arXiv subjects

M. Sato

Publications and source records attributed to M. Sato.

At least 55 records · Page 3Linked to original sources

arXiv2014

Trigonometric Parallaxes of Star Forming Regions in the Scutum Spiral Arm

We report measurements of trigonometric parallaxes for six high-mass star-forming regions in the Scutum spiral arm of the Milky Way as part of the BeSSeL Survey. Combining our measurements with 10 previous measurements from the BeSSeL Survey yields a total sample of 16 sources in the Scutum arm with trigonometric parallaxes in the Galactic longitude range from 5 deg to 32 deg. Assuming a logarithmic spiral model, we estimate a pitch angle of 19.8 (+/-3.1) deg for the Scutum arm, which is larger than pitch angles reported for other spiral arms. The high pitch angle of the arm may be due to the arm's proximity to the Galactic bar. The Scutum arm sources show an average peculiar motion of 4 km/s slower than the Galactic rotation and 8 km/s toward the Galactic center. While the direction of this non-circular motion has the same sign as determined for sources in other spiral arms, the motion toward the Galactic center is greater for the Scutum arm sources.

astro-ph.GA↗

arXiv2014

Trigonometric parallaxes of star forming regions in the Sagittarius spiral arm

We report measurements of parallaxes and proper motions of ten high-mass star-forming regions in the Sagittarius spiral arm of the Milky Way as part of the BeSSeL Survey with the VLBA. Combining these results with eight others from the literature, we investigated the structure and kinematics of the arm between Galactocentric azimuth around -2 and 65 deg. We found that the spiral pitch angle is 7.3 +- 1.5 deg; the arm's half-width, defined as the rms deviation from the fitted spiral, is around 0.2 kpc; and the nearest portion of the Sagittarius arm is 1.4 +- 0.2 kpc from the Sun. Unlike for adjacent spiral arms, we found no evidence for significant peculiar motions of sources in the Sagittarius arm opposite to Galactic rotation.

astro-ph.GA↗

arXiv2014

High-resolution kaonic-atom x-ray spectroscopy with transition-edge-sensor microcalorimeters

We are preparing for an ultra-high resolution x-ray spectroscopy of kaonic atoms using an x-ray spectrometer based on an array of superconducting transition-edge-sensor microcalorimeters developed by NIST. The instrument has excellent energy resolutions of 2 - 3 eV (FWHM) at 6 keV and a large collecting area of about 20 mm^2. This will open new door to investigate kaon-nucleus strong interaction and provide new accurate charged-kaon mass value.

physics.ins-det↗

arXiv2014

The poisoning effect of Mn in LaFe(1-x)Mn(x)AsO(0.89)F(0.11): unveiling a quantum critical point in the phase diagram of iron-based superconductors

A superconducting-to-magnetic transition is reported for LaFe$_{1-x}$Mn$_x$AsO$_{0.89}$F$_{0.11}$ where a per thousand amount of Mn impurities is dispersed. By employing local spectroscopic techniques like muon spin rotation (muSR) and nuclear quadrupole resonance (NQR) on compounds with Mn contents ranging from x=0.025% to x=0.75%, we find that the electronic properties are extremely sensitive to the Mn impurities. In fact, a small amount of Mn as low as 0.2% suppresses superconductivity completely. Static magnetism, involving the FeAs planes, is observed to arise for x > 0.1% and becomes further enhanced upon increasing Mn substitution. Also a progressive increase of low energy spin fluctuations, leading to an enhancement of the NQR spin-lattice relaxation rate 1/T1, is observed upon Mn substitution. The analysis of 1/T1 for the sample closest to the the crossover between superconductivity and magnetism (x = 0.2%) points towards the presence of an antiferromagnetic quantum critical point around that doping level.

