• 천문학회지
• /
• 제41권3호
• /
• pp.49-58
• /
• 2008

Resonance doublets including O VI 1032, 1038, NV 1239, 1243 and C IV 1548, 1551 constitute prominent emission lines in symbiotic stars and planetary nebulae. Spectroscopic studies of symbiotic stars and planetary nebulae from UV space telescopes show various line ratios of these doublets deviating from the theoretical ratio of 2:1. Using a Monte Carlo technique, we investigate the collisional de-excitation effect in these emission nebulae. We consider an emission nebula around the hot component of a symbiotic star characterized by the collisional de-excitation probability $p_{coll}\;{\sim}\;10^{-3}\;-\;10^{-4}$ per each resonance scattering, and the line center optical depths for major resonance doublets in the range ${\tau}_0\;{\sim}\;10^2\;-\;10^5$. We find that various line ratios are obtained when the product $p_{coll}{\tau}_0$ is of order unity. Our Monte Carlo calculations show that the flux ratio can be approximately fitted by a linear function of ${\log}{\tau}_0$ when ${\tau}_0p_{coll}\;{\sim}\;1$. It is briefly discussed that this corresponds to the range relevant to the emission nebulae of symbiotic stars.

• 천문학회지
• /
• 제46권4호
• /
• pp.151-159
• /
• 2013

We discuss the orbital period changes of the Algol semi-detached eclipsing binary DI Peg by constructing the (O-C) residual diagram via using all the available precise minima times. We conclude that the period variation can be explained by a sine-like variation due to the presence of a third body orbiting the binary, together with a long-term orbital period increase (dP/dt=0.17 sec/century) that can be interpreted to be due to mass transfer from the evolved secondary component (of rate $1.52{\times}10^{-8}M_{\odot}/yr$) to the primary one. The detected low-mass third body ($M_{3min.}=0.22{\pm}0.0006M_{\odot}$) is responsible for a periodic variation of about 55 years light time effect. We have determined the orbital parameters of the third component which show a considerable eccentricity $e_3=0.77{\pm}0.07$ together with a longitude of periastron ${\omega}_3=300^{\circ}{\pm}10^{\circ}$.

• Current Optics and Photonics
• /
• 제8권1호
• /
• pp.30-37
• /
• 2024

Implemented at the Geochang Observatory in South Korea, our slope detection and ranging (SLO-DAR) system features a 508 mm Cassegrain telescope (f /7.8), incorporating two Shack-Hartmann wave-front sensors (WFS) for precise measurements of atmospheric phase distortions, particularly from nearby binary or double stars, utilizing an 8 × 8 grid of sampling points. With an ability to reconstruct eight-layer vertical atmospheric profiles, the system quantifies the refractive index structure function (C_n²) through the crossed-beam method. Adaptable in vertical profiling altitude, ranging from a few hundred meters to several kilometers, contingent on the separation angle of binary stars, the system operates in both wide (2.5 to 12.5 arcminute separation angle) and narrow modes (11 to 15 arcsecond separation angle), covering altitudes from 122.3 to 611.5 meters and 6.1 to 8.3 kilometers, respectively. Initial measurements at the Geochang Observatory indicated C_n² values up to 181.7 meters with a Fried parameter (r₀) of 8.4 centimeters in wide mode and up to 7.8 kilometers with an r₀ of 8.0 centimeters in narrow mode, suggesting similar seeing conditions to the Bohyun Observatory and aligning with a comparable 2014-2015 seeing profiling campaign in South Korea.

• 천문학회지
• /
• 제44권3호
• /
• pp.89-96
• /
• 2011

We present results of two-color VR photometry of the intermediate polar RXS J1803. The data were aquired using the Korean 1-m telescope located at Mt. Lemmon, USA. Different "high" and "low" luminosity states, similar to other intermediate polars, were discovered. No statistically significant variability of the color index with varying luminosity was detected. The orbital variability was found to be not statistically significant. Spin maxima timings were determined, as well as the photometric ephemeris for the time interval of our observations. The spin period variations, caused by interaction of the accretion structure with the rotating magnetic white dwarf, were also detected. These variations are of complicated character, and their study requires further observations. We determine the color transformation coefficients for our photometric systems, and improve on the secondary photometric standards.

