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1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 45/123
441
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.125-128
- 2006
- 원문 바로보기
In order to determine the precise effective temperature and surface gravity of warm stars, all synthetic spectral lines in the wavelength range of <TEX>$4000-5700{\AA}$</TEX> with T=6000-7750 K, and log g=3.5, 4.0, and 4.5 for [M/H]=0.0, <TEX>$V_{rot}$</TEX>=10 km <TEX>$s^{-1}$</TEX>, and <TEX>$V_{tubl}$</TEX>=2 km <TEX>$s^{-1}$</TEX> were calculated using the SYNSPEC package(Hubeny, et al., 1995) and the Kurucz(1995) model. Then, the depth-ratios for all line pairs were investigated and we selected two and six depth-ratios appropriate for the surface gravity and temperature indicators, respectively. We plotted six grids with X- and Y-axes for the depth-ratios of surface gravity and temperature, respectively, for the simultaneous estimation of these two atmospheric parameters. This method was applied to the spectum of <TEX>$\delta$</TEX> Scu for the determination of its temperature and surface gravity simultaneously.
442
- Lee, Sung-Ho
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.151-155
- 2006
- 원문 바로보기
Long slit spectrometers are widely used in optical and infrared bands in astronomy. Absolute flux calibration for extended sources, however, is not straightforward, because a portion of the radiation energy from a flux calibration star is blocked by the narrow slit width. Assuming that the point spread function(PSF) of the star is circularly symmetric, we develop a robust method to extrapolate the detected stellar flux to the unobscured flux using the measured PSF along the slit-length direction. We apply this method to our long slit data and prove that the uncertainty of the absolute flux calibration is less than a few percents.
443
- Lee Jae-Woo
- Journal of the Korean astronomical society = 천문학회지
- 39, n.2
- pp.41-50
- 2006
- 원문 바로보기
We present the results of new multi-color CCD photometry for the contact binary XZ Leo, together with reasonable explanations for the period and light variations. Six new times of minimum light have been determined. A period study with all available timings confirms Qian's (2001) finding that the O-C residuals have varied secularly according to <TEX>$dP/dt\;=\;+8.20{\times}10^{-8}\;d\;yr^{-l}$</TEX>. This trend could be interpreted as a conservative mass transfer from the less massive cool secondary to the more massive hot primary in the system with a mass flow rate of about <TEX>$5.37{\times}10^{-8}\;M_{\odot}\;yr^{-l}$</TEX>. By simultaneous analysis of our light curves and the previously published radial-velocity data, a consistent set of light and velocity parameters for XZ Leo is obtained. The small differences between the observed and theoretical light curves are modelled by a blue third light and by a hot spot near the neck of the primary component. Our period study does not support the tertiary light but the hot region which may be formed by gas streams from the cool secondary. The solution indicates that XZ Leo is a deep contact binary with the values of q=0.343, <TEX>$i=78^{\circ}.8$</TEX>, <TEX>${\Delta}(T_1-T_2)=126\;K$</TEX>, and f=33.6 %, differing much from those of Niarchos et al. (1994). Absolute parameters of XZ Leo are determined as follows: <TEX>$M_1=1.84\;M_{\odot},\;M_2=0.63\;M_{\odot},\;R_1=1.75\;R_{\odot},\;R_2=1.10\;R_{\odot},\;L_1=7.19\;L_{\odot},\;and\;L_2=2.66\;L_{\odot}$</TEX>.
444
- 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.
445
- 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.
446
- 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.
447
- 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.
448
- 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>.
449
- 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.
450
- 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.