Microscopic Theory of Current-Spin Interaction in Ferromagnets

Interplay between magnetization dynamics and electric current in a conducting ferromagnet is theoretically studied based on a microscopic model calculation. First, the effects of the current on magnetization dynamics (spin torques) are studied with special attention to the "dissipative" torques arising from spin-relaxation processes of conduction electrons. Next, an analysis is given of the "spin motive force", namely, a spin-dependent 'voltage' generation due to magnetization dynamics, which is the reaction to spin torques. Finally, an attempt is presented of a unified description of these effects.Comment: Written in December 2008, published in July 200

The interface between the stellar wind and interstellar medium around R Cassiopeiae revealed by far-infrared imaging

The circumstellar dust shells of intermediate initial-mass (about 1 to 8 solar masses) evolved stars are generated by copious mass loss during the asymptotic giant branch phase. The density structure of their circumstellar shell is the direct evidence of mass loss processes, from which we can investigate the nature of mass loss. We used the AKARI Infrared Astronomy Satellite and the Spitzer Space Telescope to obtain the surface brightness maps of an evolved star R Cas at far-infrared wavelengths, since the temperature of dust decreases as the distance from the star increases and one needs to probe dust at lower temperatures, i.e., at longer wavelengths. The observed shell structure and the star's known proper motion suggest that the structure represents the interface regions between the dusty wind and the interstellar medium. The deconvolved structures are fitted with the analytic bow shock structure to determine the inclination angle of the bow shock cone. Our data show that (1) the bow shock cone of 1 - 5 x 10^-5 solar masses (dust mass) is inclined at 68 degrees with respect to the plane of the sky, and (2) the dust temperature in the bow shock cone is raised to more than 20 K by collisional shock interaction in addition to the ambient interstellar radiation field. By comparison between the apex vector of the bow shock and space motion vector of the star we infer that there is a flow of interstellar medium local to R Cas whose flow velocity is at least 55.6 km/s, consistent with an environment conducive to dust heating by shock interactions.Comment: 7 pages, 2 figures, accepted for publication in Astronomy and Astrophysic

An AKARI Search for Intracluster Dust of Globular Clusters

We report the observations of 12 globular clusters with the AKARI/FIS. Our goal is to search for emission from the cold dust within clusters. We detect diffuse emissions toward NGC 6402 and 2808, but the IRAS 100-micron maps show the presence of strong background radiation. They are likely emitted from the galactic cirrus, while we cannot rule out the possible association of a bump of emission with the cluster in the case of NGC 6402. We also detect 28 point-like sources mainly in the WIDE-S images (90 micron). At least several of them are not associated with the clusters but background galaxies based on some external catalogs. We present the SEDs by combining the near-and-mid infrared data obtained with the IRC if possible. The SEDs suggest that most of the point sources are background galaxies. We find one candidate of the intracluster dust which has no mid-infrared counterpart unlike the other point-like sources, although some features such as its point-like appearance should be explained before we conclude its intracluster origin. For most of the other clusters, we have confirmed the lack of the intracluster dust. We evaluate upper limits of the intracluster dust mass to be between 1.0E-05 and 1.0E-03 solar mass depending on the dust temperature. The lifetime of the intracluster dust inferred from the upper limits is shorter than 5 Myr (T=70K) or 50 Myr (35K). Such short lifetime indicates some mechanism(s) are at work to remove the intracluster dust. We also discuss its impact on the chemical evolution of globular clusters.Comment: Accepted for publication in PASJ AKARI special issue. 14 pages, 11 figure

AKARI Near- to Mid-Infrared Imaging and Spectroscopic Observations of the Small Magellanic Cloud. I. Bright Point Source List

We carried out a near- to mid-infrared imaging and spectroscopic observations of the patchy areas in the Small Magellanic Cloud using the Infrared Camera on board AKARI. Two 100 arcmin2 areas were imaged in 3.2, 4.1, 7, 11, 15, and 24 um and also spectroscopically observed in the wavelength range continuously from 2.5 to 13.4 um. The spectral resolving power (lambda/Delta lambda) is about 20, 50, and 50 at 3.5, 6.6 and 10.6 um, respectively. Other than the two 100 arcmin2 areas, some patchy areas were imaged and/or spectroscopically observed as well. In this paper, we overview the observations and present a list of near- to mid-infrared photometric results, which lists ~ 12,000 near-infrared and ~ 1,800 mid-infrared bright point sources detected in the observed areas. The 10 sigma limits are 16.50, 16.12, 13.28, 11.26, 9.62, and 8.76 in Vega magnitudes at 3.2, 4.1, 7, 11, 15, and 24 um bands, respectively.Comment: 16 pages, 7 figures, accepted for publication in PASJ. Full resolution version is available at http://www-irc.mtk.nao.ac.jp/%7Eyita/smc20100112.pd

