모달창 닫기
- 홈으로 이동
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 59/123
581
- LEE CHANG WON
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.257-259
- 2004
- 원문 바로보기
We compare the results of the surveys of starless cores performed with CS (2-1) and (3-2) lines to study inward motions in the cores. The velocity shifts of the CS(3-2) and (2-1) lines with respect to <TEX>$N_2H^+$</TEX> are found to correlate well with each other and to have similar number distributions, implying that, in many cores, systematic inward motions of gaseous material may occur over a range of density of at least a factor <TEX>${\~}$</TEX>4. Fits of the CS spectra to a 2-layer radiative transfer model in ten infall candidates suggest that the median effective line-of-sight speed of the inward-moving gas is <TEX>${\~}0.07 km\;s^{-l}$</TEX> for CS (3-2) and <TEX>${\~} 0.04 km\;s^{-l}$</TEX> for CS(2-1). Considering that the optical depth obtained from the fits is usually smaller in CS(3-2) than in (2-1) line, this may indicate that CS(3-2) usually traces inner, denser gas with greater inward motions than CS(2-1) implying that many of the infall candidates have faster infall toward the center. However, this conclusion may not be representative of all starless core infall candidates, due to the statistically small number analyzed here. Further line observations will be useful to test this conclusion.
582
- JOKIPII J. R.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.399-404
- 2004
- 원문 바로보기
Cosmic rays are ubiquitous in space, and are apparently present wherever the matter density is small enough that they are not removed by collisions with ambient particles. The essential similarity of their energy spectra in many different regions places significant general constraints on the mechanisms for their acceleration and confinement. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in Kolmogorov turbulence, can account for the universal specta. In comparison to shock acceleration, statistical acceleration, invoked in many situations, has significant disadvantages. The basic physics of acceleration and transport are discussed, and examples shown where it apparently works very well. However, there are now well-established situations where diffusive shock acceleration cannot be the accelerator. This problem will be discussed and possible acceleration mechanism evaluated. Statistical acceleration in these places is possible. In addition, a new mechanism, called diffusive compression acceleration, will be discussed and shown to be an attractive candidate. It has similarities with both statistical acceleration and shock acceleration.
583
- LEE YOUNGUNG
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.137-141
- 2004
- 원문 바로보기
We have estimated the fractal dimension of the molecular clouds in the Antigalactic Center based on the <TEX>$^{12}CO$</TEX> (J = 1- 0) and <TEX>$^{13}CO$</TEX> (J = 1- 0) database obtained using the 14m telescope at Taeduk Radio Astronomy Observatory. Using a developed code within IRAF, we were able to identify slice-clouds, and determined the dispersions of two spatial coordinates as well as perimeters and areas. The fractal dimension of the target region was estimated to be D = 1.34 for low resolution <TEX>$^{12}CO$</TEX> (J = 1 - 0) database, and D = 1.4 for higher resolution <TEX>$^{12}CO$</TEX> (J = 1 - 0) and <TEX>$^{13}CO$</TEX> (J = 1 - 0) database, where <TEX>$P {\propto} A^{D/2}$</TEX>. The sampling rate (spatial resolution) of observed data must be an important parameter when estimating fractal dimension. Our database with higher resolution of 1 arcminute, which is corresponding to 0.2 pc at a distance of 1.1 kpc, gives us the same estimate of fractal dimension to that of local dark clouds. Fractal dimension is apparently invariant when varying the threshold temperatures applied to cloud identification. According to the dispersion pattern of longitudes and latitudes of identified slice-clouds, there is no preference of elongation direction.
584
- GARCIA-SEGURA G.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.217-222
- 2004
- 원문 바로보기
High ambient interstellar pressure is suggested as a possible factor to explain the ubiquitous ob-served growth-rate discrepancy for supernova-driven super bubbles and stellar wind bubbles. Pressures of P / k <TEX>${\~} 10^5\;cm^{-3}$</TEX> K are plausible for regions with high star formation rates, and these values are intermediate between the estimated Galactic mid-plane pressure and those observed in starburst galaxies. High-pressure components also are commonly seen in Galactic ISM localizations. We demonstrate the sensitivity of shell growth to the ambient pressure, and suggest that super bubbles ultimately might serve as ISM barometers.
