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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 32/123
311
- Kwon, Young-Joo
- Journal of the Korean astronomical society = 천문학회지
- 45, n.6
- pp.139-146
- 2012
- 원문 바로보기
We investigate the properties of OH, SiO, and <TEX>$H_2O$</TEX> maser emission in O-rich AGB stars. We use a sample of 3373 objects, which is an updated version of the list of O-rich AGB stars presented in Suh & Kwon (2011). We divide the 3373 O-rich AGB stars into four different groups based on the maser emission: OH maser sources (1533), SiO sources (1627), <TEX>$H_2O$</TEX> sources (452), and sources with no maser (610). To understand the nature of the maser sources, we present various infrared two-color diagrams (2CDs) using IRAS, 2MASS, and AKARI data. For each group, we compare the positions on various infrared 2CDs with theoretical models. We find that the OH maser sources generally show larger color indices and larger dust optical depths than SiO or <TEX>$H_2O$</TEX> sources. We suggest that the differences of the color indices for different maser sources are due to different mass-loss rates and dust formation processes.
312
- Park, Jong-Ho
- Journal of the Korean astronomical society = 천문학회지
- 45, n.6
- pp.147-156
- 2012
- 원문 바로보기
We present a test of the emission statistics of active galactic nuclei (AGN), probing the connection between the red-noise temporal power spectra and multi-modal flux distributions known from observations. We simulate AGN lightcurves under the assumption of uniform stochastic emission processes for different power-law indices of their respective power spectra. For sufficiently shallow slopes (power-law indices (<TEX>${\beta}{\leq}1$</TEX>), the flux distributions (histograms) of the resulting lightcurves are approximately Gaussian. For indices corresponding to steeper slopes (<TEX>${\beta}{\geq}1$</TEX>), the flux distributions become multi-modal. This finding disagrees systematically with results of recent mm/radio observations. Accordingly, we conclude that the emission from AGN does not necessarily originate from uniform stochastic processes even if their power spectra suggest otherwise. Possible mechanisms include transitions between different activity states and/or the presence of multiple, spatially disconnected, emission regions.
313
- Choi, Chang-Su
- Journal of the Korean astronomical society = 천문학회지
- 45, n.1
- pp.7-17
- 2012
- 원문 바로보기
Y-band is a broad passband that is centered at ~1 <TEX>${\mu}m$</TEX>. It is becoming a new, popular window for extragalactic study especially for observations of red objects thanks to recent CCD technology developments. In order to better understand the general characteristics of objects in Y-band, and to investigate the promise of Y-band observations with small telescopes, we carried out imaging observations of several extragalactic fields, brown dwarfs, and high redshift quasars with Y-band filter at the Mt. Lemmon Optical Astronomy Observatory and the Maidanak observatory. From our observations, we constrain the bright end of the galaxy and the stellar number counts in Y-band. We also test the usefulness of high redshift quasar (z >6) selection via i - z - Y color-color diagram, to demonstrate that the i - z - Y color-color diagram is effective for the selection of high redshift quasars even with a conventional optical CCD camera installed at a 1-m class telescope.
314
- Youn, So-Young
- Journal of the Korean astronomical society = 천문학회지
- 45, n.4
- pp.93-99
- 2012
- 원문 바로보기
We present a 1.1mm emission map of the OMC1 region observed with AzTEC, a new large-format array composed of 144 silicon-nitride micromesh bolometers, that was in use at the James Clerk Maxwell Telescope (JCMT). These AzTEC observations reveal dozens of cloud cores and a tail of filaments in a manner that is almost identical to the submillimeter continuum emission of the entire OMC1 region at 450 and <TEX>$850{\mu}m$</TEX>. We perform Fourier analysis of the image with a modified periodogram and the density power spectrum, which provides the distribution of the length scale of the structures, is determined. The expected value of the periodogram converges to the resulting power spectrum in the mean squared sense. The present analysis reveals that the power spectrum steepens at relatively smaller scales. At larger scales, the spectrum flattens and the power law becomes shallower. The power spectra of the 1.1mm emission show clear deviations from a single power law. We find that at least three components of power law might be fitted to the calculated power spectrum of the 1.1mm emission. The slope of the best fit power law, <TEX>${\gamma}{\approx}-2.7$</TEX> is similar to those values found in numerical simulations. The effect of beam size and the noise spectrum on the shape and slope of the power spectrum are also included in the present analysis. The slope of the power law changes significantly at higher spatial frequency as the beam size increases.
