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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 36/122
351
- Kang, Hye-Sung
- Journal of the Korean astronomical society = 천문학회지
- 43, n.2
- pp.25-39
- 2010
- 원문 바로보기
We perform kinetic simulations of diffusive shock acceleration (DSA) in Type Ia supernova remnants (SNRs) expanding into a uniform interstellar medium (ISM). Bohm-like diffusion due to self-excited <TEX>$Alfv\acute{e}n$</TEX> waves is assumed, and simple models for <TEX>$Alfv\acute{e}nic$</TEX> drift and dissipation are adopted. Phenomenological models for thermal leakage injection are considered as well. We find that the preshock gas temperature is the primary parameter that governs the cosmic ray (CR) acceleration efficiency and energy spectrum, while the CR injection rate is a secondary parameter. For SNRs in the warm ISM of <TEX>$T_0\lesssim10^5K$</TEX>, if the injection fraction is <TEX>$\xi\gtrsim10^{-4}K$</TEX>, the DSA is efficient enough to convert more than 20% of the SN explosion energy into CRs and the accelerated CR spectrum exhibits a concave curvature flattening to <TEX>$E^{-1.6}$</TEX>, which is characteristic of CR modified shocks. Such a flat source spectrum near the knee energy, however, may not be reconciled with the CR spectrum observed at Earth. On the other hand, SNRs in the hot ISM of<TEX>$T_{0}\approx10^{6}K$</TEX> with a small injection fraction, <TEX>$\xi$</TEX><<TEX>$10^{-4}$</TEX>, are inefficient accelerators with less than 10% of the explosion energy getting converted to CRs. Also the shock structure is almost test-particle like and the ensuing CR spectrum can be steeper than <TEX>$E^{-2}$</TEX>. With amplified magnetic field strength of order of <TEX>$30{\mu}G$</TEX> <TEX>$Alfv\acute{e}n$</TEX> waves generated by the streaming instability may drift upstream fast enough to make the modified test-particle power-law as steep as <TEX>$E^{-2.3}$</TEX>, which is more consistent with the observed CR spectrum.
352
- Oh, Seung-Kyung
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.105-105
- 2009
- 원문 바로보기
353
- Abdel-Rahman, H.I.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.71-79
- 2009
- 원문 바로보기
In this paper, statistical distribution functions are developed for distance determination of stellar groups. This method depends on the assumption that absolute magnitudes and apparent magnitudes follow a Gaussian distribution function. Due to the limits of the integrands of the frequency function of apparent and absolute magnitudes, we introduce Case A, B, and C Gaussian distributions. The developed approaches have been implemented to determine distances to some clusters and stellar associations. The comparison with the distances derived by different authors reveals good agreement.
354
- Moon, Y.J.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.2
- pp.27-32
- 2009
- 원문 바로보기
Recently, we suggested a CME earthward direction parameter as an important geoeffective parameter that has been demonstrated by front-side halo CME data. In this study, we present the geometrical implication of this parameter by comparing with the parameters from a CME cone model. Major results from this study can be summarized as follows. First, we derive an analytic relationship between the cone model parameters(the half angular width of a cone and the angle between the cone axis and the plane of sky) and the earthward direction parameter. Second, we demonstrate a close relationship between the earthward direction parameter and the cone axis angle using 32 front-side full halo CMEs. Third, we found that there is noticeable inconsistency between the cone axis angles estimated from the cone model fitting to the CMEs and from their associated flare positions, implying that the flare position should not be considered as a good earthward direction parameter. Finally we present several advantages of our earthward direction parameter in terms of the forecast of a geomagnetic storm based on CME parameters.
355
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.155-159
- 2009
- 원문 바로보기
In order to determine color excess in the <TEX>$uvby\beta$</TEX> color system for high amplitude <TEX>$\delta$</TEX> Scuti stars, reddening free <TEX>$[m_1]$</TEX>, <TEX>$[c_1]$</TEX>, and <TEX>$\beta$</TEX> indices data were obtained from the existing literature for 21 stars. Then, the three intrinsic relations of <TEX>$(b-y)_0$</TEX> - <TEX>$[m_1]$</TEX>, <TEX>$(b-y)_0$</TEX> - <TEX>$[c_1]$</TEX>, and <TEX>$(b-y)_0$</TEX> - <TEX>$\beta$</TEX> were investigated. Among these, it was shown that the <TEX>$(b-y)_0$</TEX>-<TEX>$[c_1]$</TEX> relation is the most useful. By establishing intrinsic <TEX>$(b-y)_0$</TEX>-<TEX>$[c_1]$</TEX> relations for six reddening calibration stars, color excesses of other stars were determined.
