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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 37/122
361
- Chae, Jong-Chul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.61-69
- 2009
- 원문 바로보기
Transverse velocity vectors can be determined from a pair of images successively taken with a time interval using an optical flow technique. We have tested the performance of the new technique called NAVE (non-linear affine velocity estimator) recently implemented by Chae & Sakurai using real image data taken by the Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT) aboard the Hinode satellite. We have developed two methods of estimating the errors in the determination of velocity vectors, one resulting from the non-linear fitting <TEX>${\sigma}_{\upsilon}$</TEX> and the other <TEX>${\epsilon}_u$</TEX> resulting from the statistics of the determined velocity vectors. The real error is expected to be somewhere between <TEX>${\sigma}_{\upsilon}$</TEX> and <TEX>${\epsilo</TEX><TEX>n}_u$</TEX>. We have investigated the dependence of the determined velocity vectors and their errors on the different parameters such as the critical speed for the subsonic filtering, the width of the localizing window, the time interval between two successive images, and the signal-to-noise ratio of the feature. With the choice of <TEX>$v_{crit}$</TEX> = 2 pixel/step for the subsonic filtering, and the window FWHM of 16 pixels, and the time interval of one step (2 minutes), we find that the errors of velocity vectors determined using the NAVE range from around 0.04 pixel/step in high signal-to-noise ratio features (S/N <TEX>$\sim$</TEX> 10), to 0.1 pixel/step in low signa-to-noise ratio features (S/N <TEX>$\sim$</TEX> 3) with the mean of about 0.06 pixel/step where 1 pixel/step corresponds roughly to 1 km/s in our case.
362
- Oh, Seung-Kyung
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.105-105
- 2009
- 원문 바로보기
363
- Abdel-Rahman, H.I.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.71-79
- 2009
- 원문 바로보기
In this paper, statistical distribution functions are developed for distance determination of stellar groups. This method depends on the assumption that absolute magnitudes and apparent magnitudes follow a Gaussian distribution function. Due to the limits of the integrands of the frequency function of apparent and absolute magnitudes, we introduce Case A, B, and C Gaussian distributions. The developed approaches have been implemented to determine distances to some clusters and stellar associations. The comparison with the distances derived by different authors reveals good agreement.
364
- Moon, Y.J.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.2
- pp.27-32
- 2009
- 원문 바로보기
Recently, we suggested a CME earthward direction parameter as an important geoeffective parameter that has been demonstrated by front-side halo CME data. In this study, we present the geometrical implication of this parameter by comparing with the parameters from a CME cone model. Major results from this study can be summarized as follows. First, we derive an analytic relationship between the cone model parameters(the half angular width of a cone and the angle between the cone axis and the plane of sky) and the earthward direction parameter. Second, we demonstrate a close relationship between the earthward direction parameter and the cone axis angle using 32 front-side full halo CMEs. Third, we found that there is noticeable inconsistency between the cone axis angles estimated from the cone model fitting to the CMEs and from their associated flare positions, implying that the flare position should not be considered as a good earthward direction parameter. Finally we present several advantages of our earthward direction parameter in terms of the forecast of a geomagnetic storm based on CME parameters.
365
- Kim, Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.135-144
- 2009
- 원문 바로보기
We present JHK near-infrared photometric study for the old open cluster (OC) Trumpler 5 (Tr 5), based on the 2MASS data. From the color-magnitude diagrams of Tr 5, we have located the position of the red giant clump (RGC) stars, and used the mean magnitude of the RGC stars in K-band to estimate the distance to Tr 5, d = <TEX>$3.1{\pm}0.1$</TEX> kpc (<TEX>$(m-M)_0$</TEX> = <TEX>$12.46{\pm}0.04$</TEX>). From fitting the theoretical isochrones of Padova group, we have estimated the reddening, metallicity, and age : E(B-V) = <TEX>$0.64{\pm}0:05$</TEX>, [Fe/H] = <TEX>$-0.4{\pm}0.1$</TEX> dex, and t = <TEX>$2.8{\pm}0.2$</TEX> Gyr (log t = <TEX>$9.45{\pm}0.04$</TEX>), respectively. These parameters generally agree well with those obtained from the previous studies on Tr 5 and confirms that this cluster is an old OC with metallicity being metal-poorer than solar abundance, located in the anti-Galactic center region.
