• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.75.2-75.2
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• 2019

This poster introduces the ongoing "Narrow-band Ca Photometry for Dwarf Spheroidal Galaxies" project and presents the latest results. The project aims to explain the formation and evolution of dwarf spheroidal galaxies by examining the structural properties of stellar populations as a function of metallicity. To overcome the lack of stars with known spectroscopic metallicities for dwarf spheroidal galaxies, we apply the hk index as a photometric metallicity indicator to three galaxies-Draco, Sextans, and Canes Venatici I. For all three galaxies, we found that metal-poor and metal-rich groups of red-giant-branch stars have distinct spatial distributions, in which metal-rich stars are centrally concentrated while metal-poor stars are relatively dispersed. In Sextans, we found an off-centered peak of metal-poor stars which is presumed to be a disrupting star cluster in this galaxy. We will discuss the implications of our results for the dwarf galaxy formation and possible directions on future work of this project.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.35.2-35.2
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• 2020

Submillimeter galaxies (SMGs) have played an important role in the understanding of galaxy evolution and cosmic star formation history at high redshift because they are known as being located at z ~ 2 and harbor a vigorous star formation. Therefore studying properties of SMGs can lead us to understand evolution of massive and actively star forming galaxies and distribution of cosmic star formation density. Recently we detected 548 SMGs near North Ecliptic Pole with JCMT/SCUBA-2 from the JCMT large program covering about 2 deg2 so far. To derive their physical parameters, we compiled a multi-wavelength photometry ranging from optical (0.3 ㎛) to submillimeter (850 ㎛) by cross-identifying counterparts at different wavelengths. In order to find counterparts, we used either VLA-1.4 GHz image and/or Spitzer/IRAC 3.6 ㎛, 4.5 ㎛ image. The number of SMGs with relatively robust counterparts is 349. In this talk, we present photometric redshifts, stellar mass, star formation rates, total infrared luminosity, and AGN fraction of these 349 SMGs derived through SED fitting analysis.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.34.3-34.3
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• 2021

We present Ca-CN-CH-NH photometry for the globular cluster (GC) M3. Our new photometric system combined with robust and self-consistent theoretical fine model grids allows us to measure key elements in stellar populations, [Fe/H], [C/Fe], and [N/Fe], even in the extremely crowded fields. Our results show that M3 consists of two GCs with different chemical abundances, structural and kinematical properties. Furthermore, each GC has its own carbon-nitrogen anticorrelation with whose fractions of the CN-weak populations are consistent with those in the Magellanic Clouds. We suggest that M3 is a merger remnant of two GCs, most likely in a dwarf galaxy environment and accreted to our Milky Way Galaxy later in time.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.275-279
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• 2012

We investigate the mid-infrared (MIR) to far-infrared (FIR) properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert telescope (BAT) all-sky hard X-ray (14-195 keV) survey, based on the cross correlation with the infrared survey catalogs of AKARI, IRAS and WISE. Out of 135 non-blazar AGNs in the Swift/BAT 9-month catalog, we obtain the MIR photometric data for 128 sources in either the 9, 12, 18, 22, and $25{\mu}m$ band. We find a good correlation between their hard X-ray and MIR luminosities ranging three orders of magnitude (42 < log ${\lambda}L_{\lambda}$(9, $18{\mu}m$) < 45), which is tighter than that with the FIR luminosities at $90{\mu}m$. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori models rather than homogeneous ones.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.51.2-51.2
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• 2014

Ultra faint dwarf galaxies (UFDs) are larger but fainter than globular clusters, being the faintest galaxies in the universe. They have been found only in the Local Group. We report the discovery of an UFD in the intracluster field of the Virgo cluster (Virgo UFD1). It is located near the core of Virgo cluster, and far from any massive galaxies. The color magnitude diagram of resolved stars in Virgo UFD1 shows narrow, metal poor red giant branch (RGB), which is very similar to the UFDs in the Local Group. by comparing RGB in this galaxy with 12 Gyr stellar isochrones, we estimate its distance, $d=16.4{\pm}0.4$ Mpc and mean metallicity, $[Fe/H]=-2.4{\pm}0.4$. We derive its integrated photometric properties and structural parameters : V-band absolute magnitude of $MV=-6.3{\pm}0.2$, effective radius of $84{\pm}7pc$, and central surface brightness of ${\mu}V,0=26.49{\pm}0.09$ mag arcsec-2. These properties are similar to these of Local Group UFDs. Virgo UFD1 is the first UFD discovered beyond the Local Group. These results indicate that it may be a fossil remnant of the first galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.44.2-45
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• 2016

