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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 40/122
391
- Baek, Kyoung-Min
- Journal of the Korean astronomical society = 천문학회지
- 40, n.1
- pp.1-7
- 2007
- 원문 바로보기
About 10 percent of quasars are known to exhibit deep broad absorption troughs blueward of prominent permitted emission lines, which are usually attributed to the existence of outflows slightly above he accretion disk around the supermassive black hole. Typical widths up to 0.2c of these absorption roughs indicate the velocity scales in which special relativistic effects may not be negligible. Under he assumption of the ubiquity of the broad absorption line region in quasars, the broad emission line flux will exhibit Thomson scattered components from these fast outflows. In this paper, we provide our Monte Carlo calculation of linear polarization of singly Thomson scattered line radiation with the careful considerations of special relativistic effects. The scattering region is approximated by a collection of rings that are moving outward with speeds <TEX>${\upsilon}=c{\beta}<0.2c$</TEX> near the equatorial plane, and the scattered line photons are collected according to its direction and wavelength in the observer's rest frame. We find that the significantly extended red tail appears in the scattered radiation. We also find that the linear degree of polarization of singly Thomson scattered line radiation is wavelength-dependent and hat there are significant differences in the linear degree of polarization from that computed from classical physics in the far red tail. We propose that the semi-forbidden broad emission line C III]1909 may be significantly contributed from Thomson scattering because this line has small resonance scattering optical depth in the broad absorption line region, which leads to distinct and significant polarized flux in this broad emission line.
392
- Kurtz, Stan
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.137-140
- 2007
- 원문 바로보기
Triggered star formation is not a new idea - it's been around for at least the last 30 years. Although it has never disappeared from the scene, it seems to be enjoying something of a renaissance in recent years, in both observational and theoretical studies. Here we give a brief discussion of the background of triggered star formation, describe some of our own recent observational efforts in this regard, and briefly mention some initial conclusions that may be drawn.
393
- Migenes, Victor
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.131-132
- 2007
- 원문 바로보기
The research of OH maser emission sources with high angular resolution is complicated by the effects of interstellar scattering: more over, most of the OH maser sources are located in the galactic plane where the scattering is largest. However, the data available from pulsar studies on the spatial distribution of the amount of scattering indicate that there is a strong non-uniformity in the distribution of the amount of scattering material. There are directions in the galactic plane where the scattering is an order of magnitude higher than the average, as well as directions where the scattering is much lower. The latter provide an opportunity to investigate OH masers with the full angular resolution offered by very long baseline interferometry instruments, like the VLBA, and measure their true angular size, shape and brightness temperature. We have observed approximately 100 OH maser sources, distributed all over the northern hemisphere, with the VLBA in order to study the scattering properties of the interstellar medium.
394
- Lee, Young-Ung
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.133-135
- 2007
- 원문 바로보기
A survey project of TRAO with the fifteen beam array receiver system is presented. A multibeam array receiver system has been purchased from FCRAO, and is being installed on TRAO 14m telescope. The target region of the survey is from <TEX>${\iota}=120^{\circ}{\sim}137^{\circ},\;b=-1^{\circ}{\sim}+ 1^{\circ}$</TEX>, and velocity resolution would be 1 km/sec after smoothing from the original resolution of <TEX>$0.64km\;s^{-1}$</TEX> in the transition of J = 1-0 of <TEX>$^{13}CO$</TEX>. The survey region is a part of the <TEX>$^{12}CO$</TEX> Outer Galaxy Survey(OGS), and would be an extension of the Bell Laboratories <TEX>$^{13}CO$</TEX> Galactic Plane Survey. By combining with the existing <TEX>$^{12}CO$</TEX> database of the Outer Galaxy Survey, we will derive physical properties of identified molecular clouds and will conduct and statistical analysis of the Outer Galalxy molecular clouds. Reduction process and analysis methods will be introduced.
395
- Chae, Jong-Chul
- Journal of the Korean astronomical society = 천문학회지
- 40, n.3
- pp.67-82
- 2007
- 원문 바로보기
The basic building block of solar filaments/prominences is thin threads of cool plasma. We have studied the spectral properties of velocity threads, clusters of thinner density threads moving together, by analyzing a sequence of <TEX>$H{\alpha}$</TEX> images of a quiescent filament. The images were taken at Big Bear Solar Observatory with the Lyot filter being successively tuned to wavelengths of -0.6, -0.3, 0.0, +0.3, and +0.6 <TEX>${\AA}$</TEX> from the centerline. The spectra of contrast constructed from the image data at each spatial point were analyzed using cloud models with a single velocity component, or three velocity components. As a result, we have identified a couple of velocity threads that are characterized by a narrow Doppler width(<TEX>$\Delta\lambda_D=0.27{\AA}$</TEX>), a moderate value of optical thickness at the <TEX>$H{\alpha}$</TEX> absorption peak(<TEX>$\tau_0=0.3$</TEX>), and a spatial width(FWHM) of about 1'. It has also been inferred that there exist 4-6 velocity threads along the line of sight at each spatial resolution element inside the filament. In about half of the threads, matter moves fast with a line-of-sight speed of <TEX>$15{\pm}3km\;s^{-1}$</TEX>, but in the other half it is either at rest or slowly moving with a line-of-sight velocity of <TEX>$0{\pm}3km\;s^{-1}$</TEX>. It is found that a statistical balance approximately holds between the numbers of blue-shifted threads and red-shifted threads, and any imbalance between the two numbers is responsible for the non-zero line-of-sight velocity determined using a single-component model fit. Our results support the existence not only of high speed counter-streaming flows, but also of a significant amount of cool matter either being at rest or moving slowly inside the filament.