Edge currents in the absence of edges

We investigate a charged two-dimensional particle in a homogeneous magnetic field interacting with a periodic array of point obstacles. We show that while Landau levels remain to be infinitely degenerate eigenvalues, between them the system has bands of absolutely continuous spectrum and exhibits thus a transport along the array. We also compute the band functions and the corresponding probability current.Comment: Final version, to appear in Phys. Lett. A; 10 LaTeX pages with 3 eps figure

X Her and TX Psc: Two cases of ISM interaction with stellar winds observed by Herschel

The asymptotic giant branch (AGB) stars X Her and TX Psc have been imaged at 70 and 160 microns with the PACS instrument onboard the Herschel satellite, as part of the large MESS (Mass loss of Evolved StarS) Guaranteed Time Key Program. The images reveal an axisymmetric extended structure with its axis oriented along the space motion of the stars. This extended structure is very likely to be shaped by the interaction of the wind ejected by the AGB star with the surrounding interstellar medium (ISM). As predicted by numerical simulations, the detailed structure of the wind-ISM interface depends upon the relative velocity between star+wind and the ISM, which is large for these two stars (108 and 55 km/s for X Her and TX Psc, respectively). In both cases, there is a compact blob upstream whose origin is not fully elucidated, but that could be the signature of some instability in the wind-ISM shock. Deconvolved images of X Her and TX Psc reveal several discrete structures along the outermost filaments, which could be Kelvin-Helmholtz vortices. Finally, TX Psc is surrounded by an almost circular ring (the signature of the termination shock?) that contrasts with the outer, more structured filaments. A similar inner circular structure seems to be present in X Her as well, albeit less clearly.Comment: 11 pages, Astronomy & Astrophysics, in pres

Ab initio many-body calculation of excitons in solid Ne and Ar

Absorption spectra, exciton energy levels and wave functions for solid Ne and Ar have been calculated from first principles using many-body techniques. Electronic band structures of Ne and Ar were calculated using the GW approximation. Exciton states were calculated by diagonalizing an exciton Hamiltonian derived from the particle-hole Green function, whose equation of motion is the Bethe-Salpeter equation. Singlet and triplet exciton series up to n=5 for Ne and n=3 for Ar were obtained. Binding energies and longitudinal-transverse splittings of n=1 excitons are in excellent agreement with experiment. Plots of correlated electron-hole wave functions show that the electron-hole complex is delocalised over roughly 7 a.u. in solid Ar.Comment: 6 page

Workplans: workshop on planetary nebula observations

This workshop is the second of the WORKPLANS series, which we started in 2016. The main goal of WORKPLANS is to build up a network of planetary nebulae (PNe) experts to address the main open questions in the field of PNe research. The specific aims of the WORKPLANS workshop series are (i) to discuss and prioritize the most important topics to be investigated by the PN community in the following years; (ii) to establish a network of excellent researchers with complementary expertise; (iii) to formulate ambitious observing proposals for the most advanced telescopes and instrumentation presently available (ALMA, SOFIA, VLT, GTC, HST, etc.), addressing those topics; and (iv) to develop strategies for major proposals to future observatories (JWST, ELT, SPICA, Athena, etc.). To achieve these goals, WORKPLANS II brought together experts in all key sub-areas of the PNe research field, namely: analysis and interpretation of PNe observational data; theoretical modeling of gas and dust emission; evolution from Asymptotic Giant Branch stars (PNe progenitors) to PNe; and the instrumentation and technical characteristics of the relevant observatoriesI.A. acknowledges the support of Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. This research is supported by Space Telescope Science Institute grant HST-GO-15953.001-A to RIT (J.K.). T.U. was supported by NASA under grant NNX15AF24G issued through the Science Mission Directorate. E.V. acknowledges support from the “On the rocks II project” funded by the Spanish Ministerio de Ciencia, Innovación y Universidades under grant PGC2018-101950-B-I00. The Workshop was organized with the financial support of the Lorentz Center, which was provided by the Netherlands Organization for Scientific Research (NWO) and the Leiden Universit