The fading of supernova 1997D

We present a new set of spectroscopic and photometric data extending the observations of SN 1997D to over 400 d after the explosion. These observations confirm the peculiar properties of SN 1997D, such as the very low abundance of ⁵⁶Co (0.002 M_⊙) and the low expansion velocity of the ejecta (∼1000 km s⁻¹). We discuss the implications of these observations for the character of the progenitor and the nature of the remnant, showing that a Crab-like pulsar or an accreting neutron star formed in the explosion of a low-mass progenitor should already have produced a detectable luminosity at this epoch, in contrast with photometric data. On the other hand, the explosion of a high-mass progenitor with the formation of a black hole is consistent with the available observations. The consequences of this conclusion regarding the nature of the explosion and the prospects of directly identifying the black hole are also addressed.     

Diurnal variation of CO2 concentration, Δ14C and δ13C in an urban forest: estimate of the anthropogenic and biogenic CO2 contributions

Diurnal variation in the atmospheric CO₂ concentration and the carbon isotopic composition (Δ¹⁴C and δ¹³C) was measured in a forest in an urban area on 9 February 1999. The carbon isotope approach used in the present study differentiated between the quantitative contributions from anthropogenic and biogenic CO₂ sources in the urban atmosphere. The anthropogenic (fossil fuel) and biogenic (soil respiration) contributions was estimated, and they ranged from 1 to 16% and from 2 to 8% of the total atmospheric CO₂. The diurnal variation of the anthropogenic CO₂ was the major cause of the total atmospheric CO₂ variation, while the biogenic CO₂ remained relatively constant throughout the day. Estimating the contribution of soil respired CO₂ provided the mean residence time of soil respired CO₂ within the forest atmosphere.     

Noble gas isotopes and mineral assemblages of Antarctic micrometeorites collected at the meteorite ice field around the Yamato Mountains

Abstract— From November 1998 to January 1999, the 39th Japanese Antarctic Research Expedition (JARE) conducted a large‐scale micrometeorite collection at 3 areas in the meteorite ice field around the Yamato Mountains, Antarctica. The Antarctic micrometeorites (AMMs) collected were ancient cosmic dust particles. This is in contrast with the Dome Fuji AMMs, which were collected previously from fresh snows in 1996 and 1997 and which represent modern micrometeorites. To determine the noble gas concentrations and isotopic compositions of individual AMMs, noble gas analyses were carried out using laser‐gas extraction for 35 unmelted Yamato Mountains AMMs and 3 cosmic spherules. X‐ray diffraction analyses were performed on 13 AMMs before the noble gas measurement and mineral compositions were determined. AMMs are classified into 4 main mineralogical groups, defined from the heating they suffered during atmospheric entry. Heating temperatures of AMMs, inferred from their mineral compositions, are correlated with ⁴He concentrations and reflect the effect of degassing during atmospheric entry. Jarosite, an aqueous alteration product, is detected for 4 AMMs, indicating the aqueous alteration during long‐time storage in Antarctic ice. Jarosite‐bearing AMMs have relatively low concentrations of 4He, which is suggestive of loss during the alteration. High ³He/⁴He ratios are detected for AMMs with high ²⁰Ne/⁴He ratios, showing both cosmogenic ³He and preferential He loss. SEP (solar energetic particles)‐He and Ne, rather than the solar wind (SW), were dominant in AMMs, presumably showing a preferential removal of the more shallowly implanted SW by atmospheric entry heating. The mean ²⁰Ne/²²Ne ratio is 11.27 ± 0.35, which is close to the SEP value of 11.2. Cosmogenic ²¹Ne is not detected in any of the particles, which is probably due to the short cosmic ray exposure ages. Ar isotopic compositions are explained by 3‐component mixing of air, Q, and SEP‐Ar. Ar isotopic compositions can not be explained without significant contributions of Q‐Ar. SEP‐Ne contributed more than 99% of the total Ne. As for ³⁶Ar and ³⁸Ar, the abundance of the Q component is comparable to that of the SEP component. ⁸⁴Kr and ¹³²Xe are dominated by the primordial component, and solar‐derived Xe is almost negligible.     