We present near-infrared photometric properties of red supergiant stars (RSGs) in three galaxies NGC 4449, NGC 5055 and NGC 5457. The near-infrared imaging data of WFCAM UKIRT were used and combined with optical archive data to identify the RSGs in the galaxies. We found that the RSGs can be identified from the foreground Galactic stars in (i-K, ri) colour-colour diagram. The effective temperatures and luminosities of the identified RSGs are estimated from JHK photometry using MARCS model. In the H-R diagram, the majority of RSGs in the galaxies are distributed between $logL/L{\odot}=4.8$ and 5.7, and their effective temperature and luminosities agree with the current evolutionary tracks with masses in the range $9-30M{\odot}$. We also compared the spatial distribution of RSGs with the HII regions. A tight spatial correlation between RSGs and HII region was found in NGC 4449 and NGC 5457. We do not find a clear metallicity dependance on the RSG effective temperature in the three galaxies, but the maximum luminosity of the three galaxies is constant at $logL/L{\odot}{\sim}5.6$. Additional spectroscopy data, including photometry are essential to examine whether the physical properties of RSGs change with metallicity.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.77.1-77.1
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• 2016

We investigate the properties and detection conditions for the planetary caustic perturbation of close-separation planets. To find the properties of the planetary caustic perturbation, we construct deviation maps by subtracting the single-lensing magnification of the lens star from the planetary lensing magnification for various lensing parameters. We find that each deviation area of the positive and negative perturbations disappears at the same normalized source radius according to a given deviation threshold regardless of mass ratio but disappears at a different normalized source radius according to the separation. We also estimate the upper limit of the normalized source radius to detect the planetary caustic perturbation. We find simple relations between the upper limit of the normalized source radius and the lensing parameters. From the relations, we obtain an analytic condition for the detection limit of the planet, and which show that we can sufficiently discover a planet with the mass of sub-Earth for typical microlensing events. Therefore, we expect to add the number of low-mass planets in the next-generation microlensing experiments and conclude that our detection condition of the planet can be used as a important criteria for maximal planet detections considering the source type and the photometric accuracy.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.32.4-33
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• 2016

Recent studies suggest that the difference between global and local properties of galaxies (the local-global environmental (LoG) bias) might be important in the Type Ia supernova (SN Ia) host galaxy studies. Obtaining local spectroscopic properties of hosts at high redshift, however, is challenging. Here we will introduce a more efficient way to conduct this study by only using photometric data. We find that when we restrict a sample to the hosts whose stellar mass is less than $10^{10}$ $M_{\odot}$, a sample without LoG bias is efficiently selected. From the sample without LoG bias, we confirm that SNe Ia in locally star-forming environment are $0.103{\pm}0.010mag$ and $0.085{\pm}0.012mag$ fainter than those in locally passive region, for MLCS2k2 and SALT2, respectively. Because of ~6 times larger sample that covers much wider redshift range, our results are far more significant statistically, $10.3{\sigma}$ for MLCS2k2 and $7.1{\sigma}$ for SALT2, than previous results.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.61.3-62
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• 2016

An asteroid family is a group of asteroidal objects in the proper orbital element space (a, e, and i), considered to have been produced by a disruption of a large parent body through a catastrophic collision. Family members usually have similar surface properties such as spectral taxonomy types, colors, and visible geometric albedo with a same dynamical age. Therefore an asteroid family could be called as a natural Solar System laboratory and is also regarded as a powerful tool to investigate space weathering and non-gravitational phenomena such as the Yarkovsky/YORP effects. We carry out time series photometric observations for a number of asteroid families to obtain their physical properties, including sizes, shapes, rotational periods, spin axes, colors, and H-G parameters based on nearly round-the-clock observations, using several 0.5-2 meter class telescopes in the Northern hemisphere, including BOAO 1.8 m, LOAO 1.0 m, SOAO 0.6 m facilities in KASI, McDonald Observatory 2.1 m instrument, NARIT 2.4 m and TUG 1.0 m telescopes. This study is expected to find, for the first time, some important clues on the collisional history in our Solar System and the mechanisms where the family members are being transported from the resonance regions in the Main-belt to the near Earth space.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.69.3-70
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• 2021

We present the chemical properties of star-forming dwarf galaxies (SFDGs) in five filamentary structures (Leo II A, Leo II B, Leo Minor, Canes Venatici, and Virgo III) around the Virgo cluster using the Sloan Digital Sky Survey optical spectroscopic data and Galaxy Evolution Explorer ultraviolet photometric data. We investigate the relationship between stellar mass, gas-phase metallicity, and specific star formation rate (sSFR) of SFDGs in the Virgo filaments in comparison to those in the Virgo cluster and field. We find that, at a given stellar mass, SFDGs in the Virgo filaments show lower metallicity and higher sSFR than those in the Virgo cluster on average. We observe that SFDGs in the Virgo III filament show enhanced metallicities and suppressed star formation activities comparable to those in the Virgo cluster, whereas SFDGs in the other four filaments exhibit similar properties to the field counterparts. Moreover, about half of the galaxies in the Virgo III filament are found to be morphologically transitional dwarf galaxies that are supposed to be on the way to transforming into quiescent dwarf early-type galaxies. Based on the analysis of the galaxy perturbation parameter, we propose that the local environment represented by the galaxy interactions might be responsible for the contrasting features in "chemical pre-processing" found in the Virgo filaments.