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1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 41/119
401
- Kang, Hye-Sung
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.95-105
- 2006
- 원문 바로보기
We have calculated the cosmic ray(CR) acceleration at young remnants from Type Ia supernovae expanding into a uniform interstellar medium(ISM). Adopting quasi-parallel magnetic fields, gasdynamic equations and the diffusion convection equation for the particle distribution function are solved in a comoving spherical grid which expands with the shock. Bohm-type diffusion due to self-excited <TEX>$Alfv\acute{e}n$</TEX> waves, drift and dissipation of these waves in the precursor and thermal leakage injection were included. With magnetic fields amplified by the CR streaming instability, the particle energy can reach up to <TEX>$10^{16}Z$</TEX> eV at young supernova remnants(SNRs) of several thousand years old. The fraction of the explosion energy transferred to the CR component asymptotes to 40-50 % by that time. For a typical SNR in a warm ISM, the accelerated CR energy spectrum should exhibit a concave curvature with the power-law slope flattening from 2 to 1.6 at <TEX>$E{\gtrsim}0.1$</TEX> TeV.
402
- Hanna, Magdy A.
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.129-138
- 2006
- 원문 바로보기
A period study of the semi-detached eclipsing binary system W Delphini based on the extensive series of minimum timings covering more than a century(109 years) indicates a cyclic(O-C) variation of the system. This variation can be explained as due either to (1) stellar magnetic activity cycles of the cool subgiant G5 secondary component of the binary with a subsurface magnetic field equals to 3 kG, or (2) a long-term orbital period increases with a rate of <TEX>$1.68{\times}10^{-8}$</TEX> day/cycle caused by a mass transfer rate of <TEX>$4.9{\times}10^{-8}M_{\odot}yr^{-1}$</TEX> from the less to more massive component modulated by a light time effect due to a hypothetical third body with period of <TEX>$53.4{\pm}1.06$</TEX> years. The former explanation is more recommended than the later one since the obtained third body mass value(<TEX>$M_3=1.58\;M_{\odot}$</TEX>) is quite large but it can not manifest itself observationally and also it cannot be a white dwarf. In the contrary, from the magnetic activity point of view, the obtained characteristics are in good consistent when applying Applegate(1992) mechanism. However, further precise photometric and CCD observations for minima timings with brightness determinations are needed to confirm the present solution.
403
- Kang, Mi-Ju
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.107-114
- 2006
- 원문 바로보기
We conducted an analysis of a selected region from the FCRAO <TEX>$^{12}CO$</TEX> Outer Galaxy Survey. The selected region is located between galactic longitude <TEX>$117^{\circ}$</TEX> and <TEX>$124^{\circ}$</TEX> with the velocity of -23 km <TEX>$s^{-1}<V_{LSR}<-10\;km\;s^{-1}$</TEX>. Molecular clouds in this region show a peculiar velocity field, protruding from the Local Arm population. The selected region is divided into 7 clouds by spatial location. Though we were not able to identify the direct driving source for peculiar velocity of our target region, we find that there are several internal YSOs or star forming activities; there are many associated sources like an outflows, a high-mass protostellar candidate and <TEX>$H_2O$</TEX> maser sources. We attribute the driving energy source to older generation of episodic star formation. Masses of main clouds(cloud 1-4) estimated using a conversion factor from <TEX>$^{12}CO$</TEX> luminosity are larger than <TEX>$10^4M_{\odot}$</TEX>. Other components have a small mass as about <TEX>$10^3M_{\odot}$</TEX>. Among main clouds, cloud 2 and 4 seem to be marginally gravitational bound systems as their ratio of <TEX>$M_{CO}$</TEX> to <TEX>$M_{VIR}$</TEX> is about <TEX>$2{\sim}3$</TEX>, and the internal velocity dispersion is larger than the centroid velocity dispersion. Total mass estimated using a conversion factor from <TEX>$^{12}CO$</TEX> luminosity is <TEX>$7.9{\times}10^4M_{\odot}$</TEX>.
