• 천문학논총
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• 제26권4호
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• pp.141-146
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• 2011

In the region of the open cluster M48 (NGC 2548), time-series BV CCD images were taken for 22 nights from February 28 in 2008 to March 17 in 2011. From this observation, we found 10 new variable stars. They include five eclipsing binaries, an RR Lyrae, two ${\delta}$ Scuti, and two semi-periodic and/or slow irregular type variable stars. We fail to find the member stars of the open cluster among the 10 variable stars.

• 천문학회지
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• 제48권1호
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• pp.1-7
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• 2015

The orbital period changes of the W UMa eclipsing binary AU Ser are studied using the (O-C) method. We conclude that the period variation is due to mass transfer from the primary star to the secondary one at a very low and decreasing rate $dP/dt=-8.872{\times}10^{-8}$, superimposed on the sinusoidal variation due to a third body orbiting the binary with period $42.87{\pm}3.16$ years, orbital eccentricity $e=0.52{\pm}0.12$ and a longitude of periastron passage ${\omega}=133^{\circ}.7{\pm}15$. On studying the magnetic activity, we have concluded that the Applegate mechanism failed to describe the cycling variation of the (O-C) diagram of AU Ser.

• 천문학회보
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• 제43권1호
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• pp.49.5-50
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• 2018

Korean chronicles have a large amount of observational records over two thousand years. Many historical astronomical records are useful in modern times. In this study, we examined solar eclipses in Goguryeo-bongi(高句麗本紀) by using the modified(newest) nutation value and reviewed the observation area through eclipsing map. There are 11 solar eclipse records in the book. We calculated intersectional visible area with 0.6 eclipsing magnitude using the records of AD116, 124, 149, 158 and 219 and found the observational area of $N40-43^{\circ}$ and $E123-127^{\circ}$, which corresponds to the Liaodong(遼東). We also examined historical Chinese solar eclipse records and compared them with Korean eclipses.

• 천문학회지
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• 제43권6호
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• pp.201-211
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• 2010

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 $3.2{\times}10^{-7}$ day/yr. This period increase of V839 Oph can be interpreted in terms of mass transfer of rate $1.76{\times}10^{-7}M_{\odot}/yr$, 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.

• 천문학논총
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• 제24권1호
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• pp.19-34
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• 2009

From the short-period variability survey (SPVS) in Bohyunsan Optical Astronomy Observatory, I obtained time-series BV CCD images in the region of the young open cluster M29 (NGC 6913) for 15 nights from May 30, 2008 to September 17, 2009. I observed 48 variable stars including 45 new ones. They consisted of 5 $\delta$ Scuti, a Cepheid, 16 eclipsing binaries and 24 semi-long periodic and/or slow irregular type variable stars including $\beta$ Cephei and LPB type stars. For the rest two ones, the type of variability was not defined. I also checked the variability of the 26 known variable stars listed in the GCVS. Only three ones among 26 known variable stars confirmed variability.

• Journal of Astronomy and Space Sciences
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• 제9권1호
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• pp.30-40
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• 1992

세 종류의 식쌍성에 대한 반사 효과를 Wilson과 Devinney의 모델과 Russell과 Merrill의 모델로 분석하였다. 반사 효과를 Wilson과 Devinney의 광도 곡선 프로그램을 이용하여 이론적인 광도 곡선에 여러가지 유형별로 나타내었다. 그후 반사효과가 나타난 이론적인 광도 곡선을 Russell과 Merrill의 방법으로 근접 효과를 보정하여 두 모델을 비교 분석하였다. 두 별의 온도 차이와 반사도의 차이가 작은 경우에만 반사 효과에 관한한 두 모델이 일치함을 보였다.

• Journal of Astronomy and Space Sciences
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• 제10권1호
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• pp.44-85
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• 1993

EA형이며 준분리형에 속하는 19개의 식쌍성에 대한 공전주기 변화를 조사하였다. 그런데 각 식쌍성의 주기 변화각 갑작스러운 주기 변화를 보이는 일차항의 광도요소를 갖는다는 가정하에 주기 변화를 분석하였다. 이러한 분석을 통하여 각 식쌍성의 주기 변화와 그 별의 물리량과의 상관관계를 조사하였다.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.169-173
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• 2012

A summary is presented of what is currently known about the surface temperatures of accreting white dwarfs (WDs) detected in non-magnetic and magnetic cataclysmic variables (CVs) based upon synthetic spectral analyses of far ultraviolet data. A special focus is placed on WD temperatures above and below the CV period gap as a function of the orbital period, $P_{orb}$. The principal uncertainty of the temperatures for the CV WDs in the $T_{eff}-P_{orb}$ distribution, besides the distance to the CV, is the mass of the WD. Only in eclipsing CV systems, an area of eclipsing binary studies, which was so central to Robert H. Koch's career, is it possible to know CV WD masses with high precision.

• 천문학논총
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• 제22권4호
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• pp.141-149
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• 2007

Preliminary time-series observations for short-period variability survey (SPVS) were carried out using a 155mm refractor and a $2k{\times}3k$ CCD camera at Bohyunsan Optical Astronomy Observatory. We found 21 new variable stars in the $90'{\times}60'$ test field region : 9 eclipsing binary stars, $5{\delta}$ Scuti type stars, a ${\gamma}$ Doradus type star, and 6 long period variables. The observing field center is R.A. $05^h\;00^m\;00^s$, DEC. $50^{\circ}\;00'\;00"$ (J2000.0). The period and amplitude ranges for the short-period variables, i.e., ${\delta}$ Scuti stars, were 0.052day - 0.107day and 0.012mag - 0.064mag, respectively.

• 천문학회보
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• 제41권1호
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• pp.60.2-60.2
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• 2016

Oscillating Algol-type eclipsing binaries (oEA) are very interesting objects that have three observational features of eclipse, pulsation, and mass transfer. Direct measurement of their masses and radii from the double-lined radial velocity (RV) data and photometric light curves would be the most essential for understanding their evolutionary process and for performing the asteroseismological study. However, only handful oEA stars were studied in detail. To advance this subject, we have been obtaining high-resolution spectra for several oEA stars using Bohyunsan Optical Echelle Spectrograph (BOES). In this presentation, we present our results such as the accurate absolute parameters and evolutionary states for each object, based on the simultaneous analyses of the light and RV curves.