Real-time difference imaging analysis of MOA Galactic bulge observations during 2000     

I.A. Bond  F. Abe  R.J. Dodd  J.B. Hearnshaw  M. Honda  J. Jugaku  P.M. Kilmartin  A. Marles  K. Masuda  Y. Matsubara  Y. Muraki  T. Nakamura  G. Nankivell  S. Noda  C. Noguchi  K. Ohnishi  N.J. Rattenbury  M. Reid  To. Saito  H. Sato  M. Sekiguchi  J. Skuljan  D.J. Sullivan  T. Sumi  M. Takeuti  Y. Watase  S. Wilkinson  R. Yamada  T. Yanagisawa  P.C.M. Yock 《Monthly notices of the Royal Astronomical Society》2001,327(3):868-880

We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg² were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.  相似文献   

Noble gases in ureilites released by crushing     

Ryuji Okazaki  Tomoki Nakamura  Nobuo Takaoka  Keisuke Nagao 《Meteoritics & planetary science》2003,38(5):767-781

Abstract— Noble gases in two ureilites, Kenna and Allan Hills (ALH) 78019, were measured with two extraction methods: mechanical crushing in a vacuum and heating. Large amounts of noble gases were released by crushing, up to 26.5% of ¹³²Xe from ALH 78019 relative to the bulk concentration. Isotopic ratios of the crush‐released Ne of ALH 78019 resemble those of the trapped Ne components determined for some ureilites or terrestrial atmosphere, while the crush‐released He and Ne from Kenna are mostly cosmogenic. The crush‐released Xe of ALH 78019 and Kenna is similar in isotopic composition to Q gas, which indicates that the crush‐released noble gases are indigenous and not caused by contamination from terrestrial atmosphere. In contrast to the similarities in isotopic composition with the bulk samples, light elements in the crush‐released noble gases are depleted relative to Xe and distinct from those of each bulk sample. This depletion is prominent especially in the ²⁰Ne/¹³²Xe ratio of ALH 78019 and the ³⁶Ar/¹³²Xe ratio of Kenna. The values of measured ³He/²¹Ne for the gases released by crushing are significantly higher than those for heating‐released gases. This suggests that host phases of the crush‐released gases might be carbonaceous because cosmogenic Ne is produced mainly from elements with a mass number larger than Ne. Based on our optical microscopic observation, tabular‐foliated graphite is the major carbon mineral in ALH 78019, while Kenna contains abundant polycrystalline graphite aggregates and diamonds along with minor foliated graphite. There are many inclusions at the edge and within the interior of olivine grains that are reduced by carbonaceous material. Gaps can be seen at the boundary between carbonaceous material and silicates. Considering these petrologic and noble gas features, we infer that possible host phases of crush‐released noble gases are graphite, inclusions in reduction rims, and gaps between carbonaceous materials and silicates. The elemental ratios of noble gases released by crushing can be explained by fractionation, assuming that the starting noble gas composition is the same as that of amorphous carbon in ALH 78019. The crush‐released noble gases are the minor part of trapped noble gases in ureilites but could be an important clue to the thermal history of the ureilite parent body. Further investigation is needed to identify the host phases of the crush‐released noble gases.  相似文献   

Case a evolution of massive close binary systems     

Masaomi Nakamura  Yasuhisa Nakamura 《Astrophysics and Space Science》1987,134(2):219-234

The evolution of three close binary systems of total mass 20.4M in and after the phase of mode Br mass-transfer in caseA of mass exchange is investigated. In every case a secondary component evolves to interfere with the progress of primary's evolution and the system overflows the outer critical surface before the primary completes its nuclear-burning evolution. This strongly indicates the importance of simultaneous calculation of both components. A summary of evolution of the systems considered in this series of papers up to the stage ofL ₂-overflow is given. The observational aspects of the numerical models are also discussed.  相似文献   

A new photographic method for mapping lunar eclipse shadow     

Nakamura  Tsuko  Hirayama  Tomohiro  Noguchi  Motokazu 《Earth, Moon, and Planets》1986,35(1):55-71

A new photographic method suitable for digital processing of a two-dimensional density distribution of lunar eclipse shadow has been developed and it has been applied to the observation of the eclipse of December 30, 1982. The principle of this method is to extract the terrestrial shadow by utilizing immediate post- or pre-eclipse full Moon image as a reference template. The uncertainties of the obtained shadow maps in density and position are mostly 0.03–0.05 and 10–15 respectively. Iso-density contours of the penumbra have revealed unknown systematic deviations from a geometrical (concentric) shadow model in terms of their directions of center and radii of curvature. A density map of the umbra has shown very irregular shapes of isophotoes and density variation in the outer umbra has been proved to be consistent with the optical depth measurement of the stratosphere performed in the same period of time with lidars and aircrafts. Geographic consideration of the shadow terminator on the Earth suggests that the remnant aerosols above the northern Pacific and northern Europe flown up by a Mexican volcano 8 months ago prior to this eclipse will be mainly responsible for the formation of such variation of density in the outer penumbra.On leave from Tokyo Astronomical Observatory as Visiting Scientist (from 28 Aug. 1984 to 27 Aug. 1985).  相似文献   

