• Journal of The Korean Astronomical Society
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• v.41 no.1
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• pp.7-15
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• 2008

We carried out a set of simulations to reproduce the performance of wide-field NEO surveys based on the revised population model of Near Earth Objects (NEOs) constructed by Morbidelli (2006). This is the first time where the new model is carefully compared with discovery statistics, and with the exception of population model, the simulation is identical to the procedure described in Moon et al. (2008). Our simulations show rather large discrepancy between the number of NEO discoveries made by the actual and the simulated surveys. First of all, unlike Bottke et al. (2002)'s, Morbidelli (2006)'s population model overestimates the number of NEOs. However, the latter reproduces orbit distributions of the actual population better. Our analysis suggests that both models significantly underestimate Amors, while overestimating the number of Apollos. Our simulation result implies that substantial modifications of both models are needed for more accurate reproduction of survey observations. We also identify Hungaria region (HU) to be one of the most convincing candidates that supply a large fraction of asteroids to the inner Solar System.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.621-624
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• 2015

We present the current status (as of August 2014) of SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a mission optimized for mid- and far-infrared astronomy with a cryogenically cooled 3m-class telescope. SPICA is expected to achieve high spatial resolution and unprecedented sensitivity in the mid- and far-infrared, which will enable us to address a number of key problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets. We have carried out the "Risk Mitigation Phase" activity, in which key technologies essential to the realization of the mission have been extensively developed. Consequently, technical risks for the success of the mission have been significantly mitigated. Along with these technical activities, the international collaboration framework of SPICA has been revisited, which resulted in la arger contribution from ESA than that in the original plan. To enable the ESA participation under the new framework, a SPICA proposal to ESA is under consideration as a medium-class mission under the framework of the ESA Cosmic Vision. The target launch year of SPICA under the new framework is the mid-2020s.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.221.1-221.1
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• 2012

The Korea Astronomy and Space Science Institute (KASI) is developing three 1.6m optical telescopes with $18k{\times}18k$ mosaic CCD cameras. These telescopes will be installed and operated at Chile, South Africa, and Australia for Korea Micro-lensing Telescope Network (KMTNet) project. The main scientific goal of the project is to discover earth-like extra-solar planets using the gravitational micro-lensing technique. To achieve the goal, each telescope at three sites will continuously monitor the specific region of Galactic bulge with 2.5 minute cadence for five years. Assuming 12 hour observation in maximum for a night, the amount of 200 GB file storage is required for one night observation at one observatory. If we consider the whole project period and the data processing procedure, a few PB class data storage, high-speed network, and high performance computers are essential. In this presentation, we introduce the KMTNet data management plan that handles gigantic data; raw image collecting, image processing, photometry pipeline, database archiving, and backup.

• Journal of the Korean Magnetic Resonance Society
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• v.6 no.2
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• pp.84-88
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• 2002

Dating and dosimetry using electron spin resonance (ESR) in 20th Century developed at both Yamaguchi University and Osaka University have been reviewed with emphasis on new prospects and strategies in 21th century. Natural radiation have been generating radicals that accumulated in archaeological and geological materials. ESR detects these radicals and the ESR signal intensity is proportional to the radiation dose and therefore the age. The assessment of the total dose of natural radiation and the annual dose rate give their ESR ages. The ESR dating of stalactites and stalagmites ant Akiyoshi cave in Yamaguchi prefecture in 1975 was extended to anthropological dating using bones and tooth enamel excavated in Greek Petralona cave. Fossils of shells and corals gave the ages of marine terraces and sea-level changes. Quartz grains gave the ages of geothermal alteration and fault movements. Future ESR dating of ices at outer planets anf their satellite are also investigated as basic studies for ices od $H_2O,\;CO_2,\;SO_2$ as well as terrestrial hydrates in laboratory. Atomic bomb radiation dosimetry at Hiroshima and Nagasaki using ESR lead to the dosimetry of personnel, Chemobyl and JCO criticality accidents. Monitoring of radiation dose with sensitive materials with tissue equivalence are being developed. finally a new scanning ESR imaging apparatus (a near field microwave microscope) developed in our laboratory gave ESR images of Radicals from fossils to Si-CVD and diamond films as summarized in my book in 2002.

• Journal of the Korean Society of Earth Science Education
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• v.13 no.3
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• pp.297-304
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• 2020

This study is to find out experiments of Earth's revolution and which experiment is effective by school level. Researcher investigated and developed eight experiments for students to learn Earth's revolution. Twenty six pre-service teachers did these experiments, discuss about them, chose an effective experiment of Earth's revolution and wrote the reason why. As a result, they thought that an experiment of seasonal constellations is effective for elementary school students, an experiment of seasonal star's spectrum is effective for secondary school students and an experiment of the superior planets' retrograde motion is effective for university students. Pre-service teachers gave reasons such as hands-on experience, connection with textbooks, background knowledge and higher-level thinking.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.44.3-44.3
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• 2019

