• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.415-419
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• 2010

A phosphor-conversion white light source is demonstrated using an InGaN-based blue laser diode (LD) and a yellow-emitting phosphor excited by the blue LD. The photometric and colorimetric properties of this blue-LD-based white light source are characterized. When injection current of the LD is 100 mA, luminous flux and luminous efficiency of the white light are found to be over 5 lm and 10 lm/W, respectively. When injection current is >90 mA, luminance is estimated to be larger than 10 Mcd/$cm^2$. In addition, color characteristics of the white light such as chromaticity coordinates, a correlated color temperature, and a color rendering index are found to be quite stable as current and temperature of the LD varies. The demonstrated LD-based white light source is expected to be used in high-brightness illumination applications with good color stability.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.81.1-81.1
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• 2010

We present a study of five open clusters (Alessi 53, Berkeley 49, Berkeley 84, Czernik 5, Pfleiderer 3) based on ugriz images of the Sloan Digital Sky Survey (SDSS). Physical properties of these clusters are not yet well known. The center and size of these clusters are determined using the radial number density profile. Using the proper motion data, we select the members of the target clusters. We estimate physical parameters of the clusters based on the isochrone fitting in the Color-Magnitude Diagram (CMD) : reddening, distance, and age. The foreground reddening is determined to be E(B-V)=0.71-1.55 mag. The distances to target clusters are derived to be 2.0-4.4 kpc, corresponding to the galactocentric distances of 7.5-11.9 kpc. Their ages are in the range of 280 to 1000 Myr. Their spatial distribution in our Galaxy is similar to that of other intermediate-age open clusters. We find ten blue straggler star candidates in Berkeley 49. This number of blue stragglers is a typical value for the age of Berkeley 49.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.58.1-58.1
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• 2018

The redshift range $1.4{\lesssim}z{\lesssim}2.5$ is often called the 'redshift desert' because of the difficulties in measuring spectroscopic redshifts due to the shifting of the major spectroscopic features into near-infrared wavelength (Steidel et al. 2004). One of the most efficient and fast way to select galaxies at this redshift range is the BzK technique designed by Daddi et al. (2004). Combining deep BVRz data from Deep Lens Survey with the wide-field (~4.08 deg2) K-band image, we select 1200 star-forming BzKs (sBzKs) and 120 passive BzKs (pBzKs) at K < 21.25. We discuss about the photometric redshifts, star formation rates, and stellar mass of the selected BzKs. Possible large scale structure at $1.4{\lesssim}z$ < 1.6 based on the spatial distribution of the BzKs is also introduced.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.27-27
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• 2013

Development of bolometer array and camera at millimeter and submillimeter wavelengths plays an important role for detecting submillimeter galaxies (SMGs) which appear to be very bright at the submillimeter and millimeter wavelengths. These SMGs, luminous infrared galaxies detected at mm/submm wavelengths seem to be progenitors of present-day massive galaxies and account for their considerable contributions to the light from the early universe and their expected high star formation rates (SFRs) if there is a close link between the SMG phenomena and the star formation activities and the interstellar dust in galaxies is mainly heated by the star light. In this talk, we review assembly of SMGs compiled with observations using the bolometer arrays and cameras and investigate their spectral energy distribution fits including the data at other wavelengths which trace the photometric properties and the red-shift distribution of galaxies. We find that these bright SMGs significantly contribute to the cosmic star formation rate density at red-shifts of 2-3 (about 8 %) for the spatial distribution of these galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.66.3-66.3
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• 2016

We report preliminary results from our analyses on the star-forming galaxies in the Herschel/SPIRE survey data over the AKARI/NEP-Wide Field. In this work, we utilize a combination of the SPIRE point source catalogue containing ~ 4,800 sources distributed over the wide (5.6 sq. deg) field and the spectroscopic redshift (zSPEC) data for 1790 selected targets obtained by MMT/Hectospec and WIYN/Hydra. Our analyses take advantages of multi-wavelengths photometric data (28 bands at most) covering from u* to $500{\mu}m$ band as well as continuous MIR wavelengths sampling by AKARI and WISE (4 to $25{\mu}m$). Various physical properties such as total infrared luminosity (LTIR), star formation rate (SFR), and luminosity functions (LFs) will be presented.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.100.2-100.2
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• 2012

