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Photometric Properties of the HW Vir-type Binary OGLE-GD-ECL-11388
Hong, Kyeongsoo,Lee, Jae Woo,Lee, Dong-Joo,Kim, Seung-Lee,Koo, Jae-Rim,Park, Jang-Ho,Lee, Chung-Uk,Kim, Dong-Jin,Cha, Sang-Mok,Lee, Yongseok Astronomical Society of the Pacific 2017 Publications of the Astronomical Society of the Pa Vol.129 No.971
<P>We present the first extensive photometric results for the eclipsing binary OGLE-GD-ECL-11388 with a period of about 3.5 hours located in the Galactic disk. For the photometric solutions, we obtained the BVI light curves from both the KMTNet observations in 2015 and the OGLE -III survey data from 2001-2009, which show striking reflection effects and very sharp eclipses. The light curve synthesis indicates that the eclipsing system is a HW Virtype binary with a mass ratio of q = 0.289, an orbital inclination of i = 81.9 deg, and a temperature ratio between both components of T-2/T-1 = 0.091. A frequency analysis was applied to the light residuals from our binary model; however, no pulsating periodicity from the subdwarf B -type primary component was detected under signal-tonoise amplitude ratios larger than 4 0 A total of 27 minimum epochs spanning 15 yr were used to analyze the eclipse timing variations of OGLE-GD-ECL-11388. It was found that the orbital period has varied due to a continuous period decrease at a rate of dP/dt = -1.1 x 10(-8) day yr(-1) or a sinusoidal oscillation with a semiamplitude of K = 35 s and a cycle of P-3 = 8.9 yr. The period decrease may be explained by an angular momentum loss via magnetic stellar wind braking or may be only a part of the sinusoidal variation. We think the most likely interpretation of the orbital period change, at present, is the light -time effect via the presence of a third body with a mass of M-3 sin i(3) = 12.5 M-Jup, putting it in the boundary zone between planets and brown dwarfs.</P>
Time-series Spectroscopy of the Oscillating Algol-type Binary AB Cas
Hong, Kyeongsoo,Lee, Jae Woo,Koo, Jae-Rim,Kim, Seung-Lee,Lee, Chung-Uk,Park, Jang-Ho,Rittipruk, Pakakaew American Astronomical Society 2017 The Astronomical journal Vol.153 No.6
<P>This study presents the high-resolution spectra of the eclipsing binary AB Cas with a delta Sct-type pulsating component, which were obtained using the Bohyunsan Optical Echelle Spectrograph in Korea. In this paper, the radial velocities for the primary and secondary stars were measured from a total of 27 spectra made during two nights in 2015 October. We derived accurate physical properties of the system for the first time by simultaneously analyzing our radial velocity curves together with previously published uvby light curves. Individual masses, radii, and effective temperatures of both components were determined to be M-1= 2.01 +/- 0.02 M-circle dot and M-2= 0.37 +/- 0.02 M-circle dot, R-1= 1.84 +/- 0.02 R-circle dot and R-2= 1.69 +/- 0.03 R-circle dot, and T-eff,T-1= 8080 +/- 170 K and T-eff,T-2= 4925 +/- 150 K, respectively. The results should be more accurate than previous photometric studies. We investigated the evolutionary history of AB Cas by comparing its physical parameters with stellar evolutionary models. The primary component is not a classical delta Sct pulsator but is the result of mass accretion transferred from the initial more massive star, which is the present secondary. This indicates that AB Cas is an oscillating Algoltype eclipsing binary with a low-mass and oversized secondary component filling its inner Roche lobe.</P>
SHORT APSIDAL PERIOD OF THREE ECCENTRIC ECLIPSING BINARIES DISCOVERED IN THE LARGE MAGELLANIC CLOUD
Hong, Kyeongsoo,Lee, Chung-Uk,Kim, Seung-Lee,Kang, Young-Woon American Institute of Physics 2014 The Astronomical journal Vol.147 No.6
<P>We present new elements of apsidal motion in three eccentric eclipsing binaries located in the Large Magellanic Cloud. The apsidal motions of the systems were analyzed using both light curves and eclipse timings. The OGLE-III data obtained during the long period of 8 yr (2002-2009) allowed us to determine the apsidal motion period from their analyses. The existence of third light in all selected systems was investigated by light curve analysis. The O – C diagrams of EROS 1018, EROS 1041, and EROS 1054 were analyzed using the 30, 44, and 26 new times of minimum light, respectively, determined from full light curves constructed from EROS, MACHO, OGLE-II, OGLE-III, and our own observations. This enabled a detailed study of the apsidal motion in these systems for the first time. All of the systems have a significant apsidal motion below 100 yr. In particular, EROS 1018 shows a very fast apsidal period of 19.9 ± 2.2 yr in a detached system.</P>