200 research outputs found

    The first determination of the actinide Th abundance for a red giant of the Ursa Minor dwarf galaxy

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    The Thorium abundance for the red giant COS82 in the Ursa Minor dwarf spheroidal galaxy is determined based on a high resolution spectrum. This is the first detection of actinides in an extra Galactic object. A detailed abundance pattern is determined for 12 other neutron-capture elements from the atomic number 39 to 68. These elements are significantly over-abundant with respect to other metals like Fe (> 1 dex) and their abundance pattern agrees well with those of the r-process-enhanced, very metal-poor stars known in the Galactic halo, while the metallicity of this object ([Fe/H] ~ -1.5) is much higher than these field stars ([Fe/H] ~ -3.0). The results indicate that the mechanism and the astrophysical site that are responsible for neutron-capture elements in COS82 is similar to that for field r-process-enhanced stars, while the condition of low mass star formation is quite different. An estimate of the age of this object based on the Th abundance ratio is discussed.Comment: 5 pages, 2 figures, 1 table, to appear in PAS

    Chemical compositions of six metal-poor stars in the ultra-faint dwarf spheroidal galaxy Bo\"otes I

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    Ultra-faint dwarf galaxies recently discovered around the Milky Way (MW) contain extremely metal-poor stars, and might represent the building blocks of low-metallicity components of the MW. Among them, the Bo\"otes I dwarf spheroidal galaxy is of particular interest because of its exclusively old stellar population. We determine chemical compositions of six red giant stars in Bo\"otes I, based on the high-resolution spectra obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of 12 elements, including C, Na, alpha, Fe-peak, and neutron capture elements, were determined for the sample stars. The abundance results were compared to those in field MW halo stars previously obtained using an abundance analysis technique similar to the present study. We confirm the low metallicity of Boo-094 ([Fe/H]=-3.4). Except for this star, the abundance ratios ([X/Fe]) of elements lighter than zinc are generally homogeneous with small scatter around the mean values in the metallicities spanned by the other five stars (-2.7-2.7 show no significant enhancement of carbon. The [Mg/Fe] and [Ca/Fe] ratios are almost constant with a modest decreasing trend with increasing [Fe/H] and are slightly lower than the field halo stars. The [Sr/Fe] and [Sr/Ba] ratios also tend to be lower in the Bo\"otes I stars than in the halo stars. Our results of small scatter in the [X/Fe] ratios for elements lighter than zinc suggest that these abundances were homogeneous among the ejecta of prior generation(s) of stars in this galaxy.Comment: 16 pages, 12 figures. Accepted to A&A, language correcte

    Buoyancy-driven circulation as horizontal convection on β-plane

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    The nature of the steady buoyancy-driven circulation is investigated using multi-level numerical models. An ocean which extends over the northern and southern hemispheres is forced by cooling in a confined region and heating in the rest of the ocean through the sea surface. As is already known, the circulation and associated thermal structure strongly depend upon the effect of the vertical diffusivity. This nature of the buoyancy-driven circulation is found in the thermodynamic balance. The vertical diffusion plays an essential role in the whole ocean domain. In counterbalancing the vertical diffusion, the horizontal advection at the deepest levels and the vertical advection in the rest of the interior region plays a dominant role. Thus, horizontal transport of cold water from the convective (cooling) to the diffusive (heating) region occurs mainly in the lowest part of the deep water. It is a natural consequence of predominance of the vertical diffusion that the buoyancy-driven circulation has a significant vertical shear well below the thermocline; the Stommel and Arons pattern for the deep circulation tends to be confined in the lower part of the deep water. Details of a set of alternating zonal jets along the equator and associated meridional circulation are obtained and discussed, and dependence on diffusivity and viscosity is also discussed

    Accessing surface Brillouin zone and band structure of picene single crystals

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    We have experimentally revealed the band structure and the surface Brillouin zone of insulating picene single crystals (SCs), the mother organic system for a recently discovered aromatic superconductor, with ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction with laser for photoconduction. A hole effective mass of 2.24 m_0 and the hole mobility mu_h >= 9.0 cm^2/Vs (298 K) were deduced in Gamma-Y direction. We have further shown that some picene SCs did not show charging during UPS even without the laser, which indicates that pristine UPS works for high-quality organic SCs.Comment: 5 pages, 4 figures, Phys. Rev. Lett. 108, 226401 (2012

