arXiv subjects

Masahiko Hayashi

Publications and source records attributed to Masahiko Hayashi.

At least 91 records · Page 5Linked to original sources

arXiv2007

SUBARU HDS Observations of a Balmer-Dominated Shock in Tycho's Supernova Remnant

We present an Ha spectral observation of a Balmer-dominated shock on the eastern side of Tycho's supernova remnant using the Subaru Telescope. Utilizing the High Dispersion Spectrograph (HDS), we measure the spatial variation of the line profile between preshock and postshock gas. Our observation clearly shows a broadening and centroid shift of the narrow-component postshock Ha line relative to the Ha emission from the preshock gas. The observation supports the existence of a thin precursor where gas is heated and accelerated ahead of the shock. Furthermore, the spatial profile of the emission ahead of the Balmer filament shows a gradual gradient in the Ha intensity and line width ahead of the shock. We propose that this region (~10^16 cm) is likely to be the spatially resolved precursor. The line width increases from ~30 up to ~45 km/s, and its central velocity shows a redshift of ~5 km/s across the shock front. The characteristics of the precursor are consistent with a cosmic-ray precursor, although the possibility of a fast neutral precursor is not ruled out.

astro-ph↗

arXiv2007

The Mixed State of Charge-Density-Wave in a Ring-Shaped Single Crystals

Charge-density-wave (CDW) phase transition in a ring-shaped crystals, recently synthesized by Tanda et al. [Nature, 417, 397 (2002)], is studied based on a mean-field-approximation of Ginzburg-Landau free energy. It is shown that in a ring-shaped crystals CDW undergoes frustration due to the curvature (bending) of the ring (geometrical frustration) and, thus, forms a mixed state analogous to what a type-II superconductor forms under a magnetic field. We discuss the nature of the phase transition in the ring-CDW in relation to recent experiments.

cond-mat.other↗

arXiv2006

Adaptive Optics Spectroscopy of the [Fe II] Outflows from HL Tauri and RW Aurigae

We present new results of [Fe II] 1.644-micron spectroscopy toward the jets from HL Tau and RW Aur carried out with the Subaru Telescope combined with the adaptive optics system. We observed the regions within 2" - 3" from the stars with the sub-arcsecond resolutions of 0."5 and 0."2 for HL Tau and RW Aur, respectively. In addition to the strong, high velocity emission extended along each jet, we detected a blueshifted low velocity emission feature seen as a wing or shoulder of the high velocity emission at each stellar position. Detailed analysis shows that the position-velocity diagrams (PVDs) of HL Tau and RW Aur show a characteristic similar to those of the cold disk wind and X-wind models in that the [Fe II] line width is broad in the vicinity of the stellar position and is narrower at the extended jet. A closer comparison suggests, however, that the disk wind model tends to have too large line width at the jet while the X-wind model has excess emission on the redshifted side at the stellar position. The narrow velocity width with symmetric line profiles of the observed high velocity emission supports an X-wind type model where the launching region is localized in a small radial range, while the low velocity emission located away from the star favors the presence of a disk wind. The [Fe II] emission from the HL Tau jet shows a gap of 0."8 between the redshifted jet and the star, indicating the presence of an optically thick disk of ~ 160 AU in radius. The [Fe II] emission from the RW Aur jet shows a marked drop from the redshifted peak at Y ~ -0."2 toward the star, suggesting that its disk radius is smaller than 40 AU.

astro-ph↗

arXiv2006

Variability of the NGC 1333 IRAS 4A Outflow: Molecular Hydrogen and Silicon Monoxide Images

The NGC 1333 region was observed in the H2 1-0 S(1) line. The H2 images cover a 5' x 7' region around IRAS 4. Numerous H2 emission features were detected. The northeast-southwest bipolar outflow driven by IRAS 4A was studied by combining the H2 images with SiO maps published previously. The SiO-H2 outflows are continuous on the southwestern side but show a gap on the northeastern side. The southwestern outflow lobe curves smoothly, and the position angle increases with the distance from the driving source. The base and the outer tip of the northeastern outflow lobe are located at positions opposite to the corresponding parts of the southwestern lobe. This point-symmetry suggests that the outflow axis may be drifting or precessing clockwise in the plane of the sky and that the cause of the axis drift may be intrinsic to the outflow engine. The axis drift model is supported by the asymmetric lateral intensity profile of the SiO outflow. The axis drift rate is about 0.011 deg yr-1. The middle part of the northeastern outflow does not exactly follow the point symmetry because of the superposition of two different kinds of directional variability: the axis drift of the driving source and the deflection by a dense core. The axis drift model provides a good explanation for the large deflection angle of the northeastern outflow. Other H2 emission features around the IRAS 4 region are discussed briefly. Some of them are newly found outflows, and some are associated with outflows already known before.

