• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.69.2-69.2
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• 2010

We investigate the southeastern region of the Vela supernova remnant (SNR) in the multi-wavelength domains. This region is quite interesting because it includes the bullet feature D/D´ and another SNR (the Vela Jr.). The C IV $\lambda\lambda1548$, 1551 emission-line morphologies obtained from the FIMS/SPEAR data show that there are several local peaks of C IV on the bullet D/D´ and the Vela Jr. SNR. This may provide clues to direct interaction between both SNRs. Also, we found that the southeastern side of the Vela is in direct contact with an H-alpha ring feature whose central source seems to be a B-type star, HD 76161. The C IV emission peaks along this contact boundary. We investigate this interacting region in detail.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.47.1-47.1
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• 2015

We present an optical spectroscopic study of 28 supernova remnant (SNR) candidates in M81 and two SNR candidates in M82. The optical spectra of these SNR candidates were obtained using the MMT/Hectospec as a part of the K-GMT Science Program. Based on the [S II]/$H{\alpha}$ ratio and the radial velocity, we find that twenty six out of the M81 candidates are genuine SNRs. Two SNR candidates in M82 are thought to be shocked condensations in the galactic outflow or SNRs. In the spectral line ratio diagrams, M81 SNRs are divided into two groups: an [O III]-strong group and an [O III]-weak group. The [O III]-weak SNRs have larger sizes, and may have faster shock velocity. We estimate the nitrogen and oxygen abundance of the SNRs from the comparison with shock-ionization models. We find a radial gradient in nitrogen abundance, $dLog(N/H)/dlogR=-0.023{\pm}0.009\;dex\;kpc^{-1}$ little evidence for the gradient in oxygen abundance. The nitrogen abundance shows shallower gradient than those of the planetary nebulae and H II regions of M81. We find five X-ray emitting SNRs. Their X-ray hardness colors are consistent with thermal SNRs.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.35.1-35.1
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• 2015

We present the results of extinction measurements toward the main ejecta shell of the Cassiopeia A supernova (SN) remnant using the flux ratios between the two near-infrared (NIR) [Fe II] lines at 1.26 and $1.64{\mu}m$. We find a clear correlation between the NIR extinction (E(J-H)) and the radial velocity of ejecta knots, showing that redshifted knots are systematically more obscured than blueshifted ones. This internal "self-extinction" strongly indicates that a large amount of SN dust resides inside and around the main ejecta shell. At one location in the southern part of the shell, we measure E(J-H) by the SN dust of $0.23{\pm}0.05mag$. By analyzing the spectral energy distribution of thermal dust emission at that location, we show that there are warm (~100K) and cool (~40K) SN dust components and that the latter is responsible for the observed E(J-H). We investigate the possible grain species and size of each component and find that the warm SN dust needs to be silicate grains such as $MgSiO_3$, $Mg_2SiO_4$, and $SiO_2$, whereas the cool dust could be either small (${\leq}0.01{\mu}m$) Fe or large (${\geq}0.01{\mu}m$) Si grains. We suggest that the warm and cool dust components in Cassiopeia A represent grain species produced in diffuse SN ejecta and in dense ejecta clumps, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.94.1-94.1
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• 2014

We have carried out IGRINS test observations during its May commissioning run. Our targets were composed of three Luminous Blue Variables (LBVs), one supernova remnant (SNR), and an unidentified stellar source emitting [Fe II] 1.644 um line. In the preliminary results, three LBVs MWC 314, P Cygni, and AFGL 2298 show different characteristics: the spectrum of MWC 314 which is known to be in a binary system clearly shows double-peak structures in hydrogen and iron lines, the P Cygni spectrum reveals the Brackett series of hydrogen emission lines with prominent P-Cygni profiles, and AFGL 2298 likely at its visual minimum phase shows rather different spectrum with relatively weak hydrogen lines. The SNR (G11.2-0.3) was to test the sensitivity of IGRINS for diffuse emission. We successfully detected a dozen H2 emission lines with a velocity width of ~13 km/s, which might indicate a C-shock origin. The unidentified stellar source was one of stellar/compact sources of unknown nature detected in the survey of the Galactic plane in [Fe II] 1.644 um emission line (http://gems0.kasi.re.kr/uwife/). Its spectrum is under investigation. We will present the spectra of test observations and will discuss their scientific significance.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.69.1-69.1
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• 2017

