• Publications of The Korean Astronomical Society
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• v.20 no.1 s.24
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• pp.29-35
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• 2005

Time-series observations were carried out using a 155mm refractor and a $2k{\times}3k$ CCD camera at Bohyunsan Optical Astronomy Observatory. We found 38 new variable stars in the $2.3^{\circ}{\times}2.4^{\circ}$ region around the Cepheid variable TU Cas: 22 eclipsing binary stars, 11 ${\delta}$ Scuti type stars and an RR Lyrae star, and 4 unclassified variables.

• Publications of The Korean Astronomical Society
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• v.20 no.1 s.24
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• pp.21-27
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• 2005

We have been performing a wide-field photometric monitoring program, named SPVS (Short-Period Variability Survey), at the Bohyunsan Optical Astronomy Observatory (BOAO). The observation system consists of a small refracting telescope (D = 155 mm, f = 1050 mm) and a $2k{\times}3k$ CCD Camera. The field of view is $1.0^{\circ}{\times}1.5^{\circ}$. Detection limit is about V = 13 for short-period small amplitude variables such as ${\delta}$ Scuti-type pulsating stars, and about V = 15 for long-period large amplitude variables such as eclipsing binaries and RR Lyrae stars. The instrument is designed to be remote-controlled through internet. The primary purpose of this project is to search for variable objects in bright Galactic open clusters. We present results of test observations conducted towards NGC 7092.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.80-80
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• 2013

대규모 광도곡선 자료에서 다양한 주기변광성들의 정확한 주기를 효율적으로 검출하는 실험을 시도하였다. 실험을 위해 OGLE-III 맥동 변광성(RR Lyrae, Delta Scuti, Cepheid) 목록 중, I 필터로 관측된 총 31,324개의 광도 곡선을 사용하였다. 이 실험에 사용한 주기분석 알고리즘 MS_Period(Multi-Step period searching method)는 주기를 놓치지 않기 위해 두 가지 다른 방법(Multi Polynomial function, Phase Dispersion)으로 후보 주기를 구하고 정밀주기를 도출하기 위해 후보 주기 주변부를 Spline fitting을 통해 재탐색하는 방법이다. 기존의 MS_Period 방식은 주기 탐색 간격(dP/P)이 일정하였으나, 우리는 탐색 주기 구간을 나누고 짧은 주기에서는 작은 간격으로, 긴 주기에서는 보다 넓은 간격으로 주기를 탐색하는 과정을 추가하였다. 그 결과 98% 이상의 별에서 OGLE-III와 거의 일치하는 주기를 얻었으며, 긴 주기에서의 불필요한 정밀 탐색을 회피함으로써 분석시간도 단축되었다. 주기 결정이 어려운 경우들은 주로 1) periodogram에서 실제 주기가 아닌 1일 근처에서 noise보다 큰 peak가 보이는 경우, 2) 하나의 별에 대해 여러 주기가 비슷한 Phase diagram을 보이고, periodogram에서도 비슷한 peak를 갖는 경우, 3) OGLE-III의 주기와 전혀 다른 주기만 찾은 경우, 4) OGLE-III에서 제시하지 않은 혼합된 주기의 존재가 의심되는 경우인 것을 확인하였고, 각 사례들의 특징을 살펴보았다.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.86-86
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• 2019

We present BV photometric observations and high-resolution spectra of AO Ser, which were obtained at the Mt. Lemmon Optical Astronomy Observatory (LOAO) and the Bohyunsan Optical Astronomy Observatory (BOAO), respectively, in 2017. The radial velocities (RVs) for both components were measured, and the effective temperature of the primary star was found to be $T_{eff,1}=8,820{\pm}62K$ by a comparison of the observed spectra and the Kurucz models. A unique set of fundamental parameters of AO Ser were derived for the first time by a simultaneous analysis of the light and RV curves. The results indicate that our program target is a semi-detached eclipsing system with values of $M_1=2.06{\pm}0.11M_{\odot}$ and $M_2=0.41{\pm}0.03M_{\odot}$, $R_1=1.54{\pm}0.03R_{\odot}$ and $R_2=1.30{\pm}0.02R_{\odot}$, and $L_1=12.9{\pm}0.2L_{\odot}$ and $L_2=0.9{\pm}0.3L_{\odot}$. We applied multiple frequency analyses to the eclipse-subtracted light residuals. As a result, two frequencies of $f_1=21.85151days^{-1}$ and $f_2=23.48405days^{-1}$ were detected and their pulsation constants were calculated to $Q_1=0.0344days$ and $Q_2=0.0320days$. The pulsational characteristics and the position in the HR diagram demonstrate that the primary star is a ${\delta}$ Sct pulsator.

• Journal of the Korean earth science society
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• v.28 no.1
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• pp.87-104
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• 2007

As part of the SPVS (Short-Period Variability Survey) which is a wide-field $(90'{\times}60')$ photometric monitering program at Bohyunsan Optical Astronomy (BOAO), we performed V band time-series CCD photometric observations ofthe young open cluster NGC 129 for 11 nights between October 12, 2004 and November 3, 2005 using the 155mm refractor equipped with $3K{\times}2K$ CCD camera. From the observation we obtained 2400 V band CCD frames and color-magnitude diagram of the cluster. To transform instrumental magnitude to standard magnitude, we applied ensemble normalization technique to all observed time-series data. After the photometric reduction process, we examined variations of 9537 stars. As a result, sixty six of the new variable stars were discovered. To determine the periods of the sevariables, we used DFT(Discrete Fourier Transform) and phase-matching technique. According to light curve shape, period, amplitude and the position on a C-M diagram, we classified these variables as 9 SPB type, 9 ${\delta}$ Scuti type, 29 eclipsing, 17 long term variables. However, two of them were not classified. From this study, we learned that small telescopes could be a very useful tool to observe variable stars in the open cluster in survey program.

• Journal of The Korean Astronomical Society
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• v.49 no.5
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• pp.199-208
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• 2016

We present photometric results of the δ Sct star V1162 Ori, which is extensively monitored for a total of 49 nights from mid-December 2014 to early-March 2015. The observations are made with three KMTNet (Korea Microlensing Telescope Network) 1.6 m telescopes installed in Chile, South Africa, and Australia. Multiple frequency analysis is applied to the data and resulted in clear detection of seven frequencies without an alias problem: five known frequencies and two new ones with small amplitudes of 1.2-1.7 mmag. The amplitudes of all but one frequency are significantly different from previous results, confirming the existence of long-term amplitude changes. We examine the variations in pulsation timings of V1162 Ori for about 30 years by using the times of maximum light obtained from our data and collected from the literatures. The O − C (Observed minus Calculated) timing diagram shows a combination of a downward parabolic variation with a period decreasing rate of (1/P)dP/dt = −4.22 × 10⁻⁶ year⁻¹ and a cyclic change with a period of about 2780 days. The most probable explanation for this cyclic variation is the light-travel-time effect caused by an unknown binary companion, which has a minimum mass of 0.69 M_⊙. V1162 Ori is the first δ Sct-type pulsating star of which the observed fast period decrease can be interpreted as an evolutionary effect of a pre-main sequence star, considering its membership of the Orion OB 1c association.