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1
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
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  ScienceON
  
  코리아스칼라
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.
2
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
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  ScienceON
  
  코리아스칼라
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.