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RISS 인기검색어
- 검색키워드
- 저자 : Takeru SUZUKI (검색결과 4 건)
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A SIGNATURE OF CHROMOSPHERIC ACTIVITY IN BROWN DWARFS: A RECENT RESULT FROM NIRLT MISSION PROGRAM
Satoko Sorahana,Takeru K. Suzuki,ISSEI YAMAMURA 한국천문학회 2017 天文學論叢 Vol.32 No.1
We present the latest results from the Mission Program NIRLT (PI: I.Yamamura), the near-infrared spectroscopy of brown dwarfs using the AKARI/IRC grism mode with the spectral resolution of $\sim120$. The near-infrared spectra in the wavelength range between 2.5 and 5.0~$\mu$m are especially important to study the brown dwarf atmospheres because of the presence of major molecular bands, including CH$_4$ at 3.3~$\mu$m, CO$_2$ at 4.2~$\mu$m, CO at 4.6 ~$\mu$m, and H$_2$O around 2.7~$\mu$m. We observed 27 sources, and obtained 16 good spectra. Our model fitting reveals deviations between theoretical model and observed spectra in this wavelength range, which may be attributed to the physical condition of the upper atmosphere. The deviations indicate additional heating, which we hypothesize to be due to chromospheric activity. We test this effect by modifying the brown dwarf atmosphere model to artificially increase the temperature of the upper atmosphere, and compare the revised model with observed spectra of early- to mid-L type objects with H$\alpha$ emission. We find that the chemical structure of the atmosphere changes dramatically, and the heating model spectra of early-type brown dwarfs can be considerably improved to match the observed spectra. Our result suggests that chromospheric activity is essential to understand early-type brown dwarf atmospheres.
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Tatsuya SAKURAI,Takeru SUZUKI,Misato YOSHIOKA 한국대기환경학회 2018 Asian Journal of Atmospheric Environment (AJAE) Vol.12 No.1
This study aims to evaluate the performance of the Air Quality Model (AQM) for the seasonal and spatial distribution of the NH3 concentration in the atmosphere. To obtain observational data for the model validation, observations based on biweekly sampling have been conducted using passive samplers since April 2015 at multiple monitoring sites in the Tokyo metropolitan area. AQM, built based on WRF/CMAQ, was applied to predict the NH3 concentration observed from April 2015 to March 2016. The simulation domain includes the Kanto region, which is the most densely populated area in Japan. Because the area also contains large amount of livestock, especially in its northern part, the density of the NH3 emissions derived from human activities and agriculture there are estimated to be the highest in Japan. In the model validation, the model overestimated the observed NH3 concentration in the summer season and underestimated it in the winter season. In particular, the overestimation in the summer was remarkable at a rural site (Komae) in Tokyo. It was found that the overestimation at Komae was caused by the transportation of NH3 emitted in the northern part of the Kanto region during the night. It is suggested that the emission input used in this study overestimated the NH3 emission from human sources around the Tokyo suburbs and agricultural sources in the northern part of the Kanto region in the summer season. In addition, the current emission inventories might overestimate the difference of the agricultural NH3 emissions among seasons. Because the overestimation of NH3 in the summer causes an overestimation of NO3 - in PM2.5 in the AQM simulation, further investigation is necessary for the seasonal variation in the NH3 emissions.
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COSMIC RAYS AND GAMMA-RAYS IN LARGE-SCALE STRUCTURE
INOUE SUSUMU,NAGASHIMA MASAHIRO,SUZUKI TAKERU K.,AOKI WAKO The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.5
During the hierarchical formation of large scale structure in the universe, the progressive collapse and merging of dark matter should inevitably drive shocks into the gas, with nonthermal particle acceleration as a natural consequence. Two topics in this regard are discussed, emphasizing what important things nonthermal phenomena may tell us about the structure formation (SF) process itself. 1. Inverse Compton gamma-rays from large scale SF shocks and non-gravitational effects, and the implications for probing the warm-hot intergalactic medium. We utilize a semi-analytic approach based on Monte Carlo merger trees that treats both merger and accretion shocks self-consistently. 2. Production of $^6Li$ by cosmic rays from SF shocks in the early Galaxy, and the implications for probing Galaxy formation and uncertain physics on sub-Galactic scales. Our new observations of metal-poor halo stars with the Subaru High Dispersion Spectrograph are highlighted.
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