According to structure formation simulations, weak shocks with typical Mach number, M<3, are expected to form in merging galaxy clusters. The presence of such shocks has been indicated by X-ray and radio observations of many merging clusters. In particular, diffuse radio sources known as radio relics could be explained by synchrotron-emitting electrons accelerated via diffusive shock acceleration (Fermi I) at quasi-perpendicular shocks. Here we also consider possible roles of stochastic acceleration (Fermi II) by compressive MHD turbulence downstream of the shock. Then we explore a puzzling discrepancy that for some radio relics, the shock Mach number inferred from the radio spectral index is substantially larger than that estimated from X-ray observations. This problem could be understood, if shock surfaces associated with radio relics consist of multiple shocks with different strengths. In that case, X-ray observations tend to pick up the part of shocks with lower Mach numbers and higher kinetic energy flux, while radio emissions come preferentially from the part of shocks with higher Mach numbers and higher cosmic ray (CR) production. We also show that the Fermi I reacceleration model with preexisting fossil electrons supplemented by Fermi II acceleration due to postshock turbulence could reproduce observed profiles of radio flux densities and integrated radio spectra of two giant radio relics. This study demonstrates the CR electrons can be accelerated at collisionless shocks in galaxy clusters just like supernova remnant shock in the interstellar medium and interplanetary shocks in the solar wind.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.69.1-69.1
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• 2010

IC 443 is famous for its interaction with nearby molecular clouds and intense H2 emission lines in infrared. Therefore, it has been studied extensively for the understanding of molecular shocks. We observed H2 mission lines toward the shock-cloud interaction regions of IC 443, known as clumps B, C, and G. The observations were performed with the InfraRed Camera (IRC) onboard a satellite AKARI over 2.5-5.0 um, where previous space observations, e.g. Infrared Space Observatory (ISO) and Spitzer, do not cover. Our AKARI observations provide spectra of sequential pure-rotational and ro-vibrational H2 emission lines. For the clumps C and G, combining with previous mid-infrared observational results, we found that the H2 level populations show a significant separation between v=0 and v=1 levels; v=1 levels are under-populated than v=0 levels, therefore, the population cannot be described by two temperature LTE model, as many people have analyzed for the shocked H2 gas. We also applied the thermal admixture model, dN(H2; T)~T^(-b) dT, with varying ortho-to-para ratios according to the temperature, to describe the level population, and obtained plausible ranges of the H2 gas density and power-law index b.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.225-232
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• 2004

Shocks are ubiquitous in astrophysical environments and cosmic-rays (CRs) are known to be accelerated at collisionless shocks via diffusive shock acceleration. It is believed that the CR pressure is important in the evolution of the interstellar medium of our galaxy and most of galactic CRs with energies up to ${\~}\;10^{15}$ eV are accelerated by supernova remnant shocks. In this contribution we have studied the CR acceleration at shocks through numerical simulation of 1D, quasi-parallel shocks for a wide range of shock Mach numbers and shock speeds. We show that CR modified shocks evolve to time-asymptotic states by the time injected particles are accelerated to moderately relativistic energies, and that two shocks with the same Mach number, but with different shock speeds, evolve qualitatively similarly when the results are presented in terms of a characteristic diffusion length and diffusion time. We find that $10^{-4} - 10^{-3}$ of the particles passed through the shock are accelerated to form the CR population, and the injection rate is higher for shocks with higher Mach number. The time asymptotic value for the CR acceleration efficiency is controlled mainly by shock Mach number, and high Mach number shocks all evolve towards efficiencies ${\~}50\%$, regardless of the injection rate and upstream CR pressure. We conclude that the injection rates in strong quasi-parallel shocks are sufficient to lead to significant nonlinear modifications to the shock structures, implying the importance of the CR acceleration at astrophysical shocks.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.37.1-37.1
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• 2020

Cosmic-ray protons (CRp) are efficiently produced at starburst galaxies (SBGs), where the star formation rate (SFR) rate is high. In this talk, we present estimates of gamma-ray and neutrino emissions from nearby SBGs, M82, NGC253, and Arp220. Inside the starburst nucleus (SBN), CRp are accelerated at supernova remnant (SNR) shocks as well as at stellar wind (SW) termination shocks, and their transport is governed by the advection due to starburst-driven wind and diffusion mediated by turbulence. We here model the momentum distributions of SNR and SW-produced CRp with single or a double power-law forms. We also employ two different diffusion models, where CRp are resonantly scattered off large-scale turbulence in SBN or self-excited waves driven by CR streaming instability. We then calculate gamma-ray/neutrino fluxes. The observed gamma-ray fluxes by Fermi-LAT, Veritas, and H.E.S.S are well reproduced with double power-law distribution for SNR-produced CRp and the CRp diffusion by self-excited turbulence. The estimated neutrino fluxes are <~10-3 of the atmospheric neutrino flux in the energy range of Eneutrino <~100 GeV and <~10-1 of the IceCube point source sensitivity in the energy range of Eneutrino >~60 TeV.