• 천문학회보
• /
• 제42권2호
• /
• pp.86.4-87
• /
• 2017

Symbiotic stars are binary systems composed of a hot white dwarf and a mass losing giant. Many symbiotic stars are known to exhibit broad wings around Balmer emission line. We show high resolution spectra of S-type symbiotic stars, Z Andromedae and AG Draconis, obtained with the ESPaDOnS and the 3.6 m Canada-France-Hawaii Telescope, in which we find prominent broad wings around Balmer lines. We adopt Monte-Carlo technique to consider two types of wing formation mechanisms, which are Thomson scattering by free electron in H II region and Raman scattering by atomic hydrogen in H I region. We find that Thomson wings of $H{\alpha}$ and $H{\beta}$ have the same widths in the Doppler space due to the cross section independent of wavelength. In contrast, Raman $H{\alpha}$ wings are 3 times broader widths than $H{\beta}$ counterparts, which is attributed to the different cross sections and branching ratios. Our CFHT data show that $H{\alpha}$ wings of Z Andromedae and AG Draconis are broader than $H{\beta}$ wings, lending strong support to the Raman scattering origin of Balmer wings in these objects.

• 천문학논총
• /
• 제28권3호
• /
• pp.83-93
• /
• 2013

NGC 6871을 중심으로 한 Cyg OB3 성협 영역에 대한 변광성 탐사로부터 Paper I에 이어 27개의 식쌍성과 19개의 장주기형 불규칙 변광성을 찾았다. 이 중에서 5개를 제외한 나머지는 모두 새로 발견한 것이다. 27개의 식쌍성 중에서 20개는 주기와 변광진폭 등을 구하였으며, 나머지 7개는 모두 EA형 식쌍성으로 보이지만 관측자료의 부족으로 주기를 결정하지는 못하였다. 주기를 구한 20개의 식쌍성 중에서 주극소의 깊이를 확실하게 구하지 못한 V27를 제외한 V와 B등급의 변광진폭비 $A_V/A_B$가 0.88로서 Paper I의 ${\delta}$ Scuti형 변광성의 결과를 이용한 0.72와 뚜렷이 구분된다. EW형 식쌍성 만을 이용할 경우 변광진폭비는 0.92로 더 뚜렷이 구분되었다. 19개의 장주기형 불규칙 변광성은 주기가 너무 길고, 또한 비주기성 변광성으로 보이므로 주기를 얻지는 못하고, 밝기 변화만 알 수 있었다. 이 연구에서 찾은 변광성은 V등급이 9.05등급부터 16.47등급까지 분포하며, 변광진폭이 클 경우 16.5등급까지도 변광 여부를 확인할 수 있었다.

• Journal of Astronomy and Space Sciences
• /
• 제26권1호
• /
• pp.1-8
• /
• 2009

질량비가 작은 접촉쌍성 FP Boo를 3색(B, V, R) CCD 측광관측하여 새로운 광도곡선을 얻었으며, Rucinski et al.(2005)의 시선속도곡선과 함께 Wilson-Devinney 프로그램에 적용하여 FP Boo의 새로운 측광학적 해와 절대물리량을 구하였다. FP Boo를 포함한 24개의 질량비가 작은 접촉쌍성의 H-R도로부터 FP Boo의 진화 상태도 일반적인 질량비가 작은 접촉쌍성의 진화 상태와 일치하는 위치에 놓이고 있음을 다시 확인하였다. 이번 관측을 통하여 얻은 우리의 광도곡선에서는 작지만 약간의 비대칭성을 보였다.