315
- Lee, Jung-Won
- Journal of the Korean astronomical society = 천문학회지
- 45, n.5
- pp.117-125
- 2012
- 원문 바로보기
We present <TEX>$^{12}CO$</TEX> J = 2-1 line observations of G54.1+0.3, a composite supernova remnant with a mid-infrared (MIR) loop surrounding the central pulsar wind nebula (PWN). We map an area of <TEX>$12^{\prime}{\times}9^{\prime}$</TEX> around the PWN and its associated MIR loop. We confirm two velocity components that have been proposed to be possibly interacting with the PWN/MIR-loop; the +53 km <TEX>$s^{-1}$</TEX> cloud, which appears in contact with the eastern boundary of the PWN and the +23 km <TEX>$s^{-1}$</TEX> cloud, which has CO emission coincident with the MIR loop. However, we have not found a direct evidence for the interaction in either of these clouds. Instead, we detected an 5'-long arc-like cloud at +15-+23 km <TEX>$s^{-1}$</TEX> with a systematic velocity gradient of ~3 km <TEX>$s^{-1}$</TEX> <TEX>$arcmin^{-1}$</TEX> and broad-line emitting CO gas with widths (FWHM) of <TEX>${\leq}7km\;s^{-1}$</TEX> in the western interior of the supernova remnant. We discuss their association with the supernova remnant.
316
- Li, Xue-Bao
- Journal of the Korean astronomical society = 천문학회지
- 45, n.1
- pp.19-24
- 2012
- 원문 바로보기
Microthermal fluctuations are introduced by atmospheric turbulence very near the ground. In order to detect microthermal fluctuations at Fuxian Solar Observatory (FSO), a microthermal instrument has been developed. The microthermal instrument consists of a microthermal sensor, which is based on a Wheatstone bridge circuit and uses fine tungsten filaments as resistance temperature detectors, an associated signal processing unit, and a data collection, & communication subsystem. In this paper, after a brief introduction to surface layer seeing, we discuss the instrumentation behind the microthermal detector we have developed and then present the results obtained. The results of the evaluation indicate that the effect of the turbulent surface boundary layer to astronomical seeing would become sufficiently small when installing a telescope at a height of 16m or higher from the ground at FSO.
317
- Ghaderi, Kamal
- Journal of the Korean astronomical society = 천문학회지
- 45, n.1
- pp.1-6
- 2012
- 원문 바로보기
We use a Probabilistic Neural Network (PNN) technique to derive the orbital parameters of spectroscopic binary stars. Using measured radial velocity data of five double-lined spectroscopic binary systems (i.e., EQ Tau, V376 And, V776 Cas, V2377 Oph and EE Cet), we find the corresponding orbital and spectroscopic elements. Our numerical results are in good agreement with those obtained by other groups via more traditional methods.
318
- Choi, Seong-Hwan
- Journal of the Korean astronomical society = 천문학회지
- 45, n.2
- pp.31-38
- 2012
- 원문 바로보기
In this study we apply Support Vector Machine (SVM) to the prediction of geo-effective halo coronal mass ejections (CMEs). The SVM, which is one of machine learning algorithms, is used for the purpose of classification and regression analysis. We use halo and partial halo CMEs from January 1996 to April 2010 in the SOHO/LASCO CME Catalog for training and prediction. And we also use their associated X-ray flare classes to identify front-side halo CMEs (stronger than B1 class), and the Dst index to determine geo-effective halo CMEs (stronger than -50 nT). The combinations of the speed and the angular width of CMEs, and their associated X-ray classes are used for input features of the SVM. We make an attempt to find the best model by using cross-validation which is processed by changing kernel functions of the SVM and their parameters. As a result we obtain statistical parameters for the best model by using the speed of CME and its associated X-ray flare class as input features of the SVM: Accuracy=0.66, PODy=0.76, PODn=0.49, FAR=0.72, Bias=1.06, CSI=0.59, TSS=0.25. The performance of the statistical parameters by applying the SVM is much better than those from the simple classifications based on constant classifiers.
319
- Hwang, Jai-Chan
- Journal of the Korean astronomical society = 천문학회지
- 45, n.3
- pp.65-69
- 2012
- 원문 바로보기
Physical cosmology tries to understand the Universe at large with its origin and evolution. Observational and experimental situations in cosmology do not allow us to proceed purely based on the empirical means. We examine in which sense our cosmological assumptions in fact have shaped our current cosmological worldview with consequent inevitable limits. Cosmology, as other branches of science and knowledge, is a construct of human imagination reflecting the popular belief system of the era. The question at issue deserves further philosophic discussions. In Whitehead's words, 'philosophy, in one of its functions, is the critic of cosmologies'. (Whitehead 1925).
320
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 45, n.2
- pp.25-29
- 2012
- 원문 바로보기
New methods are developed to estimate the effective temperature (Te), surface gravity (log g), and metallicity ([A/H]) simultaneously with the spectral line depth ratios. Using the model atmosphere grids, depth values are calculated for the wavelength range of <TEX>$4000{\AA}-5600{\AA}$</TEX> for various temperatures, gravities, and metallicities. All possible different combinations of line depth ratios for different pairs of ratios are investigated. A graphical 3D figure is produced with X, Y, and Z axes corresponding to Te, log g, and [A/H], respectively. By reading a cross point of two curves plotted by a connection of three parameters obtained from spectral line depth ratio pairs on each of the three projected planes, Te, log g, and [A/H] are determined simultaneously. In addition, an analytical method is devised based on the similar algorithm developed for the graphical method. Our methods were applied to estimate the fundamental atmospheric parameters of the Sun and Arcturus.