Near-infrared imaging survey of faint companions around young dwarfs in the Pleiades cluster

We conducted a near-infrared imaging survey of 11 young dwarfs in the Pleiades cluster using the Subaru Telescope and the near-infrared coronagraph imager. We found ten faint point sources,with magnitudes as faint as 20 mag in the K-band,with around seven dwarfs.Comparison with the Spitzer archive images revealed that a pair of the faint sources around V 1171 Tau is very red in infrared wavelengths,which indicates very low-mass young stellar objects.However,the results of our follow-up proper motion measure...     

Carbon isotope anatomy of a single graphite crystal in a metapelitic migmatite revealed by high-spatial resolution SIMS analysis

High-spatial resolution carbon isotope analyses of natural graphite using secondary ion mass spectrometry (SIMS), together with conventional mass spectrometry techniques, demonstrate isotopic heterogeneity within single graphite crystals precipitated from a partially melted metamorphic rock. SIMS ¹³C/¹²C measurements were calibrated using an internal graphite standard previously analyzed by conventional isotope ratio mass spectrometry, which gave a reproducibility of 0.3‰ (1σ) at a spatial resolution of 2–3 μm. This resolution helped to identify an unusual carbon isotope distribution in a single graphite crystal from a metapelitic leucosome, showing remarkable core to rim variations with sharp δ¹³C steps up to 10‰. The results suggest that the graphite crystal grew from one edge to other forming layers perpendicular to the c-axis. The sharp isotopic steps indicate the presence of disequilibrium carbon isotope zoning in graphite and points to the possible existence of carbon isotope sector zoning. Intra-crystalline carbon isotope disequilibrium in graphite is believed to have resulted from the difference in diffusivity between ¹²C and ¹³C in the growth medium to the interface of graphite precipitation in different growth sectors.     

Abundances of 23 field RR Lyrae stars

We present stellar parameters and abundances of 15 elements （Na, Mg, A1, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Y and Ba） for 23 field RR Lyrae variables based on high-resolution （R ~ 60 000） and high signal-to-noise （S/N~ 200） spectra obtained using the High Dispersion Spectrograph on the Subaru Telescope. Six stars in the sample have more than one spectrum observed at different pulsation phases. The derived abundance ratios of [X/Fe] for 14 elements （except for Ba） do not vary during the pulsation cycle. An interesting curve of [Ba/Fe] versus phase is detected for the first time and it shows decreasing [Ba/Fe] with increasing temperature at a given metallicity. Combining with data in the literature, abundances of most RR Lyrae stars as a function of [Fe/H] follow the same trends as those of dwarf stars, but [Sc/Fe] and [Y/Fe] ratios of RR Lyrae stars at solar metallicity are lower than those of dwarf stars. The kinematics of RR Lyrae stars indicate that three comparatively metal-rich RR Lyrae stars might originate from the thick disk and they show higher [a/Fe] ratios than RR Lyrae stars with thin disk kinematics. Among 23 RR Lyrae stars, two special objects are found with abnormal abundances; TV Lib has high [a/Fe], [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios while TW Her has solar [a/Fe] but significantly lower [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios as compared with other RR Lyrae stars.     

Integrated description of deformation modes in a sedimentary basin: A case study around a shallow drilling site in the Mizunami area, eastern part of southwest Japan

Abstract   Tectonic episodes in a sedimentary basin are described on the basis of an integrated study combining reflection seismic interpretation, drilling survey and paleomagnetism. A shallow inclined borehole penetrated a fault shown by reflection seismic and geological surveys in the Mizunami area, in the eastern part of southwest Japan. Paleomagnetic measurements were carried out on core samples successfully oriented using side-wall image logging of structural attitude. At six horizons, stable characteristic remanent magnetization (ChRM) was confirmed through thermal and alternating field demagnetization tests, which were carried by magnetite with minor amounts of high coercivity minerals, as revealed by experiments of stepwise acquisition of isothermal remanent magnetization. After correction of multiphase deformation inferred from borehole structural analysis, ChRM directions were combined with previous data and confirmed an easterly deflection reflecting the coherent clockwise rotation of the arc before the Middle Miocene. Compilation of reliable paleomagnetic data described differential rotation of the eastern part of southwest Japan raised by collision of the Izu–Bonin Arc since the Middle Miocene. The present study suggests that (i) the Mizunami area is adjacent to a highly deformed zone bounded by the Akaishi Tectonic Line (ATL), and (ii) forearc deformation of southwest Japan is localized around the ATL, which is quite different from gradual bending on the back-arc side without remarkable crustal break related to the collision event.     

