• Journal of Astronomy and Space Sciences
• /
• v.26 no.3
• /
• pp.295-304
• /
• 2009

We present BV light curves of EROS 1010 which is located in the central bar of the Large Magellanic Cloud. The BV light curves including BR and I light curves observed by the EROS and OGLE projects, have been analyzed using the 2005 version of the Wilson & Devinney Differential Correction program for the photometric solutions. The absolute dimensions of EROS 1010 were calculated by adopting the distance modulus of the Large Magellanic Cloud, $m-M=18.^m3{\sim}18.^m5$.

• Journal of The Korean Astronomical Society
• /
• v.44 no.3
• /
• pp.97-108
• /
• 2011

The photometric light curves of the W-type W UMa eclipsing contact binary system BB Pegasi have been found to be extremely asymmetric over all the observed 63 years in all wavelengths UBVR. The light curves have been characterized by occultation primary minima. Hence, the morphology of these light curves has been studied in view of these different asymmetric degrees. The system shows a distinct O'Connell effect, as well as depth variation. A 22.96 years of stellar dark spots cycle has been determined for the system. Almost the same cycle (22.78 yr) has been found for the depth variation of MinI and MinII. We also present an analysis of mid-eclipse time measurements of BB Peg. The analysis indicates a period decrement of $5.62{\times}10^{-8}$ day/yr, which can be interpreted in terms of mass transfer at a rate of $-4.38{\times}10^{-8}M_{\odot}$/yr, from the more to the less massive component. The O - C diagram shows a damping sine wave covering two different cycles of 17.0 yr and 12.87 yr with amplitudes equal to 0.0071 and 0.0013 day, respectively. These unequal durations show a non-periodicity which may be explained as a result of magnetic activity cycling variations due to star spots. The obtained characteristics are consistent with similar chromospherically active stars, when applying the Applegate's (1992) mechanism.

• The Bulletin of The Korean Astronomical Society
• /
• v.38 no.1
• /
• pp.43.1-43.1
• /
• 2013

We present here the preliminary results of the fast variability of AGN radio light curves. The shortest time scale of minute in AGN light curves is needed to probe the AGN activity for a few reasons; First, to check if there is any kind of shortest time scale activity. Secondly, to find out what high frequency end of AGN spectra look like. For the last, to see the time delay at several wavelength bands and the change of the spectral index with time. The observation was conducted with three KVN(Korea VLBI Network) antennas with single dish cross scan mode. In order not to lose the target at any given time, whenever one station needs to observe the calibrator, the other station is on the target. Though the detailed data reduction is still going on, there might exist varying feature in the radio light curve. The more fine calibration will be done in near future and another good data set is ready for the reduction.

• Journal of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.25-30
• /
• 2006

We completed four color light curves of the near-contact binary CN And during three nights from September to December 2004 using the 61-cm reflector and BV RI filters at Sobaeksan Observatory. We determined four new times of minimum light (two timings for primary eclipse, two for secondary). Newly obtained BV RI light curves and the radial velocity curves from Rucinski et a1. (2000) were simultaneously analyzed to derive the system parameters of CN And. We used the semi-detached mode 4 of the 2003-version of the Wilson-Devinney binary model, and interpreted the asymmetry of the light curve by introducing two spots; a cool spot on the primary component and a hot spot on the secondary component. New photometric parameters are not much different from those of Cicek et a1. (2005), and it is considered that the system is in the era of broken contact. From the orbital period study with all available timings including our data, we found a continous period decrease with a rate of $P_{obs}=--1.82{\times}10^{-7}\;d\;yr^{-1}$ that can be explained with two possible mechanisms. We think the most likely cause of the period decrease is a thermal mass transfer from the primary to the secondary component, rather than angular momentum loss due to a magnetic stellar wind.

• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.227-228
• /
• 1996

The long-term light curves of the novalikes TT Ari, KR Aur, AM Her and MV Lyr, were compiled and analysed for solar-like cyclical behaviour. The frequency analysis showed long-term cyclical modulations of the brightness of the stars, which can be ascribed to changes of the radii of the late type secondaries in order of ${\Delta}R/R{\simeq} 10^{-4}-10^{-5}$.

