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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 60/122
591
- RICHER M. G.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.269-272
- 2004
- 원문 바로보기
We present the first results of a wide field survey for planetary nebulae throughout M31 undertaken at the KPNO 0.9m telescope with the Mosaic camera. So far, images in [O III]<TEX>$\lambda$</TEX>5007 and its continuum filter have been analyzed. Our survey appears to be at least <TEX>$90\%$</TEX> complete to about 2 mag below the peak of the planetary nebula luminosity function. Over 900 planetary nebulae candidates have been found within a 12 square degree area.
592
- OKABE NOBUHIRO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.547-551
- 2004
- 원문 바로보기
We showed that magnetic fields are generated in the plasma which have the temperature inhomogeneities. The mechanism is the same as the Weibel instability because the velocity distribution functions are at non-equilibrium and anisotropic under the temperature gradients. The growth timescale is much shorter than the dynamical time of structure formation. The coherence length of magnetic fields at the saturated time is much shorter than kpc scale and then, at nonlinear phase, become longer by inverse-cascade process. We report the application of our results to clusters of galaxies, not including hydrodynamic effects.
593
- CLARKE TRACY E.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.337-342
- 2004
- 원문 바로보기
The presence of magnetic fields in the intracluster medium in clusters of galaxies has been revealed through several different observational techniques. These fields may be dynamically important in clusters as they will provide additional pressure support to the intracluster medium as well as inhibit transport mechanisms such as thermal conduction. Here, we review the current observational state of Faraday rotation measure studies of the cluster fields. The fields are generally found to be a few to 10 <TEX>$\mu$</TEX>G in non-cooling core clusters and ordered on scales of 10 - 20 kpc. Studies of sources at large impact parameters show that the magnetic fields extend from cluster cores to radii of at least 500 kpc. In central regions of cooling core systems the field strengths are often somewhat higher (10 - 40 <TEX>$\mu$</TEX>G) and appear to be ordered on smaller scales of a few to 10 kpc. We also review some of the recent work on interpreting Faraday rotation measure observations through theory and numerical simulations. These techniques allow us to build up a much more detailed view of the strength and topology of the fields.
594
- BOHRINGER HANS
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.361-369
- 2004
- 원문 바로보기
Galaxy clusters as the densest and most prominent regions within the large-scale structure can be used as well characterizable laboratories to study astrophysical processes on the largest scales. X-ray observations provide currently the best way to determine the physical properties of galaxy clusters and the environmental parameters that describe them as laboratories. We illustrate this use of galaxy clusters and the precision of our understanding of them as laboratory environments with several examples. Their application to determine the matter composition of the Universe shows good agreement with results from other methods and is therefore a good test of our understanding. We test the reliability of mass measurements and illustrate the use of X-ray diagnostics to study the dynamical state of clusters. We discuss further studies on turbulence in the cluster ICM, the interaction of central AGN with the radiatively cooling plasma in cluster cooling cores and the lessons learned from the ICM enrichment by heavy elements.
595
- BRUNETTI GIANFRANCO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.493-500
- 2004
- 원문 바로보기
The existence and extent of non-thermal phenomena in galaxy clusters is now well established. A key question in our understanding of these phenomena is the origin of the relativistic electrons which may be constrained by the modelling of the fine radio properties of radio halos and of their statistics. In this paper we argue that present data favour a scenario in which the emitting electrons in the intracluster medium (ICM) are reaccelerated in situ on their way out. An overview of turbulent-particle acceleration models is given focussing on recent time-dependent calculations which include a full coupling between particles and MHD waves.
596
- HALLMAN ERIC J.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.593-596
- 2004
- 원문 바로보기
We introduce a method of identifying evidence of shocks in the X-ray emitting gas in clusters of galaxies. Using information from synthetic observations of simulated clusters, we do a blind search of the synthetic image plane. The locations of likely shocks found using this method closely match those of shocks identified in the simulation hydrodynamic data. Though this method assumes nothing about the geometry of the shocks, the general distribution of shocks as a function of Mach number in the cluster hydrodynamic data can be extracted via this method. Characterization of the cluster shock distribution is critical to understanding production of cosmic rays in clusters and the use of shocks as dynamical tracers.