    1006-44 A Prognostic Factor in Coronary Artery Disease (CAD): Platelet-Dependent Thrombin Generation in Patients with CAD

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    We examined platelet-dependent thrombin generation in patients with coronary artery disease (CAD). Thrombin generation was measured according to the method of Aronson et al (Circulation, 1992). 0.5ml of platelet rich plasma (PRP, 15×104/ml) was prepared, and 40mM of CaCl, was added to start clotting. 0.5mM of S-2238 was added to each sample in a microtiter plate every 10min, and the plate was read kinetically at a wavelength of 405nm on a microtiter plate reader. The patients with CAD devided into 3 groups.Thrombin generation 20 min after CaCI2, additon is:Control (n=12)48±10(mOD)Stable angina (SAP) (n=15)79±27Unstable angina (UAP) (n=15)**562±155Acute myocardial infarct (AMI) (n=43)**440±269**p<0.01 compared to SAPThe patients with UAP and AMI showed marked increase in thrombin generation compared to SAP and control subjects. AMI patients with severe coronary artery disease (Group B) showed higher levels of thrombin generation (Group A, Gensini score<32: 382±248 mOD vs Group B, Gensini score> 31: 578±238, P<0.05). LVEF of group A is significantly higher than that of group B (P < 0.05). These findings indicate that patients with UAP and AMI have an evidence of hypercoagulable states and that platelet-dependent thrombin generation may play an important role in pathophysiology of UAP or AMI, and may be a prognostic factor in CAD

    Prediction of Electric Field Strength at 10m Distance Using Emission Source Finding Method

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    The equipment under test (EUT) was modeled by current sources. The current positions were estimated using the finding method of radiated emission source by electric field strength data alone. The current vectors were determined by the conditions, where Norm (deviation between the calculated electric field and the measured one) was minimized. Using estimated current sources model, the electric filed strength at 10m distance was predicted. The predicted results were compared with the measured data for an imitated equipment and a personal computer. The results indicate that the radiation patterns were similar to the measured ones, and the maximum electric field strength at10m distance was comparable to the measured value and the calculated value on the assumption where electric field decreases in proportion to distance.2004 International Symposium on Electromagnetic Compatibility (EMC\u2704/Sendai), June 1-4, 2004, Sendai International Center, Sendai, Japa

    Chemical Abundances in the Secondary Star of the Black Hole Binary V4641 Sagittarii (SAX J1819.3-2525)

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    We report on detailed spectroscopic studies performed for the secondary star in the black hole binary (micro-quasar) V4641 Sgr in order to examine its surface chemical composition and to see if its surface shows any signature of pollution by ejecta from a supernova explosion. High-resolution spectra of V4641 Sgr observed in the quiescent state in the blue-visual region are compared with those of the two bright well-studied B9 stars (14 Cyg and ν\nu Cap) observed with the same instrument. The effective temperature of V4641 Sgr (10500 ±\pm 200 K) is estimated from the strengths of He~{\sc i} lines, while its rotational velocity, v\it v sin i\it i (95 ±\pm 10 km s1{}^{-1}), is estimated from the profile of the Mg~{\sc ii} line at 4481 \AA. We obtain abundances of 10 elements and find definite over-abundances of N (by 0.8 dex or more) and Na (by 0.8 dex) in V4641 Sgr. From line-by-line comparisons of eight other elements (C, O, Mg, Al, Si, Ti, Cr, and Fe) between V4641 Sgr and the two reference stars, we conclude that there is no apparent difference in the abundances of these elements between V4641 Sgr and the two normal late B-type stars, which have been reported to have solar abundances. An evolutionary model of a massive close binary system has been constructed to explain the abundances observed in V4641 Sgr. The model suggests that the progenitor of the black hole forming supernova was as massive as ~ 35 Msun on the main-sequence and, after becoming a ~ 10 Msun He star, underwent "dark" explosion which ejected only N and Na-rich outer layer of the He star without radioactive 56^{56}Ni.Comment: 13 pages, 14 figures. Accepted for publication in the PASJ: Publications of the Astronomical Society of Japa
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