astro-ph↗

arXiv2006

Geometrically Frustrated Crystals: Elastic Theory and Dislocations

Elastic theory of ring-(or cylinder-)shaped crystals is constructed and the generation of edge dislocations due to geometrical frustration caused by the bending is studied. The analogy to superconducting (or superfluid) vortex state is pointed out and the phase diagram of the ring-crystal, which depends on radius and thickness, is discussed.

cond-mat.mtrl-sci↗

arXiv2005

Superconductivity on a Möbius strip: numerical studies on order parameter and quasiparticles

Superconducting states of an anisortopic s-wave superconductor on a Möbius strip are studied numerically based on the Ginzburg-Landau theory and the Bogoliubov-de Gennes theory. In both, the equations are solved numerically on discitized lattice and the nonlinearity and the self-consistency are fully taken into account. First, we study the superconducting states on the Möbius strip in the presence of the Aharonov-Bohm flux threading the ring by employing the Ginzburg-Landau theory, and confirm the phase diagram previously proposed by Hayashi and Ebisawa [J. Phys. Soc. Jpn. {\bf 70}, 3495 (2002)]. The metastable states as well as the equilibrium energy state are studied and the nonequiriblium processes when the magnetic field is varied at a fixed temperature are discussed. Next, we study the microscopic superconducting states on the Möbius strip based on the Bogoliubov-de Gennes theory, especially focusing on the state with a real-space node in the superconducting gap, which is expected to appear when the flux threading the ring is half the superconducting flux quantum. The local density of states in this {\it nodal state} is calculated in detail and the existence of the zero-energy bound states is shown.

cond-mat.supr-con↗

arXiv2004

A Young Brown Dwarf Companion to DH Tauri

We present the detection of a young brown dwarf companion DH Tau B associated with the classical T Tauri star DH Tau. Near-infrared coronagraphic observations with CIAO on the Subaru Telescope have revealed DH Tau B with H = \~15 mag located at 2.3" (330 AU) away from the primary DH Tau A. Comparing its position with a Hubble Space Telescope archive image, we confirmed that DH Tau A and B share the common proper motion, suggesting that they are physically associated with each other. The near-infrared color of DH Tau B is consistent with those of young stellar objects. The near-infrared spectra of DH Tau B show deep water absorption bands, a strong K I absorption line, and a moderate Na I absorption line. We derived its effective temperature and surface gravity of Teff = 2700 -- 2800 K and log g = 4.0--4.5, respectively, by comparing the observed spectra with synthesized spectra of low-mass objects. The location of DH Tau B on the HR diagram gives its mass of 30 -- 50 M_Jupiter.

astro-ph↗

arXiv2004

H$_2$ Emission Nebulosity Associated with KH 15D

An H$_2$ emission filament is found in close proximity to the unique object KH 15D using the adaptive optics system of the Subaru Telescope. The morphology of the filament, the presence of spectroscopic outflow signatures observed by Hamilton et al., and the detection of extended H$_2$ emission from KH 15D by Deming, Charbonneau, & Harrington suggest that this filament arises from shocked H$_2$ in an outflow. The filament extends about 15" to the north of KH 15D.

astro-ph↗

arXiv2003

A Subarcsecond Companion to the T Tauri Star AS 353B

Adaptive optics imaging of the bright visual T Tauri binary AS 353 with the Subaru Telescope shows that it is a hierarchical triple system. The secondary component, located 5.6" south of AS 353A, is resolved into a subarcsecond binary, AS 353Ba and Bb, separated by 0.24". Resolved spectroscopy of the two close components shows that both have nearly identical spectral types of about M1.5. Whereas AS 353A and Ba show clear evidence for an infrared excess, AS 353Bb does not. We discuss the possible role of multiplicity in launching the large Herbig-Haro flow associated with AS 353A.

astro-ph↗

arXiv2003

Topological Defects and Morphology of Graphitic Carbon Materials: An Approach Based on Differential Geometry

It has been known that pentagons and heptagons in hexagonal graphitic network give rise to a certain amount of curvature in the three dimensional structure of graphitic carbon materials. The amount of curvature is quantized due to the symmetry of graphite and, as a result, the structure formed by the network is also restricted. We clarify the effects of curvature quantization on the forms of graphitic carbon materials, employing the knowledge of differential geometry, especially the Gauss-Bonnet theorem.

cond-mat.str-el↗

arXiv2002

SDSSp J104433.04$-$012502.2 at $z=5.74$ is Gravitationally Magnified by an Intervening Galaxy

During the course of our optical deep survey program on L$α$ emitters at $z \approx 5.7$ in the sky area surrounding the quasar SDSSp J104433.04$-$012502.2 at $z=5.74$, we found that a faint galaxy with $m_B$(AB) $\approx 25$ is located at \timeform{1".9} southwest of the quasar. Its broad-band color properties from $B$ to $z^\prime$ suggest that the galaxy is located at a redshift of $z \sim 1.5$ -- 2.5. This is consistent with no strong emission line in our optical spectroscopy. Since the counter image of the quasar cannot be seen in our deep optical images, the magnification factor seems not to be very high. Our modest estimate is that this quasar is gravitationally magnified by a factor of 2.