585
- OLINTO ANGELA V.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.413-420
- 2004
- 원문 바로보기
The current state and future prospects of ultra high energy cosmic ray physics are reviewed. These cosmic rays with energies well above <TEX>$10^{18}$</TEX> eV are messengers of an unknown extremely high-energy universe.
586
- O'NEILL SEAN M.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.605-609
- 2004
- 원문 바로보기
We present a set of high-resolution 3D MHD simulations exploring the evolution of light, supersonic jets in cluster environments. We model sets of high- and low-Mach jets entering both uniform surroundings and King-type atmospheres and propagating distances more than 100 times the initial jet radius. Through complimentary analyses of synthetic observations and energy flow, we explore the detailed interactions between these jets and their environments. We find that jet cocoon morphology is strongly influenced by the structure of the ambient medium. Jets moving into uniform atmospheres have more pronounced backflow than their non-uniform counterparts, and this difference is clearly reflected by morphological differences in the synthetic observations. Additionally, synthetic observations illustrate differences in the appearances of terminal hotspots and the x-ray and radio correlations between the high- and low-Mach runs. Exploration of energy flow in these systems illustrates the general conversion of kinetic to thermal and magnetic energy in all of our simulations. Specifically, we examine conversion of energy type and the spatial transport of energy to the ambient medium. Determination of the evolution of the energy distribution in these objects will enhance our understanding of the role of AGN feedback in cluster environments.
587
- ENBLIN TORSTEN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.439-446
- 2004
- 원문 바로보기
A critical discussion of our knowledge about extragalactic cosmic rays and magnetic fields is at-tempted. What do we know for sure? What are our prejudices? How do we confront our models with the observations? How can we assess the uncertainties in our modeling and in our observations? Unfortunately, perfect answers to these questions can not be given. Instead, I describe efforts I am involved in to gain reliable information about relativistic particles and magnetic fields in extragalactic space.
588
- SANCHEZ-SALCEDO F. J.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.205-210
- 2004
- 원문 바로보기
The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanism of the generation of galactic warps. Here we discuss conditions under which intergalactic flows can be relevant for warping field galaxies. Constraints include the heating of the outer disk, the level of asymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, the symmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and the speed of the intergalactic flow whether subsonic or supersonic. These constraints are discussed in this paper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequence of accretion flows onto the disk.
589
- NARASIMHA D.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.355-359
- 2004
- 원문 바로보기
Differential Faraday Rotation measurements between the images of same background source, of multiply-imaged gravitational lens systems can be effectively used to provide a valuable probe to establish the existence of large-scale ordered magnetic fields in lensing galaxies as well as galaxy clusters. Estimates of the magnetic field in lens galaxies, based on the radio polarization measurements do not appear to show any clear evidence for evolution with redhsift of the coherent large scale magnetic field between redshift of 0.9 and the present epoch. However, our method clearly establishes the presence of coherent large scale magnetic field in giant ellitpical galaxies.
590
- CASSANO R.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.589-592
- 2004
- 원문 바로보기
We calculate the probability to form giant radio halos (<TEX>${\~}$</TEX> 1 Mpc size) as a function of the mass of the host clusters by using a Statistical Magneto-Turbulent Model (Cassano & Brunetti, these proceedings). We show that the expectations of this model are in good agreement with the observations for viable values of the parameters. In particular, the abrupt increase of the probability to find radio halos in the more massive galaxy clusters (<TEX>$M {\ge} 2{\times}10^{15} M_{\bigodot}$</TEX>) can be well reproduced. We calculate the evolution with redshift of such a probability and find that giant radio halos can be powered by particle acceleration due to MHD turbulence up to z<TEX>${\~}$</TEX>0.5 in a ACDM cosmology. Finally, we calculate the expected Luminosity Functions of radio halos (RHLFs). At variance with previous studies, the shape of our RHLFs is characterized by the presence of a cut-off at low synchrotron powers which reflects the inefficiency of particle acceleration in the case of less massive galaxy clusters.