Tourist preferences for agricultural landscapes: a case study of terraced paddy fields in Noto Peninsula,Japan

Many agricultural landscapes have been formed through the interaction and co-evolution of nature and people, and represent the living landscapes shaped over time through intensive and continuous human cultivation. Terraced paddy fields are being re-evaluated to take into account the multiple functions they fill beyond only rice cultivation, particularly their contribution to the national biodiversity strategy of Japan. Since the 1990s, terraced paddy fields have been considered a representative cultural landscape of Japan and, at the same time, multi-stakeholder conservation activities have been conducted throughout Japan to reverse the increasing abandonment of terraces. Shiroyone Senmaida is an outstanding cultural landscape and a major tourist attraction in Noto Peninsula, Ishikawa Prefecture, which was designated through an initiative by the Food and Agriculture Organization (FAO) as a Globally Important Agricultural Heritage Systems (GIAHS) pilot site in 2011. It is important to clarify tourist preference for terraced paddy field landscapes to contribute to future policy making toward improved agricultural landscape conservation. A key finding of this study is that tourists visiting to enjoy the agricultural landscape are also concerned on the sustainability of the farming methods and preferred to maintain the naturalness of the landscape. Respondents with higher educational levels and greater concern for the biological and traditional farming knowledge aspects of the rice terraces were also more inclined to favor sustainable farming practices. Tourists preferred to maintain the naturalness and rurality of the agricultural landscape, and indicated that construction of excessive tourist facilities would cause the landscape to deteriorate. It was suggested that the local community and surroundings, including rural settlements, hills, and forests, should also be conserved together with the scenic terrace.     

The Hayabusa Spacecraft Asteroid Multi-band Imaging Camera (AMICA)

The Hayabusa Spacecraft Asteroid Multi-band Imaging Camera (AMICA) has acquired more than 1400 multispectral and high-resolution images of its target asteroid, 25143 Itokawa, since late August 2005. In this paper, we summarize the design and performance of AMICA. In addition, we describe the calibration methods, assumptions, and models, based on measurements. Major calibration steps include corrections for linearity and modeling and subtraction of bias, dark current, read-out smear, and pixel-to-pixel responsivity variations. AMICA v-band data were calibrated to radiance using in-flight stellar observations. The other band data were calibrated to reflectance by comparing them to ground-based observations to avoid the uncertainty of the solar irradiation in those bands. We found that the AMICA signal was linear with respect to the input signal to an accuracy of ?1% when the signal level was <3800 DN. We verified that the absolute radiance calibration of the AMICA v-band (0.55 μm) was accurate to 4% or less, the accuracy of the disk-integrated spectra with respect to the AMICA v-band was about 1%, and the pixel-to-pixel responsivity (flat-field) variation was 3% or less. The uncertainty in background zero level was 5 DN. From wide-band observations of star clusters, we found that the AMICA optics have an effective focal length of 120.80 ± 0.03 mm, yielding a field-of-view (FOV) of 5.83° × 5.69°. The resulting geometric distortion model was accurate to within a third of a pixel. We demonstrated an image-restoration technique using the point-spread functions of stars, and confirmed that the technique functions well in all loss-less images. An artifact not corrected by this calibration is scattered light associated with bright disks in the FOV.     

The shape distribution of boulders on Asteroid 25143 Itokawa: Comparison with fragments from impact experiments

Laboratory impact experiments have found that the shape of fragments over a broad size range is distributed around the mean value of the axial ratio 2:√2:1, which is independent of a wide range of experimental conditions. We report the shape statistics of boulders with size of 0.1-30 m on the surface of Asteroid 25143 Itokawa based on high-resolution images obtained by the Hayabusa spacecraft in order to investigate whether their shape distribution is similar to the distribution obtained for fragments (smaller than 0.1 m) in laboratory impact experiments. We also investigated the shapes of boulders with size of 0.1-150 m on Asteroid 433 Eros using a few arbitrary selected images by the NEAR spacecraft, in order to compare those with the shapes on Asteroid Itokawa. In addition, the shapes of small- and fast-rotating asteroids (diameter <200 m and rotation period <1 h), which are natural fragments from past impact events among asteroids, were inferred from archived light curve data taken by ground-based telescopes. The results show that the shape distributions of laboratory fragments are similar to those of the boulders on Eros and of the small- and fast-rotating asteroids, but are different from those on Itokawa. However, we propose that the apparent difference between the boulders of Itokawa and the laboratory fragments is due to the migration of boulders. Therefore, we suggest that the shape distributions of the boulders ranging from 0.1 to 150 m in size and the small- and fast-rotating asteroids are similar to those obtained for the fragments generated in laboratory impact experiments.     

