• Journal of The Korean Astronomical Society
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• v.49 no.4
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• pp.163-173
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• 2016

In this paper, we study the lunar eclipse records in the Goryeosa (History of the Goryeo Dynasty), an official history book of the Goryeo dynasty (A.D. 918 - 1392). In the history book, a total of 228 lunar eclipse accounts are recorded, covering the period from 1009 to 1392. However, we find that two accounts are duplications and four accounts correspond to no known lunar eclipses around the dates. For the remaining lunar eclipses, we calculate the magnitude and the time of the eclipse at different phases using the DE406 ephemeris. Of the 222 lunar eclipse accounts, we find that the minimum penumbral magnitude was 0.5583. For eclipses which occurred after midnight, we find that some accounts were recorded on the day before the eclipse, like the astronomical records of the Joseonwangjosillok (Annals of the Joseon Dynasty), while others were on the day of the lunar eclipse. We also find that four accounts show a difference in the Julian dates between this study and that of Ahn et al., even though it is assumed that the Goryeo court did not change the dates in the accounts for lunar eclipses that occurred after midnight. With regard to the contents of the lunar eclipse accounts, we confirm that the accounts recorded as total eclipses are accurate, except for two accounts. However, both eclipses were very close to the total eclipse. We also confirm that all predicted lunar eclipses did occur, although one eclipse happened two days after the predicted date. In conclusion, we believe that this study is very helpful for investigating the lunar eclipse accounts of other periods in Korea, and furthermore, useful for verifying the calendar dates of the Goryeo dynasty.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.65.2-65.2
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• 2010

We present four new transits of the planetary system TrES-3 observed between 2009 May and 2010 June. Among those, the third transit by itself indicates possible evidence for brightness disturbance, which could originate from a starspot or an overlapping double transit. A total of 107 transit times, including our measurements, were used to determine the improved ephemeris with a transit epoch of $2454185.910950\pm0.000073$ HJED (Heliocentric Julian Ephemeris Date) and an orbital period of $1.30618698\pm0.00000016$ d. We analyzed the transit light curves using the JKTEBOP code and adopting the quadratic limb-darkening law. In order to derive the physical properties of the TrES-3 system, the transit parameters are combined with the empirical relations from eclipsing binary stars and stellar evolutionary models, respectively. The stellar mass and radius obtained from a calibration using $T_{eff}$, log $\rho$ and [Fe/H] are in good agreement with those from the isochrone analysis within the uncertainties. We found that the exoplanet TrES-3b has a mass of $1.93\pm0.07\;M_{Jup}$, a radius of $1.30\pm0.04\;R_{Jup}$, a surface gravity of $28.2\pm1.1\;m\;s^{-1}$, a density of $0.82\pm0.06\;\rho_{Jup}$, and an equilibrium temperature of $1641\pm23K$.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.591-592
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• 2015

X1822-371 is a low mass X-ray binary with an accretion disk corona exhibiting partial eclipses and pulsations in the X-ray band. We update its orbital ephemeris by combining new RXTE observations and historical records, with a total time span of 34 years. There were 11 RXTE observations in 2011 but the eclipsing profile can be seen in only 4 of them. The eclipsing center times were obtained by fitting the profile with the same model as previous studies. Combined with the eclipsing center times reported by Iaria et al. (2011), the O-C analysis was processed. A quadratic model was applied to fit the O-C results and produced a mean orbital period derivative of $\dot{P}_{orb}=1.339(25){\times}10^{-10}s/s$, which is slightly smaller than previous records. In addition to the orbital modulation from the orbital profile, we also present our preliminary results for measuring the orbital parameters using the orbital Doppler effect from the pulsation of the neutron star in X1822-371. The updated orbital parameters from eclipsing profiles will be further compared with the ones from pulsar timing.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.89.1-89.1
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• 2015

Period changes found in the 10 years CCD BVR photometry data (2005 - 2014) of the Intermediate Polar MU Cam will be discussed. The timings of extrema of the data are determined and the new ephemeris for the spin period and orbital period have been calculated by using multi-periodic approximation as follows: BJD(orb)=2454085.46(19)+0.19664 $10(26){\cdot}E$ and BJD(spin)=2454085.50725(91)+0.013740942(13) ${\cdot}$ $E-1.51(10){\times}10^{-12}{\cdot}E^2$. The O-C diagram shows an increasing of the spin period as $P=-2.20(14){\cdot}10^{-12}s/s$. It is also found in MU Cam that the white dwarf's rotation seems to be switched from a state of spin-down to spin-up by the white dwarf's equilibrium spin period in 2005.

