676 research outputs found
Minimum model and its theoretical analysis for superconducting materials with BiS layers
We perform first principles band calculation of the newly discovered
superconductor LaOFBiS, and study the lattice structure and the
fluorine doping dependence of the gap between the valence and conduction bands.
We find that the distance between La and S as well as the fluorine doping
significantly affects the band gap. On the other hand, the four orbital model
of the BiS layer shows that the lattice structure does not affect this
portion of the band. Still, the band gap can affect the carrier concentration
in the case of light electron doping, which in turn should affect the transport
properties.Comment: submitted as Proc. ISS2012, 4 pages, 4 figure
The Outcome of Supernovae in Massive Binaries; Removed Mass, and its Separation Dependence
The majority of massive stars are formed in binary systems. It is hence
reasonable to expect that most core-collapse supernovae (CCSNe) take place in
binaries and the existence of a companion star may leave some imprints in
observed features. Having this in mind, we have conducted two-dimensional
hydrodynamical simulations of the collisions of CCSNe ejecta with the companion
star in an almost-equal-mass () binary to find out possible
consequences of such events. In particular we pay attention to the amount of
mass removed and its dependence on the binary separation. In contrast to the
previous surmise, we find that the companion mass is stripped not by momentum
transfer but by shock heating. Up to of the original mass can be removed
for the closest separations and the removed mass decreases as with the binary separation . By performing some experimental
computations with artificially-modified densities of incident ejecta, we show
that if the velocity of ejecta is fixed, the density of incident ejecta is the
single important parameter that actually determines the removed mass as . On the other hand, another set of simulations with
modified velocities of incident ejecta demonstrate that the strength of the
forward shock, which heats up the stellar material and causes the mass loss of
the companion star, is actually the key parameter for the removed mass.Comment: 16 pages, accepted for publication in the Astrophysical Journa
Numerical Simulations of Equatorially-Asymmetric Magnetized Supernovae: Formation of Magnetars and Their Kicks
A series of numerical simulations on magnetorotational core-collapse
supernovae are carried out. Dipole-like configurations which are offset
northward are assumed for the initially strong magnetic fields together with
rapid differential rotations. Aims of our study are to investigate effects of
the offset magnetic field on magnetar kicks and on supernova dynamics. Note
that we study a regime where the proto-neutron star formed after collapse has a
large magnetic field strength approaching that of a ``magnetar'', a highly
magnetized slowly rotating neutron star. As a result, equatorially-asymmetric
explosions occur with a formation of the bipolar jets. Resultant magnetar's
kick velocities are km s. We find that the acceleration
is mainly due to the magnetic pressure while the somewhat weaker magnetic
tension works toward the opposite direction, which is due to stronger magnetic
field in the northern hemisphere. Noted that observations of magnetar's proper
motions are very scarce, our results supply a prediction for future
observations. Namely, magnetars possibly have large kick velocities, several
hundred km s, as ordinary neutron stars do, and in an extreme case they
could have those up to 1000 km s.Comment: 36 pages, 9 figures, accepted by the Astrophysical Journa
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