Since the detection of 3.3-micron PAH (polycyclic aromatic hydrocarbon) and 3.4-micron aliphatic hydrocarbon features in the spectra of Titan (Bellucci et al. 2009; Kim et al. 2011) and Saturn (Kim et al. 2012), respectively, the 3.3-micron feature of gaseous CH4 has been thought to be still the important spectral feature in the 3-micron absorption structures of Titan and Saturn. However, the analyses of the 3.3-and 3.4-micron emission structures of Saturn revealed that the influence of the gaseous CH4 on the structures is rather minimal (Kim et al. 2019). We present synthetic spectra of gaseous CH4, and the PAH and aliphatic haze particles in order to show the degree of influence of their spectra on the 3.3-and 3.4-micron emission structures of Saturn, and we compare these synthetic spectra with currently available observations. We constructed these synthetic spectra using newly developed radiative transfer equations. These equations are able to address detailed radiative processes in the atmospheres containing various gases and haze particles. We expect these radiative transfer equations can also be widely applied to the investigation of radiative transfer processes and the analyses of the spectra of celestial objects such as the Earth, the Moon, planets, and interstellar nebulae.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.45.3-45.3
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• 2019

Since the high throughput for diffuse objects and the wide-area survey even with a small telescope can be achieved in space, infrared (IR) obervations have been tried through small missions in Korea. Based upon the previous technical development for infrared spectro-photometric instrument, NISS (Near-infrared Imaging Spectrometer for Star formation history) onboard NEXTSat-1, we participated in the all-sky infrared spectro-photometric survey mission, SPHEREx. The SPEHREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) was selected as the NASA MIDEX (Medium-class Explorer) mission (PI Institute: Caltech) in this February. As an international partner, KASI will take part in the hardware development, the operation and the science for the SPHEREx. The SPHEREx will perform the first all-sky infrared spectro-photometric survey to probe the origin of our Universe, to explore the origin and evolution of galaxies, and to explore whether planets around other stars could harbor life. For the purpose of the all-sky survey, the SPHEREx is designed to have a wide FoV of 3.5 × 11.3 deg. as well as wide spectral range from 0.75 to 5.0㎛. Here, we report the status of the SPHEREx project and the progress in the Korean participation.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.63.3-63.3
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• 2019

Nearby young moving groups (NYMGs hereafter) are gravitationally unbound loose young stellar associations located within 100 pc of the Sun. Since NYMGs are crucial laboratories for studying low-mass stars and planets, intensive searches for NYMG members have been performed. For identification of NYMG members, various strategies and methods have been applied. As a result, the reliability of the members in terms of membership is not uniform, which means that a careful membership re-assessment is required. In this study, I developed a NYMG membership probability calculation tool based on Bayesian inference (Bayesian Assessment of Moving Groups: BAMG). For the development of the BAMG tool, I constructed ellipsoidal models for nine NYMGs via iterative and self-consistent processes. Using BAMG, memberships of claimed members in the literature (N~2000) were evaluated, and 35 per cent of members were confirmed as bona fide members of NYMGs. Based on the deficiency of low-mass members appeared in mass function using these bona fide members, low mass members from Gaia DR2 are identified. About 2000 new M dwarf and brown dwarf candidate members were identified. Memberships of ~70 members with RV from Gaia were confirmed, and the additional ~20 members were confirmed via spectroscopic observation. Not relying on previous knowledge about the existence of nine NYMGs, unsupervised machine learning analyses were applied to NYMG members. K-means and Agglomerative Clustering algorithms result in similar trends of grouping. As a result, six previously known groups (TWA, beta-Pic, Carina, Argus, AB Doradus, and Volans-Carina) were rediscovered. Three the other known groups are recognized as well; however, they are combined into two new separate groups (ThOr+Columba and TucHor+Columba).

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.53.1-53.1
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• 2021

The KASI team are participating in the NASA MIDEX mission (PI Institute: Caltech), the all-sky infrared spectro-photometric surveyor SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer). The SPHEREx will provide us the first all-sky infrared spectro-photometric data set to probe the origin of our Universe, to explore the origin and evolution of galaxies, and to explore whether planets around other stars could harbor life. After the project PDR (Preliminary Design Review) was successfully passed on the last September, the fabrication of flight hardware is in progress. As an international partner, KASI deeply involved in all fields of projects, i.e., the development of calibration facility, the construction of data reduction modules and the science studies for the SPHEREx. After finishing the fabrication and test of calibration facility for the SPHEREx in this year, it will be delivered to Caltech. Here, we report the status of the SPHEREx project and the progress in the Korean participation.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.4
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• pp.444-453
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• 2014

A throttleable rocket engine enables operational possibilities such as the docking of spacecraft, maneuvering in a certain orbit and landing on a planet's surface, altitude control, and entrance to atmosphere-less planets. Thus, throttling methods have long been researched. However, dual-manifold injectors, which represent one throttling method, have been investigated less than others. In this study, dual-manifold and single-manifold injectors were compared to determine the characteristics of dual-manifold injectors. Also, the effects of gas injection were investigated with various F/O ratios. To investigate the characteristics, mass flow rate, spray pattern, spray angle, and droplet size were measured. The spray angle and droplet size were captured by indirect photography. About 30 images were taken to assess the spray patterns and spray angle. Also, 700 images were analyzed to understand the droplet distribution and targeting area, moving to the right from the centerline with 1.11-cm intervals. The droplet size was obtained from an image processing procedure. From the results, the spray angle showed two transition regions, due to swirl momentum in the swirl chamber regardless of the F/O ratio. The droplet size showed similar trends in both dual-manifold and single-manifold injectors except in the low mass flow rate region. In the case of the dual- manifold injector, the spray cone was not fully developed in the low mass flow rate region due to low angular momentum in the swirl chamber.