• 천문학회지
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• 제12권1호
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• pp.17-25
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• 1979

The two methods for the derivation of helium abundance are presented. The magnitude of the largest bump along the red giant branch is fainter as helium abundance decreases and metal abundance increases. Using this relation and observed bump magnitude, the He-abundances of globular clusters are estimated. The another method is to use the relation that the ratio of asymptotic giant branch and horizontal branch stars increases with decreasing He-abundance. The comparison of the He-abundances derived from the two methods with those derived from the other two methods shows that they are consistent within the dispersion less than ${\Delta}Y=0.1$.

• 천문학회보
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• 제42권1호
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• pp.42.2-42.2
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• 2017

We performed low-resolution spectroscopy for the red giant stars in the Galactic globular cluster (GC) NGC 5286, which is known to show intrinsic heavy element variations. We found that these stars are clearly divided into two subpopulations by CN index. These two subpopulations also show significant differences in the HK'and CH indices, where the CN-strong stars are more enhanced in both indices. From the comparison with high-resolution spectroscopic data of Marino et al. (2015), we found that the CN- and HK'-strong stars are also increased in the abundances of s-process elements and Fe. It appears that, therefore, these stars are later generation stars probably affected by supernova enrichment. In addition, NGC 5286 shows the CN-CH positive correlation among the whole sample, which is only discovered in the GCs with heavy element variations such as M22 and NGC 6273. Therefore, these results strengthen our previous suggestion that the CN-CH positive correlation may be associated with the heavy element variations in the GCs.

• 천문학회보
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• 제34권2호
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• pp.38.2-38.2
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• 2009

• 천문학회보
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• 제34권1호
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• pp.96.1-96.1
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• 2009

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권1호
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• pp.49.1-49.1
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• 2009

• 천문학회지
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• 제56권1호
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• pp.59-73
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• 2023

The second generation of stars in the globular clusters (GCs) of the Milky Way (MW) exhibit unusually high N, Na, or Al, compared to typical Galactic halo stars at similar metallicities. The halo field stars enhanced with such elements are believed to have originated in disrupted GCs or escaped from existing GCs. We identify such stars in the metallicity range -3.0 < [Fe/H] < 0.0 from a sample of ~36,800 giant stars observed in the Sloan Digital Sky Survey and Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, and present their dynamical properties. The N-rich population (NRP) and N-normal population (NNP) among our giant sample do not exhibit similarities in either in their metallicity distribution function (MDF) or dynamical properties. We find that, even though the MDF of the NRP looks similar to that of the MW's GCs in the range of [Fe/H] < -1.0, our analysis of the dynamical properties does not indicate similarities between them in the same metallicity range, implying that the escaped members from existing GCs may account for a small fraction of our N-rich stars, or the orbits of the present GCs have been altered by the dynamical friction of the MW. We also find a significant increase in the fraction of N-rich stars in the halo field in the very metal-poor (VMP; [Fe/H] < -2.0) regime, comprising up to ~20% of the fraction of the N-rich stars below [Fe/H] = -2.5, hinting that partially or fully destroyed VMP GCs may have in some degree contributed to the Galactic halo. A more detailed dynamical analysis of the NRP reveals that our sample of N-rich stars do not share a single common origin. Although a substantial fraction of the N-rich stars seem to originate from the GCs formed in situ, more than 60% of them are not associated with those of typical Galactic populations, but probably have extragalactic origins associated with Gaia Sausage/Enceladus, Sequoia, and Sagittarius dwarf galaxies, as well as with presently unrecognized progenitors.

• 천문학회보
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• 제41권2호
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• pp.56.2-56.2
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• 2016

We present chemical abundances for about 800 red giant stars in Omega Centauri, based on medium-resolution spectra obtained using Hydra multi-fiber spectrograph at the CTIO 4-m telescope. Our sample covers 14.2 < V < 15.0, and is almost unbiased against colors (and therefore metallicity). The metallicity distribution function (MDF) constructed from our data has an overall shape and local peaks that approximately match those for brighter giant stars in Johnson et al.. We also find that more metal-rich cluster members are more concentrated in the cluster center, which is consistent with previous studies. On the other hand, we find no clear evidence for such a spatial dependence with respect to alpha elemental abundance ([${\alpha}/Fe$]).

• 천문학회보
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• 제42권2호
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• pp.87.1-87.1
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• 2017

We present preliminary results of elemental abundances of six ultra-metal poor (UMP; [Fe/H] < -4.0) stars derived from high-resolution spectra obtained by Gemini/GRACES. The UMP candidates were selected for the high-resolution follow-up from the low-resolution spectra of Sloan Digital Sky Survey (SDSS). We investigate possible progenitors of the UMP objects by comparing the measured abundance patterns with yields that various supernova models predict. Our results can provide stringent constraints on the mass range of the first generation of stars, which are the progenitors of the UMP objects.

• 천문학회보
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• 제35권2호
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• pp.83.2-83.2
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• 2010

To understand about Gould Belt, we intend to study chemical abundances for two young open clusters - IC 2391 which is a member of Gould Belt and NGC 6475 which is not. UVES POP (Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project) provides the spectra of twelve stars in IC 2391 and five stars in NGC 6475 with spectral resolution R of 80,000. In this study, we have determined the stellar parameters (Teff, logg, metallicity, and microturbulant velocity) using Fe I and Fe II lines. The equivalent widths of iron lines have been measured by TAME. The results of stellar parameters are presented.

• 천문학회보
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• 제35권2호
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• pp.82.2-82.2
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• 2010

We investigate the distribution of stars along the red giant branch (RGB) in the globular clusters (GCs) NGC 288 and NGC 362 from Caby photometry using the CTIO 4m Blanco telescope. Our color-magnitude diagrams in hk index show that the RGB stars have two distinct subpopulations with different Ca abundances apparently supplied by the Type II supernovae explosions. However, the RGB splits are not shown in the b - y color, as indicated by previous observations. Our stellar population models show that the presence of two distinct RGBs in these GCs can be reproduced if metal-rich second generation stars are also enhanced in helium and younger by 1 ~ 2 Gyrs.