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    • Several versions

    Environment of the gamma-ray burst grb 971214: a giant h ii region surrounded by a galactic supershell

    Ahn, Sang-Hyeon
    The Astrophysical Journal, 2000, Vol.530(1), pp.L9-L12 [Peer Reviewed Journal]

    • Several versions

    Intrinsic DNA Curvature of Double-Crossover Tiles

    Kim, Seungjae, Kim, Junghoon, Qian, Pengfei, Shin, Jihoon, Amin, Rashid, Ahn, Sang Jung, Labean, Thomas H., Kim, Moon Ki, Park, Sung Ha
    Nanotechnology 22, 245706 (2011) [Peer Reviewed Journal]

    • Several versions

    Polarization of the ly line from an anisotropically expanding h i shell in primeval galaxies

    Lee, Hee-Won, Ahn, Sang-Hyeon
    The Astrophysical Journal, 1998, Vol.504(2), pp.L61-L64 [Peer Reviewed Journal]

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    Singly peaked asymmetric ly from starburst galaxies

    Ahn, Sang-Hyeon
    The Astrophysical Journal, 2004, Vol.601(1), pp.L25-L28 [Peer Reviewed Journal]
    IOPscience (IOP Publishing)
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    Title: Singly peaked asymmetric ly from starburst galaxies
    Author: Ahn, Sang-Hyeon
    Subject: Astronomy & Astrophysics ; Physics;
    Description: We present results of Monte Carlo calculations for the Ly line transfer in an expanding dusty supershell, surrounding Ly sources in a starburst galaxy. The Ly photons escape the system by a number of backscatterings, which results in a series of emission peaks redward of the systemic redshift, in contrary to observed singly peaked asymmetric profiles. We find that in order to form a singly peaked asymmetric Ly emission, dust should be distributed in the ionized bubble, as well as within the supershell of neutral hydrogen. We also find that the overall escape probability of Ly photons is determined by H I column density, Doppler width, and expansion velocity of the supershell, as well. The kinematic information of the expanding supershell is preserved in the profile of Ly emission even when the supershell is dusty. Our results are potentially useful to fit the P Cygni-type Ly line profiles from starburst galaxies, either nearby galaxies or high- z Lyman break galaxies.
    Is part of: The Astrophysical Journal, 2004, Vol.601(1), pp.L25-L28
    Identifier: 0004-637X (ISSN); 1538-4357 (E-ISSN); 10.1086/381750 (DOI)

    • Several versions

    Ly line formation in starbursting galaxies. i. moderately thick, dustless, and static h i media

    Ahn, Sang-Hyeon, Lee, Hee-Won, Lee, Hyung Mok
    The Astrophysical Journal, 2001, Vol.554(1), pp.604-614 [Peer Reviewed Journal]

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    Ly line formation in starbursting galaxies. ii. extremely thick, dustless, and static h i media

    Ahn, Sang-Hyeon, Lee, Hee-Won, Lee, Hyung Mok
    The Astrophysical Journal, 2002, Vol.567(2), pp.922-930 [Peer Reviewed Journal]
    IOPscience (IOP Publishing)
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    Title: Ly line formation in starbursting galaxies. ii. extremely thick, dustless, and static h i media
    Author: Ahn, Sang-Hyeon; Lee, Hee-Won; Lee, Hyung Mok
    Subject: Astronomy & Astrophysics ; Physics;
    Description: The Ly line transfer in an extremely thick medium of neutral hydrogen is investigated by adopting an accelerating scheme in our Monte Carlo code to skip a large number of core or resonant scatterings. This scheme reduces computing time significantly, with no sacrifice in the accuracy of the results. We applied this numerical method to the Ly transfer in a static, uniform, dustless, and plane-parallel medium. Two types of photon sources have been considered; the midplane source and the uniformly distributed sources. The emergent profiles show double peaks and absorption trough at the line center. We compared our results with the analytic solutions derived by previous researchers and confirmed that both solutions are in good agreement with each other. We investigated the directionality of the emergent Ly photons and found that limb brightening is observed in slightly thick media, while limb darkening appears in extremely thick media. The behavior of the directionality is noted to follow that of the Thomson scattered radiation in electron clouds, because both Ly wing scattering and Thomson scattering share the same Rayleigh scattering phase function. The mean number of wing scatterings just before escape is in exact agreement with the prediction of the diffusion approximation. The Ly photons constituting the inner part of the emergent profiles follow the relationship derived from the diffusion approximation. We present a brief discussion on the application of our results to the formation of Ly broad absorption troughs and P Cygni type Ly profiles seen in the UV spectra of starburst galaxies.
    Is part of: The Astrophysical Journal, 2002, Vol.567(2), pp.922-930
    Identifier: 0004-637X (ISSN); 1538-4357 (E-ISSN); 10.1086/338497 (DOI)

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    Raman-scattered he ii 4850, 6545 in the young and compact planetary nebula ic 5117

    Lee, Hee-Won, Jung, Yang-Chan, Song, In-Ok, Ahn, Sang-Hyeon
    The Astrophysical Journal, 2006, Vol.636(2), pp.1045-1053 [Peer Reviewed Journal]
    IOPscience (IOP Publishing)
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    Title: Raman-scattered he ii 4850, 6545 in the young and compact planetary nebula ic 5117
    Author: Lee, Hee-Won; Jung, Yang-Chan; Song, In-Ok; Ahn, Sang-Hyeon
    Description: We report the discovery of He II 4850 and 6545 Raman-scattered by atomic hydrogen in the high-resolution spectrum of the very compact and young planetary nebula IC 5117 obtained with the ESPaDOnS (Echelle Spectropolarimetric Device for the Observation of Stars) installed on the 3.6 m Canada-France-Hawaii Telescope. By adopting case B recombination atomic data and considering all the fine-structure emission components, we calculate the weighted averages for the line centers of the Raman-scattered features, as well as those for the emission lines He II 4859 and 6560 to determine redward velocity shifts of v 4850 = +29 km s -1 and v 6545 = +24 km s -1 . We compute the Raman conversion efficiency by a Monte Carlo technique adopting a simple scattering geometry, in which the hot central star is surrounded by a hollow cylindrical H I region characterized by thickness T that is in turn parameterized by the H I column density. It is proposed that the central far-UV emission region is covered significantly by the neutral scattering region characterized by the H I column density N 4 × 10 21 cm -2 . The H I column density is higher by an order of magnitude than the value proposed from 21 cm radio observations. We briefly discuss the importance of Raman scattering as a probe of neutral material around a newly formed hot white dwarf and the mass-loss process occurring in the late stage of stellar evolution.
    Is part of: The Astrophysical Journal, 2006, Vol.636(2), pp.1045-1053
    Identifier: 0004-637X (ISSN); 1538-4357 (E-ISSN); 10.1086/498143 (DOI)