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

Yoichi Itoh  Yumiko Oasa  Hitoshi Funayama  Masahiko Hayashi  Misato Fukagawa  Toshio Hashiguchi  Thayne Currie 《中国天文和天体物理学报》2011,11(3)

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...  相似文献   

A possible substellar companion to the intermediate-mass giant HD 175679     

Liang Wang  Bun＇ei Sato  Gang Zhao  Yu-Juan Liu  Kunio Noguchi  Hirovasu Ando  Hideyuki Izumiura  Eiji Kambe  Masashi Omiya  Hiroki Harakawa  Fan Liu  Xiao-Shu Wu  Yoichi Takeda  Michitoshi Yoshida  Eiichiro Kokubo 《天体物理学报》2012,(1):84-92

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Abundances of 23 field RR Lyrae stars     

Shu Liu  Gang Zhao  Yu-Qin Chen  Yoichi Takeda  Satoshi Honda 《天文和天体物理学研究(英文版)》2013,(11):1307-1329

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.  相似文献   

Climate teleconnections influence on West Africa's terrestrial water storage          下载免费PDF全文

Christopher E. Ndehedehe  Joseph L. Awange  Michael Kuhn  Nathan O. Agutu  Yoichi Fukuda 《水文研究》2017,31(18):3206-3224

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.  相似文献   

Thermal Energy Balance Analysis of the Tokyo Metropolitan Area Using a Mesoscale Meteorological Model Incorporating an Urban Canopy Model     

Ryozo Ooka  Taiki Sato  Kazuya Harayama  Shuzo Murakami  Yoichi Kawamoto 《Boundary-Layer Meteorology》2011,138(1):77-97

The summer climate around the Tokyo metropolitan area has been analysed on an urban scale, and the regional characteristics of the thermal energy balance of a bayside business district in the centre of Tokyo (Otemachi) have been compared with an inland residential district (Nerima), using a mesoscale meteorological model incorporating an urban canopy model. From the results of the analysis, the mechanism of diurnal change in air temperature and absolute humidity in these areas is quantitatively demonstrated, with a focus on the thermal energy balance. Moreover, effective countermeasures against urban heat-islands are considered from the viewpoint of each region’s thermal energy balance characteristics. In addition to thermal energy outflux by turbulent diffusion, advection by sea-breezes from Tokyo Bay discharges sensible heat in Otemachi. This mitigates temperature increases during the day. On the other hand, because all sea-breezes must first cross the centre of Tokyo, it has less of a cooling effect in Nerima. As a result, the air temperature during the day in Nerima is higher than that in Otemachi.  相似文献   

Dating of the Dome Fuji shallow ice core based on a record of volcanic eruptions from AD 1260 to AD 2001     

Makoto Igarashi  Yoichi Nakai  Yuko Motizuki  Kazuya Takahashi  Hideaki Motoyama  Kazuo Makishima 《Polar Science》2011,5(4):411-420

We measured the concentration of non-sea-salt sulfate () in the Dome Fuji shallow ice core (Antarctica) from the surface to 40 m depth with the aim of dating the core with reference to the record of volcanic eruptions. Three huge spikes related to large-scale volcanic eruptions were detected at depths of 12.5, 29.9, and 38.8 m, correlated to the eruptions of Tambora (AD 1815), Kuwae (AD 1452) and an unknown event (AD 1259), respectively. We identified another nine spikes related to accurately dated eruption events. The shallow ice core was dated from AD 1260 to AD 2001 based on these 12 eruption events and the assumption of constant annual snow accumulation in the periods between eruption events. The results yield a maximum correction of ∼20 years compared with the dating proposed in a previous study. The annual accumulation varied within ±∼15% of the average water equivalent value over the study period (25.5 mm).  相似文献   

Non－LTE Analysis of the Sodium Abundance of Metal－Poor Stars in the Galactic Disk and Halo     

Yoichi Takeda  Gang Zhao  Masahide Takada-Hidai  Yu-Qin Chen  Yu-ji Saito  Hua-Wei Zhang 《中国天文和天体物理学报》2003,3(4):316-340

We performed an extensive non-LTE analysis of the neutral sodiumlines of Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halo starsof types F-K covering a wide metallicity range (-4 [Fe/H] +0.4), using ourown data as well as data collected from the literature. For comparatively metal-rich disk stars (-1 [Fe/H] +0.4) where the weaker 6154/6161 lines are thebest abundance indicators, we confirmed [Na/Fe] ～ 0 with an "upturn" (i.e., ashallow/broad dip around -0.5 [Fe/H] 0) as already reported in previousstudies. For the metal-deficient halo stars, where the much stronger 5890/5896 or8183/8195 lines subject to considerable (negative) non-LTE corrections amountingto 0.5 dex have to be used, our analysis suggests mildly "subsolar" [Na/Fe] valuesdown to ～ -0.4 (with a somewhat large scatter of ～±0.2 dex) on the average at thetypical halo metallicity of [Fe/H] ～ -2, followed by a rise again to a near-solar ratioof [Na/Fe] ～ 0 at the very metal-poor regime [Fe/H] ～ -3 to -4. These resultsare discussed in comparison with the previous observational studies along with thetheoretical predictions from the available chemical evolution models.  相似文献   

Phase transition of zircon at high P-T conditions     

Shigeaki?OnoEmail author  Kenichi?Funakoshi  Yoichi?Nakajima  Yoshinori?Tange  Tomoo?Katsura 《Contributions to Mineralogy and Petrology》2004,147(4):505-509

Abstract In situ observations of the zircon-reidite transition in ZrSiO₄ were carried out using a multianvil high-pressure apparatus and synchrotron radiation. The phase boundary between zircon and reidite was determined to be P (GPa) = 8.5+0.0017×(T-1200) (K) for temperatures between 1100–1900 K. When subducted slabs, including igneous rocks and sediments, descend into the upper mantle, the zircon in the subducted slab transforms into reidite at pressures of about 9 GPa, corresponding to a depth of 270 km. Reidite found in an upper Eocene impact ejecta layer in marine sediments is thought to have been transformed from zircon by a shock event. The peak pressure generated by the shock event in this occurrence is estimated to be higher than 8 GPa.Editorial responsibility: J. Hoefs  相似文献   

Reply to the comments by K. R. Koch and J. Kusche on Xu et al. (2006) Variance component estimation in linear inverse ill-posed models,J Geod 80:69–81     

Peiliang Xu  Yunzhong Shen  Yoichi Fukuda  Yumei Liu 《Journal of Geodesy》2007,81(9):633-635

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Calibration of the superconducting gravimeter T011 by parallel observation with the absolute gravimeter FG5 #210—a Bayesian approach     

Yuichi Imanishi  Toshihiro Higashi  Yoichi Fukuda 《Geophysical Journal International》2002,151(3):867-878

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