He–Ar and Nd–Sr isotopic compositions of late Pleistocene felsic plutonic back arc basin rocks from Ulleungdo volcanic island, South Korea: Implications for the genesis of young plutonic rocks in a back arc basin     

Kyu Han Kim  Keisuke Nagao  Hirochika Sumino  Tsuyoshi Tanaka  Takamasa Hayashi  Toshio Nakamura  Jong Ik Lee 《Chemical Geology》2008,253(3-4):180-195

We report analyses of noble gases and Nd–Sr isotopes in mineral separates and whole rocks of late Pleistocene (< 0.2 Ma) monzonites from Ulleungdo, South Korea, a volcanic island within the back arc basin of the Japan island arc. A Rb–Sr mineral isochron age for the monzonites is 0.12 ± 0.01 Ma. K–Ar biotite ages from the same samples gave relatively concordant ages of 0.19 ± 0.01and 0.22 ± 0.01 Ma. ⁴⁰Ar/³⁹Ar yields a similar age of 0.29 ± 0.09 Ma. Geochemical characteristics of the felsic plutonic rocks, which are silica oversaturated alkali felsic rocks (av., 12.5 wt% in K₂O + Na₂O), are similar to those of 30 alkali volcanics from Ulleungdo in terms of concentrations of major, trace and REE elements. The initial Nd–Sr isotopic ratios of the monzonites (⁸⁷Sr/⁸⁶Sr = 0.70454–0.71264, ¹⁴³Nd/¹⁴⁴Nd = 0.512528–0.512577) are comparable with those of the alkali volcanics (⁸⁷Sr/⁸⁶Sr = 0.70466–0.70892, ¹⁴³Nd/¹⁴⁴Nd = 0.512521–0.512615) erupted in Stage 3 of Ulleungdo volcanism (0.24–0.47 Ma). The high initial ⁸⁷Sr/⁸⁶Sr values of the monzonites imply that seawater and crustally contaminated pre-existing trachytes may have been melted or assimilated during differentiation of the alkali basaltic magma.A mantle helium component (³He/⁴He ratio of up to 6.5 RA) associated with excess argon was found in the monzonites. Feldspar and biotite have preferentially lost helium during slow cooling at depth and/or during their transportation to the surface in a hot host magma. The source magma noble gas isotopic features are well preserved in fluid inclusions in hornblende, and indicate that the magma may be directly derived from subcontinental lithospheric mantle metasomatized by an ancient subduction process, or may have formed as a mixture of MORB-like mantle and crustal components. The radiometric ages, geochemical and Nd–Sr isotopic signatures of the Ulleungdo monzonites as well as the presence of mantle-derived helium and argon, suggests that these felsic plutonic rocks evolved from alkali basaltic magma that formed by partial melting of subcontinental lithospheric mantle beneath the back arc basin located along the active continental margin of the southeastern part of the Eurasian plate.  相似文献   

Effect of emersion and immersion on the porewater nutrient dynamics of an intertidal sandflat in Tokyo Bay   总被引：2，自引：0，他引：2  

Tomohiro Kuwae  Eiji Kibe  Yoshiyuki Nakamura 《Estuarine, Coastal and Shelf Science》2003,57(5-6):929-940

Porewater nutrient dynamics during emersion and immersion were investigated during different seasons in a eutrophic intertidal sandflat of Tokyo Bay, Japan, to elucidate the role of emersion and immersion in solute transport and microbial processes. The water content in the surface sediment did not change significantly following emersion, suggesting that advective solute transport caused by water table fluctuation was negligible. The rate of change in nitrate concentration in the top 10 mm of sediments ranged from −6.6 to 4.8 μmol N l⁻¹ bulk sed. h⁻¹ during the whole period of emersion. Steep nutrient concentration gradients in the surface sediment generated diffusive flux of nutrients directed downwards into deeper sediments, which greatly contributed to the observed rates of change in porewater nutrient concentration for several cases. Microbial nitrate reduction within the subsurface sediment appeared to be strongly supported by the downward diffusive flux of nitrate from the surface sediment. The stimulation of estimated nitrate production rate in the subsurface layer in proportion to the emersion time indicates that oxygenation due to emersion caused changes in the sediment redox environment and affected the nitrification and/or nitrate reduction rates. The nitrate and soluble reactive phosphorus pools in the top 10 mm of sediment decreased markedly during immersion (up to 68% for nitrate and up to 44% for soluble reactive phosphorus), however, this result could not be solely explained by molecular diffusion.  相似文献   

