591 research outputs found
Numerical Study of Two-fluid Flowing Equilibria of Helicity-driven Spherical Torus Plasmas
Two-fluid flowing equilibrium configurations of a helicity-driven spherical
torus (HD-ST) are numerically determined by using the combination of the finite
difference and the boundary element methods. It is found from the numerical
results that electron fluids near the central conductor are tied to an external
toroidal field and ion fluids are not. The magnetic configurations change from
the high- HD-ST (>1) with paramagnetic toroidal field and low-
(volume average value, ( 2 %) through the
helicity-driven spheromak and RFP to the ultra low- HD-ST (0<q<1) with
diagmagnetic toroidal field and high- ($\beta\approx 18\%) as the
external toroidal field at the inner edge region decreases and reverses the
sign. The two-fluid effecs are more significant in this equilibrium transition
when the ion diagmagnetic drift is dominant in the flowing two-fluid.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Orbital characterization of GJ1108A system, and comparison of dynamical mass with model-derived mass for resolved binaries
We report an orbital characterization of GJ1108Aab that is a low-mass binary
system in pre-main-sequence phase. Via the combination of astrometry using
adaptive optics and radial velocity measurements, an eccentric orbital solution
of =0.63 is obtained, which might be induced by the Kozai-Lidov mechanism
with a widely separated GJ1108B system. Combined with several observed
properties, we confirm the system is indeed young. Columba is the most probable
moving group, to which the GJ1108A system belongs, although its membership to
the group has not been established. If the age of Columba is assumed for
GJ1108A, the dynamical masses of both GJ1108Aa and GJ1108Ab ( and ) are more massive than what an
evolutionary model predicts based on the age and luminosities. We consider the
discrepancy in mass comparison can attribute to an age uncertainty; the system
is likely older than stars in Columba, and effects that are not implemented in
classical models such as accretion history and magnetic activity are not
preferred to explain the mass discrepancy. We also discuss the performance of
the evolutionary model by compiling similar low-mass objects in evolutionary
state based on the literature. Consequently, it is suggested that the current
model on average reproduces the mass of resolved low-mass binaries without any
significant offsets.Comment: Accepted in Ap
A spatially-resolved large cavity of the J0337 protoplanetary disk in perseus
Stars and planetary system
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