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- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 31/119
301
- Kim, Jae-Yeong
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.135-142
- 2011
- 원문 바로보기
A <TEX>$200'{\times}200'$</TEX> region around 30 Doradus in the Large Magellanic Cloud (LMC) is observed and analyzed in the near-infrared. We obtain polarimetry data in the J, H, and Ks bands using the SIRIUS polarimeter SIRPOL at the Infrared Survey Facility 1.4 m telescope. We measure the Stokes parameters of 2562 point-like sources to derive the degree of polarization and the polarization position angles. We discuss the statistics of the groups classified by color-magnitude diagram and proper motions of the sources, in order to separate the Galactic foreground sources from those present in the LMC. We notice that groups classified by the proper motion data show a tendency towards different polarimetric properties.
302
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.73-79
- 2011
- 원문 바로보기
We collect 24 times of light maxima data from sources in the literature, unpublished data and open databases, and investigate the variations of the observed and calculated (O-C) values for light maxima of V1719 Cyg. We found no evidence of the variations in the (O-C) values. We estimate the effective temperature and surface gravity using both the Kurucz and MARCS/SSG grids for different metallicity values [A/H]=0.0 and +0.5 for V1719 Cyg. It is confirmed that the temperature is almost the same, but, in the case of surface gravity, the MARCS/SSG grid gives the value closest to that obtained from the period-gravity relation derived by using the pulsation-evolution theory. We obtain two spectra of V1719 Cyg from spectroscopic observation which permitted us to find the effective temperature and the surface gravity of the star directly. We estimate the metallicity and it is found that the abundance of iron is equal to the solar value.
303
- Hanna, Magdy A.
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.97-108
- 2011
- 원문 바로보기
The photometric light curves of the W-type W UMa eclipsing contact binary system BB Pegasi have been found to be extremely asymmetric over all the observed 63 years in all wavelengths UBVR. The light curves have been characterized by occultation primary minima. Hence, the morphology of these light curves has been studied in view of these different asymmetric degrees. The system shows a distinct O'Connell effect, as well as depth variation. A 22.96 years of stellar dark spots cycle has been determined for the system. Almost the same cycle (22.78 yr) has been found for the depth variation of MinI and MinII. We also present an analysis of mid-eclipse time measurements of BB Peg. The analysis indicates a period decrement of <TEX>$5.62{\times}10^{-8}$</TEX> day/yr, which can be interpreted in terms of mass transfer at a rate of <TEX>$-4.38{\times}10^{-8}M_{\odot}$</TEX>/yr, from the more to the less massive component. The O - C diagram shows a damping sine wave covering two different cycles of 17.0 yr and 12.87 yr with amplitudes equal to 0.0071 and 0.0013 day, respectively. These unequal durations show a non-periodicity which may be explained as a result of magnetic activity cycling variations due to star spots. The obtained characteristics are consistent with similar chromospherically active stars, when applying the Applegate's (1992) mechanism.
304
- Kim, Kee-Tae
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.81-87
- 2011
- 원문 바로보기
We carry out 100-GHz band test observations with the newly-constructed KVN 21-m radio telescopes in order to evaluate their performance. The three telescopes have similar performance parameters. The pointing accuracies are about 4' rms for the entire sky. The main beam sizes are about 30' (FWHMs), which is nearly the diffraction limit of the telescopes at the observing frequency (97 GHz). The measured aperture and main-beam efficiencies are about 52% and 46%, respectively, for all three telescopes. The estimated moon efficiency is ~84% for the KVN Tamna telescope. The first sidelobes appear 50' (~1.6<TEX>${\times}$</TEX>FWHM) from the main beam centers and the levels are on average -14 dB.
305
- Lee, Hyun-Chul
- Journal of the Korean astronomical society = 천문학회지
- 44, n.5
- pp.195-200
- 2011
- 원문 바로보기
We have revisited the ACS Virgo Cluster Survey (ACSVCS), a Hubble Space Telescope program to obtain ACS/WFC g and z bands imaging for a sample of 100 early-type galaxies in the Virgo Cluster. In this study, we examine 51 nucleated early-type galaxies in the ACSVCS in order to look into the relationship between the photometric and structural properties of stellar nuclei and their host galaxies. We morphologically dissect galaxies into five classes. We note that (1) the stellar nuclei of dwarf early-type galaxies (dS0, dE, and dE,N) are generally fainter and bluer with g > 18.95 and (g-z) < 1.40 compared to some brighter and redder counterparts of the ellipticals (E) and lenticular galaxies (S0), (2) the g-band half-light radii of stellar nuclei of all dwarf early-type galaxies (dS0, dE, and dE,N) are smaller than 20 pc and their average is about 4 pc, and (3) the colors of red stellar nuclei with (g - z) > 1.40 in bright ellipticals and lenticular galaxies are bluer than their host galaxies colors. We also show that most of the unusually 'red' stellar nuclei with (g-z) > 1.54 in the ACSVCS are the central parts of bright ellipticals and lenticular galaxies. Furthermore, we present multi photometric band color - color plots that can be used to break the age-metallicity degeneracy particularly by inclusion of the thermally pulsing-asymptotic giant branch (TP-AGB) phases of stellar evolution in the stellar population models.
