• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.49.3-50
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• 2015

Early-type dwarf galaxy (ETDG), the most abundant galaxy type in clusters, were recently shown to exhibit a wide variety in their properties. Particularly, the presence of blue cores in some ETDGs supports the scenario of late-type galaxy infall and subsequent transformation into red, quiescent ETDGs. While several transformation mechanisms for these ETDGs with blue core within cluster environment have been proposed, all these processes are able to explain only some of the observational properties of ETDGs such as stellar populations and structural parameters. In this context, internal kinematic properties of blue-cored ETDGs provide the most crucial evidence to discriminate different processes for the formation of these galaxies. We present a kinematic analysis of two blue-cored ETDGs in the Virgo cluster based on long-slit data obtained from Gemini Multi-Object Spectrographs (GMOS) observations. We find that the observed galaxies show kinematically decoupled sub-components in the velocity profile such as discontinuity or counter-rotating component. We discuss possible scenarios of formation of these transitional galaxies.

• Journal of The Korean Astronomical Society
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• v.47 no.4
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• pp.147-152
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• 2014

We present measurements of the Fe $K{\alpha}$ emission line of the intermediate polar V1223 Sagittarii observed with the Suzaku satellite. The spectrum is modeled with an absorbed thermal bremsstrahlung spectrum and three Gaussians for the three components of the Fe $K{\alpha}$ lines. We resolve the neutral or low-ionized (6.41keV), He-like (6.70keV), and H-like (7.00keV) iron lines. We also obtain a thermal continuum temperature of 25 keV, which supports a thermal origin of the hard X-rays observed from the shock heated layers of gas between the white dwarf and the shock front. Hence, we believe that the He-like and H-like lines are from the collisional plasma. On the origin of the Fe $K{\alpha}$ fluorescence line, we find that it could be partly from reflections of hard X-rays from the white dwarf surface and the $N_H$ absorption columns. We also discuss the Fe $K{\alpha}$ emission line as veritable tool for the probe of some astrophysical sites.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.73.2-73.2
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• 2013

In the current ${\Lambda}CDM$ hierarchical merging paradigm, a galaxy like the Milky Way formed by numerous mergers of ancient subsystems. Most of the relics of these building blocks, however, are yet to be discovered or identified. Recent progress in the Milky Way globular cluster research is throwing new light on this perspective. The discoveries of multiple stellar populations having different heavy element abundances in some massive globular clusters are suggesting that they are most likely the remaining cores or relics of disrupted dwarf galaxies. In this talk, we will report our progress in the (1) narrow-band photometry, (2) low-resolution spectroscopy, and (3) population modeling for this growing group of peculiar globular clusters.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.34 no.s01
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• pp.4-15
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• 1989

The objective of this paper is to compare and summarize the procedure and effectiveness of some bioassay systems and to point out ways to obtain reliable results from each bioassay. Detailed C:escriptions were given for those widely-adapted bioassay methods, such as mungbean rooting (auxin), Avena first internode straight growth (auxin), dwarf rice growth (gibberellin), dwarf pea epicotyl elongation (gibberellin), radish cotyledon expansion test (cytokinin), and tobacco stem pith callus growth (cytokinin), and the effects of various plant growth regulators including some recently introduced growth retardants (Paclobutrazol, Uniconazol, etc.) were also summarized.

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.421-424
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• 2009

The $JHK_S$ magnitudes of the red giant branch tip (TRGB) and the distance moduli of the nearby dwarf irregular galaxy IC 1613 have been determined from the near-infrared luminosity functions (LFs) of the resolved stars in the galaxy. Applying a Savitzky-Golay filtering, we derived the second derivatives of the LFs, and estimated the apparent magnitudes of the TRGB as $m_J\;=\;19.1$, $m_H\;=\;18.4$, and $m_{Ks}\;=\;18.0$. The mean values of the theoretical absolute magnitudes of the TRGB were measured by using the Yonsei-Yale isochrones with a metallicity range of -2.1 < [Fe/H] < -0.5 and age of 12 Gyr. The derived values of near-infrared TRGB distance moduli for IC 1613 are (m - M) = $24.12{\pm}0.25$, $24.20{\pm}0.44$, and $24.00{\pm}0.52$ for J, H, and $K_S$ bands, respectively.