366
- Kim, Do-Eon
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.33-37
- 2009
- 원문 바로보기
We propose a diagnostic that can resolve the planet/binary degeneracy of central perturbations in caustic-crossing high-magnification microlensing events. The diagnostic is based on the difference in the morphology of perturbation inside the central caustics induced by a planet and a wide-separation binary companion. We find that the contours of excess exhibit a concentric circular pattern around the caustic center for the binary-lensing case, while the contours are elongated or off-centered for the planetary case. This difference results in the distinctive features of the individual lens populations in the residual of the trough region between the two peaks of the caustic crossings, where the shape of the residual is symmetric for binary lensing while it tends to be asymmetric for planetary lensing. We determine the ranges of the planetary parameters for which the proposed diagnostic can be used. The diagnostic is complementary to previously proposed diagnostics in the sense that it is applicable to caustic-crossing events with small finite-source effect.
367
- Yoo, Kye-Hwa
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.93-103
- 2009
- 원문 바로보기
This article reports the spectral behavior of CH Cygni, using data obtained in October 2005 and June 2006. In these epochs, CH Cygni showed emission lines of H I, Fe II, [Fe II], [O III], [N II], [Ne III] and [S II]. Many of these lines were more enhanced since 2004. The underlying M-type spectrum was removed to get the intrinsic emission profile, and the resulting profiles were deconvoluted into several Gaussian components. Also, the radial velocities for all the lines that appeared in these spectra of CH Cygni were measured. The resultant lines were compared with each other and with those obtained in 2004; the findings are explained in terms of an accretion disk and jets.
368
- Jeong, Hye-Won
- Journal of the Korean astronomical society = 천문학회지
- 42, n.1
- pp.9-15
- 2009
- 원문 바로보기
A necessary condition for the formation of a filament is magnetic helicity. In the present paper we seek the origin of magnetic helicity of intermediate filaments. We observed the formation of a sinistral filament at the boundary of a decaying active region using full-disk <TEX>$H_{\alpha}$</TEX> images obtained from Bi Bear Solar Observatory. We have measured the rate of helicity injection during the formation of the filament using full-disk 96 minute-cadence magnetograms taken by SOHO MDI. As a result we found that 1) no significant helicity was injected around the region (polarity inversion line; PIL) of filament formation and 2) negative helicity was injected in the decaying active region. The negative sign of the injected helicity was opposite to that of the filament helicity. On the other hand, at earlier times when the associated active region emerged and grew, positive helicity was intensively injected. Our results suggest that the magnetic helicity of the intermediate filament may have originated from the helicity accumulated during the period of the growth of its associated active region.
369
- Bong, Su-Chan
- Journal of the Korean astronomical society = 천문학회지
- 42, n.1
- pp.1-7
- 2009
- 원문 바로보기
The e-CALLISTO is a global network of frequency-agile solar radio spectrometers that was constructed in a collaboration between Swiss Federal Institute of Technology Zurich (ETH Zurich) and local host institutes. It is intended to monitor solar radio bursts 24 hours a day in frequency range between 45 MHz and 870 MHz. One of e-CALLISTO spectrometer was installed at Korea Astronomy and Space Science Institute (KASI) in 2007 October. The spectrometer gets signals from a horizontally polarized log-periodic antenna mounted on an automatic Sun-tracking system. Tracking status and data are monitored in Space Weather Monitoring Laboratory (SWML) of KASI in real time, and flare time data are transferred to ETH Zurich data archive daily. Using this spectrometer we obtained a couple of type II solar radio bursts on 2007 December 31, and found that these bursts are associated with a CME which occurred on the east limb.
370
- Son, Dong-Hoon
- Journal of the Korean astronomical society = 천문학회지
- 42, n.5
- pp.125-134
- 2009
- 원문 바로보기
We investigated the circumnuclear region of the Seyfert 2 galaxy NGC 5728, using the CFHT 3.6 m OASIS <TEX>$[S_{II}]$</TEX>, <TEX>$[O_{III}]$</TEX> & <TEX>$H\beta$</TEX> spectral images complemented with the IUE spectra. The physical condition of the circumnuclear zone has been derived: the gas density (indicated by <TEX>$[S_{II}]$</TEX>6716/31 ratio) around the C core is generally similar to that around the NW core, i.e., <TEX>$\sim500cm^{-3}$</TEX>. However, there appears to be evidence of a higher density shell in front of the NW core, <TEX>$\sim10^4cm^{-3}$</TEX> at -250 km <TEX>$s^-1$</TEX>. The IUE <TEX>$Si_{III}$</TEX>]1892/<TEX>$C_{III}$</TEX>]1909 ratio implies a possible presence of a broad emission region of gas densities of <TEX>$\sim10^{10}cm^{-3}$</TEX>. The SE cone and surrounding area show several prominent features, while the NW cone does not show any particular structure: we identified three prominent blobs in the SE cone and one possible candidate in the NW cone. The outflow activities exist within the relatively large conic opening angle. We discussed the possibility of inflow or outflow activities of blobs found in the circumnuclear region of NGC 5728. The gas around two cores, two cones, and several blobs, is likely to be excited by the AGN hot source(s).