Degassing, crystallization and eruption dynamics at Stromboli: trace element and lithium isotopic evidence from 2003 ashes

During its 1800-year-long persistent activity the Stromboli volcano has erupted a highly porphyritic (HP) volatile-poor scoriaceous magma and a low porphyritic (LP) volatile-rich pumiceous magma. The HP magma is erupted during normal Strombolian explosions and lava effusions, while the LP one is related to more energetic paroxysms. During the March–April 2003 explosive activity, Stromboli ejected two typologies of juvenile glassy ashes, namely highly vesicular LP shards and volatile-poor HP shards. Their textural and in situ chemical characteristics are used to unravel mutual relationships between HP and LP magmas, as well as magma dynamics within the shallow plumbing system. The mantle-normalized trace element patterns of both ash types show the typical arc-lava pattern; however, HP glasses possess incompatible element concentrations higher than LP glasses, along with Sr and Eu negative anomalies. HP shards are generally characterized by higher Li contents (to ~20 ppm) and lower δ⁷Li values (+1.2 to −3.8‰) with respect to LP shards (Li contents of 7–14 ppm and δ⁷Li ranging between +4.6 and +0.9‰). Fractional crystallization models based on major and trace element compositions, combined with a degassing model based on open-system Rayleigh distillation and on the assumption that ^melt/fluidD_Li > 1, show that abundant (~30%) plagioclase precipitation and variable degrees of degassing can lead the more primitive LP magma to evolve toward a differentiated (isotopically lighter) HP magma ponding in the upper conduit and undergoing slow continuous degassing-induced crystallization. This study also evidences that in March 2003 Stromboli volcano poured out a small early volume of LP magma that traveled slower within the conduit with respect to later and larger volumes of fast ascending LP magma erupted during the April 5 paroxysm. The different ascent rates and cooling rates of the two LP magma batches (i.e., pre- and post-paroxysm) resulted in small, but detectable, differences in their chemical signatures. Finally, this study highlights the high potential of in situ investigations of juvenile glassy ashes in petrologic and geochemical monitoring the volcanic activity and of Li isotopes as tracers of degassing processes within the shallow plumbing system.     

Estimate of exceedance probability of tsunami occurrence in the Eastern Pacific

The exceedance probability of tsunami occurrence in the eastern Pacific was estimated as an extended Poisson process. Estimation was also undertaken for several blocks in the eastern Pacific. Some tsunamis that originated off South America hit the Japanese islands after crossing the Pacific.     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.     

Paleoenvironmental analysis of the Mawaki archaeological site,central Japan,in relation to the stratigraphic position of dolphin bones

In order to elucidate the paleoenvironment associated with the early Holocene Mawaki archaeological site on the Noto Peninsula of central Japan, a high‐resolution stratigraphic study was conducted of 17 boreholes drilled at the archaeological site. We selected three boreholes for which lithological and/or chronological data are reported. Initial magnetic susceptibility was utilized for correlation of clastic core samples with the assistance of 26 radiocarbon dates. Four lithological units (A, B, C, and D in ascending order) were identified and interpreted as a sequence in a cycle of marine transgression and regression. Dated coastal horizons were chosen to indicate former sea levels. A Holocene relative sea level curve was generated on the basis of the geological data, and a rapid rise from 8000cal. yr B.P. to 7000cal. yr B.P. and a succeeding minor sea level fall represent the basic eustatic trend around the Sea of Japan because hydroisostatic and tectonic effects are moderate in the study area. Abundant dolphin bones lay just above the top of the marine sequence (boundary between Units C and D), located in the seashore environment. Cultural artifacts are found in a subaerial deposit (Unit D) near the dolphin bone level that is assigned to a period of high, stable sea level after the post‐glacial eustatic highstand. Dolphin bones are associated with stone artifacts (arrowheads, knives, and scrapers) and ritual wood columns, indicating the presence of a longstanding fishery during the early Holocene on the Sea of Japan coast. © 2011 Wiley Periodicals, Inc.