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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 57/122
561
- SOHN J,
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.261-263
- 2004
- 원문 바로보기
We present a progress report on HCN(1-0) line observations toward starless cores to probe inward motions. We have made a single pointing survey toward the central regions of 85 starless cores and performed mapping observations of 6 infall candidate starless cores. The distributions of the velocity difference between HCN(1-0) hyperfine lines and the optically thin tracer <TEX>$N_2H^+$</TEX>(1-0) are significantly skewed to the blue, meaning that HCN(1-0) frequently detects inward motions. Their skewness to the blue is even greater than that of CS(2-1) Lee et al., possibly implying more infall occurrence than CS(1-0). We identify 19 infall candidates by using several characteristics illustrating spectral infall asymmetry seen in HCN(1-0) hyperfine lines, CS(3-2), CS(2-1), <TEX>$DCO^+(2-1)$</TEX> and <TEX>$N_2H^+$</TEX> observations. The HCN(1-0) F(O-l) with the least optical depth usually shows a similar intensity distribution to that of <TEX>$N_2H^+$</TEX> which closely traces the density distribution of the cores, indicating that HCN(1-0) is less chemically affected and so believed to reflect kinematics occurring in rather inner regions of the cores. Detailed radiative transfer model fits of the spectra are underway to analyze central infall kinematics in starless cores.
562
- LEE J.-J.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.223-224
- 2004
- 원문 바로보기
The Tycho supernova remnant (SNR), as one of the few historical SNRs, has been widely studied in various wavebands and previous observations have shown evidence that Tycho is interacting with a dense ambient medium toward the northeast direction, In this paper, we report our high-resolution (16') <TEX>$^{12}CO$</TEX> observation of the remnant using the Nobeyama 45m radio telescope. The Nobeyama data shows that a large molecular cloud surrounds the SNR along the northeastern boundary. We suggest that the Tycho SNR and the molecular cloud are both located in the Perseus arm and that the dense medium interacting with the SNR is possibly the molecular cloud. We also discuss the possible connection between the molecular cloud and the Balmer-dominated optical filaments, and suggest that the preshock gas may be accelerated within the cosmic ray and/or fast neutral precursor.
563
- KURTZ S.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.265-268
- 2004
- 원문 바로보기
Molecular clouds present many levels of structure, including clumps and cores of varying size and density. We present a brief summary of these cores, describing their observed physical properties and their place in the star formation process. We conclude with some speculation about pre-proto-stellar stages of molecular cores and the observational challenges in their observation.
564
- MAZZOTTA PASQUALE
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.381-385
- 2004
- 원문 바로보기
Similarly to other cluster of galaxies previously classified as cooling flow systems, the Chandra observation of MKW 3s reveals that this object has a complex X-ray structure hosting both a X-ray cavity and a X-ray filament. Unlike the other clusters, however, the temperature map of the core of MKW 3s shows the presence of extended regions of gas heated above the radially averaged gas temperature at any radius. As the cluster does not show evidences for ongoing major mergers Mazzotta et al. suggest a connection between the heated gas and the activity of the central AGN. Nevertheless, due to the lack of high quality radio maps, this interpretation was controversial. In this paper we present the results of two new radio observations of MKW 3s at 1.28 GHz and 604 MHz obtained at the GMRT. Together with the Chandra observation and a separate VLA observation at 327 MHz from Young, we show unequivocal evidences for a close connection between the heated gas region and the AGN activity and we briefly summarize possible implications.
