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The stellar core formation and high speed jets driven by the formed
core are studied by using three-dimensional resistive magnetohydrodynamical
(MHD) nested grid simulations. Starting with a Bonnor-Ebert isothermal cloud
rotating in a uniform magnetic field, we calculate the cloud evolution from
the molecular cloud core (n_c = 10^6 cm^-3, r_c = 4.6 x 10^4 AU) to the
stellar core (n_c ~ 10^23 cm^-3, $r_c ~ 1 R_sun), where n_c and
r_c denote the central density and radius of the objects, respectively.
We resolve cloud structure over 7 orders of magnitude in spatial extent and
over 17 orders of magnitude in density contrast. For comparison, we calculate
two models: resistive and ideal MHD models. Both models have the same initial
condition, but the former includes dissipation process of magnetic field
while the latter does not. The magnetic fluxes in resistive MHD model are
extracted from the first core during 10^12 cm^-3 < n_c < 10^16 cm^-3 by
Ohmic dissipation. Magnetic flux density of the formed stellar core
(n_c ~ 10^20 cm^-3) in resistive MHD model is two orders of magnitude
smaller than that in ideal MHD model. Since magnetic braking is less effective
in resistive MHD model, rapidly rotating stellar core (the second core) is
formed. After stellar core formation, the magnetic field of the core is
largely amplified both by magneto-rotational instability and the shearing
motion between the stellar core and ambient medium. As a consequence, high speed
(~ 45 km/s) jets are driven by the second core, which results in strong mass
ejection. A cocoon-like structure around the second core also forms with clear
bow shocks.
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