SHRIMP U-Pb Zircon Age of the Inishi Migmatite around the Kamioka Mining Area, Hida Metamorphic Complex, Central Japan

Abstract. SHRIMP U-Pb ages were determined on single zircons separated from the Inishi migmatite in the Kamioka mining area, Hida metamorphic complex, central Japan. Twenty one determinations were distributed within the age of 234.2±1.8 Ma, excluding one inner core of a grain. As the analyzed crystals were mostly euhedral igneous zircons, the age indicates the crystallization of zircons from granitic melt during the formation of Inishi migmatite. The age of ca. 234 Ma corresponded to the later stage of the major regional metamorphic event in the Hida complex, while the age of ca. 265 Ma determined in a grain suggested the inherited age of the earlier phase of the metamorphism.     

Surface morphological features of boulders on Asteroid 25143 Itokawa

On the sub-kilometer S-type asteroid, 25143 Itokawa, some boulders on rough terrains seem to be exposed without any powdery material covering. Based on surface morphological features, there are two major types of boulders: one has rounded edges and corners (rounded boulders), while the other has angular edges and corners (angular boulders). The surface features of the rounded boulders suggest that they have hardness heterogeneity and that some may be breccias. The angular boulders appear to be more resistant to impact disruption than the rounded ones, which may be due to a difference in lithology. The major constituents of Itokawa may be LL chondrite-like brecciated lithology (rounded boulders) along with a remarkable number of boulders suggesting that lithology is atypical among LL chondrites (angular boulders). Some of both types of boulders contain intersecting and stepped planar foliations. Comparison with meteorite ALH76009 suggests that the planar foliations may be marks where rocks were torn apart. As lithified breccias cannot be formed on present-day sub-kilometer-sized Itokawa, it is reasonable that boulders with various lithologies on Itokawa were formed on its large ancestor(s). The rubble-pile structure of Itokawa suggested by its low density (∼1.9 g/cm³) indicates that boulders on Itokawa are reassembled fragments formed by catastrophic disruption of large ancestor(s).     

Proton migration in portlandite inferred from activation energy of self-diffusion and potential energy curve of OH bond

A fundamental mechanism on the atomic level for self-diffusion in the proton layer of portlandite, Ca(OH)₂, was investigated by conducting hydrogen–deuterium (H–D) exchange diffusion experiments and by deriving potential energy curves of OH vibrations from optical absorption measurements. Synthetic single crystals of portlandite were used in H–D experiments between 250 and 450°C at 150 MPa. Arrhenius parameters for proton diffusion perpendicular to the c-axis gave a frequency factor of 1.0 × 10⁻¹⁰ m²/s and activation energy of 0.61 eV (58.5 kJ/mol). The activation energy corresponds to the height of the potential barrier between two oxygen atoms across an interlayer. The potential barrier height was also theoretically estimated using the OH potential energy curve (OH-PEC) determined by optical absorption measurements. Experimental and theoretical results suggest that the potential barrier height cannot be simply determined by overlapping two OH-PECs. The potential barrier derived theoretically was 3.11 eV. This is too high for the activation energy of the proton diffusion. It implies that the interaction between a diffusing proton and the vacancy of a proton site, and the shortening of interlayer oxygen distance by thermal vibration reduce the potential barrier.     

Polarization Calibration of the Solar Optical Telescope onboard Hinode

The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial resolution of 0.2 – 0.3 arcsec. A photometric accuracy of 10⁻³ is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter of the SOT and its final polarization characteristics.     

The Solar Optical Telescope for the Hinode Mission: An Overview

The Solar Optical Telescope (SOT) aboard the Hinode satellite (formerly called Solar-B) consists of the Optical Telescope Assembly (OTA) and the Focal Plane Package (FPP). The OTA is a 50-cm diffraction-limited Gregorian telescope, and the FPP includes the narrowband filtergraph (NFI) and the broadband filtergraph (BFI), plus the Stokes Spectro-Polarimeter (SP). The SOT provides unprecedented high-resolution photometric and vector magnetic images of the photosphere and chromosphere with a very stable point spread function and is equipped with an image-stabilization system with performance better than 0.01 arcsec rms. Together with the other two instruments on Hinode (the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS)), the SOT is poised to address many fundamental questions about solar magnetohydrodynamics. This paper provides an overview; the details of the instrument are presented in a series of companion papers. M. Otsubo is a former NAOJ staff scientist.     

