44 citations · 393 across the 34 of their papers we have counts for
34 papers
Relic of quadrupole deformation produced in a hot neutron star era
Yasufumi Kojima, Akira Dohi, Shota Kisaka +1
A newly born neutron star is expected to exhibit significant deviations from spherical symmetry, which decay with time. Determining how much deformation remains at present is cruci…
Asymmetric emissions of neutrinos in the cooling of rotating proto-neutron stars
Laura Barrio, Kotaro Fujisawa, Ryuichiro Akaho +2
We evaluate global asymmetry in the luminosities of neutrinos emitted from rapidly-rotating proto-neutron stars (PNS's). We build axisymmetric models of PNS's in mechanical equilib…
The optically thick rotating magnetic wind from a massive white dwarf merger product -- II. axisymmetric magnetohydrodynamic simulations
Yici Zhong, Kazumi Kashiyama, Shinsuke Takasao +2
We numerically construct a series of axisymmetric rotating magnetic wind solutions, aiming at exploring the observation properties of massive white dwarf (WD) merger remnants with…
A dynamical model for IRAS 00500+6713: the remnant of a type Iax supernova SN 1181 hosting a double degenerate merger product WD J005311
Takatoshi Ko, Hiromasa Suzuki, Kazumi Kashiyama +6
IRAS 00500+6713 is a hypothesized remnant of a type Iax supernova SN 1181. Multi-wavelength observations have revealed its complicated morphology; a dusty infrared ring is sandwich…
Equilibriums of extremely magnetized compact stars with force-free magnetotunnels
Koji Uryu, Shijun Yoshida, Eric Gourgoulhon +5
We present numerical solutions for stationary and axisymmetric equilibriums of compact stars associated with extremely strong magnetic fields. The interior of the compact stars is…
Evolutionary deformation toward the elastic limit by a magnetic field confined in the neutron--star crust
Yasufumi Kojima, Shota Kisaka, Kotaro Fujisawa
Occasional energetic outbursts and anomalous X-ray luminosities are expected to be powered by the strong magnetic field in a neutron star. For a very strong magnetic field, elastic…
Quantum algorithm for collisionless Boltzmann simulation of self-gravitating systems
Soichiro Yamazaki, Fumio Uchida, Kotaro Fujisawa +2
The collisionless Boltzmann equation (CBE) is a fundamental equation that governs the dynamics of a broad range of astrophysical systems from space plasma to star clusters and gala…
Strong toroidal magnetic fields sustained by the elastic crust in a neutron star
Kotaro Fujisawa, Yasufumi Kojima, Shota Kisaka
We investigate new solutions for magnetized neutron stars with a barotropic core in magnetohydrodynamic (MHD) equilibrium and a magneto-elastic crust, which was neglected by previo…
Modeling photometric variations due to a global inhomogeneity on an obliquely rotating star: application to lightcurves of white dwarfs
Yasushi Suto, Shin Sasaki, Masataka Aizawa +2
We develop a general framework to compute photometric variations induced by the oblique rotation of a star with an axisymmetric inhomogeneous surface. We apply the framework to com…
Self-Similar solution of rotating eruptive outflows on its equatorial plane
Takatoshi Ko, Kotaro Fujisawa, Toshikazu Shigeyama
We construct axisymmetric self-similar solutions of transonic outflows emanating from a point source including the effect of the rotation. The solutions are constructed exclusively…
A Lagrangian construction of rotating stars
Misa Ogata, Hirotada Okawa, Kotaro Fujisawa +3
We present a new formulation for numerically obtaining axisymmetric equilibrium structures of rotating stars in two spatial dimensions. With a view to apply it to the secular evolu…
Magnetically confined mountains on accreting neutron stars with multipole magnetic fields
Kotaro Fujisawa, Shota Kisaka, Yasufumi Kojima
