• 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.

• 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.

• 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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• 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.

• 천문학회지
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• 제29권spc1호
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• pp.243-243
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• 1996

UBV observations have been made jointly at three observatories for the recent eclipse of the long period atmospheric eclipsing binary star Zeta Aur in 1995-6. Observations covered successfully the phases before, during, and after the eclipse enable us to determine the accurate time of mid-eclipse and the duration of the totality. The hypothesis of the expansion of the K supergiant has been tested and the positive conclusion may be derived.

• Journal of Astronomy and Space Sciences
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• 제5권2호
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• pp.97-109
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• 1988

The photometric behaviour of XY U Ma, an eclipsing binary showing photospheric and chromospheric activity, has been described by spot hypothesis. They are based on the all the available UBV light curves, which were carried out by Geyer since 1955. A "spherical rectangular" spot model shows very pronounced spot activities during the last 30 years. On the average, the spot covered about 16% of the visible hemisphere. Observational evidence for photospheric and chromospheric activities on the XY UMa and related systems are also discussed.

• 천문학논총
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• 제22권2호
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• pp.35-41
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• 2007

We present the result of radial velocity observation of a W UMa type binary star EX Leo. We observed the star on February 16, 2003, using Long-Slit spectrograph of BOAO(Bohyunsan Optical Astronomical Observatory). Since the spectral lines are broad due to its fast rotation, it is difficult to distinguish two radial velocities from cross correlation function. Instead of cross correlation function, we used broadening function to develop our own code which estimate the radial velocity of the broadened line spectra. With our own code, radial velocities of primary and secondary stars are derived simultaneously. From the radial velocity curve fit, we obtained $K_1=50.24{\pm}8.29km/s$ and $K_2=254.05{\pm}20.984km/s$ respectively.

• Journal of Astronomy and Space Sciences
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• 제2권1호
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• pp.35-45
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• 1985

Standardized B and V photoelectric light curves of Algol are made with the obsevations obtained during 1982-84 with the 40-cm and the 61-cm reflectors of Yonsei University Observatory. These light curves show asymmetry between ascending and descending shoulders. The ascending shoulder is 0.02 mag brighter than descending shoulder in V light curve and 0.03mag in B light curve. These asymmetric light crves are interpreted as the result of inhomogeneous energy distribution on the surface of one star of the eclipsing pair rather than the result of gaseous stream flowing from KOIV to B8V star. The 180-year periodicity, so called great inequality, are most likely the result proposed by Kim et al.(1983) that the abrupt and discrete mass losses of cooler component may be the cause of this orbital change. The amount of mass loss deduced from these discrete period changes turned out to be of the order of $10^{-6}$ - $10^{-5}M_\odot$.

• Journal of Astronomy and Space Sciences
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• 제9권1호
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• pp.89-96
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• 1992

UBV observations of VV Cep were made in 1988-1992 as a part of the Ten-year Observing Program for Long Period Eclipsing Binary Stars(1982-1992) at Yonsei University Observatory. In addition to these the observations in the longer passbands in R and I are also made in the 1991-1992 season at the same observatory. Atmospheric extinction coefficinets determined by a comparison star 20 Cap for B and V each night have been deduced a linear relation, $K_B$=0.159+1.066kV. In this paper, light curves of this star in BVRI passbands for the 1991-1992 season only are presented. Two periodic light variations of both long-term and short-term are found as for 90 days and 20 days, respectively.

• Journal of Astronomy and Space Sciences
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• 제10권1호
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• pp.94-102
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• 1993

소백산천문대의 61cm 망원경에 사용하기 위하여 광섬유를 이용한 다중채널 광전측광기를 개발하였다. 이 측광기의 채널간 광전송 효율 차이를 검증하기 위한 시험관측을 실시한 결과 큰 차이가 없음을 알았다. 또한 관측 정밀도 및 효율을 검증하기 위하여 W UMa형 식쌍성인 BV Dra를 관측한 결과 측광기가 매우 안정되어 있으며 관측정밀도도 향상되었음을 알았다. 관측 효율은 단일채널 측광기에 비하여 매우 향상되어, 하나의 필터를 사용하는 관측의 경우 적어도 5배의 관측자료를 얻을 수 있었다.