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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 44/122
431
- 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>.
432
- 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.
433
- 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.
434
- 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.
435
- Bondar, A.
- Journal of the Korean astronomical society = 천문학회지
- 39, n.3
- pp.73-80
- 2006
- 원문 바로보기
We analyze the extinction law towards several B1V stars-members of our Galaxy, searching for possible discrepancies from the galactic average extinction curve. Our photometric data allow to build extinction curves in a very broad range: from extreme UV till infrared. Two-colour diagrams, based on the collected photometric data from the ANS UV satellite, published UBV measurements and on the infrared 2MASS data of the selected stars, are constructed. Slopes of the fitted straight lines are used to build the average extinction curve and to search for discrepant objects. The selected stars have also been observed spectroscopically from the Terskol and ESO Observatories; these spectra allow to check their Sp/L's. The spectra of only about 30% of the initially selected objects resemble closely that of HD144470, considered as the standard of B1 V type. Other spectra either show some emission features or belong clearly to another spectral types. They are not used to build the extinction curve. Two-colour diagrams, constructed for the selected B1 V stars, showing no emission stellar features, prove that the interstellar extinction law is homogeneous in the Galaxy. Both the shape of the curve and the total-to-selective extinction ratio do not differ from the galactic average and the canonical value(3.1) respectively. The circumstellar emissions usually cause some discrepancies from the average interstellar extinction law; the discrepancies observed in the extraterrestrial ultraviolet, usually follow some misclassifications.
436
- Park Geum-Sook
- Journal of the Korean astronomical society = 천문학회지
- 39, n.2
- pp.31-40
- 2006
- 원문 바로보기
Near-IR <TEX>$H_2$</TEX> emission features in the northern region of the Orion A giant molecular cloud were observed in the <TEX>$CO\;J\;=\;1\;{\rightarrow}\;0$</TEX> line in search of CO outflows. Out of the 30 sources surveyed, CO line wings were detected toward 28 positions, suggesting a strong correlation between <TEX>$H_2$</TEX> jets and CO outflows. Blueshifted wings were detected toward 26 positions while redshifted wings were detected toward 15 positions, which suggests that there is a bias in the source selection. The bias is more severe in OMC 3 than in OMC 2. Since the protostars in OMC 3 are younger and more deeply embedded, the bias may be caused by the difference of extinction between blueshifted and redshifted outflows. Some physical parameters of the outflows were derived from the line profiles.
437
- Morcos, A.B.
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.81-87
- 2006
- 원문 바로보기
A relation between temperature and time has been constructed in the self-consistent model(SCM). This relation is used to calculate the a CMBR temperature. This temperature has been found to be 2.9K. The temperature gradient of microwave background radiation(CMBR) is calculated in the Self Consistent Model. Two relations between Hubble parameter and time derivative of the temperature, have been presented in two different cases. In the first case the temperature is treated as a function of time only, while in the other one, it is assumed to be a function in time and solid angle, beside the assumption that the universe expands adiabatically.
438
- Park Yong-Sun
- Journal of the Korean astronomical society = 천문학회지
- 39, n.2
- pp.51-56
- 2006
- 원문 바로보기
We report the development of a semi-VLBI observation system operating at 21 cm and present the measurement of visibility function toward the sun using this system. The system consists of two 2.3 meter antennas with a maximum separation of 35 meter, a conventional high speed data acquisition system, and a set of programs for software correlation. Since two local oscillators of receiver modules are independent, data had to be fringe-fitted to yield the visibility amplitude. It is found that the visibility amplitude decreases and then bounces back as baseline increases. We confirm that solar disk with brighter limb best explains the measured visibility amplitude.
439
- 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.
440
- SUH KYUNG-WON
- Journal of the Korean astronomical society = 천문학회지
- 38, n.2
- pp.267-270
- 2005
- 원문 바로보기
We investigate the spectral energy distributions (SEDs) of low mass-loss rate O-rich asymptotic giant branch (AGB) stars using the infrared observational data including the Infrared Space Observatory (ISO) data. Comparing the results of detailed radiative transfer model calculations with observations, we find that the dust formation temperature is much lower than 1000 K for standard dust shell models. We find that the superwind model with a density-enhanced region can be a possible alternative dust shell model for LMOA stars.