• Journal of The Korean Astronomical Society
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• v.13 no.1
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• pp.35-44
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• 1980

Various assumptions used in interpreting the observations of hydrogen recombination lines are critically assessed to confirm the gradient of electron temperature with distance from the galactic center. The total temperature increase from 5 to 13 kpc is about 2,500 K. Among many suggestions, we have singled out the decrease of trace dement abundances with the galactoccntric distance as the most viable cause for the temperature gradient. This will impose an important constraint on evolutionary models of the Galaxy.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.51.1-51.1
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• 2011

We introduce new methods to measure distance in precision using large scale structure formation. The accuracy to determine geometrical factors is enhanced in comparison to the previous method known as BAO. We determine both D_A and H simultaneously as well as structure of growth of density fluctuations and peculiar velocities. Our method is independent of any given prior on large scale structure formation such as the shape of spectra.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.179-180
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• 1996

The aim of the paper is to analyse the extinction law in the giant H II region NGC 3603. The ratio R is found to be greater than 5.0. In front of the cluster the reddening law is found to be normal. We have obtained a distance of $\~$5.3 Kpc which is significantly smaller than those adopted so far.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.119-120
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• 2015

We report results of the measurement of the trigonometric parallax of an $H_2O$ maser source in IRAS 22555+6213 with the VLBI Exploration of Radio Astrometry (VERA). The annual parallax was determined to be $0.278{\pm}0.019$ mas, corresponding to a distance of $3.66^{+0.30}_{-0.26}kpc$. Our results confirm that IRAS 22555+6213 is located in the Perseus arm. We computed the peculiar motion of IRAS 22555+6213 to be ($U_{src}$, $V_{src}$, $W_{src}$) = ($0{\pm}1$, $-32{\pm}1$, $9{\pm}1$) $km\;s^{-1}$, where $U_{src}$, $V_{src}$, and $W_{src}$ are directed toward the Galactic center, in the direction of Galactic rotation and toward the Galactic north pole, respectively. IRAS 22555+6213, NGC7538 and Cepheus A lie along the same line of sight, and are within $2^{\circ}$ on the sky. Their parallax distances, with which we derived their absolute position in the Milky Way, show that IRAS 22555+6213 and NGC7538 are associated with the Perseus arm, while Cepheus A is located in the Local arm. We compared the kinematic distances of IRAS 22555+6213 derived with flat and non-flat rotation curve with its parallax distance and found the kinematic distance derived from the non-flat rotation assumption ($-32km\;s^{-1}$ lag) to be consistent with the parallax distance.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.81.3-81.3
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• 2016

We examine whether the observational stand-off distance ratios of CMEs and their associated ICMEs could be explained by theoretical model or not. For this, we select 16 CME-ICME pairs from September 2009 to October 2012 with the following conditions: (1) limb CMEs by SOHO and their associated ICMEs by twin STEREO spacecraft and vice versa when both spacecraft were roughly in quadrature; (2) the faint structure ahead of a limb CME is well identified; and (3) its associated ICME clearly has a sheath structure. We determine the observational stand-off distance ratios of the CMEs by using brightness profiles from LASCO-C2 (or SECCHI-COR2) observations and those of the ICMEs by solar wind data from STEREO-IMPACT/PLASTIC (or OMNI database) observations. We also determine the theoretical stand-off distance ratios of the CME-ICME pairs using semi-empirical relationship based on the bow shock theory. We find the following results. (1) Observational CME stand-off distance ratio decreases with increasing Mach number at the Mach numbers between 2 and 6. This tendency is consistent with the results from the semi-empirical relationship. (2) The observational stand-off distance ratios of several ICMEs can be explained by the relationship.

• Publications of The Korean Astronomical Society
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• v.25 no.4
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• pp.155-165
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• 2010

In this study, we investigate the changes in the equatorial lodge degrees and polar distance degrees of determinative stars in the ancient Chinese archives. Confirmed is the fact that the coordinate values of those determinative stars defined in B.C. 104 had been used until the 8th century but were modified by the observations of Li Chunfeng (李淳風) in the early 7th century and Yixing (一行) in 723 A.D. The results of this study are compared with those in History of Chinese Astronomical Observations of Pan Nai. By applying the results of comtemporary astrodynamical calculations, their reliability is checked, and the corrected catalogues of Shi Shi (石氏) and Yixing are provided. The positional accuracy of those observations is estimated to be one degree.

• The Bulletin of The Korean Astronomical Society
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• v.26 no.1
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• pp.28.1-28.1
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• 2001

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.61-62
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• 1996

The photometry is reported for galaxies in two clusters A1983, 2065 with redshifts 0.046, 0.072 respectively. The luminosity segregation is observed only within a magnitude from the brightest galaxy. The alignment of the galaxy major axis is observed in the Corona Borealis cluster. The intermediate distance clusters (0.05 < z < 0.15) will be studied by CCD mounted on 125cm RCh and 70cm meniscus type telescopes.

• The Bulletin of The Korean Astronomical Society
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• v.26 no.2
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• pp.27-27
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• 2001

• Journal of The Korean Astronomical Society
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• v.25 no.2
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• pp.91-104
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• 1992

New photoelectric UBV Photometry of 112 stars in open cluster M35 field was obtained. The distance modulus and age of the cluster are $9.^m3$(725pc) and $8.5{\times}10^7yrs$, respectively. The internal differential reddening within the cluster is apparent.