cond-mat.supr-con↗

arXiv2014

Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way

Over 100 trigonometric parallaxes and proper motions for masers associated with young, high-mass stars have been measured with the BeSSeL Survey, a VLBA key science project, the EVN, and the Japanese VERA project. These measurements provide strong evidence for the existence of spiral arms in the Milky Way, accurately locating many arm segments and yielding spiral pitch angles ranging from 7 to 20 degrees. The widths of spiral arms increase with distance from the Galactic center. Fitting axially symmetric models of the Milky Way with the 3-D position and velocity information and conservative priors for the solar and average source peculiar motions, we estimate the distance to the Galactic center, Ro, to be 8.34 +/- 0.16 kpc, a circular rotation speed at the Sun, To, to be 240 +/- 8 km/s, and a rotation curve that is nearly flat (a slope of -0.2 +/- 0.4 km/s/kpc) between Galactocentric radii of 5 and 16 kpc. Assuming a "universal" spiral galaxy form for the rotation curve, we estimate the thin disk scale length to be 2.44 +/- 0.16 kpc. The parameters Ro and To are not highly correlated and are relatively insensitive to different forms of the rotation curve. Adopting a theoretically motivated prior that high-mass star forming regions are in nearly circular Galactic orbits, we estimate a global solar motion component in the direction of Galactic rotation, Vsun = 14.6 +/- 5.0 km/s. While To and Vsun are significantly correlated, the sum of these parameters is well constrained, To + Vsun = 255.2 +/- 5.1 km/s, as is the angular speed of the Sun in its orbit about the Galactic center, (To + Vsun)/Ro = 30.57 +/- 0.43 km/s/kpc. These parameters improve the accuracy of estimates of the accelerations of the Sun and the Hulse-Taylor binary pulsar in their Galactic orbits, significantly reducing the uncertainty in tests of gravitational radiation predicted by general relativity.

astro-ph.GA↗

arXiv2013

The Parallax of W43: a Massive Star Forming Complex near the Galactic Bar

We report trigonometric parallax measurements of masers in the massive star forming complex W43 from VLBA observations as part of the BeSSeL Survey. Based on measurements of three 12 GHz methanol maser sources (G029.86-00.04, G029.95-00.01 and G031.28+00.06) and one 22 GHz water maser source (G031.58+00.07) toward W43, we derived a distance of $5.49^{+0.39}_{-0.34}$ kpc to W43. By associating the masers with CO molecular clouds, and associating the clouds kinematically with CO longitude-velocity spiral features, we assign W43 to the Scutum spiral arm, close to the near end of the Galactic bar. The peculiar motion of W43 is about 20 km/s toward the Galactic Center and is very likely induced by the gravitational attraction of the bar.

astro-ph.GA↗

arXiv2013

Trigonometric parallaxes to star-forming regions within 4 kpc of the galactic center

We report four trigonometric parallaxes for high-mass star-forming regions within 4 kpc of the Galactic center. These measurements were made with the VLBA as part of the BeSSeL Survey. By associating these sources kinematically with large-scale features in CO and HI longitude-velocity diagrams, we begin to outline some major features of the inner Milky Way: the Connecting arm, the near and far 3 kpc arms, and the Norma arm. The Connecting arm in the first Galactic quadrant lies closer to the Galactic center than the far 3 kpc arm and is offset by the long-bar's major axis near its leading edge, supporting the presence of an inner Lindblad resonance. Assuming the 3 kpc arms are a continuous physical structure, the relative Galactocentric distance of its near and far sides suggests highly elliptical streamlines of gas around the bar(s) and a bar corotation radius, r_CR > 3.6 kpc. At a Galactic longitude near 10° and a heliocentric distance of about 5 kpc, the near 3 kpc arm and the Norma arm intersect on a face-on view of our Galaxy, while passing at different Galactic latitudes. We provide an accurate distance measurement to the W31 star-forming complex of 4.95 (+0.5;-0.43) kpc from the Sun, which associates it with a bright CO feature belonging to the near 3 kpc arm.

astro-ph.GA↗

arXiv2013

Thermally populated intrinsic localized modes in pure alkali halide crystals

The possibility of thermal excitation of intrinsic localized modes (ILMs) arising from anharmonicity in ionic perfect crystals is studied numerically for realistic model systems in one and three dimensions. Implications are discussed for an interesting high-temperature feature seen in earlier inelastic neutron scattering experiments on single crystal NaI. The general conclusion is that ILM formation energies are far too large for thermal excitation of ILMs to account for the observed feature in a pure crystal.