Magnetically confined mountains on accreting neutron stars are candidates for producing continuous gravitational waves. We formulate a magnetically confined mountain on a neutron s…
Fast optical flares from M dwarfs detected by a one-second-cadence survey with Tomo-e Gozen
Masataka Aizawa, Kojiro Kawana, Kazumi Kashiyama +18
We report a one-second-cadence wide-field survey for M-dwarf flares using the Tomo-e Gozen camera mounted on the Kiso Schmidt telescope. We detect 22 flares from M3-M5 dwarfs with…
A novel formulation for the evolution of relativistic rotating stars
Hirotada Okawa, Kotaro Fujisawa, Nobutoshi Yasutake +3
We present a new formulation to construct numerically equilibrium configurations of rotating stars in general relativity. Having in mind the application to their quasi static evolu…
Singularity-Avoiding Multi-Dimensional Root-Finder
Hirotada Okawa, Kotaro Fujisawa, Yu Yamamoto +3
We proposed in this paper a new method, which we named the W4 method, to solve nonlinear equation systems. It may be regarded as an extension of the Newton-Raphson~(NR) method to b…
Magnetic field sustained by the elastic force in neutron star crusts
Yasufumi Kojima, Shota Kisaka, Kotaro Fujisawa
We investigate the magneto--elastic equilibrium of a neutron star crust and magnetic energy stored by the elastic force. The solenoidal motion driven by the Lorentz force can be co…
Magneto-elastic equilibrium of a neutron-star crust
Yasufumi Kojima, Shota Kisaka, Kotaro Fujisawa
We examine the equilibrium of a magnetized neutron-star-crust. We calculate axially symmetric models in which an elastic force balances solenoidal motion driven by a Lorentz force.…
Evolution of magnetic deformation in neutron star crust
Yasufumi Kojima, Shota Kisaka, Kotaro Fujisawa
In this study, we examine the magnetic field evolution occurring in a neutron star crust. Beyond the elastic limit, the lattice ions are assumed to act as a plastic flow. The Ohmic…
The optically thick rotating magnetic wind from a massive white dwarf merger product
Kazumi Kashiyama, Kotaro Fujisawa, Toshikazu Shigeyama
WD J005311 is a newly identified white dwarf (WD) in a mid-infrared nebula. The spectroscopic observation indicates the existence of a neon-enriched carbon/oxygen wind with a termi…
New code for equilibriums and quasiequilibrium initial data of compact objects. IV. Rotating relativistic stars with mixed poloidal and toroidal magnetic fields
Koji Uryu, Shijun Yoshida, Eric Gourgoulhon +5
A new code for computing fully general relativistic solutions of strongly magnetized rapidly rotating compact stars is developed as a part of the COCAL (Compact Object CALculator)…
The W4 method: a new multi-dimensional root-finding scheme for nonlinear systems of equations
Hirotada Okawa, Kotaro Fujisawa, Yu Yamamoto +4
We propose a new class of method for solving nonlinear systems of equations, which, among other things,has four nice features: (i) it is inspired by the mathematical property of da…
Effects of rotation and magnetic field on the revival of a stalled shock in supernova explosions
Kotaro Fujisawa, Hirotada Okawa, Yu Yamamoto +1
We investigate axisymmetric steady solutions of (magneto)hydrodynamics equations that describe approximately accretion flows through a standing shock wave and discuss the effects o…
Rotational equilibria by Lagrangian variational principle: toward multi-dimensional stellar evolutions
Nobutoshi Yasutake, Kotaro Fujisawa, Shoichi Yamada
We have developed a new formulation to obtain self-gravitating, axisymmetric configurations in permanent rotation. The formulation is based on the Lagrangian variational principle…
Hyperbolic Self-Gravity Solver for Large Scale Hydrodynamical Simulations
Ryosuke Hirai, Hiroki Nagakura, Hirotada Okawa +1
A new computationally efficient method has been introduced to treat self-gravity in mesh based hydrodynamical simulations. It is applied simply by slightly modifying the Poisson eq…