모달창 닫기
- 홈으로 이동
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 34/122
331
- 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.
332
- 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.
333
- 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.
334
- 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.
335
- 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.
336
- 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.
337
- 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.
338
- 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.
339
- 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.
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.