• Journal of The Korean Astronomical Society
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• v.39 no.2
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• pp.41-50
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• 2006

We present the results of new multi-color CCD photometry for the contact binary XZ Leo, together with reasonable explanations for the period and light variations. Six new times of minimum light have been determined. A period study with all available timings confirms Qian's (2001) finding that the O-C residuals have varied secularly according to $dP/dt\;=\;+8.20{\times}10^{-8}\;d\;yr^{-l}$. This trend could be interpreted as a conservative mass transfer from the less massive cool secondary to the more massive hot primary in the system with a mass flow rate of about $5.37{\times}10^{-8}\;M_{\odot}\;yr^{-l}$. By simultaneous analysis of our light curves and the previously published radial-velocity data, a consistent set of light and velocity parameters for XZ Leo is obtained. The small differences between the observed and theoretical light curves are modelled by a blue third light and by a hot spot near the neck of the primary component. Our period study does not support the tertiary light but the hot region which may be formed by gas streams from the cool secondary. The solution indicates that XZ Leo is a deep contact binary with the values of q=0.343, $i=78^{\circ}.8$, ${\Delta}(T_1-T_2)=126\;K$, and f=33.6 %, differing much from those of Niarchos et al. (1994). Absolute parameters of XZ Leo are determined as follows: $M_1=1.84\;M_{\odot},\;M_2=0.63\;M_{\odot},\;R_1=1.75\;R_{\odot},\;R_2=1.10\;R_{\odot},\;L_1=7.19\;L_{\odot},\;and\;L_2=2.66\;L_{\odot}$.

• Journal of Astronomy and Space Sciences
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• v.29 no.2
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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.

• Journal of Astronomy and Space Sciences
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• v.31 no.3
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• pp.187-197
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• 2014

We have investigated the dynamical stability of the proposed companions orbiting the Algol type short-period eclipsing binary SW Lyncis (Kim et al. 2010). The two candidate companions are of stellar to substellar nature, and were inferred from timing measurements of the system's primary and secondary eclipses. We applied well-tested numerical techniques to accurately integrate the orbits of the two companions and to test for chaotic dynamical behavior. We carried out the stability analysis within a systematic parameter survey varying both the geometries and orientation of the orbits of the companions, as well as their masses. In all our numerical integrations we found that the proposed SW Lyn multi-body system is highly unstable on time-scales on the order of 1000 years. Our results cast doubt on the interpretation that the timing variations are caused by two companions. This work demonstrates that a straightforward dynamical analysis can help to test whether a best-fit companion-based model is a physically viable explanation for measured eclipse timing variations. We conclude that dynamical considerations reveal that the proposed SW Lyncis multi-body system most likely does not exist or the companions have significantly different orbital properties from those conjectured in Kim et al. (2010).

• Journal of Astronomy and Space Sciences
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• v.22 no.2
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• pp.113-124
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• 2005

All times of minimum light for two eclipsing binaries V343 Aql and CX Aqr were collected and analyzed to study their orbital period variations. It was found that the orbital periods for both stars have varied in a cyclical way superposed on a parabola. A secular period decrease of $-261{\times}10^{-7}$ d/y for V343 Aql was calculated while CX Aqr showed a secular period increase of $+2.55{\times}10^{-8}$8 d/y. Possible causes of secular period variations for two systems were discussed. The cyclical period variation was interpreted as light-time effect due to a third body. The resultant period, semiamplitude and eccentricity of the light time orbit were calculated to be 30.3y, 0.0092d and 0.85, respectively, for V343 Aql and 33.0y, 0.0037d and 0.64, respectively, for CX Aqr. The properties of the third bodies suggested in V343 Aql and CX Aqr systems were discussed.

• Journal of Astronomy and Space Sciences
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• v.29 no.1
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• pp.47-49
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• 2012

Massive binary stars lose mass by two mechanisms: jet-driven mass loss during periods of active mass transfer and by wind-driven mass loss. Beta Lyrae is an eclipsing, semi-detached binary whose state of active mass transfer provides a unique opportunity to study how the evolution of binary systems is affected by jet-driven mass loss. Roche lobe overflow from the primary star feeds the thick accretion disk which almost completely obscures the mass-gaining star. A hot spot predicted to be on the edge of the accretion disk may be the source of beta Lyrae's bipolar outflows. I present results from spectropolarimetric data taken with the University of Wisconsin's Half-Wave Spectropolarimeter and the Flower and Cook Observatory's photoelastic modulating polarimeter instrument which have implications for our current understanding of the system's disk geometry. Using broadband polarimetric analysis, I derive new information about the structure of the disk and the presence and location of a hot spot. These results place constraints on the geometrical distribution of material in beta Lyrae and can help quantify the amount of mass lost from massive interacting binary systems during phases of mass transfer and jet-driven mass loss.

