• 천문학논총
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• 제30권2호
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• pp.201-204
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• 2015

The common-envelope process is a complicated phase in binary evolution. A lot of effort has been dedicated to study the common-envelope stage, but many questions related to this process are yet to be answered. If one member of the binary survives the common-envelope phase, the binary will emerge as a white dwarf accompanied by a low-mass main sequence star in close orbit, often referred as a post common-envelope binary (PCEB). SDSS J0745+2631 is among the list of newly found PCEBs from the Sloan Digital Sky Survey (SDSS). This star is proposed to be a strong eclipsing system candidate due to the ellipsoidal modulation in its light curve. In this work, we aim to confirm the eclipsing nature of SDSS J0745+2631 and to determine the stellar and orbital parameters using the software Binary Maker 3.0 (BM3.0). We detected the primary eclipse in the light curve of SDSS J0745+2631 in our follow-up observation from January 2014 using the ULTRASPEC instrument at the Thai National Observatory. The data obtained on 7th and 8th January 2014 in g filter show an evident drop in brightness during the eclipse of the white dwarf, but this eclipse is less prominent in the data taken on the next night using a clear filter. According to our preliminary model, we find that SDSS J0745+2631 hosts a rather hot white dwarf with an effective temperature of 11500K. The companion star is a red dwarf star with a temperature of 3800K and radius of 0.3100 $R_{\odot}$. The red dwarf star almost fills its Roche lobe, causing a large ellipsoidal modulation. The mass ratio of the binary given by the Binary Maker 3.0 (BM3.0) model is M2/M1 = 0.33.

• 천문학논총
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• 제30권2호
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• pp.217-218
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• 2015

In this work, we present the result of our follow-up observations of SDSS J092741.73+332959.1 and SDSS J130733.49+215636.7 using the 2.35 m Thai National Telescope and ULTRASPEC instrument. Both systems are listed among the recently found white dwarf main sequence binaries from the Sloan Digital Sky Survey. SDSS J092741.73+332959.1 is a new PCEB with a period of 2.3 days, the longest orbital period known to date for white dwarf binaries. SDSS J130733.49+215636.7 is confirmed to be an eclipsing system with a period of 0.21 days from the Catalina Survey's light curve, however the parameters for the white dwarf are still uncertain. Our goal is to determine precise parameters for both systems using the Binary Maker 3 software. The observation for SDSS J0927+3329 was done on 9 January 2014 in the SDSS r' filter while the data for SDSS J1307+2156 were taken in the z' filter on 27 April 2014. Our models show that the red dwarf companions in both systems are well constrained inside their Roche Lobes. We find that the binary M2/M1 ratio in SDSS J0927+3329 is close to 0.5, with white dwarf and M-dwarf temperatures of 12000 K and 3300 K, respectively. Our preliminary result for SDSS J1307+2156 show that this system has an extreme mass ratio of 0.3. The white dwarf in this system has a temperature of 7500 K and the companion star has an effective temperature of 3150 K.

• 천문학회지
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• 제47권3호
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• pp.99-104
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• 2014

We present the rst period variation study for the Algol eclipsing binary V346 Cyg by constructing the (O-C) residual diagram using all the available precise minima times. We conclude that the period variation can be explained by a sine-like variation due to the presence of a third body orbiting the binary in about $68.89{\pm}4.69$ years, together with a long-term orbital period decrease ($dP/dt=-1.23{\times}10^{-7}day/yr$) that can be interpreted to be due to slow mass loss from the ${\delta}$-Scuti primary component. The sinusoidal variation may also be explained by using the the Applegate (1992) mechanism involving cyclic magnetic activity due to star-spots on the secondary component. The present preliminary solution needs more precise photometric observations to be confirmed.

• Journal of Astronomy and Space Sciences
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• 제29권2호
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• pp.131-140
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• 2012

We presented fundamental stellar parameters and evolutionary statuses of six solar type detached eclipsing binaries whose masses are in the range of 0.97-1.43 $M_{\odot}$. EK Cep and FL Lyr belong to the zero age main sequence. HS Hya, IT Cas and CD Tau are on the main sequence. Their ages are 1.3, 1.9 and 2.2 Gyr, respectively. Both component stars of AI Phe evolved to sub giants and its age is 4.0 Gyr. Those ages of the detached binary systems show good agreement with the time scale for synchronization and circularization of the binary systems.

• 천문학회보
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• 제28권1호
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• pp.58-58
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• 2003

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2007년도 한국우주과학회보 제16권2호
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• pp.33-33
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• 2007

• 천문학회지
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• 제29권spc1호
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• pp.239-240
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• 1996

Precise masses, radii, and luminosities from eclipsing binaries and colour-magnitude diagrams for open clusters are classic tools in empirical tests of stellar evolution models. We review the accuracy and completeness required for such data to discriminate between current models and describe some recent. results with implications for convection theory.

• 천문학회보
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• 제41권1호
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• pp.78.3-78.3
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• 2016

The Kepler mission of NASA has enabled to discover a lot of new W UMa-type binaries with continuous light curves measured with unprecedented accuracy. Interestingly, their eclipsing time variation (hereafter ETV) diagrams show anti-correlation between primary and secondary minima, presumably occurred by continuous spot variation (Tran et al. 2013; Balaji et al. 2014). Two active Kepler binaries (KIC06118779 & KIC08682849), reported as showing the anti-correlation in ETV diagram, were investigated to see that the anti-correlations are correlated with time-variable O'connell effects appeared in their light curves. As a result, it was found that the O'connell effects for two binary stars have varied in quasi-sinusoidal ways similar to the patterns of their anti-correlation variations. In addition, our light curve syntheses of two binary stars with the latest version of the Wilson-Devinney code (Wilson & devinney 1971) show that they are very deep-contact binary system with extremely low mass ratios.

• 천문학회지
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• 제44권3호
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• pp.97-108
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• 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.

• 천문학논총
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• 제20권1호
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• pp.21-27
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• 2005

We have been performing a wide-field photometric monitoring program, named SPVS (Short-Period Variability Survey), at the Bohyunsan Optical Astronomy Observatory (BOAO). The observation system consists of a small refracting telescope (D = 155 mm, f = 1050 mm) and a $2k{\times}3k$ CCD Camera. The field of view is $1.0^{\circ}{\times}1.5^{\circ}$. Detection limit is about V = 13 for short-period small amplitude variables such as ${\delta}$ Scuti-type pulsating stars, and about V = 15 for long-period large amplitude variables such as eclipsing binaries and RR Lyrae stars. The instrument is designed to be remote-controlled through internet. The primary purpose of this project is to search for variable objects in bright Galactic open clusters. We present results of test observations conducted towards NGC 7092.