A preliminary study of carbon system in the East China Sea   总被引：1，自引：0，他引：1  

Shizuo Tsunogai  Shuichi Watanabe  Junya Nakamura  Tsuneo Ono  Tetsuro Sato 《Journal of Oceanography》1997,53(1):9-17

In the central part of the East China Sea, the activity of CO₂ in the surface water and total carbonate, pH and alkalinity in the water column were determined in winter and autumn of 1993. The activity of CO₂ in the continental shelf water was about 50 ppm lower than that of surface air. This decrease corresponds to the absorption of about 40 gC/m²/yr of atmospheric CO₂ in the coastal zone or 1 GtC/yr in the global continental shelf, if this rate is applicable to entire coastal seas. The normalized total carbonate contents were higher in the water near the coast and near the bottom. This increase toward the bottom may be due to the organic matter deposited on the bottom. This conclusion is supported by the distribution of pH. The normalized alkalinity distribution also showed higher values in the near-coast water, but in the surface water, indicating the supply of bicarbonate from river water. The residence time of the East China Sea water, including the Yellow Sea water, has been calculated to be about 0.8 yr from the excess alkalinity and the alkalinity input. Using this residence time and the excess carbonate, we can estimate that the amount of dissolved carbonate transported from the coastal zone to the oceanic basin is about 70 gC/m²/yr or 2 GtC/yr/area-of-global-continental-shelf. This also means that the rivers transport carbon to the oceans at a rate of 30 gC/m²/yr of the coastal sea or 0.8 GtC/yr/ area-of-global shelf, the carbon consisting of dissolved inorganic carbonate and terrestrial organic carbon decomposed on the continental shelf.  相似文献   

A field study of physico-chemical states of artificial radionuclides in seawater     

Yutaka Nagaya  Kiyoshi Nakamura 《Journal of Oceanography》1974,30(4):179-184

The physico-chemical states of artificial radionuclides,⁹⁰Sr,¹³⁷Cs and¹⁴⁴Ce in seawater were investigated by radiochemical analysis of filtered and unfiltered seawater. The difference of radionuclide concentrations between unfiltered and filtered seawaters was defined as the particulate form radioisotope and its particle ratio was discussed.Practically no particulate⁹⁰Sr, greater than 0.22 in size, was observed in both coastal and open seawaters, but some of¹³⁷Cs seemed to be insoluble in some circumstances, especially in coastal waters. A considerable amount of¹⁴⁴Ce was found to be particulate.An estimation of the radionuclides in particulate form was made for Kashima-nada seawaters collected in 1970 to 1972, and it was shown that the possible occurrence of particulate radionuclides, greater than 0.22 in size, were 1% or less for⁹⁰Sr and 6% for¹³⁷Cs. In the coastal water, 80 % of¹⁴⁴Ce were seemed to be in particulate form, but in the open seawater only a few%. The influences of suspended materials to¹³⁷Cs and¹⁴⁴Ce concentration levels in seawater were not negligible and further investigations are desirable.  相似文献   

A Note on Tsunami Bore Front     

Shigehisa Nakamura 《Marine Geodesy》2005,28(4):305-312

A note is presented on tsunami bore front. This tsunami bore front is an old dynamical problem but also a new problem to be understood. The tsunami event on 2004 December 26 has raised this is an urgent problem. The author introduces here a model in order to see a hydrodynamical specific property of the tsunami bore front. This modeling gives us a new understanding about what mechanics is for the interested tsunami bore front, especially, around a coastal zone. This work adds a new understanding about mechanics of water motions as the tsunamis generated by the earthquake undersea at a distant area from the coast. The model in this work points out a specific transitional pattern as a function of time and space of tsunami bore front. This modeling gives what is essential at considering tsunami bore front.  相似文献   

State Estimation of the North Pacific Ocean by a Four-Dimensional Variational Data Assimilation Experiment   总被引：1，自引：0，他引：1  

Toshiyuki Awaji  Shuhei Masuda  Yoichi Ishikawa  Nozomi Sugiura  Takahiro Toyoda  Tomohiro Nakamura 《Journal of Oceanography》2003,59(6):931-943

A four-dimensional variational data assimilation system has been applied to an experiment to describe the dynamic state of the North Pacific Ocean. A synthesis of available observational records and a sophisticated ocean general circulation model produces a dynamically consistent dataset, which, in contrast to the nudging approach, provides realistic features of the seasonally-varying ocean circulation with no artificial sources/sinks for temperature and salinity fields. This new dataset enables us to estimate heat and water mass transports in addition to the qualification of water mass formation and movement processes. A sensitivity experiment on our assimilation system reveals that the origin of the North Pacific Intermediate Water can be traced back to the Sea of Okhotsk and the Bering Sea in the subarctic region and to the subtropical Kuroshio region further south. These results demonstrate that our data assimilation system is a very powerful tool for the identification and characterization of ocean variabilities and for our understanding of the dynamic state of ocean circulation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献