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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 56/122
551
- RHEE MYUNG-HYUN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.1
- pp.15-39
- 2004
- 원문 바로보기
We analyse the results of mass models derived from the HI rotation! curves of spiral galaxies and find that the slope of the luminous mass-circular velocity relation is close to 4. The luminous mass-circular velocity relation with a slope of about 4 can be explained by an anti-correlation between the mass surface density of luminous matter and the mass ratio of the dark and luminous components. We also argue that the conspiracy between luminous and dark matter exists in a local sense (producing a flat or smooth rotation curve) and in a global sense (affecting the mass ratio of the dark and luminous matter), maintaining the luminous mass-circular velocity relation with a slope of about 4. We therefore propose that the physical basis of the Tully-Fisher relation lies in the luminous mass-circular velocity relation. While the slope of the luminous mass-circular velocity relation is fairly well defined regardless of the dark matter contribution, the zero-point of the relation is still to be determined. The determination of the slope of the Tully-Fisher relation needs one more step: the mean trend of the luminosity-luminous mass relation determines the overall shape (slope) of the Tully-Fisher relation. The key parameter needed to determine the zero-point of the luminous mass-circular velocity relation and the slope of the Tully-Fisher relation obviously is the luminous mass-to-light ratio.
552
- KIM YOONBAI
- Journal of the Korean astronomical society = 천문학회지
- 37, n.1
- pp.1-14
- 2004
- 원문 바로보기
Basic idea of Randall-Sundrum brane world model I and II is reviewed with detailed calculation. After introducing the brane world metric with exponential warp factor, metrics of Randall-Sundrum models are constructed. We explain how Randall-Sundrum model I with two branes makes the gauge hierarchy problem much milder, and derive Newtonian gravity in Randall-Sundrum model II with a single brane by considering small fluctuations.
553
- HENRIKSEN MARK
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.299-305
- 2004
- 원문 바로보기
We find evidence of a hard X-ray excess above the thermal emission in two cool clusters (Abell 1750 and IC 1262) and a soft excess in two hot clusters (Abell 754 and Abell 2163). Our modeling shows that the excess components in Abell 1750, IC 1262, and Abell 2163 are best fit by a steep power law indicative of a significant non-thermal component. In the case of Abell 754, the excess emission is thermal, 1 ke V emission. We analyze the dynamical state of each cluster and find evidence of an ongoing or recent merger in all four clusters. In the case of Abell 2163, the detected, steep spectrum, non-thermal X-ray emission is shown to be associated with the weak merger shock seen in the temperature map. However, this shock is not able to produce the flatter spectrum radio halo which we attribute to post-shock turbulence. In Abell 1750 and IC 1262, the shocked gas appears to be spatially correlated with non-thermal emission suggesting cosmic-ray acceleration at the shock front.
554
- BOWYER STUART
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.295-297
- 2004
- 원문 바로보기
Observations with EUVE, ROSAT, and BeepoSAX have shown that some clusters of galaxies produce intense EUV emission. These findings have produced considerable interest; over 100 papers have been published on this topic in the refereed literature. A notable suggestion as to the source of this radiation is that it is a 'warm' (106 K) intracluster medium which, if present, would constitute the major baryonic component of the universe. A more recent variation of this theme is that this material is 'warm-hot' intergalactic material condensing onto clusters. Alternatively, inverse Compton scattering of low energy cosmic rays against cosmic microwave background photons has been proposed as the source of this emission. Various origins of these particles have been posited, including an old (<TEX>${\~}$</TEX>Giga year) population of cluster cosmic rays; particles associated with relativistic jets in the cluster; and cascading particles produced by shocks from sub-cluster merging. The observational situation has been quite uncertain with many reports of detections which have been subsequently contradicted by analyses carried out by other groups. Evidence supporting a thermal and a non-thermal origin has been reported. The existing EUV, FUV, and optical data will be briefly reviewed and clarified. Direct observational evidence from a number of different satellites now rules out a thermal origin for this radiation. A new examination of subtle details of the EUV data suggests a new source mechanism: inverse Compton scattered emission from secondary electrons in the cluster. This suggestion will be discussed in the context of the data.
