• Journal of Astronomy and Space Sciences
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• v.34 no.1
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• pp.19-30
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• 2017

The optical wide-field patrol network (OWL-Net) is a Korean optical surveillance system that tracks and monitors domestic satellites. In this study, a batch least squares algorithm was developed for optical measurements and verified by Monte Carlo simulation and covariance analysis. Potential error sources of OWL-Net, such as noise, bias, and clock errors, were analyzed. There is a linear relation between the estimation accuracy and the noise level, and the accuracy significantly depends on the declination bias. In addition, the time-tagging error significantly degrades the observation accuracy, while the time-synchronization offset corresponds to the orbital motion. The Cartesian state vector and measurement bias were determined using the OWL-Net tracking data of the KOMPSAT-1 and Cryosat-2 satellites. The comparison with known orbital information based on two-line elements (TLE) and the consolidated prediction format (CPF) shows that the orbit determination accuracy is similar to that of TLE. Furthermore, the precision and accuracy of OWL-Net observation data were determined to be tens of arcsec and sub-degree level, respectively.

• Journal of Astronomy and Space Sciences
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• v.40 no.4
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• pp.247-258
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• 2023

Studying the accretion phenomena provides a window into understanding most heavenly bodies, from the birth of stars to active galactic nuclei (AGN). We would adopt the effect of the radiation pressure, which reduces accretion rates (Ṁ), on the accretion phenomena. The Shakura-Sunyaev α-disk model of disk accretion is a good candidate theory of advection dominated accretion flow (ADAF). Reduction in the angular velocity leads to the suppression the disk luminosity and surface temperature, essentially indicating the transition of the standard accretion disk model from convection dominated accretion flow (CDAF) to ADAF.

• Journal of Astronomy and Space Sciences
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• v.21 no.4
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• pp.303-314
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• 2004

In this paper we report some properties of inner magnetospheric structure inferred from the T01_s code, one of the latest magnetospheric models by Tsyganenko. We have constructed three average storms representing moderate, strong, and severe intensity storms using 95 actual storms. The three storms are then modelled by the T01_s code to examine differences in magnetic structure among them. We find that the magnetic structure of intense storms is strikingly different from the normal structure. First, when the storm intensity is large, the field lines anchored at dayside longitudinal sectors become warped tailward to align to the solar wind direction. This is particularly so for the field lines anchored at the longitudinal sectors from postnoon through dusk. Also while for the moderate storm the equatorial magnetic field near geosynchronous altitude is found to be weakest near midnight sector, this depression region expands into even late afternoon sector during the severe storm. Accordingly the field line curvature radius at the equator in the premidnight geosynchronous region becomes unusually small, reaching down to a value less than 500 km. We attribute this strong depression and the dawn-dusk asymmetry to the combined effect from the enhanced tail current and the westward expansion/rotation of the partial ring current.

• Journal of Astronomy and Space Sciences
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• v.31 no.4
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• pp.295-301
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• 2014

Whistler mode chorus wave is considered to play a critical role in accelerating and precipitating the electrons in the outer radiation belt. In this paper we test a conventional scenario of triggering chorus using THEMIS satellite observations of waves and particles. Specifically, we test if the chorus onset is consistent with development of anisotropy in the electron phase space density (PSD). After analyzing electron PSD for 73 chorus events, we find that, for ~80 % of them, their onsets are indeed associated with development of the positive anisotropy in PSD where the pitch angle distribution of electron velocity peaks at 90 degrees. This PSD anisotropy is prominent mainly at the electron energy range of ${\leq}$ ~20 keV. Interestingly, we further find that there is sometimes a time delay among energies in the increases of the anisotropy: A development of the positive anisotropy occurs earlier by several minutes for lower energy than for an adjacent higher energy.

• Journal of Astronomy and Space Sciences
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• v.23 no.2
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• pp.97-104
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• 2006

From the BV images of the metal-poor globular cluster NGC 1904 obtained with the 2K CCD camera equipped on the BOAO 1.8m telescope, we construct (B - V, V) color-magnitude diagram of the cluster. The apparent V magnitudes of the RGB bump and tip have been measured from the luminosity function of the iteratively selected RGB stars in NGC 1904. Theoretical absolute $M_v$ magnitudes of the RGB bump and tip are estimated using the Yonsei-Yale isochrones. The distance modulus of NGC 1904 has been derived by comparing the observed apparent V magnitude with the estimated absolute $M_v$ magnitude of the RGB bump and tip.