cond-mat.mtrl-sci↗

arXiv2013

Intrinsic Localized Modes in a Nonlinear Electrical Lattice with Saturable Nonlinearity

This experimental study of driven intrinsic localized modes (ILMs) in an electronic circuit lattice with saturable nonlinearity follows the theoretical work of Hadzievski and coworkers. They proposed that a saturable nonlinearity could introduce transition points where localized excitations in nonintegrable lattices would move freely. In our experiments MOS capacitors provide the saturable nonlinearity in an electric lattice. Because of the soft nonlinearity driver locked, auto-resonance stationary ILMs are observed below the bottom of a linear frequency band of the lattice. With decreasing driver frequency the width of the ILM changes in a step-wise manner as does the softening of the barrier between site-centered and bond-centered ILM locations in agreement with theoretical expectations. However, the steps show hysteresis between up and down frequency scans and such hysteresis inhibits the free motion of ILMs.

nlin.PS↗

arXiv2013

The onset of magnetism peaked around x=1/4 in optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) (Ln = La, Nd or Sm) superconductors

The appearance of static magnetism, nanoscopically coexisting with superconductivity, is shown to be a general feature of optimally electron-doped LnFe(1-x)Ru(x)AsO(1-y)F(y) superconductor (Ln - lanthanide ion) upon isovalent substitution of Fe by Ru. The magnetic ordering temperature T_N and the magnitude of the internal field display a dome-like dependence on x, peaked around x=1/4, with higher T_N values for those materials characterized by a larger z cell coordinate of As. Remarkably, the latter are also those with the highest superconducting transition temperature (T_c) for x=0. The reduction of T_c(x) is found to be significant in the x region of the phase diagram where the static magnetism develops. Upon increasing the Ru content superconductivity eventually disappears, but only at x=0.6.

cond-mat.supr-con↗

arXiv2012

Development of liquid helium-3 target for experimental studies of antikaon-nucleon interaction at J-PARC

A liquid helium-3 target system was developed for experimental studies of kaonic atoms and kaonic nuclei at J-PARC. helium-3 gas is liquefied in a heat exchanger cooled below 3.2 K by decompression of liquid helium-4. To maintain a large acceptance of the cylindrical detector system for decay particles of kaonic nuclei, efficient heat transport between the separate target cell and the main unit is realized using circulation of liquid helium-3. To minimize the amount of material, a vacuum vessel containing a carbon fiber reinforced plastic cylinder having an inside diameter of 150 mm and a thickness of 1 mm was produced. A target cell made of pure beryllium and beryllium-aluminum alloy was developed not only to minimize the amount of material but to obtain also high x-ray transmission. During a cooling test, the target cell was kept at 1.3 K at a pressure of 33 mbar. The total estimated heat load to the components including the target cell and heat exchanger cooled by liquid helium-4 decompression, was 0.21 W, and the liquid helium-4 consumption rate was 50 L/day.

physics.ins-det↗

arXiv2012

Search for the $Θ^{+}$ pentaquark via the $π^-p\to K^-X$ reaction at 1.92 GeV/$c$

The $Θ^+$ pentaquark baryon was searched for via the $π^-p\to K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $π^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $Θ^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame was obtained to be 0.26 $μ$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $Θ^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_Θ=1/2^+$ and $J^P_Θ=1/2^-$, respectively.

nucl-ex↗

arXiv2011

Experimental observation of the bifurcation dynamics of an intrinsic localized mode in a driven 1-D nonlinear lattice

Linear response spectra of a driven intrinsic localized mode in a micromechanical array are measured as it approaches two fundamentally different kinds of bifurcation points. A linear phase mode associated with this autoresonant state softens in frequency and its amplitude grows as the upper frequency bifurcation point is approached, similar to the soft mode kinetic transition for a single driven Duffing resonator. A lower frequency bifurcation point occurs when the four-wave-mixing partner of this same phase mode intercepts the top of the extended wave branch, initiating a second kinetic transition process.