356
- Hasan, M. Khayrul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.5
- pp.107-123
- 2009
- 원문 바로보기
We investigate the wave properties for isothermal plasma state around to the de Sitter black hole's horizon using 3+1 split of spacetime. The corresponding Fourier analyzed perturbed perfect GRMHD equations are used to obtain the complex dispersion relations. We obtain the real values of the wave number k, from these relations, which are used to evaluate the quantities like phase and group velocities etc. These have been analyzed graphically in the neighborhood of the horizon.
357
- Shanmugarju, A.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.55-60
- 2009
- 원문 바로보기
The properties of SOHO/LASCO CMEs are subjected to projection effects. Their dependence on the source position is important to be studied. Our main aim is to study the dependence of CME properties on helio-longitude and latitude using the CMEs associated with type IIs observed by Wind/WAVES spacecraft (Deca-hecta metric type IIs - DH type IIs). These CMEs were identified as a separate population of geo-effective CMEs. We considered the CMEs associated with the Wind/WAVE type IIs observed during the period January 1997 - December 2005. The source locations of these CMEs were identified using their associated GOES X-ray flares and listed online. Using their locations and the cataloged properties of CMEs, we carried out a study on the dependence of CME properties on source location. We studied the above for three groups of CMEs: (i) all CMEs, (ii) halo and non-halo CMEs, and (iii) limb and non-limb CMEs. Major results from this study can be summarized as follows. (i) There is a clear dependence of speed on both the longitude and latitude; while there is an increasing trend with respect to longitude, it is opposite in the case of latitude. Our investigations show that the longitudinal dependence is caused by the projection effect and the latitudinal effect by the solar cycle effect. (ii) In the case of width, the disc centered events are observed with more width than those occurred at higher longitudes, and this result seems to be the same for latitude. (iii) The dependency of speed is confirmed on the angular distance between the sun-center and source location determined using both the longitude and latitude. (iv) There is no dependency found in the case of acceleration. (v) Among all the three groups of CMEs, the speeds of halo CMEs show more dependency on longitude. The speed of non-halo and non-limb CMEs show more dependency on latitude. The above results may be taken into account in correcting the projection effects of geo-effective CMEs.
358
- Kim, Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.135-144
- 2009
- 원문 바로보기
We present JHK near-infrared photometric study for the old open cluster (OC) Trumpler 5 (Tr 5), based on the 2MASS data. From the color-magnitude diagrams of Tr 5, we have located the position of the red giant clump (RGC) stars, and used the mean magnitude of the RGC stars in K-band to estimate the distance to Tr 5, d = <TEX>$3.1{\pm}0.1$</TEX> kpc (<TEX>$(m-M)_0$</TEX> = <TEX>$12.46{\pm}0.04$</TEX>). From fitting the theoretical isochrones of Padova group, we have estimated the reddening, metallicity, and age : E(B-V) = <TEX>$0.64{\pm}0:05$</TEX>, [Fe/H] = <TEX>$-0.4{\pm}0.1$</TEX> dex, and t = <TEX>$2.8{\pm}0.2$</TEX> Gyr (log t = <TEX>$9.45{\pm}0.04$</TEX>), respectively. These parameters generally agree well with those obtained from the previous studies on Tr 5 and confirms that this cluster is an old OC with metallicity being metal-poorer than solar abundance, located in the anti-Galactic center region.
359
- Yoo, Kye-Hwa
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.93-103
- 2009
- 원문 바로보기
This article reports the spectral behavior of CH Cygni, using data obtained in October 2005 and June 2006. In these epochs, CH Cygni showed emission lines of H I, Fe II, [Fe II], [O III], [N II], [Ne III] and [S II]. Many of these lines were more enhanced since 2004. The underlying M-type spectrum was removed to get the intrinsic emission profile, and the resulting profiles were deconvoluted into several Gaussian components. Also, the radial velocities for all the lines that appeared in these spectra of CH Cygni were measured. The resultant lines were compared with each other and with those obtained in 2004; the findings are explained in terms of an accretion disk and jets.
360
- Kim, Do-Eon
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.33-37
- 2009
- 원문 바로보기
We propose a diagnostic that can resolve the planet/binary degeneracy of central perturbations in caustic-crossing high-magnification microlensing events. The diagnostic is based on the difference in the morphology of perturbation inside the central caustics induced by a planet and a wide-separation binary companion. We find that the contours of excess exhibit a concentric circular pattern around the caustic center for the binary-lensing case, while the contours are elongated or off-centered for the planetary case. This difference results in the distinctive features of the individual lens populations in the residual of the trough region between the two peaks of the caustic crossings, where the shape of the residual is symmetric for binary lensing while it tends to be asymmetric for planetary lensing. We determine the ranges of the planetary parameters for which the proposed diagnostic can be used. The diagnostic is complementary to previously proposed diagnostics in the sense that it is applicable to caustic-crossing events with small finite-source effect.