306
- Han, Cheong-Ho
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.109-113
- 2011
- 원문 바로보기
In current microlensing planet searches that are being carried out in a survey/follow-up mode, the most important targets for follow-up observations are lensing events with high magnifications resulting from the very close approach of background source stars to the lens. In this paper, we investigate the dependence of the sensitivity to planets on detailed properties of high-magnification events. From this, it is found that the sensitivity does not monotonically increase as the impact parameter between the lens and the source trajectory decreases. Instead, it is roughly the same for events with impact parameters less than a certain threshold value. It is also found that events involving main-sequence source stars are sensitive to planets in a much wider range of separation and mass ratio, than those events involved with giant source stars. Based on these results, we propose observational strategies for maximal planet detections considering the types of telescopes available for follow-up observations.
307
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 44, n.1
- pp.33-38
- 2011
- 원문 바로보기
We study near-infrared properties of the old open cluster King 11, based on the 2MASS photometric data. We determine the location of the red giant clump(RGC) in the (K, J - K) colo-magnitude diagram and derive the distance modulus of King 11 to be <TEX>$(m-M)_0$</TEX> = <TEX>$12.50{\pm}0.10$</TEX> using the mean K magnitude of RGC. From the red giant branch slope - [Fe/H] relation we obtain the metallicity of this cluster, [Fe/H]=<TEX>$-0.17{\pm}0.07$</TEX>. The age and interstellar reddening of this cluster are estimated to be log t = <TEX>$9.48{\pm}0.05$</TEX>, E(B-V)=<TEX>$0.90{\pm}0.03$</TEX>, by applying Padova isochrone fits to the data.
308
- Im, Myung-Shin
- Journal of the Korean astronomical society = 천문학회지
- 43, n.3
- pp.75-93
- 2010
- 원문 바로보기
We present the characteristics of the Seoul National University 4k Camera (SNUCAM) and report its performance on the 1.5m telescope at the Maidanak observatory in Uzbekistan. SNUCAM is a CCD camera with a pixel scale of 0.266' in <TEX>$4096{\times}4096$</TEX> format, covering <TEX>$18.1'{\times}18.1'$</TEX> field of view on the 1.5m. The camera is currently equipped with Bessell UBVRI, <TEX>$H{\alpha}$</TEX>, SDSS ugriz, and Y-band filters, allowing us to carry out a variety of scientific programs ranging from exoplanet studies to survey of quasars at high redshift. We examine properties of SNUCAM such as the bias level and its temporal variation, the dark current, the readout noise, the gain, the linearity, the fringe patterns, the amplifier bias, and the bad pixels. From our observations, we also constructed the master fringe frames in I-, z-, and Y-band. We outline some of the current scientific programs being carried out with SNUCAM, and demonstrate that SNUCAM on the 1.5m can deliver excellent images that reach to the <TEX>$5-{\sigma}$</TEX> detection limits of R~25.5 mag and z~22.7 mag in 1 hour total integration.
309
- Yushchenko, A.V.
- Journal of the Korean astronomical society = 천문학회지
- 43, n.3
- pp.65-74
- 2010
- 원문 바로보기
We investigate <TEX>${\rho}$</TEX> Pup using the high resolution spectral observations taken from the VLT archive and observations at a 1.8m-Korean telescope with BOES spectrograph. The atmospheric parameters are determined using the iron-line abundance analysis. We derive an effective temperature value of <TEX>$T_{eff}=6890{\pm}250K$</TEX>, surface gravity of log g=<TEX>$3.28{\pm}0.3$</TEX> dex, microturbulent velocity of <TEX>${\upsilon}_{micro}=4.1{\pm}0.4km\;s^{-1}$</TEX>, and the iron abundance of log N=<TEX>$7.82{\pm}0.15$</TEX>. The projected rotational velocity of the star is close to <TEX>${\upsilon}$</TEX> sin i=3.5km <TEX>$s^{-1}$</TEX>. Asymmetric line profiles in the observed spectra and variation of this asymmetry with time show that both strong radial pulsation and weak non-radial pulsations are present in <TEX>${\rho}$</TEX> Pup.
310
- Chae, Jong-Chul
- Journal of the Korean astronomical society = 천문학회지
- 43, n.3
- pp.55-64
- 2010
- 원문 바로보기
We investigate how plasma structures in the solar chromosphere and corona can extend to altitudes much above hydrostatic scale heights from the solar surface even under the force of gravity. Using a simple modified form of equation of motion in the vertical direction, we argue that there are two extreme ways of non-hydrostatic support: dynamical support and magnetic support. If the vertical acceleration is downward and its magnitude is a significant fraction of gravitational acceleration, non-hydrostatic support is dynamical in nature. Otherwise non-hydrostatic support is static, and magnetic support by horizontal magnetic fields is the only other possibility. We describe what kind of observations are needed in the clarification of the nature of non-hydrostatic support. Observations available so far seem to indicate that spicules in the quiet regions and dynamic fibrils in active regions are dynamically supported whereas the general chromosphere as well as prorninences is magnetically supported. Moreover, it appears that magnetic support is required for plasma in some coronal loops as well. We suspect that the identification of a coronal loop with a simple magnetic flux tube might be wrong in this regard.