Precessing Jet and Large Dust Grains in the V380 Ori NE Star-forming
  Region
  The V380 Ori NE bipolar outflow was imaged in the SiO and CO J = 1 - 0 lines,
and dense cores in L1641 were observed in the 2.0-0.89 mm continuum. The highly
collimated SiO jet shows point-symmetric oscillation patterns in both position
and velocity, which suggests that the jet axis is precessing and the driving
source may belong to a non-coplanar binary system. By considering the position
and velocity variabilities together, accurate jet parameters were derived. The
protostellar system is viewed nearly edge-on, and the jet has a flow speed of
35 km/s and a precession period of 1600 years. The CO outflow length gives a
dynamical timescale of 6300 years, and the protostar must be extremely young.
The inferred binary separation of 6-70 au implies that this protobinary system
may have been formed through the disk instability process. The continuum
spectra of L1641 dense cores indicate that the emission comes from dust, and
the fits with modified blackbody functions give emissivity power indices of
beta = 0.3-2.2. The emissivity index shows a positive correlation with the
molecular line width, but no strong correlation with bolometric luminosity or
temperature. V380 Ori NE has a particularly low value of beta = 0.3, which
tentatively suggests the presence of millimeter-sized dust grains. Because the
dust growth takes millions of years, much longer than the protostellar age,
this core may have produced large grains in the starless core stage. HH 34 MMS
and HH 147 MMS also have low emissivity indices.
