• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.35.1-35.1
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• 2021

RR Lyrae stars are sensitive probe for the precision stellar astrophysics and also for the cosmic distance scale thanks to their well-defined near-infrared Period-Luminosity relations (PLRs). These horizontal branch variables can be used for primary calibration of the first-rung of population II distance ladder providing an evaluation of the ongoing tension between Cepheid-Supernovae based Hubble constant and the Planck results. Therefore, absolute calibration of RR Lyrae PLRs is now crucial to complement or test the tip of the red giant branch based distances, and in turn, population II star based Hubble constant measurements. While the pulsation models of RR Lyrae can reproduce most observables, they predict a significant metallicity effect on their JHKs-band PLRs that is inconsistent with so-far limited observational studies. We remedy this inconsistency of metallicity dependence in RR Lyrae PLRs by combining their near-infrared observations in the globular clusters of different mean-metallicities with the new parallaxes from the Gaia early data release 3 (EDR3). Our empirical results on Period-Luminosity-Metallicity (PLZ)relations are consistent with theoretical predictions but the precision of absolute calibrations is still affected by the parallax uncertainties and the systematic zero-point offset present in the Gaia EDR3.

• Journal of The Korean Astronomical Society
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• v.49 no.3
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• pp.93-107
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• 2016

Augmenting the Wide Field Infrared Survey Telescope (WFIRST) microlensing campaigns with intensive observations from a ground-based network of wide-field survey telescopes would have several major advantages. First, it would enable full two-dimensional (2-D) vector microlens parallax measurements for a substantial fraction of low-mass lenses as well as planetary and binary events that show caustic crossing features. For a significant fraction of the free-floating planet (FFP) events and all caustic-crossing planetary/binary events, these 2-D parallax measurements directly lead to complete solutions (mass, distance, transverse velocity) of the lens object (or lens system). For even more events, the complementary ground-based observations will yield 1-D parallax measurements. Together with the 1-D parallaxes from WFIRST alone, they can probe the entire mass range M ≳ M_⊕. For luminous lenses, such 1-D parallax measurements can be promoted to complete solutions (mass, distance, transverse velocity) by high-resolution imaging. This would provide crucial information not only about the hosts of planets and other lenses, but also enable a much more precise Galactic model. Other benefits of such a survey include improved understanding of binaries (particularly with low mass primaries), and sensitivity to distant ice-giant and gas-giant companions of WFIRST lenses that cannot be detected by WFIRST itself due to its restricted observing windows. Existing ground-based microlensing surveys can be employed if WFIRST is pointed at lower-extinction fields than is currently envisaged. This would come at some cost to the event rate. Therefore the benefits of improved characterization of lenses must be weighed against these costs.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.452-455
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• 2007

3D stereoscopic viewing of large scale imagery, such as aerial photography and satellite images, needs different parallaxes relative to the display scale. For example, when a viewer sees a stereoscopic image of aerial photography, the optimal parallax of its zoom-in image should be smaller than that of its zoom-out. Therefore, relative parallax adjustment according to the display scale is required. Merely adjusting the spacing between stereo images is not appropriate because the depths of the whole image are either exaggerated or reduced entirely. This paper focuses on the improving stereoscopic viewing with a single remote sensing image and a digital surface model (DSM). We present the parallax adjustment technique to maximize the 3D realistic effect and the visual comfort. For remote sensing data, DSM height value can be regarded as disparity. There are two possible kinds of methods to adjust the relative parallax with a single image performance. One is the DSM compression technique: the other is an adjustment of the distance between the original image and its stereo-mate. In our approach, we carried out a test to evaluate the optimal distance between a single remote sensing image and its stereo-mate, relative to the viewing scale. Several synthetic stereo-mates according to certain viewing scale were created using a parallel projection model and their anaglyphs were estimated visually. The occlusion of the synthetic stereo-mate was restored by the inpainting method using the fields of experts (FoE) model. With the experiments using QuickBird imagery, we could obtain stereoscopic images with optimized parallax at varied display scales.