404
- Chi Seung-Youp
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.19-24
- 2006
- 원문 바로보기
We carried out CO survey toward IR-excess clouds using SRAO 6-m telescope in search of molecular <TEX>$H_2$</TEX>. These clouds, which show far-infrared excess over what is expected from HI column density, are considered to be candidates of molecular clouds. In order to find new high Galactic latitude clouds, we made mapping observations for 14 IR-excess clouds selected from Reach et al.(1998) in <TEX>$^{12}CO$</TEX> J = 1 - 0 line, supplementing the similar survey in southern hemisphere (Onishi et al. 2001). <TEX>$^{12}CO$</TEX> emission is detected from three IR-excess clouds among 14 objects. Three newly detected clouds exhibit somewhat clumpy morphology and column densities amount to <TEX>${\sim}10^{21}\;cm^{-2}$</TEX>. One of three clouds, DIR120-28, show discrepancy between IR-excess center and CO emission center. It seems that IR-excess may not be an effective tracer of molecular gas. Instead, optical depth<TEX>$(\tau)$</TEX> excess, i.e., IR-excess corrected for temperature dependence, may be more effective tracer of molecular clouds, since, by combining statistics from both hemispheres, we found that the detection rate is higher for IR-excess clouds with lower dust temperature.
405
- Sharaf, M.A.
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.147-150
- 2006
- 원문 바로보기
In this paper, initial value problem for dynamical astronomy will be established using parabolic cylindrical coordinates. Computation algorithm is developed for the initial value problem of gravity perturbed trajectories. Applications of the algorithm for the problem of final state predication are illustrated by numerical examples of seven test orbits of different eccentricities. The numerical results are extremely accurate and efficient in predicating final state for gravity perturbed trajectories which is of extreme importance for scientific researches as well as for military purposes. Moreover, an additional efficiency of the algorithm is that, for each of the test orbits, the step size used for solving the differential equations of motion is larger than 70% of the step size used for obtaining its reference final state solution.
406
- Moon, Y.J.
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.139-145
- 2006
- 원문 바로보기
We have made a comprehensive statistical study on the coronal mass ejections(CMEs) associated with helmet streamers. A total number of 3810 CMEs observed by SOHO/LASCO coronagraph from 1996 to 2000 have been visually inspected. By comparing their LASCO images and running difference images, we picked out streamer-associated CMEs, which are classified into two sub-groups: Class-A events whose morphological shape seen in the LASCO running difference image is quite similar to that of the pre-existing streamer, and Class-B events whose ejections occurred in a part of the streamer. The former type of CME may be caused by the destabilization of the helmet streamer and the latter type of CME may be related to the eruption of a filament underlying the helmet streamer or narrow CMEs such as streamer puffs. We have examined the distributions of CME speed and acceleration for both classes as well as the correlation between their speed and acceleration. The major results from these investigations are as follows. First, about a quarter of all CMEs are streamer-associated CMEs. Second, their mean speed is 413 km <TEX>$s^{-1}$</TEX> for Class-A events and 371 km <TEX>$s^{-1}$</TEX> for Class-B events. And the fraction of the streamer-associated CMEs decreases with speed. Third, the speed-acceleration diagrams show that there are no correlations between two quantities for both classes and the accelerations are nearly symmetric with respect to zero acceleration line. Fourth, their mean angular width are about <TEX>$60^{\circ}$</TEX>, which is similar to that of normal CMEs. Fifth, the fraction of streamer-associated CMEs during the solar minimum is a little larger than that during the solar maximum. Our results show that the kinematic characteristics of streamer-associated CMEs, especially Class-A events, are quite similar to those of quiescent filament-associated CMEs.
