• 천문학회지
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• 제49권5호
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• pp.209-223
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• 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.

• 천문학회보
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• 제43권1호
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• pp.41.2-41.2
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• 2018

EL CVn-type eclipsing binaries are composed of a massive A-type main-sequence primary star and a hotter B-type secondary one. These are worthy of particular attention because the secondary stars are rare objects to be extremely low-mass white dwarf precursors (ELM proto-WD) with the mass of ${\leq}0.2M_{\odot}$, evolving to higher effective temperatures and higher surface gravities. A few of them were discovered to show multi-periodic pulsations in one or both components. We monitored one of these rare and interesting objects, J0247-25 (=1SWASP J024743.37-251549.2), at two KMTNet sites of SAAO in South Africa and SSO in Australia. The observations were performed with the KMTNet 1.6m telescopes and pre-science 4K CCD cameras during the system test run from July to November 2014. Using the photometric data obtained for a total of 23 nights, we constructed well-defined eclipsing light curves in B/V-bands and derived absolute parameters (mass and radius, etc.) of each binary component. After subtracting model eclipsing curves from the data, we detected seven frequencies with 33~53 cycles per day (c/d) and identified them to be Delta Sct-type pulsations originated from the A-type primary component. Five frequencies were turned out to be excited by rotational splitting of non-radial pressure modes, enabled us to investigate rotational properties. We could not detect any frequency higher than 100 c/d, implying that pulsation amplitudes of the proto-WD secondary decrease greatly.

• Journal of Astronomy and Space Sciences
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• 제26권3호
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• pp.295-304
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• 2009

대마젤란은하 중심부에 위치한 식쌍성 EROS 1010에 대한 CCD 측광관측을 2006년과 2007년에 수행하여 BV 광도곡선을 완성하였다. BV 광도곡선은 EROS팀과 OGLE팀이 각각 관측한 BR과 I 광도곡선과 함께 Wilson & Devinney 차등보정법으로 분석하여 측광학적인 해를 제시하였다. 한편 대마젤란은하의 거리지수를 $m-M=18.^m3{\sim}18.^m5$ 사이로 가정하고, EROS 1010에 대한 절대량을 구하였다.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.115-121
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• 2012

Existing but largely unused binary star model capabilities are examined. An easily implemented scheme is parameterization of starspot growth and decay that can stimulate work on outer convection zones and their dynamos. Improved precision in spot computation now enhances analysis of very precise data. An existing computational model for blended spectral line profiles is accurate for binary system effects but needs to include damping, thermal Doppler, and other intrinsic broadening effects. Binary star ephemerides had been found exclusively from eclipse timings until recently, but now come also from whole light and radial velocity curves. A logical further development will be to expand these whole curve solutions to include eclipse timings. An attenuation model for circumstellar clouds, with several absorption and scattering mechanisms, has been applied only once, perhaps because the model clouds have fixed locations. However the clouds could be made to move dynamically and be combined into moving streams and disks. An area of potential interest is polarization curve analysis, where incentive for modeling could follow from publication of observed polarization curves. Other recent advances include direct single step solutions for temperatures of both stars of an eclipsing binary and third body kinematics from combined light and velocity curves.

• 천문학회지
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• 제49권3호
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• pp.65-71
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• 2016

We obtain the first complete CCD light curves (LCs) of the contact binary AP UMi in the VRI bands and analyzed them by means of the PHOEBE code. A spotted model is applied to treat the asymmetry in the LCs. The LC morphology clearly shows the O'Connell effect and the solution shows an influence of star spots on both components. Such effect of star spots is common between the RS CVn and W UMa chromospherically active stars. Based on the obtained solution of the LCs we investigate the evolutionary state of the components and conclude that the system is a pre-intermediate contact binary (f = 0.29) with mass ratio q = 0.38, and it is an A-type W UMa system where the less massive secondary component is cooler than the more massive primary one.

