• 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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• 제39권1호
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• pp.45.2-45.2
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• 2014

We carry out the first survey for globular clusters (GCs) of three galaxies in cosmic voids using Hubble Space Telescope (HST) Advanced Camera for Survey archival F606W and F814W images. While all sample galaxies are classified as early-type galaxies based on ground-based imaging, the high resolution HST images reveal that they are actually spiral galaxies. We identify the point sources with red colors typical for GCs as GC candidates in the color-magnitude diagrams. As a result, we find a significant number of GC candidates. The spatial and radial distribution of GCs show central concentration on each galaxy region. Their mean colors are similar to that of the Milky Way and M31 GCs. The void GCs are somewhat bluer by, and than cluster and field GCs in early-type galaxies with similar luminosity to our samples, but the discrepancy is not significant. We also estimate the specific frequencies of GCs in these galaxies and the values are consistent with those in field and cluster galaxies with similar luminosity. From these results, we suggest that the formation process of void GCs is similar to that of GCs in other environments. The further implications will be discussed.

• Journal of Astronomy and Space Sciences
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• 제21권1호
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• pp.1-10
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• 2004

이 논문에서는 우리 은하 구상 성단 M7l에 대한 B, V CCD 영상 관측 자료로부터 색-등급도(color-magnitude diagram)를 구하고, 이로부터 이 성단의 거리와 상대적 나이를 결정하였다. M7l의 적색화 현상(E(B - V) = 0.28)과 금속함량(-0.79 < 〔Fe/H〕 < -0.70)은 최근 논문의 값을 채택하였다 이 자료를 토대로 관측으로부터 얻은 M71 색등급도의 기준선을 Hipparcos준왜성의 측광 특성과 비교하여 M71의 거리지수를 (m- M)v = 13.46(${\pm}0.17$)과 같이 결정하였다. 비슷한 금속 함량을 가지는 구상 성단47 Tuc의 색등급도를 이 연구에서 구한M71의 색등급도와 비교한 결과 두 성단의 나이는 상당한 차이가 있음을 확인할 수 있었고, isochrone과의 비교 결과 적어도 20억년 이상의 차이가 존재한다는 사실을 알 수 있었다.

• 한국지구과학회지
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• 제27권5호
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• pp.557-568
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• 2006

구상성단 M30의 $20'.5{\times}20'.5$ 영역에 대한 CCD UBVI 측광 관측을 수행하여 색-등급도로부터 주계열 전향점과 색지수 $V_{TO}=18.63{\pm}0.05,\;(B-V)_{TO}=0.44{\pm}0.05,\;(V-I)_{TO}=0.63{\pm}0.05$를 얻었으며, 색-색도로부터 $E(B-V)=0.05{\pm}0.01$과 중원소 함량의 지표인 UV 색 초과량 ${\delta}(U-B)=0.27{\pm}0.01$을 얻었다. 측광학적인 방법과 분광 관측 자료를 이용하여 중원소 함량 $[Fe/H]=-2.05{\pm}0.09$를 구하였다. 관측된 M30의 광도 함수는 이론적 모델에 비하여 전향점 부근에 비하여 적색 거성열의 초과 현상을 보였다. Hipparcos 위성에서 측정된 삼각 시차로부터 거리가 알려진 준왜성을 이용하여 주계열 맞추기를 하여 거리 지수 $(m-M)_o=14.75{\pm}0.12$를 구하였다. 헬륨 함량을 구하기 위하여 R과 R' 방법을 사용하여 $Y(R)=0.23{\pm}0.02,\;Y(R')=0.29{\pm}0.02$를 얻었다. 성단의 나이는 적용하는 방법과 모델에 따라서 10.7 Gyr에서 17 Gyr까지 분산을 보인다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2009년도 한국우주과학회보 제18권2호
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• pp.29.4-30
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• 2009

Extra-tidal feature of the globular clusters such as tidal tails and halos can be a crucial evidence of the merging scenario of the Galaxy formation in the dynamical point of view. To search for such an extra-tidal feature of globular clusters located in the Galactic bulge(RGC<3kpc), we obtained wide-field near-infrared JHKs images of 6 metal-poor ([Fe/H]<-1.0) clusters and 3 metal-rich ([Fe/H]>-1.0) clusters. Observations were carried out using IRSF 1.4m telescope and SIRIUS near-infrared camera, during 2006~2007. The obtained images have a total maximum field-of-view of ~ $21'\times 21'$. To select clusters' member stars and minimize the field star contaminations, we applied CMD masking algorithm. Smoothed surface density contour maps with selected stars for each cluster show overdensity features around the tidal radius and beyond. Also, radial surface density profiles within the tidal radius of the clusters show an overdensity feature as a change of slope of the radial profile. The results add further observational constraints of the formation of the Galactic bulge.