407
- Kim, Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.115-123
- 2006
- 원문 바로보기
We present <TEX>$JHK_S$</TEX> near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age <TEX>$1.6{\pm}0.2$</TEX> Gyr, metallicity <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, distance modulus<TEX>$(m-M)_0=10.4{\pm}0.3\;mag(d=1.2{\pm}02\;kpc)$</TEX>, and reddening <TEX>$E(B-V)=0.10{\pm}0.05$</TEX> mag. The parameters for the other old open cluster NGC 2394 are estimated to be <TEX>$age=1.1{\pm}0.2$</TEX> Gyr, <TEX>$[Fe/H]=0.0{\pm}0.2$</TEX> dex, <TEX>$(m-M)_0=9.1{\pm}0.4\;mag(d=660{\pm}120\;pc)$</TEX>, and <TEX>$E(B-V)=0.05{\pm}0.10$</TEX> mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be <TEX>${\Delta}[Fe/H]/{\Delta}R_{gc}=-0.067{\pm}0.009\;dex\;kpc^{-1}$</TEX>.
408
- Kim, Kyoo-Hyun
- Journal of the Korean astronomical society = 천문학회지
- 39, n.3
- pp.57-71
- 2006
- 원문 바로보기
We investigated the structural parameters of a sample of 30 dwarf galaxies(15 dEs and 15 dS0s) in the Virgo Cluster using i-band images from the Sloan Digital Sky Survey Data Release 4. Among 28 galaxies for which surface brightness profiles were derived from ellipse fittings, 23 galaxies had a single component that was adequately described by a generalized <TEX>$S\acute{e}rsic$</TEX> function with a shape parameter ranging from n=0.5 to 2, while 5 galaxies(2 dEs and 3 dS0s) had bulge and disk components that were fitted by a generalized <TEX>$S\acute{e}rsic$</TEX> function and an exponential function, respectively. Since the majority of dwarf galaxies in the present sample had a single component, it seems likely that genuine dS0 galaxies that have disk and bulge components are quite rare in the Virgo Cluster. The similarity in structural parameters of genuine dS0 galaxies in the Virgo Cluster with those of Magellanic-type galaxies implies that the progenitors of dwarf lenticular galaxies in the Virgo Cluster were most likely Magellanic-type galaxies if dS0s are harassed late-type spirals.
409
- Lee Chung-Uk
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.25-30
- 2006
- 원문 바로보기
We completed four color light curves of the near-contact binary CN And during three nights from September to December 2004 using the 61-cm reflector and BV RI filters at Sobaeksan Observatory. We determined four new times of minimum light (two timings for primary eclipse, two for secondary). Newly obtained BV RI light curves and the radial velocity curves from Rucinski et a1. (2000) were simultaneously analyzed to derive the system parameters of CN And. We used the semi-detached mode 4 of the 2003-version of the Wilson-Devinney binary model, and interpreted the asymmetry of the light curve by introducing two spots; a cool spot on the primary component and a hot spot on the secondary component. New photometric parameters are not much different from those of Cicek et a1. (2005), and it is considered that the system is in the era of broken contact. From the orbital period study with all available timings including our data, we found a continous period decrease with a rate of <TEX>$P_{obs}=--1.82{\times}10^{-7}\;d\;yr^{-1}$</TEX> that can be explained with two possible mechanisms. We think the most likely cause of the period decrease is a thermal mass transfer from the primary to the secondary component, rather than angular momentum loss due to a magnetic stellar wind.
410
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.89-94
- 2006
- 원문 바로보기
We present JHK-band near-infrared photometry of the star clusters in the dwarf irregular galaxy IC 5152. After excluding possible foreground stars, a number of candidate star clusters are identified in the near-infrared images of IC 5152, which include young populations. Especially, five young star clusters are identified in the(J-H, H-K) two color diagram and the total extinction values toward these clusters are estimated to be <TEX>$A_v=2-6$</TEX> from the comparison with the theoretical values given by the Leitherer et al.(1999)'s theoretical star cluster model.