The Solar Optical Telescope of Solar-B (Hinode): The Optical Telescope Assembly

The Solar Optical Telescope (SOT) aboard the Solar-B satellite (Hinode) is designed to perform high-precision photometric and polarimetric observations of the Sun in visible light spectra (388 – 668 nm) with a spatial resolution of 0.2 – 0.3 arcsec. The SOT consists of two optically separable components: the Optical Telescope Assembly (OTA), consisting of a 50-cm aperture Gregorian with a collimating lens unit and an active tip-tilt mirror, and an accompanying Focal Plane Package (FPP), housing two filtergraphs and a spectro-polarimeter. The optomechanical and optothermal performance of the OTA is crucial to attain unprecedented high-quality solar observations. We describe in detail the instrument design and expected stable diffraction-limited on-orbit performance of the OTA, the largest state-of-the-art solar telescope yet flown in space.     

Development of an Automatic Echo-counting Program for HROFFT Spectrograms

Radio meteor observations by Ham-band beacon or FM radio broadcasts using “Ham-band Radio meteor Observation Fast Fourier Transform” (HROFFT) an automatic operating software have been performed widely in recent days. Previously, counting of meteor echoes on the spectrograms of radio meteor observation was performed manually by observers. In the present paper, we introduce an automatic meteor echo counting software application. Although output images of the HROFFT contain both the features of meteor echoes and those of various types of noises, a newly developed image processing technique has been applied, resulting in software that enables a useful auto-counting tool. There exists a slight error in the processing on spectrograms when the observation site is affected by many disturbing noises. Nevertheless, comparison between software and manual counting revealed an agreement of almost 90%. Therefore, we can easily obtain a dataset of detection time, duration time, signal strength, and Doppler shift of each meteor echo from the HROFFT spectrograms. Using this software, statistical analyses of meteor activities is based on the results obtained at many Ham-band Radio meteor Observation (HRO) sites throughout the world, resulting in a very useful “standard” for monitoring meteor stream activities in real time.     

Stardust in Antarctic micrometeorites

Abstract— We report the discovery of presolar silicate, oxide (hibonite), and (possibly) SiC grains in four Antarctic micrometeorites (AMMs). The oxygen isotopic compositions of the eighteen presolar silicate (and one oxide) grains found are similar those observed previously in primitive meteorites and interplanetary dust particles, and indicate origins in oxygen‐rich red giant or asymptotic giant branch stars, or in supernovae. Four grains with anomalous C isotopic compositions were also detected. ¹²C/¹³C as well as Si ratios are similar to those of mainstream SiC grains; the N isotopic composition of one grain is also consistent with a mainstream SiC classification. Presolar silicate grains were found in three of the seven AMMs studied, and are heterogeneously distributed within these micrometeorites. Fourteen of the 18 presolar silicate grains and 3 of the 4 C‐anomalous grains were found within one AMM, T98G8. Presolar silicate‐bearing micrometeorites contain crystalline silicates that give sharp X‐ray diffractions and do not contain magnesiowüstite, which forms mainly through the decomposition of phyllosilicates and carbonates. The occurrence of this mineral in AMMs without presolar silicates suggests that secondary parent body processes probably determine the presence or absence of presolar silicates in Antarctic micrometeorites.     

Particle size effect on the saturation of methane hydrate in sediments – Constrained from experimental results

Except for those occurring at seafloor, most of natural gas hydrate form in sediments and are subject to the influence of sediment. Among these factors, the particle size effect on hydrate saturation level in sediment have been studied with a series of silica sands with various sizes, and the results obtained clearly indicate that particle size does play an important role in affecting the saturation level of hydrate in sediments. The proton relaxation times of water confined in the same series of silica sands, which were determined with NMR measurement, show logarithmic relationship with particle size. By comprehensive consideration of the results of hydrate saturation and water proton relaxation times, the particle size effect observed is tentatively explained by the water availability for hydrate formation in sediments.