597
- VOGT CORINA
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.349-353
- 2004
- 원문 바로보기
Magnetic fields are an important ingredient of galaxy clusters and are indirectly observed on cluster scales as radio haloes and radio relics. One promising method to shed light on the properties of cluster wide magnetic fields is the analysis of Faraday rotation maps of extended extragalactic radio sources. We developed a Fourier analysis for such Faraday rotation maps in order to determine the magnetic power spectra of cluster fields. In an advanced step, here we apply a Bayesian maximum likelihood method to the RM map of the north lobe of Hydra A on the basis of our Fourier analysis and derive the power spectrum of the cluster magnetic field. For Hydra A, we measure a spectral index of -5/3 over at least one order of magnitude implying Kolmogorov type turbulence. We find a dominant scale of about 3 kpc on which the magnetic power is concentrated, since the magnetic autocorrelation length is <TEX>${\lambda}_B = 3 {\pm} 0.5\;kpc$</TEX>. Furthermore, we investigate the influences of the assumption about the sampling volume (described by a window function) on the magnetic power spectrum. The central magnetic field strength was determined to be <TEX>${\~}7{\pm}2{\mu}G$</TEX> for the most likely geometries.
598
- SUTO YASUSHI
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.387-392
- 2004
- 원문 바로보기
X-ray observations of galaxy clusters have played an important role in cosmology, especially in determining the cosmological density parameter and the fluctuation amplitude. While they represent the bright side of the universe together with the other probes including the cosmic microwave background and the Type Ia supernovae, the resulting information clearly indicates that the universe is dominated by dark components. Even most of cosmic baryons turns out to be dark. In order to elucidate the nature of dark baryons, we propose a dedicated soft-X-ray mission, DIOS (Diffuse Intergalactic Oxygen Surveyor). Recent numerical simulations suggest that approximately 30 to 50 percent of total baryons at z = 0 take the form of the warm-hot intergalactic medium (WHIM) with <TEX>$10^5K < T < 10^7K $</TEX>which has evaded the direct detection so far. The unprecedented energy resolution (<TEX>${\~} 2eV$</TEX>) of the XSA (X-ray Spectrometer Array) on-board DIGS enables us to identify WHIM with gas temperature <TEX>$T = 10^6 {\~} 10^7K$</TEX> and overdensity <TEX>$\delta$</TEX> = 10 <TEX>${\~}$</TEX> 100 located at z < 0.3 through emission lines of OVII and OVIII. In addition, WHIMs surrounding nearby clusters are detectable with a typical exposure time of a day, and thus constitute realistic and promising targets for DIOS.
599
- RHEE MYUNG-HYUN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.3
- pp.91-117
- 2004
- 원문 바로보기
We analyze the dependence of the mass-to-light ratio of spiral galaxies on the present star formation rate (SFR), and find that galaxies with high present star formation rates have low mass-to-light ratios, presumably as a result of the enhanced luminosity. On this basis we argue that variations in the stellar content of galaxies result in a major source of intrinsic scatter in the Tully-Fisher relation (TF relation). Ideally one should use a 'population-corrected' luminosity. We have also analyzed the relation between the (maximum) luminous mass and rotational velocity, and find it to have a small scatter. We therefore propose that the physical basis of the Tully-Fisher relation lies in a relationship between the luminous mass and rotational velocity, in combination with a 'well-behaved' relation between luminous and dark matter. This implies that the Tully-Fisher relation is a combination of two independent relations: (i) a relation between luminosity and (luminous) mass, based mainly on the star formation history in galaxies, and (ii) a relation between mass and rotation velocity, which is the outcome of the process of galaxy formation. In addition to a 'population-corrected' Tully-Fisher relation, one may also use the relation between mass and luminosity, and the relation between luminous mass and rotation velocity as distance estimators.
600
- SARAZIN CRAIG L.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.433-438
- 2004
- 원문 바로보기
Clusters of galaxies generally form by the gravitational merger of smaller clusters and groups. Major cluster mergers are the most energetic events in the Universe since the Big Bang. The basic properties of cluster mergers and their effects are discussed. Mergers drive shocks into the intracluster gas, and these shocks heat the intracluster gas. As a result of the impulsive heating and compression associated with mergers, there is a large transient increase in the X-ray luminosities and temperatures of merging clusters. These merger boost can affect X-ray surveys of clusters and their cosmological interpretation. Similar boosts occur in the strong lensing cross-sections and Sunyaev-Zeldovich effect in merging clusters. Merger shock and turbulence associated with mergers should also (re)accelerate nonthermal relativistic particles. As a result of particle acceleration in shocks and turbulent acceleration following mergers, clusters of galaxies should contain very large populations of relativistic electrons and ions. Observations and models for the radio, extreme ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles accelerated in these shocks will also be described. Gamma-ray observations with GLAST seem particularly promising.