| Summary: | 博士 === 國立臺灣大學 === 天文物理研究所 === 106 === Molecular outflows associated with the youngest Class 0 protostars can bear clues of the early protostellar systems in the star formation process. These young outflows are characterized by dual components of extremely high velocity jets and low-velocity cavities, which are naturally understood in context of the unified wind model of Shang et al. 2006. The jet and cavity features are associated with the intrinsic density concentration of the magnetized primary wind and the swept-up ambient gas, respectively. Based on this framework, we develop understanding through numerical experiments and construct synthetic line emissions to bridge the gap between theory and observation.
By using a wind tracer field, we employ a two-temperature scheme to study the problem of a warm wind running into a cold ambient. Our exploration shows that the jet can be well maintained even at a high temperature for a sufficiently magnetized wind, but can be otherwise diffused. We also find that the presence of poloidal magnetic field in the ambient mass can help suppress instabilities at the wind-ambient interface to produce a less corrugated shell boundary.
Synthetic images, position-velocity diagrams, and spectra for molecular transition lines are presented, and the dual jet and shell components are clearly seen in CO J=2-1. The model power-law spectral index γ of the mass-velocity relation (m ~ v^-γ) falls in the range of ~1 to 3, and a dependency on the wind magnetization is revealed.
We analyze the observed sawtooth-like velocity pattern of the Class 0 IRAS 04166+2706 outflow and propose that a spherical wind-like velocity field with mass concentration near axis could underly the pattern. The systematic change of the teeth slope with distance is a natural consequence in this case, and the overall pattern is consistently explained with an inclination angle of ~52 degree.
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