nlin.PS↗

arXiv2011

Temperature dependencies of the energy and time resolution of silicon drift detectors

The response of silicon drift detectors (SDDs), which were mounted together with their preamplifiers inside a vacuum chamber, was studied in a temperature range from 100 K to 200 K. In particular, the energy resolution could be stabilized to about 150 eV at 6 keV between 130 K and 200 K, while the time resolution shows a temperature dependence of T^3 in this temperature range. To keep a variation of the X-ray peak positions within 1 eV, it is necessary to operate the preamplifier within a stability of 1 K around 280 K. A detailed investigation of this temperature influences on SDDs and preamplifiers is presented.

physics.ins-det↗

arXiv2011

Enhancement of Thermal Conductivity due to Spinons in the One-Dimensional Spin System SrCuO_2

We have measured the thermal conductivity along the c-axis parallel to the spin-chains, kappa_c, of the one-dimensional antiferromagnetic spin system SrCuO_2, using as-grown and O_2-annealed single-crystals grown from raw materials with 99.9% (3N) and 99.99% (4N) purity. The value of kappa_c around 50K, where large contribution of the thermal conductivity due to spinons, kappa_spinon, is observed, is markedly enhanced by both the increase of the purity of raw materials and the O_2-annealing. Therefore, the increase of kappa_c implies that kappa_spinon is enhanced due to the decrease of spin defects caused by impurities in raw materials and by oxygen defects. The mean free path of spinons is as large as about 24000 angstrom at low temperatures in the O_2-annealed single-crystal grown from raw materials with 4N purity.

cond-mat.str-el↗

arXiv2011

Thermal Conductivity of the Quasi One-Dimensional Spin System Sr_2_V_3_O_9_

We have measured the thermal conductivity along the [101] direction, kappa_[101]_, along the [10-1] direction, kappa_[10-1]_, and along the b-axis, kappa_b_, of the quasi one-dimensional S=1/2 spin system Sr_2_V_3_O_9_ in magnetic fields up to 14 T, in order to find the thermal conductivity due to spinons and to clarify whether the spin-chains run along the [101] or [10-1] direction. It has been found that both kappa_[101]_, kappa_[10-1]_ and kappa_b_ show one peak around 10 K in zero field and that the magnitude of kappa_[10-1]_ is larger than those of kappa_[101]_ and kappa_b_. By the application of magnetic field along the heat current, the peak of kappa_[10-1]_ is markedly suppressed, while the peaks of kappa_[101]_ and kappa_b_ little change. These results indicate that there is a large contribution of spinons to kappa_[10-1]_ and suggest that the spin-chains run along the [10-1] direction.

cond-mat.str-el↗

arXiv2010

Spin and Valley Splittings in Multilayered Massless Dirac Fermion System

The inter-layer magnetoresistance in a multilayered massless Dirac fermion system, $α$-(BEDT-TTF)$_2$I$_3$, under hydrostatic pressure was investigated. We succeeded in detecting the zero-mode (n=0) Landau level and its spin splitting in the magnetic field normal to the 2D plane. We demonstrated that the effective Coulomb interaction in the magnetic field intensifies the spin splitting of zero-mode Landau carriers. At temperatures below 2K, magnetic fields above several Tesla break the twofold valley degeneracy.

cond-mat.mtrl-sci↗

arXiv2010

Three- and four-nucleon absorption processes observed in the $K^-$-$^4$He reaction at rest

Correlations of back-to-back coincident $Λd$ and $Λt$ pairs from the stopped $K^-$ reaction on $^4$He had been investigated, thereby $Λd$ and $Λt$ branches of non-mesonic three- and four-nucleon absorption processes of antikaon at rest were identified as well-separable processes, respectively. The branching ratio of the three-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λd "n"$, is estimated to be $(0.9 \pm 0.1 (stat) \pm 0.2 (syst)) \times 10^{-3}$ from the normalized $Λd$ spectrum in a $Λd n$ final state, while the fraction of the four-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λt$, is obtained to be $(3.1 \pm 0.4 (stat) \pm 0.5 (syst)) \times 10^{-4}$ per stopped $K^-$.

nucl-ex↗