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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 36/123
351
- 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.
352
- 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.
353
- 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.
354
- 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.
355
- 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.
356
- Lee, In-Duk
- Journal of the Korean astronomical society = 천문학회지
- 43, n.3
- pp.95-104
- 2010
- 원문 바로보기
We outline our GRB afterglow observation program using the 1-m telescope at Mt. Lemmon Optical Astronomy Observatory (LOAO), and report the first observations of the GRB afterglows. During the 2007B semester, we performed follow-up imaging obsrevations of 6 GRBs, and succeeded in detecting four GRB afterglows (GRB 071010B, GRB 071018, GRB 071020, and GRB 071025) while placing useful upper limits on the light curves of the other GRBs. Among the observed events, we find that three events are special and interesting. GRB 071010B has a light curve which has an unusually long jet break time of 11.8 days. For GRB 071025, its red R-I(~2) color suggests that it is likely to be at z~5. GRB 071020 has a light curve which shows a clear brightening at 0.3-1 days after the burst, where our LOAO data play a crucial role by providing an unambiguous evidence for the brightening. These are the first successful detections of GRB afterglows by a facility owned and operated by a Korean institution, demonstrating the usefulness of the 1-m telescope for transient phenomena such as GRBs up to very high redshift.
357
- 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.
358
- Kim, Sang-Hyuk
- Journal of the Korean astronomical society = 천문학회지
- 43, n.5
- pp.169-181
- 2010
- 원문 바로보기
We develop a proto-model of an off-axis reflective telescope for infrared wide-field observations based on the design of Schwarzschild-Chang type telescope. With only two mirrors, this design achieves an entrance pupil diameter of 50 mm and an effective focal length of 100 mm. We can apply this design to a mid-infrared telescope with a field of view of <TEX>$8^{\circ}{\times}8^{\circ}$</TEX>. In spite of the substantial advantages of off-axis telescopes in the infrared compared to refractive or on-axis reflective telescopes, it is known to be difficult to align the mirrors in off-axis systems because of their asymmetric structures. Off-axis mirrors of our telescope are manufactured at the Korea Basic Science Institute (KBSI). We analyze the fabricated mirror surfaces by fitting polynomial functions to the measured data. We accomplish alignment of this two-mirror off-axis system using a ray tracing method. A simple imaging test is performed to compare a pinhole image with a simulated prediction.
359
- Cho, Jae-Sang
- Journal of the Korean astronomical society = 천문학회지
- 43, n.2
- pp.41-54
- 2010
- 원문 바로보기
We report relative proper motion measurements of <TEX>$H_{2}O$</TEX> masers in massive star-forming region W51 Main, based on data sets of VLBI observations for <TEX>$H_{2}O$</TEX> masers at 22 GHz with Japanese VERA telescopes from 2003 to 2006. Data reductions and single-beam imaging analysis are to measure internal kinematics of maser spots and eventually to estimate the three-dimensional kinematics of <TEX>$H_{2}O$</TEX> masers in W51 Main. Average space motions and proper motion measurements of <TEX>$H_{2}O$</TEX> masers are given both graphical and in table formats. We find in this study that W51 Main appears to be associated with hyper-compact H II region with multiple massive proto-stars whose spectral types are of late O.
360
- Ha, Ji-Sung
- Journal of the Korean astronomical society = 천문학회지
- 43, n.6
- pp.213-223
- 2010
- 원문 바로보기
Young Stellar Objects (YSOs) in the early evolutionary stages are very embedded, and thus they emit most of their energy at long wavelengths such as far-infrared (FIR) and submillimeter (Submm). Therefore, the FIR observational data are very important to classify the accurate evolutionary stages of these embedded YSOs, and to better constrain their physical parameters in the dust continuum modeling. We selected 28 YSOs, which were detected in the AKARI Far-Infrared Surveyor (FIS), from the Spitzer c2d legacy YSO catalogs to test the effect of FIR fluxes on the classification of their evolutionary stages and on the constraining of envelope properties, internal luminosity, and UV strength of the Interstellar Radiation Field (ISRF). According to our test, one can mis-classify the evolutionary stages of YSOs, especially the very embedded ones if the FIR fluxes are not included. In addition, the total amount of heating of YSOs can be underestimated without the FIR observational data.