An Ordered Envelope-disk Transition in the Massive Protostellar Source
  G339.88-1.26
  We report molecular line observations of the massive protostellar source
G339.88-1.26 with the Atacama Large Millimeter/Submillimeter Array. The
observations reveal a highly collimated SiO jet extending from the 1.3 mm
continuum source, which connects to a slightly wider but still highly
collimated CO outflow. Rotational features perpendicular to the outflow axis
are detected in various molecular emissions, including SiO, SO2, H2S, CH3OH,
and H2CO emissions. Based on their spatial distributions and kinematics, we
find that they trace different parts of the envelope-disk system. The SiO
emission traces the disk and inner envelope in addition to the jet. The CH3OH
and H2CO emissions mostly trace the infalling-rotating envelope, and are
enhanced around the transition region between envelope and disk, i.e., the
centrifugal barrier. The SO2 and H2S emissions are enhanced around the
centrifugal barrier, and also trace the outer part of the disk. Envelope
kinematics are consistent with rotating-infalling motion, while those of the
disk are consistent with Keplerian rotation. The radius and velocity of the
centrifugal barrier are estimated to be about 530 au and 6 km/s, leading to a
central mass of about 11 solar masses, consistent with estimates based on
spectral energy distribution fitting. These results indicate that an ordered
transition from an infalling-rotating envelope to a Keplerian disk through a
centrifugal barrier, accompanied by changes of types of molecular line
emissions, is a valid description of this massive protostellar source. This
implies that at least some massive stars form in a similar way as low-mass
stars via Core Accretion.
