• Journal of The Korean Astronomical Society
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• v.44 no.5
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• pp.195-200
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• 2011

We have revisited the ACS Virgo Cluster Survey (ACSVCS), a Hubble Space Telescope program to obtain ACS/WFC g and z bands imaging for a sample of 100 early-type galaxies in the Virgo Cluster. In this study, we examine 51 nucleated early-type galaxies in the ACSVCS in order to look into the relationship between the photometric and structural properties of stellar nuclei and their host galaxies. We morphologically dissect galaxies into five classes. We note that (1) the stellar nuclei of dwarf early-type galaxies (dS0, dE, and dE,N) are generally fainter and bluer with g > 18.95 and (g-z) < 1.40 compared to some brighter and redder counterparts of the ellipticals (E) and lenticular galaxies (S0), (2) the g-band half-light radii of stellar nuclei of all dwarf early-type galaxies (dS0, dE, and dE,N) are smaller than 20 pc and their average is about 4 pc, and (3) the colors of red stellar nuclei with (g - z) > 1.40 in bright ellipticals and lenticular galaxies are bluer than their host galaxies colors. We also show that most of the unusually "red" stellar nuclei with (g-z) > 1.54 in the ACSVCS are the central parts of bright ellipticals and lenticular galaxies. Furthermore, we present multi photometric band color - color plots that can be used to break the age-metallicity degeneracy particularly by inclusion of the thermally pulsing-asymptotic giant branch (TP-AGB) phases of stellar evolution in the stellar population models.

• Publications of The Korean Astronomical Society
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• v.22 no.4
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• pp.97-101
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• 2007

We are often faced with the task of having to estimate the hydrogen and helium ionizing luminosities of massive stars in the study of H II regions and the warm ionized medium (WIM). Using the results of the most complete compilation of stellar parameters (the effective temperature, stellar radius and surface gravity) and the latest Kurucz stellar atmosphere models, we calculate the ionizing photon luminosities in the $H^0\;and\;He^0$ continua from O3 to B5 stars. We compared the theoretical Lyman-continuum luminosity with the observationally inferred luminosity of the H II region around ${\alpha}$ Vir, and found that the theoretical value is higher than the observed value in contrast to the eariler result.

• The Bulletin of The Korean Astronomical Society
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• v.21
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• pp.8.1-8.1
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• 1996

• The Bulletin of The Korean Astronomical Society
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• v.9
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• pp.3.1-3.1
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• 1984

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.30.2-30.2
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• 2013

The mean color of globular cluster (GCs) systems in early-type galaxies (ETGs) is, in general, bluer than the integrated color of field stars in their host galaxies. Recently, Goudfrooij & Kruijssen (2013) reported that even red GCs in the ETGs show bluer colors than their host field stars and suggested the different initial mass function (IMF) for red GCs and field stars to explain the observed offset in color. Here we suggest an alternative scenario that explains the observed color offsets between red GCs in ETGs and the field stars in the parent galaxies without invoking to the variation of the IMF. We find that the inclusion of second-generation (SG) helium-enhanced populations in the model fully explains the observed color offset between red GCs and field stars in the host galaxies. We have also tested the effect of the IMF slope on our models, but the effect is relatively small compared to the effect of the SG population. Our new model suggests that, in order to explain far-UV strong metal-rich GCs in M87 and the observed color offset between metal-rich GCs and the field stars in ETGs simultaneously, the inclusion of the SG populations with enhanced helium abundance is a more natural solution than the model that only adopted variations in the IMF.

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.290-292
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• 2004

Near-IR observations of the central few parsecs of our Galaxy from the HST/NICMOS have been analyzed to produce H, K photometry. We have cross-identified our photometry with the Keck high-resolution spectrometry of the central 0.5 pc of our galaxy to distinguish evolved late-type stars from early-type stars, and use late-type stars as tracer population. We perform several statistical tests to find the best fitting parameters of stellar density distribution and velocity dispersion models, then derive volume number densities and velocity dispersions. The volume number density distribution has power law index $1.55\~1.7$. We then derive the mass distribution in the Central region of our Galaxy using the Jeans equation.

