant specific angular momentum and
the inner part (~ 60-2000 AU) by a Keplerian rotation. The envelope seems to
also have some infall motion that is smaller than the rotation motion. Thus,
the material in the outer part of the envelope seems to be slowly spiraling
inward with its angular momentum and the rotation can indeed become Keplerian
in the inner part. A compact SO emission is seen around the VLA 1 source with a
radius of ~ 400 AU and it may trace a shock such as an (inner) accretion shock
around the disk.
