• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.40.2-40.2
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• 2015

In our recent investigation (Lim et al. 2015), we have shown that the combination of narrow-band Ca photometry and low-resolution spectroscopy can effectively search for globular clusters (GCs) with supernovae (SNe) enrichments. We apply this technique to the metal-poor bulge GC NGC 6273 and find two distinct subpopulations having different light and heavy element abundances. Our result suggests that NGC 6273 was massive enough to retain SNe ejecta, which would place this cluster in the growing group of GCs with Galactic building block characteristics, such as ${\omega}$ Centauri and M22.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.79.1-79.1
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• 2013

We present new integrated spectroscopy of 24 Galactic globular clusters, observed with the Isaac Newton Telescope in La Palma. Spectra have been extracted from one core radius for each cluster, achieving high wavelength resolution of FWHM ${\sim}2.0^{\circ}A$. In combination with two previous data sets from Puzia et al. 2002 and Schiavon et al. 2005, we construct the largest database of the Lick indices for total 53 Galactic globular clusters. The empirical metallicity.index relations are given for the 20 Lick indices for the use of deriving metallicities of remote, unresolved stellar systems.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.85.2-85.2
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• 2014

최근 10년 동안의 측광 및 분광관측을 통하여 우리은하 내 구상성단들 중 대부분이 적어도 2개 이상의 항성종족을 갖는다고 밝혀졌다. 현재까지 이루어진 대부분의 구상성단의 항성종족 연구에서는 관측된 색등급도와 항성종족 합성모델 사이에 eye-fitting을 함으로써 항성종족 파라미터, 즉 중원소함량, 나이, 헬륨함량 등을 추정해왔다. 우리는 구상성단의 항성종족을 분석하기 위해 ${\chi}^2$-Minimization에 의거하여 구상성단과 항성종족 합성모델의 Hess Diagram을 비교하고, 수치계산 기법을 도입하여 최적의 파라미터를 추정하는 알고리즘을 개발하였다. 이 연구에서는 가상으로 만든 성단에 대하여 Recovery Test를 수행함으로써 이 알고리즘의 Self-Consistency를 검증하였고, 실제 관측결과를 사용하여 이 연구의 적용 가능성을 조사하였다.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.53.1-53.1
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• 2017

The YONSEI (YOnsei Nearby Supernova Evolution Investigation) project is to investigate the luminosity evolution of Type Ia supernovae (SNe Ia) by using their early-type host galaxies. As a part of this project, we have constructed our own SN catalogue. SALT2 and MLCS2k2 light-curve fitters implemented in SNANA package are employed to analyze the light-curve data. The catalogue provides a rest-frame peak magnitude in B-band or distance modulus, a light-curve shape parameter, and a color or an extinction value of each SN in the redshift range from 0.01 to 1.4. In this poster, we will present our progress in the detailed systematic tests for this catalogue.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.62.3-63
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• 2018

Trends of Type Ia supernova (SN Ia) luminosities with the properties of host galaxies are important to study the underlying physics for an SN progenitor system and explosion mechanism. In the YONSEI SN catalog, we have a sample of ~600 SN and host data in the wider redshift range, and two independent light-curve models, SALT2 and MLCS2k2. From this catalog, here we present that SNe Ia in low-mass, globally and locally star-forming environments are fainter than those in high-mass, globally and locally passive environments, after light-curve shape and color or extinction corrections. Our results are then compared to previous studies, and show consistent results.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.66.4-67
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• 2016

Our recent investigation (Lee et al. 2015) suggests that the presence of double red clump in the Milky Way bulge is another manifestation of multiple populations observed in halo globular clusters. The origin of Helium enhancement in the 2nd generation population (G2), however, is not yet fully understood. Here we investigate the origin of this super-Helium-rich population in the framework of self-enrichment scenario. We find that chemical enrichments and pollutions by asymptotic giant branch stars and winds of massive rotating stars can naturally reproduce the observed Helium enhancement. The Helium to metal enrichment ratio appears to be ${\Delta}Y/{\Delta}Z=6$ for G2, while the standard ratio, ${\Delta}Y/{\Delta}Z=2$, is appropriate for G1, which is probably enriched mostly by typeII supernovae.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.47.4-47.4
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• 2019