• 천문학회지
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• 제44권5호
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• pp.151-160
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• 2011

We present a study searching for globular cluster systems (GCSs) of two face-on low surface bright- ness galaxies (LSBGs), UGC 5981 and UGC 6614. Based on HSTWFPC2 images of F555Wand F814W filters, we detect 12 and 18 GC candidates for UGC 5981 and UGC 6614, respectively. Although these two LSBGs have very different bulge properties, they have very similar specific frequencies ($S_N$) of 0.1. However, $S_N$ ~ 0.1 is quite small even for their late morphological types, albeit within errors. This suggests that LSBGs have had star formation histories lacking dominant initial starburst events while accumulating their stellar masses through sporadic star formation activities.

• 천문학회지
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• 제38권2호
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• pp.23-31
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• 2005

CN and CH band strengths for fourteen bright giants in the globular cluster M71 have been measured from archival spectra obtained with the Multiple Mirror Telescope. Adding the collected. data from the literature we confirm a bimodality of CN distribution on the red giant branch and the honzontal branch, and CN-CH anti-correlations on the lower giant branch and horizontal branch. However a CN-CH anti-correlation on the upper red giant branch is not quite clear as those of other branches. The small number If statistics could not be excluded as a possible cause. To confirm this, a greater number of sample stars are needed. We also confirm that the ratio of CN-strong to CN-weak stars is quite different from that in 47 Tuc, although the anti-correlation between CN and CH bands, the bimodality of the CN distribution, and the spatial distribution of CN stars in M71 are found to be similar to those III 47 Tuc.

• 천문학회보
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• 제40권2호
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• pp.50.1-50.1
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• 2015

The origin of globular cluster (GC) color bimodality, which is one of the salient phenomena observed in most large galaxies, has not yet been fully resolved. The phenomenon has conventionally been interpreted as a bimodal metallicity distribution based on an assumption of linear GC color-metallicity relations (CMRs). Recent studies however suggest that nonlinear GC CMRs can cause a bimodal color distribution even from a single-peaked metallicity spread. Using photometric and spectroscopic data on GCs in NGC 5128 (Cen A) and NGC 4594 (Sombrero), we investigate the nonlinearity of GC CMRs and compare the observed GC CMRs with the predictions of stellar population simulation models. Our careful selection of old GCs effectively reduces the scatter and reveals the nonlinear nature of the GC CMRs for various colors. The overall shape of the observed CMRs agrees well with that of the modeled CMRs, while offsets are present for some colors. We discuss the implications of our results in terms of the GC color bimodality and GC formation in NGC 5128 and NGC 4594.

• 천문학회보
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• 제35권2호
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• pp.35.1-35.1
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• 2010

Unlike the initial mass function, the initial size distribution of globular cluster (GC) systems is not well known. We calculate the evolution of the mass function (MF), radial distribution (RD), and size distribution (SD) of the Galactic GC system. By comparing the results from this calculation and the present-day MF, RD, and SD of the Galactic GC system, we infer the initial SD of the GC system. We find that a Gaussian distribution of the half-mass radius and a Gaussian distribution of the half-mass to Jacobi radius ratio are the best-fit initial SDs of the Galactic GC system.

• 천문학회보
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• 제35권2호
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• pp.31.1-31.1
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• 2010

We present a spectroscopic study of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo cluster. Line indices of GCs in NGC 4636 are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph (FOCAS) on the Subaru Telescope. We derive the [Fe/H] of the GCs in NGC 4636 using Brodie & Huchra (1990) method. The [Z/H], age, and alpha-element of the GCs are obtained from the comparison of the Lick line indices with the SSP model grid. We investigate the distribution and radial variation of the metallicity, age, and alpha-element of NGC 4636 GCs. The metallicity distribution of NGC 4636 GCs shows a bimodality. The chemical properties of these GCs show little radial variation. These results will be discussed with regard to the formation and evolution of NGC 4636.