We performed near-IR imaging polarimetry of the $5{\times}9$ fields (${\sim}39^{\prime}{\times}69^{\prime}$) around 30 Doradus in the Large Magellanic Cloud (LMC), using the InfraRed Survey Facility (IRSF). We obtained polarimetry data in the J, H, and Ks bands using the JHKs-simultaneous imaging polarimeter SIRPOL in 2008 December and 2011 December. With the reliable LMC field data which were selected using a bad-data-rejection algorithm, we measured Stokes parameters of point-like sources to derive the degree of polarization and the polarization position angle. We present physical relationship between the three bands using the photometric and the polarimetric properties of the sources.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.35.1-35.1
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• 2011

The solar X-ray telescopes, the Yohkoh SXT and the Hinode XRT, have observed for a couple of decades a variety of coronal structures in the range of wide field-of-view (FOV) covering the full solar disk. It has been emphasized that the optical structure of solar telescopes should be designed with care for improving the uniformity over the full FOV. The vignetting effect is one of the important optical characteristics for describing the performance of a telescope, which reflects the ability of collecting the incoming light at different locations and different photon energies. The correction of this vignetting effect would be an important calibration step that should be performed in advance, especially when the observed images are to be used for photometric purposes. Since the vignetting effect of solar X-ray telescopes shows wavelength dependence, a special care should be taken when, for example, performing the temperature analyses with thin and thick filters for flaring activities observed at the periphery of the full FOV. The results of analysis of pre-launch calibration data for the evaluation of vignetting effect will be introduced in detail.

• Journal of Astronomy and Space Sciences
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• v.19 no.4
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• pp.255-262
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• 2002

We present the infrared spectra of Herbig Ae/Be stars including the Infrared Space Ob-servatory (ISO) data. To investigate the overall properties of their circumstellar dust envelope and/or disk, we combine the IR spectra with photometric data ranging from the UV through the optical into the sub-mm region. We study the general characteristics of the spectral energy distributions using simple analysis. We plot the positions on the HR-diagram to compare with the theoretical pre-main-sequence evolution tracks.

• Journal of The Korean Astronomical Society
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• v.52 no.5
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• pp.145-158
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• 2019

We conducted a survey of open clusters within 1 kpc from the Sun using the astrometric and photometric data of the Gaia Data Release 2. We found 655 cluster candidates by visual inspection of the stellar distributions in proper motion space and spatial distributions in l - b space. All of the 655 cluster candidates have a well defined main-sequence except for two candidates if we consider that the main sequence of very young clusters is somewhat broad due to differential extinction. Cross-matching of our 653 open clusters with known open clusters in various catalogs resulted in 207 new open clusters. We present the physical properties of the newly discovered open clusters. The majority of the newly discovered open clusters are of young to intermediate age and have less than ~50 member stars.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.36.1-36.1
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• 2018

Star formation activity of galaxies, along with color and morphology, show significant environmental dependence in local universe, where galaxies in dense environment tend to be more quiescent and redder. However, many studies show that such environmental dependence does not continue at higher redshifts beyond z~1. The question of how the environmental dependence of galactic properties have developed over time is crucial to understanding cosmic galactic evolution. By combining data from Canada-France-Hawaii Telescope Legacy Survey(CFHTLS), Infrared Medium-Deep Survey(IMS), and other surveys, the photometric redshifts of galaxies in CFHTLS W2 field were estimated by fitting spectral energy distribution. The distribution of galaxies was mapped in redshift bins of 0.05 interval from 0.6 to 1.4. For each redshift bin, the number density was mapped. The galaxies in high density regions were grouped into clusters using friend-of-friend method. The color of galaxies were analyzed to study the correlation with redshift as well as environmental difference between field galaxies and cluster member galaxies.