• 천문학회보
• /
• 제46권1호
• /
• pp.35.2-35.2
• /
• 2021

Blue straggler stars (BSs) are "rejuvenated" main sequence stars first recognized by Allan Sandage from his observation of the prominent northern globular cluster M3 in the year of 1953. BSs are now known to be present in diverse stellar environments including open clusters, globular clusters, dwarf galaxies, and even the field populations of the Milky Way. This makes them a very useful tool in a wide range of astrophysical applications: Particularly BSs are considered to have a crucial role in the evolution of stellar clusters because they affect on the dynamics, the binary population, and the history of the stellar evolution of the cluster they belong to. Here we report a part of the preliminary results from our ongoing research on the BSs in the two metal-poor globular clusters (GCs) in the Large Magellanic Cloud (LMC), Hodge 11 and NGC1466. Using the high precision multi-band images obtained with the Advanced Camera for Survey (ACS) onboard the Hubble Space Telescope (HST), we extract time-series photometry to search for the signal of periodic variations in the luminosity of the BSs. Our preliminary results confirm that several BSs are intrinsic "short period (0.05 < P < 0.25 days)" variable stars with either pulsating or eclipsing types. We will discuss our investigation on the properties of those variable BS candidates in the context of the formation channels of these exotic main sequence stars, and their roles in the dynamical evolution of the host star clusters.

• Journal of Astronomy and Space Sciences
• /
• 제34권2호
• /
• pp.75-82
• /
• 2017

High-resolution spectroscopic observations of the eclipsing binary system RR Lyn were made using the 1.8 m telescope at the Bohuynsan Optical Astronomical Observatory in Korea. The spectral resolving power was R = 82,000, with a signal to noise ratio of S/N > 150. We found the effective temperatures and surface gravities of the primary and secondary components to be equal to $T_{eff}$ = 7,920 & 7,210 K and log(g) = 3.80 & 4.16, respectively. The abundances of 34 and 17 different chemical elements were found in the atmospheric components. Correlations between the derived abundances with condensation temperatures and the second ionization potentials of these elements are discussed. The primary component is a typical metallic line star with the abundances of light and iron group elements close to solar values, while elements with atomic numbers Z > 30 are overabundant by 0.5-1.5 dex with respect to solar values. The secondary component is a ${\lambda}$ Boo type star. In this type of stars, CNO abundances are close to solar values, while the abundance pattern shows a negative correlation with condensation temperatures.

• 천문학회지
• /
• 제49권5호
• /
• pp.209-223
• /
• 2016

We present analyses of ~1250 variable sources identified in a 20 square degree field toward NGC 2784 by the KMTNet Supernova Program. We categorize the variable sources into three groups based on their B-band variability. The first group consists of 31 high variability sources with their B-band RMS variability greater than 0.3 magnitudes. The second group of medium variability contains 265 sources with RMS variability between 0.05 and 0.3 magnitudes. The remaining 951 sources belong to the third group of low variability with an RMS variability smaller than 0.05 magnitudes. Of the entire ~1250 sources, 4 clearly show periods of variability greater than 100 days, while the rest have periods shorter than ~51 days or no reliable periods. The majority of the sources show either rather irregular variability or short periods faster than 2 days. Most of the sources with reliable period determination between 2 and 51 days belong to the low-variability group, although a few belong to the medium-variability group. All the variable sources with periods longer than 35 days appear to be very red with B - V > 1.5 and V - I > 2.1 magnitudes. We classify candidates of 51 Cepheids, 17 semi-regular variables, 3 Mira types, 2 RV(B) Tauri stars, 26 eclipsing binary systems and 1 active galactic nucleus. The majority of long-term variables in our sample belong to either Mira or semi-regular types, indicating that long-term variability may be more prominent in post-main sequence phases of late-type stars. The depth of the eclipsing dips of the 26 candidates for eclipsing binaries is equivalent to ~0.61 as the average relative size of the two stars in the binary system. Our results illustrate the power of the KMTNet Supernova Program for future studies of variable objects.