565
- FUJITA YUTAKA
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.571-574
- 2004
- 원문 바로보기
Clusters of galaxies are filled with X-ray emitted hot gas with the temperature of T <TEX>${\~}$</TEX>2-10 keV. Recent X-ray observations have been revealing unexpectedly that many cluster cores have complicated, peculiar X-ray structures, which imply dynamical motion of the hot gas. Moreover, X-ray spectra indicate that radiative cooling of the cool gas is suppressed by unknown heating mechanisms (the 'cooling flow problem'). Here we propose a novel mechanism reproducing both the inhomogeneous structures and dynamics of the hot gas in the cluster cores, based on state-of-the-art hydrodynamic simulations. We showed that acoustic-gravity waves, which are naturally expected during the process of hierarchical structure formation of the universe, surge in the X-ray hot gas, causing a serous impact on the core. This reminds us of tsunamis on the ocean surging into an distant island. We found that the waves create fully-developed, stable turbulence, which reproduces the complicated structures in the core. Moreover, if the wave amplitude is large enough, they can suppress the cooling of the core. The turbulence could be detected in near-future space X-ray missions such as ASTRO-E2.
566
- MINH Y. C.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.131-135
- 2004
- 원문 바로보기
The <TEX>$H_2S\;(2_{2,0} - 2_{1,1})$</TEX> line emission is observed to be strongly localized toward Sgr B2(M), and emissions from other positions in the more extended SgrB2 region are almost negligible. <TEX>$H_2S$</TEX> is thought to form effectively by the passage of the C-type shocks but to be quickly transformed to <TEX>$SO_2$</TEX> or other sulfur species (Pineau des Forets et al. 1993). Such a shock may have enhanced the <TEX>$H_2S$</TEX> abundance in Sgr B2(M), where massive star formation is taking place. But the negligible emission of <TEX>$H_2S$</TEX> from other observed positions may indicate that these positions have not been affected by shocks enough to produce <TEX>$H_2S$</TEX>, or if they have experienced shocks, <TEX>$H_2S$</TEX> may have transformed already to other sulfur-containing species. The <TEX>$SO_2\;22_{2,20} - 22_{1,21}$</TEX> line was also observed to be detectable only toward the (M) position. The line intensity ratios of these two molecules appear to be very similar at Sgr B2(M) and IRAS 16239-2422, where the latter is a region of low-mass star formation. This may suggest that the shock environment in these two star-forming regions is similar and that the shock chemistry also proceeds in a similar fashion in these two different regions, if we accept shock formation of these two species.
567
- MINIATI FRANCESCO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.465-470
- 2004
- 원문 바로보기
I address the issue of nonthermal processes in the large scale structure of the universe. After reviewing the properties of cosmic shocks and their role as particle accelerators, I discuss the main observational results, from radio to <TEX>$\gamma$</TEX>-ray and describe the processes that are thought be responsible for the observed nonthermal emissions. Finally, I emphasize the important role of <TEX>$\gamma$</TEX>-ray astronomy for the progress in the field. Non detections at these photon energies have already allowed us important conclusions. Future observations will tell us more about the physics of the intracluster medium, shocks dissipation and CR acceleration.
568
- RYU DONGSU
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.477-482
- 2004
- 원문 바로보기
Shock waves form in the intergalactic space as an ubiquitous consequence of cosmic structure formation. Using N-body/hydrodynamic simulation data of a ACDM universe, we examined the properties of cosmological shock waves including their morphological distribution. Adopting a diffusive shock acceleration model, we then calculated the amount of cosmic ray energy as well as that of gas thermal energy dissipated at the shocks. Finally, the dynamical consequence of those cosmic rays on cluster properties is discussed.
569
- MEDVEDEV MIKHAIL V.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.533-541
- 2004
- 원문 바로보기
The origin of magnetic fields in the universe remains an outstanding problem in cosmology. We propose that these fields are produced by shocks during the large-scale structure formation. We discuss the mechanism of the field generation via the counter-streaming (Weibel) instability. We also show that these Weibel-generated fields are long-lived and weakly coupled to dissipation. Subsequent field amplification by the intra-cluster turbulence may also take place, thus maintaining the magnetic energy density close to equipartition.
570
- HENRY J. PATRICK
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.371-374
- 2004
- 원문 바로보기
We review the observational evidence for the existence of a warm-hot intergalactic medium (WHIM). We expect that the morphology of this material is similar to that of cosmic rays and magnetic fields in large-scale structure, i.e., filaments connecting clusters of galaxies. Direct evidence for the WHIM, either in emission or absorption, is weak.