• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.78.1-78.1
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• 2010

We obtained the spectra of 93 Planet host stars and 73 normal field stars in F, G, K type using BOES at BOAO. We measured the equivalent width of Fe and 13 elements lines using the automatic EW measurement program, TAME(Tools for Automatic Measurement of Equivalent-widths) and estimated the abundances by synth and abfind driver of MOOG code. Since the absence of planets in the normal field stars cannot be "completely" proved, this work focused on the chemical abundances and planet properties of planet host stars, which have the massive planets close to the parent star relatively. We carried out an investigation for the difference of abundances between stars with "Hot Jupiter" and normal field stars with no known planets. We examined the chemical composition of 12 elements, such as Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, and Ni by EW measurements, and the S abundances were estimated using synthetic spectrum.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.147.1-147.1
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• 2011

We investigate the chemical differentiation in F, G, K type stars with and without planets to extend the work by Kang et al. (2011) to various spectral types. Since the primordial chemical composition has been preserved in the stellar atmosphere, stellar metallicity can provide the information on the primordial material, which is the potential building block of planets. Therefore, we can explore the favored conditions for planet formation through the comparison of chemical compositions between planet-host stars (PHSs) and stars without planets. In this work, we analyze 19 F, G, and K type stars. In each spectrum, we measure equivalent widths (EWs) of Fe, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, and Ni using TAME (Tools for Automatic Measurement of Equivalent width). The abundances of these species can be derived with the measured EWs and MOOG code (Sneden 1973). Like results by precedent studies, we find that planet-host stars have abundances higher than stars without planets. The typical difference in the abundances of Na, Mn, Co and Ni is $0.4{\pm}0.2dex$. In addition, as found in Kang et al. (2011), Mn is the most different element between PHSs and comparison stars.

• Journal of Astronomy and Space Sciences
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• v.35 no.1
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• pp.1-6
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• 2018

The reanalysis of the previously published abundance pattern of mild barium star HD202109 (${\zeta}$ Cyg) and the chemical compositions of 129 thin disk barium stars facilitated the search for possible correlations of different stellar parameters with second ionization potentials of chemical elements. Results show that three valuable correlations exist in the atmospheres of barium stars. The first is the relationship between relative abundances and second ionization potentials. The second is the age dependence of mean correlation coefficients of relative abundances vs. second ionization potentials, and the third one is the changes in correlation coefficients of relative abundances vs. second ionization potentials as a function of stellar spatial velocities and overabundances of s-process elements. These findings demonstrate the possibility of hydrogen and helium accretion from the interstellar medium on the atmospheres of barium stars.

• Journal of Astronomy and Space Sciences
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• v.37 no.3
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• pp.157-163
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• 2020

High resolution spectroscopic observation of V1719 Cyg were made at 1.8 meter telescope of Bohyunsan Optical Astronomy observatory in Korea. Spectral resolving power was R=45,000, signal to noise ratio S/N>100. The abundances of 28 chemical elements from carbon to dysprosium were found with the spectrum synthesis method. The abundances of oxygen, titanium, vanadium and elements with Z>30 are overabundant by 0.2-0.9 dex with respect to the solar values. Correlations of derived abundances with condensation temperatures and second ionization potentials of these elements are discussed. The possible influence of accretion from interstellar environment is not so strong as for ρ Pup and other stars with similar temperatures. The signs of accretion are absent. The comparison of chemical composition with solar system r- & s-process abundance patterns shows the enhancement of the photosphere by s-process elements.

• Journal of Astronomy and Space Sciences
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• v.39 no.4
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• pp.169-180
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• 2022

We investigated the chemical composition of the planetary host halo star HD47536 via high-resolution spectral observations recorded using a 1.5 meter Cerro Tololo Inter-American Observatory (CTIO) telescope (Chile). Furthermore, we determined the abundances of 38 chemical elements. Both light and heavy elements were overabundant compared to the iron group elements. The abundance pattern of HD47536 was similar to that of halo-type stars, with an enrichment of heavy elements. We analyzed the relationships between the relative abundances of chemical elements and their second ionization potentials and condensation temperatures. We demonstrated that the interplay of charge-exchange reactions owing to the accretion of interstellar matter and the gas-dust separation mechanism can influence the initial abundances and can be used to qualitatively explain the abundance patterns in the atmosphere of HD47536.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.27.1-27.1
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• 2011

We obtained the spectra of 93 Planet host stars and 73 normal field stars in F, G, K type using BOES at BOAO. We measured the equivalent width of Fe and 25 elements lines using the automatic EW measurement program, TAME(Tools for Automatic Measurement of Equivalent-widths) and estimated the elemental abundances by synth and abfind driver of MOOG code. Since the absence of planets in the normal field stars cannot be "completely" proved, this work focused on the chemical abundances and planet properties of planet host stars, which have the massive planets close to the parent star relatively. We carried out an investigation for the difference of abundances between stars with "Hot Jupiter" and normal field stars with no known planets. We examined the chemical composition of 25 elements, such as C, N, O, S, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Eu by EW measurements, and the S abundances were estimated using synthetic spectrum. We have found that [Mg/Fe] and [Al/Fe] for planet host stars have lower limit comparing with those of comparison stars, and [Ca/Fe] of host star with Neptunian planets is relatively lower than the other host stars with massive planets. We have performed the Kolmogorov-Smirnov test, and examined the ratio of planet host stars to all stars for each bin of [X/H]. As a result, we noted that the O, Si, and Ca abfor undances are strongly related with the presence of planets.

