Molecular Bullets in A High-mass Protostar
  We present Submillimeter Array (SMA) observations in the CO J=3-2, SiO J=5-4
and 8-7, and SO 9_8-8_7 lines, as well as Atacama Pathfinder EXperiment (APEX)
observations in the CO J=6-5 line, of an extremely high-velocity and jet-like
outflow in high-mass star-forming region HH 80--81. The outflow is known to
contain two prominent molecular bullets, namely B1 and B2, discovered from our
previous SMA CO J=2-1 observations. While B1 is detected in all the CO, SiO,
and SO lines, B2 is only detected in CO lines. The CO 3-2/2-1 line ratio in B1
is clearly greater than that in B2. We perform a large velocity gradient
analysis of the CO lines and derive a temperature of 70--210 K for B1 and
20--50 K for B2. Taking into account the differences in the velocity, distance
from the central source, excitation conditions, and chemistry between the two
bullets, we suggest that the bullets are better explained by direct ejections
from the innermost vicinity of the central high-mass protostar, and that we are
more likely observing the molecular component of a primary wind rather than
entrained or swept-up material from the ambient cloud. These findings further
support our previous suggestions that the molecular bullets indicate an
episodic, disk-mediated accretion in the high-mass star formation process.