• Korean Journal of Optics and Photonics
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• v.24 no.5
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• pp.237-244
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• 2013

Supermultiview and electro-holographic displays are promising displays for the future because they provide continuous parallaxes as their depth cue. But they are still in the early development stage due to the lack of supporting technologies. Achieving the continuous parallax in the supermultiview relies more on the number and size of pixels in the pixel cell/elemental image rather than the number of different view images. For the electro-holographic display, it also relies on the number and size of pixels in the panel. So these two methods share the same requirements for achieving the parallax. But the image displayed on the holographic display provides more impressive visual appeal than that on the supermultiview because the image can be floated on the front space of the display.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.61.3-61.3
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• 2019

We report the status of KMTNet (Korea Microlensing Telescope Network) microlensing. From KMTNet event-finder, we are annually detecting over 2500 microlensing events. In 2018, we have carried out a real-time alert for only the Northern bulge fields. It was very helpful to select Spitzer targets. Thanks to the real-time alert, KMT-only events for which OGLE and MOA could not detect have been largely increased. The KMTNet event-finder and alert-finder algorithms are being upgraded every year. From these, we found 18 exoplanets and various interesting events, such as an exomoon-candidate, a free-floating candidate, and brown dwarfs, which are very difficult to be detected by other techniques including radial velocity and transit. In 2019, the KMTNet alert will be available in real-time for all bulge fields. As before, we will continue to collaborate with Spitzer team to measure the microlens parallaxes, which are required for estimating physical parameters of the lens. Thus, the KMTNet alert will be helpful to select Spitzer targets again. Also we plan to do follow-up observations for high-magnification events to study the planet multiplicity function. The KMTNet alert will play an important role to do follow-up observations for high-magnification events. Also, we will search for free-floating planets with short timescale (< 3 days) to study the planet frequency in our Galaxy.

• 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.

• Journal of the Korean earth science society
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• v.27 no.5
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• pp.557-568
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• 2006

We present CCD UBVI photometry for more than 10,000 stars in $20'.5{\times}20'.5$ field of the halo globular cluster M30. From a color-magnitude diagram, main sequence turnoff was obtained when $V_{TO},\;(B-V)_{TO},\;and\;(V-I)_{TO}\;are\;8.63{\pm}0.05,\;0.44{\pm}0.05\;and\;0.63{\pm}0.05$, respectively. From a (U-B)-(B-V) diagram, reddening parameter, E(B-V) equals $0.05{\pm}0.01$ and a UV color excess ${\delta}(U-B)\;is\;0.27{\pm}0.01$. The abundance is derived, where [Fe/H] equals $-2.05{\pm}0.09$ according to the photometric method and spectroscopic data. The observed luminosity function of M30 shows an excess in the number of red giants relative to the number of turnoff stars, when comparing with the predictions of canonical models. Using the Hipparcos parallaxes for subdwarfs, we estimate distance modulus, $(m-M)_o\;as\;14.75{\pm}0.12$. Using the R and R' method, we find helium abundances, Y(R) as $0.23{\pm}0.02$, Y(R') as $0.29{\pm}0.02$, respectively. Finally, the cluster' sage dispersion was deduced from 10.71 Gyr to 17 Gyr.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.41.1-41.1
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• 2018

We introduce a current status and future plans of Korea Microlensing Telescope Network (KMTNet) microlensing experiments, which include an observational strategy, pipeline, event-finder, and collaborations with Spitzer. The KMTNet experiments were initiated in 2015. From 2016, KMTNet observes 27 fields including 6 main fields and 21 subfields. In 2017, we have finished the DIA photometry for all 2016 and 2017 data. Thus, it is possible to do a real-time DIA photometry from 2018. The DIA photometric data is used for finding events from the KMTNet event-finder. The KMTNet event-finder has been improved relative to the previous version, which already found 857 events in 4 main fields of 2015. We have applied the improved version to all 2016 data. As a result, we find that 2597 events are found, and out of them, 265 are found in KMTNet-K2C9 overlapping fields. For increasing the detection efficiency of event-finder, we are working on filtering false events out by machine-learning method. In 2018, we plan to measure event detection efficiency of KMTNet by injecting fake events into the pipeline near the image level. Thanks to high-cadence observations, KMTNet found fruitful interesting events including exoplanets and brown dwarfs, which were not found by other groups. Masses of such exoplanets and brown dwarfs are measured from collaborations with Spitzer and other groups. Especially, KMTNet has been closely cooperating with Spitzer from 2015. Thus, KMTNet observes Spitzer fields. As a result, we could measure the microlens parallaxes for many events. Also, the automated KMTNet PySIS pipeline was developed before the 2017 Spitzer season and it played a very important role in selecting the Spitzer target. For the 2018 Spitzer season, we will improve the PySIS pipeline to obtain better photometric results.