555
- HATTORI MAKOTO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.543-546
- 2004
- 원문 바로보기
The inverse Compton scattering of the cosmic microwave background (CMB) radiation with electrons in the intracluster medium which has a temperature gradient, was examined by the third-order perturbation theory of the Compton scattering. A new type of the spectrum distortion of the CMB was found and named as gradient T Sunyaev-Zel'dovich effect (gradT SZE). The spectrum has an universal shape. There is a zero distortion point, the cross over frequency, at 326GHz. When the hotter region locates closer to an observer, the intensity becomes brighter than the CMB in the frequency region lower than the cross over frequency and fainter than the CMB in the frequency region higher than the cross over frequency. When the cooler region locates closer to an observer, the distorted part of the spectrum has an opposite sign to the above case. The amplitude of the spectrum distortion does not de-pend on the electron density and depends on the heat conductivity and the total temperature variation along a line of sight. Therefore, the gradT SZE provides an unique opportunity to measure thermally nonequilibrium electron momentum distribution function in the ICM and combined with the X-ray measurements of the electron temperature distribution provides an opportunity of direct measurement of the heat conductivity in the ICM.
556
- SANTILLAN ALFREDO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.233-235
- 2004
- 원문 바로보기
High-velocity clouds are flows of neutral hydrogen, located at high galactic latitudes, with large velocities (<TEX>$[VLSR]{\ge} 100 km/s$</TEX>) that do not match a simple model of circular rotation for our Galaxy. Numerical simulations have been performed for the last 20 years to study the details of their evolution, and their possible interaction with the Galactic disk. Here we present a brief review of the models that have been already published, and describe newly performed three-dimensional magnetohydrodynamic simulations.
557
- SHIN MIN-SU
- Journal of the Korean astronomical society = 천문학회지
- 37, n.2
- pp.79-85
- 2004
- 원문 바로보기
We developed an algorithm to identify and determine periods of variable sources. With its robustness and high speed, it is expected to become an useful tool for surveys with large volume of data. This new scheme consists of an initial coarse. process of finding several candidate periods followed by a secondary process of much finer period search. With this multi-step approach, best candidates among statistically possible periods are produced without human supervision and also without any prior assumption on the nature of the variable star in question. We tested our algorithm with 381 stars taken from the ASAS survey and the result is encouraging. In about <TEX>$76\%$</TEX> cases, our results are nearly identical as their published periods. Our algorithm failed to provide convincing periods for only about <TEX>$10\%$</TEX> cases. For the remaining <TEX>$14\%$</TEX>, our results significantly differ from their periods. We show that, in many of these cases, our periods are superior and much closer to the true periods. However, the existence of failures, and also periods sometimes worse than manually controlled results, indicates that this algorithm needs further improvement. Nevertheless, the present experiment shows that this is a positive step toward a fully automated period analysis for future variability surveys.
558
- GIOVANNINI GABRIELE
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.323-328
- 2004
- 원문 바로보기
In this paper we review the observational results on Relic radio sources in clusters of galaxies. We discuss their observational properties, structures and radio spectra. We will show that Relics can be divided according to their size, morphology, and location in the galaxy cluster. These differences could be related to physical properties of Relic sources. The comparison with cluster conditions suggests that Relics could be related to shock waves originated by cluster mergers.
559
- PFROMMER C.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.455-460
- 2004
- 원문 바로보기
There have been many speculations about the presence of cosmic ray protons (CRps) in galaxy clusters over the past two decades. However, no direct evidence such as the characteristic <TEX>$\gamma$</TEX>-ray signature of decaying pions has been found so far. These pions would be a direct tracer of hadronic CRp interactions with the ambient thermal gas also yielding observable synchrotron and inverse Compton emission by additionally produced secondary electrons. The obvious question concerns the type of galaxy clusters most likely to yield a signal: Particularly suited sites should be cluster cooling cores due to their high gas and magnetic energy densities. We studied a nearby sample of clusters evincing cooling cores in order to place stringent limits on the cluster CRp population by using non-detections of EGRET. In this context, we examined the possibility of a hadronic origin of Coma-sized radio halos as well as radio mini-halos. Especially for mini-halos, strong clues are provided by the very plausible small amount of required CRp energy density and a matching radio profile. Introducing the hadronic minimum energy criterion, we show that the energetically favored CRp energy density is constrained to <TEX>$2\%{\pm}1\%$</TEX> of the thermal energy density in Perseus. We also studied the CRp population within the cooling core region of Virgo using the TeV <TEX>$\gamma$</TEX>-ray detection of M 87 by HEGRA. Both the expected radial <TEX>$\gamma$</TEX>-ray profile and the required amount of CRp support this hadronic scenario.
560
- 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.