• Journal of Astronomy and Space Sciences
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• v.27 no.1
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• pp.31-42
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• 2010

We developed a computer program to predict solar interference period. To calculate Sun's position, we used DE406 ephemerides and Earth ellipsoid model. The Sun's position error is smaller than 10arcsec. For the verification of the calculation, we used TU media ground station on Seongsu-dong, and MBSAT geostationary communication satellite. We analysis errors, due to satellite perturbation and antenna align. The time error due to antenna align has -35 to +16 seconds at $0.1^{\circ}$, and -27 to +41 seconds at $0.25^{\circ}$. The time errors derived by satellite perturbation has 30 to 60 seconds.

• Proceedings of the KSRS Conference
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• 2002.10a
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• pp.82-87
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• 2002

RFM is the sensor model of IKONOS imagery for end-users. IKONOS imagery vendors provide RPC (Rational Polynomial Coefficients), Ration Function Model coefficients for IKONOS, for end-users with imagery. So it is possible that end-users obtain geospatial information in their IKONOS imagery without additional any effort. But there are requirements still fur rigorous 3D positions on RPC user. Provided RPC can not satisfy user and company to generate precision 3D terrain model. In IKONOS imagery, physical sensor modeling is difficult because IKONOS vendors do not provide satellite ephemeris data and abstract sensor modeling requires many GCP well distributed in the whole image as well as other satellite imagery. Therefore RPC modification is better choice. If a few GCP are available, RPC can be modified by method which is introduced in this paper. Study on evaluation modified RPC in IKONOS reports reasonable result. Pseudo GCP generated with vendor's RPC and additional GCP make it possible through sequential solution.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.91-94
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• 2005

A numerical formula that presents relationship between a point of a satellite image and its ground position is called a sensor model. For precise geolocation of satellite images, we need an error-free sensor model. However, the sensor model based on GOES ephemeris data has some error, in particular after Image Motion Compensation (IMC) mechanism has been turned off. To solve this problem, we investigate three sensor models: Collinearity model, Direct Linear Transform (DLT) model and Orbit-based model. We apply matching between GOES images and global coastline database and use successful results as control points. With control points we improve the initial image geolocation accuracy using the three models. We compare results from three sensor models that are applied to GOES-9 images. As a result, a suitable sensor model for precise geolocation of GOES-9 images is proposed.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.38.1-38.1
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• 2017

Symbiotic stars are long-orbital-period interacting binaries characterized by extended emission over the whole electromagnetic range and by complex photometric and spectroscopic variability. In this contribution, I will present some high-cadence, long-term optical light curves of confirmed and candidate symbiotic stars in the Magellanic Clouds. By careful visual inspection and combined time series analysis techniques, we investigate for the first time in a systematic way the photometric properties of these astrophysical objects, trying in particular to distinguish the evolutionary status of the cool component, to provide its first-order pulsation ephemeris and to link all this information with the physical parameters of the binary system as a whole. Finally, I will discuss a new, promising photometric technique, potentially able to discover Symbiotic Stars in the Local Group of Galaxies without the recourse to costly spectroscopic follow-up.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.1
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• pp.8-14
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• 2013

As GNSS(Global Navigation Satellite System) is used in various filed, many countries establish GNSS system independently. But GNSS system has the limitation of accuracy and stability in stand-alone mode, because this system has error elements which are ionospheric delay, tropospheric delay, orbit ephemeris error, satellite clock error, and etc. For overcome of accuracy limitation, the DGPS(Differential GPS) and RTK(Real-Time Kinematic) systems are proposed. These systems perform relative positioning using the reference and user receivers. ETRI(Electronics and Telecommunications Research Institute) is developing precision navigation system in point of extension of GNSS usage. The precision navigation system is for providing the precision navigation solution to common users. If this technology is developed, GNSS system can be used in the fields which require precision positioning and control. In this paper, we introduce the precision navigation system and perform design and algorithm verification.

• Journal of Astronomy and Space Sciences
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• v.10 no.1
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• pp.44-85
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• 1993

Among the EA and semi-detached type binary systems, nineteen eclipsing binaries were investigated for their period variations from all of the collected times of minima available in the literature. After the period study of each individual binary, an attempt was made, in view of the linear ephemeris showing abrupt change in period, to give a physical interpretation to the combined observational result. The correlation between period changes and physical parameters of the investigated binary systems are discussed.