• Journal of Astronomy and Space Sciences
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• v.23 no.4
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• pp.311-318
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• 2006

High-precision photometric observations were performed in BVI bandpasses using Am robotic telescope at Mt. Lemmon Observatory for two binary stars, which are reclassified as W UMa-type systems from ROTSE(Robotic Optical Transient Search Experiment) follow-up observations and show peculiar light variations. In order to analyze W UMa-type eclipsing binaries systematically, the light curve analysis script using 2005 version of Wilson-Devinney binary code is constructed. The orbital inclinations of GSC2S84-1731 and GSC2576-0319 are $43.^{\circ}5\;and\;57.^{\circ}6$ from light-curve analysis, respectively. Spot model is applied to explain the asymmetric light curve for GSC2S84-1731 and the spot parameters are derived.

• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.89-96
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• 2010

BVR CCD observations of GW Cep were made on 15 nights in November through December 2008 with a 1-m reflector at the Jincheon station of the Chungbuk National University Observatory. Nineteen new times of minimum lights for GW Cep were determined and added to a collection of all other times of minima available to us. These data were then intensively analyzed, by reference to an O-C diagram, to deduce the general form of period variation for GW Cep. It was found that the O-C diagram could be interpreted as presenting two different forms of period change: an exclusively quasi-sinusoidal change with a period of 32.6 years and an eccentricity of 0.10; and a quasi-sinusoidal change with a period of 46.2 years and an eccentricity of 0.36 superposed on an upward parabola. Although a final conclusion is somewhat premature at present, the latter seems more plausible because late-type contact binaries allow an inter-exchange of both energy and mass between the component stars. The quasi-sinusoidal characteristics were interpreted in terms of a light-time effect due to an unseen tertiary component. The minimum masses of the tertiary component for both cases were calculated to be nearly the same as the $0.23-0.26M\;{\odot}$-ranges which is hardly detectable in a light curve synthesis. The upward parabolic O-C diagram corresponding to a secular period increase of about $4.12{\times}10^{-8}\;d/yr$ was interpreted as mass being transferred from the lesser to more massive component. The transfer rate for a conservative case was calculated to be about $2.66\;{\times}\;10^{-8}\;M_{\odot}/yr$ which is compatible with other W UMa-type contact binaries.

• Journal of Astronomy and Space Sciences
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• v.25 no.2
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• pp.101-112
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• 2008

Systematic CCD observations of times of minimum lights for eclipsing binaries has been carried out from 2002 to 2007 at Campus Station of Chungbuk National University Observatory which is located in Cheongju city, Korea. As a by-product of our observations, photometric data for stars in CCD images taken from 2005 to 2007 were used to determine 1st order atmospheric extinction coefficient (hereafter AEC) and seasonal and yearly variations of the AECs were studied. Total nights used for determination of AECs were 57 days in 2005, 51 days in 2006, and 63 days in 2007. As a result the annual mean value of the AECs per air mass is calculated as $0.^m34{\pm}0.^m18$ for 2005, $0.^m38{\pm}0.^m19$ for 2006, and $0.^m45{\pm}0.^m20$ for 2007. These values show that the AECs and their standard deviations are two and four times, respectively, larger than those of normal observatories which are not located near large cities. Annual comparison between concentration of atmospheric fine dust and coefficient of atmospheric extinction show strong correlation between two quantities of which time variations show similar patterns. The AECs for the east sky show larger than those for the west sky. It can be easily understood by the reasonable possibility that air pollutants remain more in the east sky than in the west because the east area of Cheongju city has been more developed than the west one. In conclusion the atmospheric extinction of the night sky of Cheongju city has an annual trend of increase of $0.^m06\;airrnass^{-1}\; year^{-1}$ implying that it may take only about 13 years for Cheongju city to have 2 times brighter night sky than the present one. Our study highlights that variations of AEC can be used as an important indicator of air pollution to monitor night skies.