• Journal of Astronomy and Space Sciences
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• 제22권2호
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• pp.113-124
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• 2005

두개의 식쌍성 V343 Aql 와 CX Aqr 의 가능한 모든 극심시각을 수집하여 두별의 공전 주기변화를 연구하였다 . 그 결과 두 별의 공전주기는 모두 포물선 모양의 영년 변화 위에 주기적인 항이 겹쳐 변화한다. V343 Aql 은 $-261{\times}10^{-7}$ d/y의 영년 주기감소를, 반면 CX Aqr 은 $+2.55{\times}10^{-8}$d/y의 영년 주기증가를 보인다. 두 별의 영년 주기변화의 가능한 원인들에 대하여 논의하였다. 공전주기의 주기적인 변화의 원인을 제3천체에 의한 광시간 효과로 해석하였다. 광시간 궤도의 주기, 반 진폭과 이심율은 V343 Aql인 경우, 각각 30.3 년, 0.0092 일, 그리고 0.85이며, 반면 CX Aqr인 경우, 각각 33.0년, 0.0037일, 그리고 0.64으로 계산되었다. V343 Aql 와 CX Aqr계에 제안된 제3천체의 성질들이 논의된다.

• 천문학회지
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• 제37권4호
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• pp.143-149
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• 2004

We present photometric results for four new variable stars discovered in the vicinity of the ZZ Ceti-type pulsating white dwarf BR Cam. Observations were performed on 5 nights in November 2003 using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory with no filter, on 3 nights in December 2003 using the 0.61m telescope at Sobaeksan Optical Astronomy Observatory with V, I filters, and on 3 nights in October 2004 using the 1.0m telescope at Mt. Lemmon Optical Astronomy Observatory with V, I filters. We estimated their periods from the phase-match technique for one eclipsing binary and the multiple frequency analysis for three pulsating stars. By considering the light curve shape, period and amplitude difference between two passbands, we classified the objects by their variability types as follows: V1 (USNO-A2.0 1425-05691757) is a W UMa-type eclipsing binary with an orbital period of $0^d.4641$; V2 (USNO-A2.0 1425-05703335) is a multi-periodic $\delta$ Set-type pulsating star with a dominant period of $0^d.0649$; V3 (USNO-A2.0 1425-05699659) is also a $\delta$ Set-type pulsating star with a period of $0^d.1408$; and V 4 (USNO-A2.0 1425-05707705) is a RR Lyr-type pulsating star with a period of $0^d.2643$.

• 천문학논총
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• 제30권2호
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• pp.219-221
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• 2015

We present our recent observations of SDSS J102102.25+174439.9, a new eclipsing white dwarf - main sequence WDMS binary with an orbital period of 0.14 days. This system belongs to the post common-envelope binary group as shown by the spectrum from the Sloan Digital Sky Survey. We obtained our data using the ULTRASPEC instrument installed on the 2.4-m telescope at the Thai National Observatory (TNO). Our multi-band observations reveal an unusual and persistent drop in brightness after the primary eclipse. These dips, which appear to show variations in amplitude, also have a complex shape that changes within days. Dips in WDMS systems have been observed on only one other occasion, in the light curve of QS Vir prior to the eclipse of the white dwarf. The dips in SDSS J1021+1744 are unique because they are present at different wavelengths and they occur approximately at similar phases. Hosting a DA white dwarf and an M4 companion star, this system is known to be the only WDMS to show these kind of dips in its light curve. It is possible that these dips are caused by ejected materials from an active companion star, such as in QS Vir. The light curve in the g' filter exhibits deep and narrow features, implying that the material which passes in front of the white dwarf in SDSS J1021 must be dense and small in size. Furthermore, we try to constrain the stellar and orbital parameters of SDSS J1021+1744 using the Binary Maker 3 software. We use g' and r' data for our light curve analysis to have a better approximation for the red dwarf star.

• 천문학논총
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• 제23권2호
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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.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 1992년도 한국우주과학회보 제1권1호
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• pp.17-17
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• 1992

As a part of the project for The Atlas of (d-C) Diagams of Eclipsing Binaries, a total of 1822 times of minimum lights for Algol distributed from 1782 to 1988 are collecte dand analyzed to investigate the period-changes of the system. An (0-C) diagram constructed shows that the orbital period of Algol has varied in complicated ways. In this paper, we would interprets these variations as the sudden changes of the periodrather than as a somewhat periodic ones. The importancy of the observations for the times of minimum lights of Algol system will be stressed.