• Journal of The Korean Astronomical Society
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• v.41 no.4
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• pp.83-98
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• 2008

In an attempt of clarifying the connection between the photospheric abundance anomalies and the stellar rotation as well as of exploring the nature of "normal A" stars, the abundances of seven elements (C, O, Si, Ca, Ti, Fe, and Ba) and the projected rotational velocity for 46 A-type field stars were determined by applying the spectrum-fitting method to the high-dispersion spectral data obtained with BOES at BOAO. We found that the peculiarities(underabundances of C, O, and Ca; an overabundance of Ba) seen in slow rotators efficiently decrease with an increase of rotation, which almost disappear at $v_esin\;i{\gtrsim}100km\;s^{-1}$. This further suggests that stars with sufficiently large rotational velocity may retain the original composition at the surface without being altered. Considering the subsolar tendency(by several tenths dex below) exhibited by the elemental abundances of such rapidly-rotating (supposedly normal) A stars, we suspect that the gas metallicity may have decreased since our Sun was born, contrary to the common picture of galactic chemical evolution.

• Journal of Astronomy and Space Sciences
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• v.38 no.3
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• pp.175-183
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• 2021

The dependencies of the chemical element abundances in stellar atmospheres with respect to solar abundances on the second ionization potentials of the same elements were investigated using the published stellar abundance patterns for 1,149 G and K giants in the Local Region of the Galaxy. The correlations between the relative abundances of chemical elements and their second ionization potentials were calculated for groups of stars with effective temperatures between 3,764 and 7,725 K. Correlations were identified for chemical elements with second ionization potentials of 12.5 eV to 20 eV and for elements with second ionization potentials higher than 20 eV. For the first group of elements, the correlation coefficients were positive for stars with effective temperatures lower than 5,300 K and negative for stars with effective temperatures from 5,300 K to 7,725 K. The results of this study and the comparison with earlier results for hotter stars confirm the variations in these correlations with the effective temperature. A possible explanation for the observed effects is the accretion of hydrogen and helium atoms from the interstellar medium.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.40.2-40.2
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• 2018

NGC 5024 and NGC 5053 are among the most metal-poor globular clusters in the Milky Way. Both globular clusters are considered to be accreted from dwarf galaxies (like Sagittarius dwarf galaxy or Magellanic clouds), and common stellar envelope and tidal tails between globular clusters are also detected. We present a search for extra-tidal cluster member candidates around these globular clusters from APOGEE survey data. Using 20 chemical elements (e.g., Fe, C, Mg, Al) and radial velocities, t-distributed stochastic neighbour embedding (t-SNE), which identifies an optimal mapping of a high-dimensional space into fewer dimensions, was explored, and we find that globular cluster stars are well separated from the field stars in 2-dimensional map from t-SNE. We also find that some stars selected in t-SNE map are placed outside of the tidal radius of the clusters. The proper motion of stars outside tidal radius is also comparable to that of globular clusters, which suggest that these stars are tidally decoupled from the globular clusters. We manually measure chemical abundances for the clusters and extra-tidal stars, and discuss the association of extra-tidal stars with the clusters.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.183-186
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• 2007

The spectroscopic properties of bright extragalactic planetary nebulae are reviewed, considering primarily their chemical abundances and their internal kinematics. Low-resolution spectroscopy is used to investigate how the precursor stars of bright planetary nebulae modify their original composition through nucleosynthesis and dredge up. At present, the evidence indicates that oxygen and neon abundances usually remain unchanged, helium abundances are typically enhanced by less than 50%, while nitrogen enhancements span a very wide range. Interpreting these changes in terms of the masses of their progenitor stars implies that the progenitor stars typically have masses or order $1.5M_{\bigodot}$ or less, though no models satisfactorily explain the nitrogen enrichment. High-resolution spectroscopy is used to study the internal kinematics of bright planetary nebulae in Local Group galaxies. At first sight, the expansion velocities are remarkably uniform, with a typical expansion velocity of 18 km/s and a range of 8-28 km/s, independent of the progenitor stellar population. Upon closer examination, bright planetary nebulae in the bulge of M31 expand slightly faster than their counterparts in M31's disk, a result that may extend generally to the planetary nebulae arising from old and young stellar populations. There are no very strong correlations between expansion velocity and global nebular properties, except that there are no large expansion velocities at the highest $H{\beta}$ luminosities (i.e., the youngest objects never expand rapidly). These results independently suggest that bright planetary nebulae arise from a similar mass range in all galaxies. Nonetheless, there are good reasons to believe that bright planetary nebulae do not arise from identical progenitor stars in all galaxies.