396
- Minh, Y.C.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.3
- pp.61-65
- 2007
- 원문 바로보기
The 2-1 and 5-4 transitions of SiO have been observed toward the Sgr B2 region, including the Principal Cloud(the GMC containing Sgr B2(M)) and its surroundings. The morphology and velocity structure of the SiO emission show a close resemblance with the HNCO Ring feature, identified by Minh & Irvine(2006), of about 10 pc in diameter, which may be expanding and colliding with the Principal Cloud. Three SiO clumps have been found around the Ring, with total column densities <TEX>$N_{SiO}{\sim}1{\times}10^{14}cm^{-2}$</TEX> at the peak positions of these clumps. The fractional SiO abundance relative to <TEX>$H_2$</TEX> has been estimated to be <TEX>${\sim}(0.5-1){\times}10^{-9}$</TEX>, which is about two orders of magnitude larger than the quiet dense cloud values. Our SiO observational result supports the existence of an expanding ring, which may be triggering active star formations in the Principal Cloud.
397
- Cho, Hyun-Jin
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.161-164
- 2007
- 원문 바로보기
We calculate the evolution of multiple supernova (SN) explosions inside a pre-exiting bubble blown up by winds from massive stars, using one-dimensional hydrodynamic simulations including radiative cooling and thermal conduction effects. First, the development of the wind bubble driven by collective winds from multiple stars during the main sequence is calculated. Then multiple SN explosion is loaded at the center of the bubble and the evolution of the SN remnant is followed for <TEX>$10^6$</TEX> years. We find the size and mass of the SN-driven shell depend on the structure of the pre-existing wind bubble as well as the total SN explosion energy. Most of the explosion energy is lost via radiative cooling, while about 10% remains as kinetic energy and less than 10% as thermal energy of the expanding bubble shell. Thus the photoionization and heating by diffuse radiation emitted by the shock heated gas is the most dominant form of SN feedback into the surrounding interstellar medium.
398
- Dib, Sami
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.157-160
- 2007
- 원문 바로보기
I present a model to explain the mass segregation and shallow mass functions observed in the central parts of starburst stellar clusters. The model assumes that the initial pre-stellar cores mass function resulting from the turbulent fragmentation of the proto-cluster cloud is significantly altered by the cores coalescence before they collapse to form stars. With appropriate, yet realistic parameters, this model based on the competition between cores coalescence and collapse reproduces the mass spectra of the well studied Arches cluster. Namely, the slopes at the intermediate and high mass ends, as well as the peculiar bump observed at <TEX>$6M_{\bigodot}$</TEX>. This coalescence-collapse process occurs on a short timescale of the order of the free fall time of the proto-cluster cloud (i.e., a few <TEX>$10^4$</TEX> years), suggesting that mass segregation in Arches and similar clusters is primordial. The best fitting model implies the total mass of the Arches cluster is <TEX>$1.45{\times}10^5M_{\bigodot}$</TEX>, which is slightly higher than the often quoted, but completeness affected, observational value of a few <TEX>$10^4M_{\bigodot}$</TEX>. The model implies a star formation efficiency of <TEX>${\sim}30$</TEX> percent which implies that the Arches cluster is likely to a gravitationally bound system.
399
- Lee, J.Y.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.99-106
- 2007
- 원문 바로보기
Statistical analyses were performed to investigate the relative success and accuracy of daily maximum X-ray flux (MXF) predictions, using both multilinear regression and autoregressive time-series prediction methods. As input data for this work, we used 14 solar activity parameters recorded over the prior 2 year period (1989-1990) during the solar maximum of cycle 22. We applied the multilinear regression method to the following three groups: all 14 variables (G1), the 2 so-called 'cause' variables (sunspot complexity and sunspot group area) showing the highest correlations with MXF (G2), and the 2 'effect' variables (previous day MXF and the number of flares stronger than C4 class) showing the highest correlations with MXF (G3). For the advanced three days forecast, we applied the autoregressive timeseries method to the MXF data (GT). We compared the statistical results of these groups for 1991 data, using several statistical measures obtained from a <TEX>$2{\times}2$</TEX> contingency table for forecasted versus observed events. As a result, we found that the statistical results of G1 and G3 are nearly the same each other and the 'effect' variables (G3) are more reliable predictors than the 'cause' variables. It is also found that while the statistical results of GT are a little worse than those of G1 for relatively weak flares, they are comparable to each other for strong flares. In general, all statistical measures show good predictions from all groups, provided that the flares are weaker than about M5 class; stronger flares rapidly become difficult to predict well, which is probably due to statistical inaccuracies arising from their rarity. Our statistical results of all flares except for the X-class flares were confirmed by Yates' <TEX>$X^2$</TEX> statistical significance tests, at the 99% confidence level. Based on our model testing, we recommend a practical strategy for solar X-ray flare predictions.
400
- Cho, Jung-Yeon
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.113-118
- 2007
- 원문 바로보기
Recently far infra-red (FIR) polarization of the <TEX>$850{\mu}m$</TEX> continuum emission from T Tauri disks has been detected. The observed degree of polarization is around 3 %. Since thermal emission from dust grains dominates the spectral energy distribution at the FIR regime, dust grains might be the cause of the polarization. We explore alignment of dust grains by radiative torque in T Tauri disks and provide predictions for polarized emission for disks viewed at different wavelengths and viewing angles. In the presence of magnetic field, these aligned grains produce polarized emission in infrared wavelengths. When we take a Mathis-Rumpl-Nordsieck-type distribution with maximum grain size of <TEX>$500-1000{\mu}m$</TEX>, the degree of polarization is around 2-3 % level at wavelengths larger than <TEX>${\sim}100{\mu}m$</TEX>. Our study indicates that multifrequency infrared polarimetric studies of protostellar disks can provide good insights into the details of their magnetic structure.