• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.169-171
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• 2015

NGC147 and NGC185, paired satellites of the Andromeda galaxy, possess the same order of mass and analogous structures, but they show different star formation and different amounts of interstellar gas and dust. Therefore, we present the first reconstruction of the star formation history of NGC147 and NGC185. Asymptotic Giant Branch stars are highly evolved stars that are brightest in K-band. This maximum K-band magnitude is related to the birth mass of stars. As a result, we have found a 9.9 Gyr old single star formation epoch for NGC185 followed by relatively continuous star formation. NGC147, however, has passed through two star formation episodes; one is as old as ~6 Gyr and the other is as recent as ~850 Myr. Asymptotic Giant Branch stars are also important dust factories; by fitting Spectral Energy Distributions to observed near and mid infrared data for each star, we were able to measure the dust production rates of individual stars; on order of $10^{-5}M_{\odot}yr^{-1}$. Hence, we estimate the total mass entering the interstellar medium to be $1.06{\times}10^{-4}M_{\odot}yr^{-1}$ and $2.89{\times}10^{-4}M_{\odot}yr^{-1}$ for NGC147 and NGC185.

• 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.37 no.2
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• pp.147.2-147.2
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• 2012

보현산 천문대 1.8m 망원경과 2K CCD를 이용하여 늙은 산개성단 NGC 2420에 대해 V ~ 22까지 VI측광 관측을 수행하였다. Chi^2 최소화를 이용한 정밀한 이론적인 등연령 곡선 맞추기 방법으로 성단의 기본 물리량을 구하고, 색-등급도(CMD)와 공간상에서의 별들의 위치를 이용하여 별들의 통계적인 구성원 확률을 결정하고자 한다. 한편 쌍성의 공간상의 분포를 조사하여 역학적 진화에 따른 쌍성의 분포특징을 살펴보고, 2차원 표면개수 밀도 분포로부터 성단의 형태를 조사하여 우리 은하면과의 상관관계에 대해 논의하고자 한다.

• Journal of The Korean Astronomical Society
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• v.41 no.6
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• pp.147-155
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• 2008

We present UBV I photometry of the old open cluster NGC 1193. Color-magnitude diagrams (CMDs) of this cluster show a well defined main sequence and a sparse red giant branch. For the inner region of r < 50", three blue straggler candidates are newly found in addition to the objects Kaluzny (1988) already found. The color-color diagrams show that the reddening value toward NGC 1193 is E(B - V ) = $0.19{\pm}0.04$. From the ultraviolet excess measurement, we derived the metallicity to be [Fe/H]= $-0.45{\pm}0.12$. A distance modulus of ${(m\;-\;M)}_0$ = $13.3{\pm}0.15$ is obtained from zero age main sequence fitting with the empirically calibrated Hyades isochrone of Pinsonneault et al. (2004). CMD comparison with the Padova isochrones by Bertelli et al. (1994) gives an age of log t = $9.7{\pm}0.1$.

• Journal of The Korean Astronomical Society
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• v.34 no.3
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• pp.143-147
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• 2001

UBVI CCD photometry of open cluster NGC 2324 is presented. C-M diagrams of this cluster show well-defined main sequence with a red giant clump centered at B - V =1.05, V =13.45. We derived the major cluster characteristics; E(B - V)=0.17$\pm$0.12 from color-color diagram and mean color of red giant clump stars, (m - M)o=13.1$\pm$0.1 from zero age main sequence fitting, and [Fe/H]$\~$-0.32 from comparison the theoretical model developed by Bertelli et al. (1994) to the observed C-M diagrams. We estimate the age of NGC 2324 to be log t$\~$8.8 by applying isochrone fitting and morphological age index method.

• Journal of Astronomy and Space Sciences
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• v.11 no.2
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• pp.147-153
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• 1994

We present a deep(B, V) color-magnitude diagram (CMD) of the Galactic globular cluster NGC 4372. According to the recent inside-out picture of Galaxy formation, this cluster is predicted to be one of the oldest globulat clusters in the Galaxy. Our CMD shows a well defined main-sequence extending ∼ 2 magnitudes below the trunoff. Despite the uncertainty that stems from the small sample size of bright stars, comparison with the Revised Yale Isochrones suggests that this cluster may indeed be one of the oldest (∼16.6 Gyrs) globular clusters in our Galaxy.

• The Bulletin of The Korean Astronomical Society
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• v.30 no.1
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• pp.66.1-66.1
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• 2005