• Journal of The Korean Astronomical Society
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• v.35 no.1
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• pp.9-28
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• 2002

We present UBVI CCD photometry of the stellar contents and globular cluster(GC) candidates in the spiral galaxy NGC 300 in the Sculptor group. Color-magnitude diagrams for 18 OB associations having more than 30 member stars are presented. The slope of the initial mass function for the bright stars in NGC 300 is estimated to be ${\Gamma}= -2.6{\pm} 0.3$. Assuming the distance to NGC 300 of (m - M)o = 26.53 $\pm$ 0.07, the mean absolute magnitude of three brightest blue stars is obtained to be < $M_v^{BSG}$ (3) > = -8.95 mag. We have performed search for GCs in NGC 300 and have found 17 GC candidates in this galaxy. Some characteristics of these GC candidates are discussed.

• Journal of The Korean Astronomical Society
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• v.56 no.1
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• pp.97-115
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• 2023

We present the deep homogeneous UBV RI photometric data of 135,071 stars down to V ~ 23 mag and I ~ 22 mag toward the Carina Nebula. These stars are cross-matched with those from the previous surveys in the X-ray, near-infrared, and mid-infrared wavelengths as well as the Gaia Early Data Release 3 (EDR3). This master catalog allows us to select reliable members and determine the fundamental parameters distance, size, stellar density of stellar clusters in this star-forming region. We revisit the reddening toward the nebula using the optical and the near-infrared colors of early-type stars. The foreground reddening [E(B-V)_fg] is determined to be 0.35 ± 0.02, and it seems to follow the standard reddening law. On the other hand, the total-to-selective extinction ratio of the intracluster medium (R_V,cl) decreases from the central region (Trumpler 14 and 16, R_V,cl ~ 4.5) to the northern region (Trumpler 15, R_V,cl ~ 3.4). It implies that the central region is more dusty than the northern region. We find that the distance modulus of the Carina Nebula to be 11.9 ± 0.3 mag (d = 2.4 ± 0.35 kpc) using a zero-age main-sequence fitting method, which is in good agreement with that derived from the Gaia EDR3 parallaxes. We also present the catalog of 3,331 pre-main-sequence (PMS) members and 14,974 PMS candidates down to V ~ 22 mag based on spectrophotometric properties of young stars at infrared, optical, and X-ray wavelengths. From the spatial distribution of PMS members and PMS candidates, we confirm that the member selection is very reliable down to faint stars. Our data will have a legacy value for follow-up studies with different scientific purposes.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.142.1-142.1
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• 2011

UBVI and $H{\alpha}$ CCD photometry of IC 1848, one of active star-forming regions in Cas OB6, is carried out as a part of Sejong Open cluster Survey (SOS) project. An OB association is an ideal laboratory for studying the triggered star formation and star formation history. Our purposes are to provide deep photometric data up to 21 mag in V and physical parameters of IC 1848. We classify 79 early-type stars and 186 pre-main sequence (PMS) stars as being the members of the cluster using photometric criteria. The IR excess emission PMS stars by Koenig et al. (2008) are also included as members of IC 1848. Total number of members is 414. We derive the interstellar reddening (=$0.659{\pm}0.058$ mag), reddening law ($R_V=4.0{\pm}0.1$), distance modulus ($V_0-M_V=12.0{\pm}0.1$ mag) using the early-type members of IC 1848. We also determine the age of the cluster ($3.5{\pm}1.5$ Myr) by placing the theoretical isochrones on the HR diagram.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.137-140
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• 2007

Triggered star formation is not a new idea - it's been around for at least the last 30 years. Although it has never disappeared from the scene, it seems to be enjoying something of a renaissance in recent years, in both observational and theoretical studies. Here we give a brief discussion of the background of triggered star formation, describe some of our own recent observational efforts in this regard, and briefly mention some initial conclusions that may be drawn.