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- 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 34/122
331
- Lee, Jeong-Eun
- Journal of the Korean astronomical society = 천문학회지
- 44, n.2
- pp.67-72
- 2011
- 원문 바로보기
We report the results of our high resolution optical spectroscopic monitoring campaign (<TEX>${\lambda}$</TEX> = 3800 ~ 8800 <TEX>${\AA}$</TEX>, R = 30000 - 45000) of the new FU Orionis-type object HBC 722. We observed HBC 722 with the BOES 1.8-m telescope between November 26 and December 29, 2010, and FU Orionis itself on January 26, 2011. We detect a number of previously unreported high-resolution K I and Ca II lines beyond 7500 <TEX>${\AA}$</TEX>. We resolve the H<TEX>${\alpha}$</TEX> and Ca II line profiles into three velocity components, which we attribute to both disk and outflow. The increased accretion during outburst can heat the disk to produce the relatively narrow absorption feature and launch outflows appearing as high velocity blue and red-shifted broad features.
332
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 43, n.1
- pp.1-8
- 2010
- 원문 바로보기
JHK near-infrared photometry of star clusters in the dwarf irregular/dwarf starburst galaxy NGC 1569 are presented. After adopting several criteria to exclude other sources (foreground stars, background galaxies, etc.), 154 candidates of star clusters are identified in the near-infrared images of NGC 1569, which include very young star clusters. Especially, from analysis based on theoretical background, we found ten very young star clusters near the center of NGC 1569. The total reddening values toward these clusters are estimated to be <TEX>$A_V$</TEX>=1-9 mag from comparison with the theoretical estimates given by the Leitherer et al. (1999)'s star cluster model.
333
- 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.
334
- Kook, Seung-Hwa
- Journal of the Korean astronomical society = 천문학회지
- 43, n.5
- pp.141-152
- 2010
- 원문 바로보기
UBV I CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V ) = <TEX>$0.37{\pm}0.03$</TEX>, <TEX>$V_0-M_V=10.60{\pm}0.08$</TEX>, log <TEX>$\tau$</TEX>= 7.7 <TEX>$\pm$</TEX> 0.1; Hogg 15 : E(B - V ) = 1.13 <TEX>$\pm$</TEX> 0.11, <TEX>$V_0-M_V$</TEX> = 12.50 <TEX>$\pm$</TEX> 0.15, log <TEX>$\tau$</TEX> <TEX>$\lesssim$</TEX> 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We also determine the mass function of these clusters and obtain a slope <TEX>$\Gamma$</TEX> = -1.2 (<TEX>$\pm$</TEX>0.3) for NGC 4609 which is normal and a somewhat shallow slope (<TEX>${\Gamma}=-0.95{\pm}0.5$</TEX>) for Hogg 15.
335
- 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.
336
- 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.
337
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 43, n.5
- pp.153-159
- 2010
- 원문 바로보기
Color excesses of classical Cepheids in the uvby color system are estimated for the calibration stars with distances from the literature that are measured independently. Intrinsic photometric indices for these stars are calculated and a calibrated empirical relation between (b - y)<TEX>$_0$</TEX>, period, [<TEX>$c_1$</TEX>], and [<TEX>$m_1$</TEX>] is derived through a linear fit. This relation is used to determine color excesses E(b-y) for 59 Cepheids. We also examine the period-color [log P : (b - y)<TEX>$_0$</TEX>] relation, and find no signs of nonlinearity. We estimate the effective temperature and surface gravity of several Cepheids using both Kurucz and MARCS/SSG grids for [Fe=H]=0.0. We confirm that both temperature and surface gravity are higher, by about 150K and 0.4 respectively, when the MARCS/SSG atmospheric grids are used.
338
- Cheon, So-Ra
- Journal of the Korean astronomical society = 천문학회지
- 43, n.4
- pp.115-121
- 2010
- 원문 바로보기
UBVI CCD photometry is obtained for the Ruprecht 93 (Ru 93)region. We are unable to confirm the existence of an intermediate-age open cluster in Ru 93 from the spatial distribution of blue stars. On the other hand, we find two young star groups in the observed field: the nearer one (Ru 93 group) comprises the field young stars in the Sgr-Car arm at <TEX>$d{\approx}2.1$</TEX> kpc, while the farther one (WR 37 group) is the young stars around WR 37 at <TEX>$d{\approx}4.8$</TEX> kpc. We derive an abnormal extinction law (<TEX>$R_V$</TEX> = 3.5) in the Ruprecht 93 region.
339
- Hanna, Magdy A.
- Journal of the Korean astronomical society = 천문학회지
- 43, n.6
- pp.201-211
- 2010
- 원문 바로보기
We present an analysis of the measurements of mid-eclipse times of V839 Oph, collected from literature sources. Our analysis indicates a period increase of <TEX>$3.2{\times}10^{-7}$</TEX> day/yr. This period increase of V839 Oph can be interpreted in terms of mass transfer of rate <TEX>$1.76{\times}10^{-7}M_{\odot}/yr$</TEX>, from the less to the more massive component. The O - C diagram shows a damping sine wave covering two different complete cycles of 36.73 yr and 19.93 yr with amplitudes approximately equal to 0.0080 and 0.0043 day, respectively. The third cycle has to be expected to cover about 13.5 years with lower amplitude than those of the former two cycles. These unequal duration cycles show a non periodicity which may be explained as resulting from either the presence of a tertiary component to the system or cyclic magnetic activity variations due to star spots. For the later mechanism, the obtained characteristics are consistent when applying Applegate (1992) mechanism.
340
- Doh, Seong-Jae
- Journal of the Korean astronomical society = 천문학회지
- 43, n.6
- pp.183-190
- 2010
- 원문 바로보기
According to the historical documents and paintings in many civilizations, rocks that fell from the sky fascinated humans as the message from the God or supernaturals. Scientific progress allows humans to recognize these exciting extraterrestrial objects as meteorites. Meteorites contain a wealth of pivotal information regarding formation of the early Solar System. Meteorites also provide broader scientific insights on, for example, the origin of life, interplanetary transfer of life forms, massive depletion of biosphere on Earth, and evolution of lithosphere on Earth-like planetary bodies.