Diurnal variation of urban structure in terms of time distance: A spatio-temporal analysis of an urban area

The purpose of this paper is to clarify the diurnal variations in structure of an urban area from the viewpoint of time distance. To accomplish this, for one entire day, and for the morning, noon, and evening periods, time maps are delineated by using MDS; also, the indices of accessibility and circuity are computed from the time distances. As a result, the difference in shape between the time and actual maps becomes clear especially in the morning and also in the evening. Both the accessibility and circuity measured from the time distance show a concentrically shaped pattern where the regional disparity is especially distinct within the morning and evening periods. The diurnal variations as described above are thought to occur against the backdrop of the topological traffic conditions within the study area. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetic properties of siliceous marine sediments in Northern Hokkaido,Japan: a quantitative tectono‐sedimentological study of basins along an active margin

The formation processes of the late Neogene sedimentary basins in Northern Hokkaido have been investigated on the basis of rock magnetism, structural geology and numerical modelling. Untilted site‐mean directions of remanent magnetization of the Wakkanai Formation, obtained from oriented core samples in Horonobe, suggest remarkable counterclockwise block rotation (ca. 70°) since the late Neogene. Uniform microscopic fabric of the siliceous sediments was inferred from the alignment of the principal axes of the anisotropy of magnetic susceptibility (AMS). After correction for tectonic rotation, the maximum axis of AMS, which reflects the sedimentary fabric of the dominant paramagnetic minerals, is in an E‐W direction, which is concordant with the influx direction of diatomaceous particles into the N‐S elongate sedimentary basins. The difference in the bulk initial magnetic susceptibility of the siliceous sediments of the Wakkanai Formation between the depocenter of the basin and its peripheral part implies that terrigenous non‐magnetic fraction has been sorted out during transportation of the detrital grains as gravity flows. As for the development mechanism of the N‐S elongate late Neogene basins in Northern Hokkaido, their depocenter arrangement and subsidence pattern indicates dextral motions upon a longitudinal fault zone along the Eurasian convergent margin. Dislocation modelling was adopted to explain vertical displacement and rotational motion around the study area and successfully restored the deformation pattern based on the assumption of dextral slip at a left‐stepping part of a strand of the transcurrent fault.     

Paleomagnetism of a pyroclastic flow deposit and its correlative widespread tephra in central Japan: Possible tectonic rotation since the late Pleistocene

Abstract The late Pleistocene Kamitakara Pyroclastic Flow Deposit (KPFD) and its correlative Kasamori (Ks22) Tephra in central Japan are found to preserve stable thermoremanent magnetization (TRM) and detrital remanent magnetization (DRM), respectively. Untilted site‐mean declinations of the KPFD are characterized by a fairly large scatter with easterly deflection, while those of the Ks22 show significantly smaller deflections. Because northerly paleomagnetic directions consistently characterize shallow marine sediments intercalating the Ks22 layer, the directional discordance is not attributed to different acquisition timing between TRM and DRM, but is probably due to a recent tectonic rotation in central Japan. Large scatter in TRM declinations of the KPFD implies that a number of right‐lateral active faults around the depositional area of the pyroclastic flow raised differential rotation of crustal blocks in central Japan, even during the late Pleistocene.     

Seasonal and annual change in community structure of meso-sized copepods in Tokyo Bay, Japan

Seasonal change in the meso-sized copepod community structure in the central part of Tokyo Bay was investigated from January 2006 to December 2008. Three seasonal community groups were detected, and seasonal shifts of these communities are explained by life history characteristics of indicator species and seasonal changes in the hydrographical environment. In the winter-spring community, Acartia omorii and Centropages abdominalis dominate because of high growth rates at low temperature. A shift to the early summer community is caused by a diapause of Ce. abdominalis as resting eggs and an increase in the growth and egg-production rate of Pseudodiaptomus marinus at high temperature. A shift to the summer-fall community is caused by a diapause of A. omorii at hypoxic and high temperature conditions and an increase of Temora turbinata, Paracalanus parvus and other oceanic species by an enhancement of the estuary circulation. Then, the community returns to a winter-spring one by the recovery of A. omorii and Ce. abdominalis with low temperatures and oxygenation of bottom water and by the disappearance of oceanic warm-water species at low temperature. Seasonal community shifts occurred almost regularly, but the shift from a winter-spring community to an early summer one occurred 1 month early in 2007 when the water temperature was warmer than in other years.     

Climate teleconnections influence on West Africa's terrestrial water storage

There is some evidence of rapid changes in the global atmosphere and hydrological cycle caused by the influence of climate variability. In West Africa, such changes impact directly on water resources leading to incessant extreme hydro‐meteorological conditions. This study examines the association of three global climate teleconnections—El‐Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Atlantic Multi‐decadal Oscillation (AMO) with changes in terrestrial water storage (TWS) derived from both Modern‐Era Retrospective Analysis for Research and Applications (MERRA, 1980–2015) and Gravity Recovery and Climate Experiment (GRACE, 2002–2014). In the Sahel region, positive phase of AMO coincided with above‐normal rainfall (wet conditions) and the negative phase with drought conditions and confirms the observed statistically significant association (r = 0.62) between AMO and the temporal evolutions of standardised precipitation index. This relationship corroborates the observed presence of AMO‐driven TWS in much of the Sahel region (though considerably weak in some areas). Although ENSO appears to be more associated with GRACE‐derived TWS over the Volta basin (r =?0.40), this study also shows a strong presence of AMO‐ and ENSO‐induced TWS derived from MERRA reanalysis data in the coastal West African countries and most of the regions below latitude 10°N. The observed presence of ENSO‐ and AMO‐driven TWS is noticeable in tropical areas with relatively high annual/bimodal rainfall and strong inter‐annual variations in surface water. The AMO has a wider footprint and sphere of influence on the region's TWS and suggests the important role of North Atlantic Ocean. IOD‐related TWS also exists in West Africa and its influence on the region's hydrology maybe secondary and somewhat complementary. Nonetheless, presumptive evidence from the study indicates that ENSO and AMO are the two major climatic indices more likely to impact on West Africa's TWS.