Recent observations on the double red clumps in the bulge validate the close connection in stellar populations between Galactic globular clusters (GCs) and the Milky Way (MW) bulge. Intriguingly, diverse phenomena observed in early-type galaxies (ETGs) and their GC systems are also indicating the similarities with Galactic GCs with multiple populations. Here, we present the population synthesis for the Galactic bulge and ETGs using stellar populations observed in the Galactic GCs with multiple populations. Our new models well explain observations of both the MW bulge and ETGs. Also, the inclusion of GC-originated population to the population synthesis model shows substantial impacts on the age-dating of stellar populations. The implication of this result for the interpretation of the formation history and the age-dating of ETGs will be discussed in detail.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.69.2-69.2
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• 2011

The discovery of dark energy from Type Ia supernovae (SN Ia) is based on the implicit assumption that the look-back time evolution of SN Ia luminosity, after light-curve corrections, would be negligible. A strong support for this assumption was the apparent insensitivity of SN Ia distances across the host galaxy morphologies. However, Hicken et al. 2009 (H09) shows a systematic difference in the Hubble residual (HR) of $0.144{\pm}0.070$ mag between the E-S0 and Scd/Sd/Irr galaxies, after light-curve corrections. If true, this indicates that the light-curve fitters used by the SN Ia community can not correct for the population age (and therefore the evolution) effect. In order to confirm this, we have combined nearby SN Ia samples and the first-year SDSS-II SN Survey. The SNANA package was used for analyzing SN Ia light-curve, both for the MLCS2k2 and SALT2 fitters. We find a systematic difference in the HR of $0.10-0.13{\pm}0.030$ mag between E-S0 and Scd/Sd/Irr galaxies, which is in agreement with the result of H09, but now at the 3-5 ${\sigma}$ level. Considering the significant difference in the mean age of stellar population between these morphological types, the difference in the HR reported here suggests that the evolution effect of SN Ia luminosity should be considered in the cosmological application of SN Ia data.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.409-411
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• 2015

Galaxy clusters, the largest gravitationally bound systems, are an important subject of study to place constraints on cosmological models. Moreover, they are excellent places to test galaxy evolution models in connection to their environments. To date, massive clusters have been found unexpectedly (Kang & Im 2009; Gonzales et al. 2012) and the evolution of galaxies in clusters is still controversial (Elbaz et al. 2007; Faloon et al. 2013). Finding galaxy cluster candidates at z > 1 in a wide, deep imaging survey data will enable us to solve such issues of modern extragalactic astronomy. We report new candidate galaxy clusters in one of the wide and deep survey fields, the European Large Area ISO Survey North1 (ELAIS-N1) and North2 (ELAIS-N2) fields, covering a sky area of $8.75deg^2$ and $4.85deg^2$ each. We also suggest a new useful color selection technique to separate z > 1 galaxies from low - z galaxies by combining multi-wavelength data.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.255-259
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• 2015

Recent narrow-band Ca photometry discovered two distinct red giant branch (RGB) populations in some massive globular clusters (GCs) including M22, NGC 1851, and NGC 288. In order to investigate the differences in light/heavy elements abundances between the two subpopulations, we have performed low-resolution spectroscopy for stars on the two RGBs in these GCs. We find a significant difference (more than $4{\sigma}$) in calcium abundance from the spectroscopic HK' index for both M22 and NGC 1851. We also find a more than $8{\sigma}$ difference in CN band strength between the Ca-strong and Ca-weak subpopulations. For NGC 288, however, we detect the presence of a large difference only in the CN strength. The calcium abundances of the two subpopulations in this GC are identical within errors. We also find interesting differences in CN-CH relations among these GCs. While CN and CH indices are correlated in M22, they show an anti-correlation in NGC 288. However, NGC 1851 shows no difference in CH between two groups of stars having different CN strengths. The CN bimodality in these GCs could be explained by pollution from intermediate-mass asymptotic giant branch stars and/or fast-rotating massive stars. For the presence or absence of calcium bimodality and the differences in CN-CH relations, we suggest these would be best explained by how strongly type II supernovae enrichment has contributed to the chemical evolutions of these GCs.