• Journal of Astronomy and Space Sciences
• /
• v.28 no.2
• /
• pp.109-116
• /
• 2011

The first presented BV light curves of BH UMa confirmed Krajci's (2005) result that BH UMa is an RR Lyr star that belongs to the RRc subgroup. The light curves showed a slight asymmetry of D = 0.453 with an amplitude of about $0.^m58$ in B, $0.^m47$ in V, and $0.^m11$ in B-V and with a small hump between $0.^p82$ and $0.^p86$. We determined nine new times of minimum light and eight times of maximum light. We also analyzed all of the available unanalyzed minimum timings and found for the first time that the period of BH UMa has varied dramatically in at least three independent sinusoidal ways superposed on a secularly downward parabola over 66 years. The secular period decreasing rate was obtained as $6.^d684{\times}10^{-8}y^{-1}$, corresponding to -0.58 s/century. The semi-amplitude and period for each of the three sinusoidal variations were ($0.^d058$, $14.^y44$), ($0.^d044$, $9.^y98$), and ($0.^d005$, $0.^y97$), respectively. It is uncertain whether the periodicity for the shortest period of $0.^y97$ is real or spurious. The secular period decrease, well consistent with those of the other RRc stars, could be considered as a natural result of the evolution of the BH UMa system. The two possible sinusoidal terms were interpreted as both two light-time effects due to two additional bodies orbiting BH UMa and combinations of random fluctuations in the pulsation period of BH UMa. Two interpretations were shortly discussed with related parameters.

• Bulletin of the Korean Space Science Society
• /
• 1992.10a
• /
• pp.15-15
• /
• 1992

AQ Cassiopeiae (BD+61`0242, uv=10, Sp=B3+Bg) is a totally eclipsing binary system with the obital period of about 12 days. 71 was observed for 15 nights in 1985 with the1.8-m telescope at the DAO, employing a Reticon and a three-stage image tube attached to the spectrograph. And also, photometric observations of AQ Cas had been made inUBv for six years from 1982 to 1988 at Yonsei University Observatory(YUO). This work includes UBV observations obtained at YUO as a part of The Ten-Year Observing Program(1982-1992). Double lined radial, velocity curves and Ufv light curves of AQC as are constructed. The light curves and radial velocity curves show a strong evidence of circumstellar matter or mass stream. It is clear at the phases of just outside externaleclipse contacts, particularly at phase 0.8-0.9, shown in Figures 1 and 2. A solution by combining the radial velocity and photometric curves of the binary was obtained with the Wilson-Devinney Code. We found that the system is semi-detached with the coolcomponent filling its Roche lobe. The absolute dimensions of AQ Cas are calculated. The result shows that this system consists of two massive and subgiant stars.

• Journal of Astronomy and Space Sciences
• /
• v.13 no.1
• /
• pp.72-78
• /
• 1996

We evaluated the orbital elements of BV light curves of a short period RS CVn type eclipsing binary system UV Picsium that shows complication light variation, by analyzing with the Winson-Devinney's differential correction method. Because the analyzed light curves shows large light variation at outside eclipse region, we assumed spotted region of the primary component and calculated its position and size. The results show the UV Psc is a detached binary system of nearly the same radii and the primary component has high mass with high temperature. However this result is not consistant with customary stellar models, thus requires more observational data to confirm this problem.

• Journal of Astronomy and Space Sciences
• /
• v.27 no.2
• /
• pp.81-88
• /
• 2010

A total of 583 observations (193 in ${\Delta}b$, 190 in ${\Delta}v$, 200 in ${\Delta}r$) for V523 Cas was made on 9 nights from September to December in 2008 using the 100 cm telescope with 2K CCD camera of the Chungbuk National University Observatory. With our data BVR light curves were constructed and 9 times of minimum light were determined. We also obtained physical parameters of the V523 Cas system by analysis of the BVR light curves using the Wilson-Devinney code.

• Journal of The Korean Astronomical Society
• /
• v.7 no.1
• /
• pp.16-18
• /
• 1974

Photolectric observations with B and V filters of the eclipsing binary system V448 Monocerotis are presented. The light curves, which cover 30% of the light cycle, show the variability of this system.