Precessing Jet and Large Dust Grains in the V380 Ori NE Star-forming Region

Abstract

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^(−1) 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 β = 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 β = 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.

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