• Publications of The Korean Astronomical Society
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• v.23 no.2
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• pp.17-23
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• 2008

From the short-period variability survey (SPVS), we obtained time-series BV CCD images in the region of an open cluster M50 (NGC 2323) for 10 nights from 2008 February 9 to 27. The observation was performed using a small refracting telescope (${\phi}$=155mm, f=1050mm) in Bohyunsan Optical Astronomy Observatory (BOAO). M50 is included in the observing field of ASAS (The All Sky Automated Survey). In the region of M50, we found 8 new variable stars including two ${\delta}$ Scuti stars with short-periods and very small amplitudes. There are known nine variable stars by the catalogues of ASAS and GCVS in the region. We confirmed the variability of the known variable stars for six and non-variability for three.

• Publications of The Korean Astronomical Society
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• v.26 no.4
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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.

• 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.

• Journal of The Korean Astronomical Society
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• v.44 no.3
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• pp.73-79
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• 2011

We collect 24 times of light maxima data from sources in the literature, unpublished data and open databases, and investigate the variations of the observed and calculated (O-C) values for light maxima of V1719 Cyg. We found no evidence of the variations in the (O-C) values. We estimate the effective temperature and surface gravity using both the Kurucz and MARCS/SSG grids for different metallicity values [A/H]=0.0 and +0.5 for V1719 Cyg. It is confirmed that the temperature is almost the same, but, in the case of surface gravity, the MARCS/SSG grid gives the value closest to that obtained from the period-gravity relation derived by using the pulsation-evolution theory. We obtain two spectra of V1719 Cyg from spectroscopic observation which permitted us to find the effective temperature and the surface gravity of the star directly. We estimate the metallicity and it is found that the abundance of iron is equal to the solar value.

• 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.

• 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.