• Journal of Astronomy and Space Sciences
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• v.25 no.3
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• pp.245-248
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• 2008

We determined values of distance modulus to nearby dwarf galaxy NGC 185 from the Tip of Red-Giant Branch (TRGB) method. Apparent magnitudes of the TRGB are estimated from the near-infrared JHK luminosity functions (LFs) of the resolved giant branch stars. Theoretical absolute magnitudes of the TRGB in near-infrared bands have been extracted from the Yonsei-Yale isochrones. The observed apparent and theoretical absolute magnitudes of the TRGB provide values of distance modulus to NGC 185 as (m - M) = $23.39{\pm}0.14$, $23.23{\pm}0.22$, and $23.27{\pm}0.26$ for J,H, and K bands, respectively. Distance modulus in bolometric magnitude is also derived as (m - M) = $23.62{\pm}0.12$.

• Publications of The Korean Astronomical Society
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• v.21 no.2
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• pp.113-119
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• 2006

The Korean Astronomical Data Center(KADC) in Korea Astronomy and Space Science Institute(KASI) has developed a database of astronomical journals published by the Korean Astronomical Society and the Korean Space Science Society. It consists of all bibliographic records of the Journal of the Korean Astronomical Society(JKAS), Publication of the Korean Astronomical Society(PKAS), and Journal of Astronomy & Space Sciences(JASS). The KADC provides useful search functions in the search page such as search criterion of bibcode, publication date, author names, title words, or abstract words. The journal name is one of the search criterion in which more than one journal can be designated at the same time. The criterion of author name is provided bilingually: English or Korean. The abstract and full text can be downloaded as PDF files. It is also possible to search papers related to a specific research topic published in Korean astronomical journals, provided by the KADC, which often cannot be found the worldwide, Astrophysics Data System(ADS) services. The KADC will become basic infrastructure for the systematic construction of bibliographic records, and hence, make the society of Korean astronomers more interactive and collaborative.

• Journal of Astronomy and Space Sciences
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• v.37 no.2
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• pp.131-142
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• 2020

As the laws of physics are expressed in a manner that makes their invariance under coordinate transformations manifest, they should be written in terms of tensors. Furthermore, tensors make manifest the characteristics and behaviors of electromagnetic fields through inhomogeneous, anisotropic, and compressible media. Electromagnetic fields are expressed completely in tensor form, F^αβ, which implies both electric field ${\overrightarrow{E}}$ and magnetic field ${\overrightarrow{B}}$ rather than separately in the vector fields. This study presents the Mathematica platform that generates and transforms a second-rank antisymmetric field-strength tensor F^αβ and whiskbroom pattern in Minkowski space. The platforms enhance the capabilities of students and researchers in tensor analysis and improves comprehension of the elegant features of complete structure in physics.

• Journal of Astronomy and Space Sciences
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• v.27 no.4
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• pp.263-278
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• 2010

Many filtered CCD measures form the basis of six new light curves of the eclipsing system SW Lyn. From these measures and additional observations for eclipse timing, 47 new times of minimum light over the time-interval of about 13 years have been calculated. The complex period variability can be sorted into a linear period improvement with 5.8-year and 33.9-year periodic terms. The shorter cyclic term of these is ascribed to a cool companion of the eclipsing pair but the longer one has no testable interpretation at present. The new light curves are synthesized by the 2003 version of the Wilson-Devinney differential corrections computer code. The results incorporate a source of "third light" which comes from the cool companion star that had been identified by the cycling of the period of the eclipsing pair and also had previously been identified spectroscopically. There is a measure of satisfaction with current understanding of the SW Lyn eclipsing system because of consistent syntheses of all historical light curves. This agreeable convergence, however, comes partly at the expense of an unanticipated temperature of the hot star and of a photospheric spot that has no obvious basis in the detached character modeled for the binary. We offer predictions of changes in the stellar parameters if the modeled detached-configuration should be wrong. The SW Lyn stellar system is still difficult to understand.

• Journal of Astronomy and Space Sciences
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• v.33 no.2
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• pp.137-146
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• 2016

The correlation between meteorological data collected at the optical wide-field patrol network (OWL-Net) Station No. 1 and the seeing of satellite optical observation data was analyzed. Meteorological data and satellite optical observation data from June 2014 to November 2015 were analyzed. The analyzed meteorological data were the outdoor air temperature, relative humidity, wind speed, and cloud index data, and the analyzed satellite optical observation data were the seeing full-width at half-maximum (FWHM) data. The annual meteorological pattern for Mongolia was analyzed by collecting meteorological data over four seasons, with data collection beginning after the installation and initial set-up of the OWL-Net Station No. 1 in Mongolia. A comparison of the meteorological data and the seeing of the satellite optical observation data showed that the seeing degrades as the wind strength increases and as the cloud cover decreases. This finding is explained by the bias effect, which is caused by the fact that the number of images taken on the less cloudy days was relatively small. The seeing FWHM showed no clear correlation with either temperature or relative humidity.