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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 43/122
421
- 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.
422
- 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.
423
- Chi Seung-Youp
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.9-17
- 2006
- 원문 바로보기
In an attempt to investigate star formation activity and statistical properties of clumps of high Galactic latitude clouds (HLCs), we mapped the Polaris Flare region, PF121.3+25.5, in <TEX>$^{12}CO\;and\;^{13}CO$</TEX> J = 1 - 0 using SRAO 6-m telescope and also observed its 12 <TEX>$^{13}CO$</TEX> peak positions in CS J = 2 - 1 with TRAO 14-m telescope. <TEX>$^{13}CO$</TEX> integrated intensity map shows clearly its clumpy structure and the locations of clumps well agree with <TEX>$^{12}CO$</TEX>morphology. CS line is not detected toward the 12 <TEX>$^{13}CO$</TEX> peak positions, so we can conclude there are no dense <TEX>$(\sim10^4\;cm^{-3})$</TEX> in this region. We decomposed 105 clumps from <TEX>$^{13}CO$</TEX> map using GAUSSCLUMPS algorithm. The mass of clumps ranges from <TEX>$7.8\;M_{\odot}\;to\;7.4{\times}10^{-2}\;M_{\odot}$</TEX> with a total mass of <TEX>$66.4\;M_{\odot}$</TEX> The mass spectrum follows a power law, dN/dM <TEX>${\propto}\;M^{-\alpha}$</TEX> with a power index of <TEX>${\alpha}=1.91{\pm}0.13$</TEX>. The virial masses of clumps are in the range of <TEX>$10{\sim}100M_{LTE}$</TEX> and so these clumps are considered to be gravitationally unbound.
424
- Lee Min-Young
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.1-7
- 2006
- 원문 바로보기
We present the results of a highly sensitive (<TEX>${\sim}10$</TEX> mK rms) survey toward the central parts of 22 barred spiral galaxies in <TEX>$^{12}CO(1-0)$</TEX> line using the NRAO 12m telescope at Kitt Peak. Seven of the target galaxies were detected in CO; NGC 3686 has been detected with CO for the first time. We estimated central CO fluxes of <TEX>$50{\sim}1000\;Jy\;km\;s^{-1}$</TEX> and molecular gas masses of <TEX>$10^7{\sim}10^8\;M_{\odot}$</TEX> for those galaxies.
425
- 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.
426
- 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>.
427
- 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.
428
- 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.
429
- 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.
430
- 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.