astro-ph↗

arXiv2002

The effect of large quantum fluctuation on the noise of a single-electron transistor

We theoretically investigate the noise of a single-electron transistor in the regime of large quantum fluctuation of charge out of equilibrium. We show that the charge noise is suppressed due to the charge renormalization caused by the quantum fluctuation. However the fluctuation is not strong enough to wash out the charge quantization. We find that the renormalization effect reduces the performance of a single-electron electrometer.

cond-mat.mes-hall↗

arXiv2002

Noise of a single-electron transistor in the regime of large quantum fluctuations of island charge out of equilibrium

By using the drone-fermion representation and the Schwinger-Keldysh approach, we calculate the current noise and the charge noise for a single-electron transistor in the non-equilibrium state in the presence of large quantum fluctuation of island charge. Our result interpolates between those of the "orthodox theory" and the "co-tunneling theory". We find the following effects which are not treated by previous theories: (i) At zero temperature T=0 and at finite applied bias voltage $|eV| \gg T_{K}$, where $T_{K}$ is the "Kondo temperature", we find the Fano factor is suppressed more than the suppression caused by Coulomb correlation both in the Coulomb blockade regime and in the sequential tunneling regime. (ii) For $T \gg |eV|/2 \gg T_{K}$, the current noise in the presence of large charge fluctuation is modified and deviates from the prediction of the orthodox theory. However, the Fano factor coincides with that of the orthodox theory and is proportional to the temperature. (iii) For $eV, T \lesssim T_{K}$, the charge noise is suppressed due to the renormalization of system parameters caused by quantum fluctuation of charge. We interpret it in terms of the modification of the "unit" of the island charge.

cond-mat.mes-hall↗

arXiv2002

The current and the charge noise of a single-electron transistor in the regime of large charge fluctuations out of equilibrium

By using the Schwinger-Keldysh approach, we evaluate the current noise and the charge noise of the single-electron transistor (SET) in the regime of large charge fluctuations caused by large tunneling conductance. Our result interpolates between previous theories; the "orthodox" theory and the "co-tunneling theory". We find that the life-time broadening effect suppresses the Fano factor below the value estimated by the previous theories. We also show that the large tunnel conductance does not reduce the energy sensitivity so much. Our results demonstrate quantitatively that SET electrometer can be used as the high-sensitivity and high-speed device for quantum measurements.

cond-mat.mes-hall↗

arXiv2002

Charge fluctuation between even and odd states of a superconducting island

We theoretically investigate effects of quantum fluctuation between even and odd charge states on the transport properties of a normal-superconducting-normal single-electron tunneling transistor. The charge fluctuation is discussed beyond the orthodox theory. We find that the charging energy renormalization enhances the parity effect: The Coulomb blockade regime for odd state is reduced and that for even state is widened. We show that the renormalization factor can be obtained by measuring the peak position of the conductance. The renormalization factor reduces with increasing the applied bias voltage.

cond-mat.mes-hall↗

arXiv2002

Orbital Magnetism in Three-Dimensional Quantum Dots

We study orbital magnetism in a three-dimensional (3D) quantum dot with a parabolic confining potential. We calculate the free energy of the system as a function of the magnetic field and the temperature. By this, we show that the temperature-field plane can be classified into three regions in terms of the characteristic behavior of the magnetization: the Landau diamagnetism, de Haas-van Alphen oscillation and mesoscopic fluctuation of magnetization. We also calculate numerically the magnetization of the system and then the current density distribution. As for the oscillation of the magnetization when the field is varied, the 3D quantum dot shows a longer period than a 2D quantum dot which contains the same number of electrons. A large paramagnetism appears at low temperatures when the magnetic field is very weak.

cond-mat.mes-hall↗

arXiv2001

Dephasing of a qubit coupled with a point-contact detector

The dephasing of a qubit coupled with a point-contact detector is theoretically studied. We calculate the time evolution of the reduced density matrix of qubit by using the perturbation expansion. We show that the dephasing rate is proportional to the temperature at zero bias-voltage, while it is proportional to the bias-voltage when the bias-voltage is large. We also evaluate the dephasing rate by using the real time renormalization group method and show that the higher order processes of the particle-hole excitation enhances dephasing of qubit.

cond-mat↗

arXiv2001

Little-Parks Oscillation of Superconducting Möbius Strip

Little-Parks oscillation of a Möbius strip (or ring equivalently) made of a superconductor is studied based on Ginzburg-Landau theory. It is shown that, if the strip is wide enough, a novel state appears when the number of magnetic flux quanta threading the ring is close to a half odd integer. As a result the shape of Little-Parks oscillation of critical temperature is modified. We estimate the free energy of this state and give the phase diagram of the superconducting Möbius strip in a magnetic field.

cond-mat.supr-con↗