• Journal of The Korean Astronomical Society
• /
• v.38 no.4
• /
• pp.415-422
• /
• 2005

UBVIJHK photometry of the open cluster NGC 2194 are presented. Color-Magnitude diagrams of this cluster show well-defined main sequence and red giant clump. The main sequence also contains clear evidence of binary populations. Based on color-color diagrams, absolute magnitude of red giant clump, ZAMS fitting, and comparisons of observed color-magnitude diagrams with theoretical models, we derive following parameters for the cluster; reddening $E(B-V)=0.44{\pm}0.04$, age of log $t{\sim}8.8$, and finally distance of $(m-M)_0=12.20{\pm}0.18$.

• Journal of Astronomy and Space Sciences
• /
• v.17 no.1
• /
• pp.1-10
• /
• 2000

To derive the metallicities of M3 and M5, we used the shape of red giant branch, horizontal branch magnitude, and red giant branch bump on the (V-I)-V color magnitude diagrams. [Fe/H] values ranging -1.46 ∼ -1.69 for M3, and -1.00 ∼ -1.49 for M5 are estimated. These values are in good agreements with the previously determined ones. This result leads the morphologies of red giant and horizontal branches on the (V-I)-V color magnitude diagrams can be good indirect metallicity indicators of galactic globular clusters.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.61.2-61.2
• /
• 2014

We present a set of fiducial sequences of horizontal-branch stars in bright Galactic globular clusters, which have previously been observed in the Sloan Digital Sky Survey (SDSS). We derive fiducial lines on color-magnitude diagrams in multiple color indices (g - r, g - i, g - z, and u - g), after rejecting foreground and background objects as well as RR Lyrae variables utilizing these color indices. We compare our fiducial sequences with model predictions from Yonsei-Yale evolutionary tracks and BaSel spectral libraries, and find a satisfactory agreement between them in terms of their color-magnitude relations, except in u - g. We also compare theoretical models to color-magnitude diagrams of two open clusters (M67 and NGC 6791). Based on our best available cluster distance and reddening, we find that the mass of red clump (RC) stars in NGC 6791 is about a factor of two smaller than an earlier estimate from the application of asteroseismic scaling relations for solar-like oscillations. The smaller RC mass implies an enhanced mass loss along the red giant branch, which is in accordance with other compelling evidences found in this metal-rich system. Our estimated luminosity of RC stars in NGC 6791 is about 0.2 mag fainter than in earlier investigations based on solar-metallicity calibrations, and results in ~10% reduction in the RC-based distance estimation, when applied to metal-rich systems such as in the Galactic bulge.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.1
• /
• pp.54.2-54.2
• /
• 2010

The most massive galactic globular cluster, $\omega$ Cen has been observed using recently mounted WFC3/UVIS cameras of Hubble Space Telescope at both near-UV and optical bands. We present the photometry of stars in the central region of $\omega$ Cen in F225W, F275W and F336W bands. The near-UV color-magnitude diagrams and color-color diagrams of stars in $\omega$ Cen show multiple red giant branches and main sequences as already discovered in both ground-based and HST/ACS observations in the optical bands. We modelled the stellar populations of $\omega$ Cen using Yonsei Isochrone, where $\alpha$-particles and helium enhancement processes have been included properly. We compare the best-fit stellar populations obtained from the current near-UV observations to the suggested stellar population models based on optical band data. We also discuss the methodological issues arising when dealing with the near-UV observations; red-leak in near-UV filters and the huge interstellar extinction in near-UV bands compared to the optical bands and its non-linear effect in color-magnitude diagrams.

• Publications of The Korean Astronomical Society
• /
• v.30 no.2
• /
• pp.539-541
• /
• 2015

We present a new tool for studying the spectral energy distributions (SEDs) and color-magnitude diagrams (CMDs) of galaxies and star clusters, BINARY STAR TO FIT (BS2fit). A key feature of this tool is that it takes the effects of binaries, stellar rotation and star formation history into account. It can be used to determine many parameters, including distance, extinction, binary fraction, rotational star fraction, and star formation history. Because more factors are included than in previous tools, BS2fit can potentially give new insight into the properties of galaxies and clusters. One can contact the authors for cooperation and helps via.

• Journal of Astronomy and Space Sciences
• /
• v.7 no.2
• /
• pp.105-111
• /
• 1990

Stars in M 68 from the observed-magnitude diagrams with CCD were integrated to find any radial gradient. The result shows that M 68 has a slightly bluer core. The main cause of these calculated radial color variations seems to come from the random distribution of ginants.

• Bulletin of the Korean Space Science Society
• /
• 2006.10a
• /
• pp.77-77
• /
• 2006

• Bulletin of the Korean Space Science Society
• /
• 2009.10a
• /
• pp.35.3-36
• /
• 2009

To investigate properties of the stellar contents of the resolved asymptotic giant branch stars in the nearby dwarf galaxies, we obtained wide-field JHKs images of the dwarf irregular galaxies NGC 6822, IC 1613 and the dwarf elliptical galaxy NGC 205, using the WIRCam near-infrared imager of the CFHT. The obtained (J-Ks, Ks) and (H-Ks, Ks) color-magnitude diagrams for the resolved stars in the galaxies contain populations of foreground stars, super giant stars, red giant stars and the asymptotic giant branch (AGB) stars. Using corollary photometric data in the visible bands, AGB stars were selected in the color-magnitude diagrams with a wide wavelength baseline in color indices. In color-color diagrams of the resolved AGB stars, we identified C stars from M giant stars for each galaxies, i.e., 726 C stars in NGC 6822, 126 C stars in IC 1613 and 593 C stars in NGC 205. The number ratios of C stars to M-giants were estimated to be $0.59\pm0.03$ in NGC 6822, $0.30\pm0.03$ in IC 1613 and $0.14\pm0.01$ in NGC 205. From analyses of the correlations of the spatial distribution of the C/M ratios with the HI properties and dynamical structures of the target galaxies, we discuss environmental effects of the star formation in the galaxies. We also discuss the epochs of the AGB star formation in the galaxies by comparing theoretical isochrones with the color distributions and luminosity functions of the AGB stars.

• Journal of The Korean Astronomical Society
• /
• v.30 no.1
• /
• pp.1-11
• /
• 1997

Near infrared JHK magnitudes are presented for two hundred two high proper motion stars. We have observed high proper motion stars in the near-infrared bands(JHK) using the COB detector on the Kitt Peak 1.3m, 2.1m and 4m telescopes. The observations and data reduction procedures are described. The infrared color magnitude diagram and color-color diagrams for the program stars are presented.

• The Bulletin of The Korean Astronomical Society
• /
• v.26 no.2
• /
• pp.44-44
• /
• 2001