• Journal of Astronomy and Space Sciences
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• v.26 no.4
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• pp.417-420
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• 2009

We have used the near-infrared $JHK_S$ photometric data of resolved stars in a nearby dwarf elliptical galaxy NGC 205 to determine the magnitudes of the red giant branch tip (TRGB). By applying Savitzky-Golay filter to the observed luminosity functions (LFs) in each band, we derived the second derivatives of the LFs so as to determine the magnitudes of the TRGB. Absolute magnitudes of the TRGB in $JHK_S$ bands were measured from the Yonsei-Yale isochrones. By comparing the determined apparent magnitudes and the theoretical absolute magnitudes of the TRGB, we estimated the distance moduli of NGC 205 to be (m - M) = $24.10{\pm}0.08$, $24.08{\pm}0.12$ and $24.14{\pm}0.14$ in J, H, and $K_S$ bands, respectively.

• Journal of Astronomy and Space Sciences
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• v.24 no.3
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• pp.203-208
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• 2007

We report the distance modulus of nearby dwarf elliptical galaxy NGC 147 estimated from the Tip of Red-giant Branch (TRGB) method applying to the color-magnitude diagrams and luminosity functions in the near-infrared JHK bands. Apparent magnitudes of TRGBs in each band are obtained by applying Savitzky-Golay filter to the luminosity functions, and the theoretical absolute magnitudes are estimated from Yonsei-Yale isochrones. The derived values of distance modulus to NGC 147 are $(m-M)=23.69{\pm}0.12,\;23.78{\pm}0.17,\;and\;23.85{\pm}0.22\;for\;J,\;H,\;and\;K$ bands, respectively. Distance modulus in bolometric magnitude is also derived as $(m-M)=23.87{\pm}0.11$. We compare the derived values of the TRGB distance modulus to NGC 147 in the near-infrared bands with the previous results in other bands.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.55.1-55.1
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• 2014

on the observation with the Gemini Multi-Object Spectrograph on the Gemini-South 8.1 m telescope. The radial velocities of four ESCs do not display any sign of systematic motion, unlike the intermediate age carbon stars in NGC 6822. The ages and metallicities derived using the Lick indices show that the ESCs are old (>=8 Gyr) and metal poor ([Fe/H] <= -1.5). NGC 6822 is found to have both metal poor ($[Fe/H]{\approx}-2.0$) and metal rich ($[Fe/H]{\approx}-0.9$) star clusters within 15' (2 kpc) from the center, whereas only metal poor clusters are observed in the outer halo with r >= 20'(2.6 kpc). Based on the kinematics, old ages, and low metallicities of ESCs, we discuss the possible origin of ESCs and the formation of the outer halo of a small dwarf irregular galaxy NGC6822.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.51.2-51.2
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• 2014

Ultra faint dwarf galaxies (UFDs) are larger but fainter than globular clusters, being the faintest galaxies in the universe. They have been found only in the Local Group. We report the discovery of an UFD in the intracluster field of the Virgo cluster (Virgo UFD1). It is located near the core of Virgo cluster, and far from any massive galaxies. The color magnitude diagram of resolved stars in Virgo UFD1 shows narrow, metal poor red giant branch (RGB), which is very similar to the UFDs in the Local Group. by comparing RGB in this galaxy with 12 Gyr stellar isochrones, we estimate its distance, $d=16.4{\pm}0.4$ Mpc and mean metallicity, $[Fe/H]=-2.4{\pm}0.4$. We derive its integrated photometric properties and structural parameters : V-band absolute magnitude of $MV=-6.3{\pm}0.2$, effective radius of $84{\pm}7pc$, and central surface brightness of ${\mu}V,0=26.49{\pm}0.09$ mag arcsec-2. These properties are similar to these of Local Group UFDs. Virgo UFD1 is the first UFD discovered beyond the Local Group. These results indicate that it may be a fossil remnant of the first galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.83.2-83.2
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• 2014

Flare and rotational variabilities induced by stellar activity are important for studying the effect of magnetic fields on the evolution of red dwarf stars. The level and frequency of magnetic activity in these stars have a different aspect at every moment of the observations due to the effect of age-rotation relation. The use of both tracers is thus essential to have a relatively homogeneous set of stellar activity data for statistical studies. The archival light curves and imaging data of the open cluster M37 taken by MMT 6.5m telescope were used for this work. In order to achieve much more accurate photometric precisions and also to make the most efficient use of the data, the entire imaging database were re-analyzed with our new time-series photometry technique and carefully calibration procedures. Based on the new light curves, we study, for the first time, a variety of aspects of those two variabilities in red dwarfs and their relation to magnetic activity. In this talk, we present all observational evidences that support the idea that the strength of magnetic activity is closely connected with the rotation rate of a star and its evolutionary status (age-activity-rotation paradigm). In conclusion, we suggest future directions to improve our understanding of stellar activity in cool stars with photometric time-series data.