Protostars and Planets VI, Heidelberg, July 15-20, 2013
Outflow Launching and Protostellar Evolution with Episodic Mass Accretion Histories
Machida, Masahiro (kyushu university)
Hosokawa, Takashi (university of tokyo)
We present our recent theoretical work on the evolution of outflow around accreting low-mass pro- tostars. The evolution of the outflow is followed with resistive magnetohydrodynamic nested-grid simulations that cover a wide range of spatial scale (1 AU – 1 pc). We follow the cloud evolution from the prestellar core stage until the infalling envelope dissipates long after the protostar formation. We also calculate the protostellar evolution to derive the protostellar luminosity with time-dependent mass accretion through a circumstellar disk. The protostellar outflow is driven by the first core before the protostar formation, and directly driven by the circumstellar disk after the protostar formation. The opening angle of the outflow is large in Class 0 stage. A large fraction of the cloud mass is ejected in this stage, which reduces the star formation efficiency down to < 50 %. After the outflow breaks out of the natal cloud, the outflow collimation is gradually improved in Class I stage. The head of the outflow travels over 10^5 AU in 10^5 yr. The outflow momentum, energy, and mass derived in our calculations agree well with observations. Our simulations also show the same correlations between the outflow momentum flux, protostellar luminosity, and envelope mass as seen in observations. These correlations differ between Class 0 and I stages, which is explained by different evolutionary stages of the outflow; in Class 0 stage the outflow is powered by the accreting mass and acquires its momentum from the infalling envelope, and in Class I stage the outflow enters the momentum-driven snow-plow phase. Our results suggest that the protostellar outflow should determine the final stellar mass and significantly affect the early evolution of the low-mass protostars.
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