535 citations · 2k across the 66 of their papers we have counts for
16 papers · 1 filter
Amplification of azimuthal modes with odd wave numbers during dynamical bar-mode growth in rotating stars
Yasufumi Kojima, Motoyuki Saijo
Nonlinear growth of the bar-mode deformation is studied for a differentially rotating star with supercritical rotational energy. In particular, the growth mechanism of some azimuth…
The correlation of black hole mass with metallicity index of host spheroid
Shota Kisaka, Yasufumi Kojima, Yosuke Otani
We investigate the correlation between the mass of the supermassive black holes (SMBHs) and metal abundance, using existing data sets. The SMBH mass is well correlated wit…
Faraday resonance in dynamical bar instability of differentially rotating stars
Motoyuki Saijo, Yasufumi Kojima
We investigate the nonlinear behaviour of the dynamically unstable rotating star for the bar mode by three-dimensional hydrodynamics in Newtonian gravity. We find that an oscillati…
Measuring Neutron Star Mass and Radius with Three Mass-Radius Relations
C. M. Zhang, H. X. Yin, Y. Kojima +5
We propose to determine the mass and the radius of a neutron star (NS) using three measurable mass-radius relationships, namely the ``apparent'' radius inferred from neutron star t…
The bottom magnetic field and magnetosphere evolution of neutron star in low mass X-ray binary
C. M. Zhang, Y. Kojima
The accretion induced neutron star magnetic field evolution is studied through considering the accretion flow to drag the field lines aside and dilute the polar field strength, and…
Propagation and Transmission of Alfven Waves in Rotating Magnetars
Yasufumi Kojima, Taishi Okita
We study the propagation and transmission of Alfven waves in the context of cylindrical geometry. This approximates the polar cap region of aligned pulsar with strong magnetic fiel…
Stationary electromagnetic fields in the exterior of a slowly rotating relativistic star: a description beyond the low-frequency approximation
Yasufumi Kojima, Norihito Matsunaga, Taishi Okita
We investigate the electromagnetic fields in the vacuum exterior of a rotating relativistic star endowed with a magnetic dipole moment, and with the stellar surface behaving as a p…
Some Properties of an Axisymmetric Pulsar Magnetosphere Constructed by Numerical Calculation
Jun Ogura, Yasufumi Kojima
We have explored the magnetosphere described by a numerical solution for an axisymmetric rotating field satisfying the force-free and ideal MHD conditions everywhere. The electric…
Discrimination of Quark Stars from Neutron Stars in Quadrupole Oscillations
Yasufumi Kojima, Koh-ichi Sakata
The frequencies and damping times due to gravitational radiation are calculated for self-bound quark star models. The results are compared with those for neutron star models. They…
Stable Operation of a 300-m Laser Interferometer with Sufficient Sensitivity to Detect Gravitational-Wave Events within our Galaxy
Masaki Ando, the TAMA collaboration
TAMA300, an interferometric gravitational-wave detector with 300-m baseline length, has been developed and operated with sufficient sensitivity to detect gravitational-wave events…
General Relativistic Modification of a Pulsar Electromagnetic Field
Kohkichi Konno, Yasufumi Kojima
We consider an exterior electromagnetic field surrounding a rotating star endowed with a dipole magnetic field in the context of general relativity. The analytic solution for a sta…
Profiles and Polarization Properties of Emission Lines from Relativistic Disks
Jun Ogura, Nobuyori Ohuo, Yasufumi Kojima
We examined the profiles and polarization properties of emission lines originating from the extremely relativistic region of Kepler disks. Because the emission region is more local…
Stability of Relativistic Blast Waves
Jun Ogura, Yasufumi Kojima
A spherical blast wave with relativistic velocity can be described by a similarity solution, that is used for theoretical models of gamma-ray bursts. We consider the linear stabili…
Flattening modulus of a neutron star by rotation and magnetic field
K. Konno, T. Obata, Y. Kojima
We calculated the ellipticity of the deformed star due to the rotation or magnetic field. These two effects are compared to each other within general relativity. It turned out that…
The R-Mode Oscillations in Relativistic Rotating Stars
Yasufumi Kojima, Masayasu Hosonuma
The axial mode oscillations are examined for relativistic rotating stars with uniform angular velocity. Using the slow rotation formalism and the Cowling approximation, we have der…
Asymmetry in Microlensing-Induced Light Curves
Kohkichi Konno, Yasufumi Kojima
We discuss distortion in microlensing-induced light curves which are considered to be curves due to single-point-mass lenses at a first glance. As factors of the distortion, we con…