• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.57.1-57.1
• /
• 2021

The icy mantles of interstellar grains are developed by the freeze-out of interstellar molecules and atoms onto grain surfaces. The ice molecules become more complex by surface chemistry induced directly by high energy photons or by the thermal energy diffused over heated grain surface. Therefore, the ice composition is an important tracer of physical conditions where the ices form. Ices have been studied via their absorption features against continuum sources, such as young stellar objects or evolved background stars, in infrared wavelengths. The Spitzer IRS was the most sensitive spectrometer for the observations of infrared ice absorption features. We has been developing an automated analysis tool for the Spitzer IRS spectra, especially for the 15 ㎛ CO₂ bending mode. The 15 ㎛ CO₂ absorption feature is very useful for the study of accretion process in star formation since its spectral shape varies with thermal condition of the dust grains. Eventually, this tool will cover the whole range of the Spitzer IRS spectrum (5~20 ㎛).

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.2
• /
• pp.61.5-62
• /
• 2021

Interstellar objects (ISOs) provide essential information on the physical and chemical properties of the environment when extrasolar systems are formed. Since 2017, two interstellar objects, 1I/2017 ('Oumuamua) and C/2019 Borisov, have been observed passing our solar system. The first interstellar object, named 1I/2017 ('Oumuamua), exhibits several peculiar properties that cannot be explained based on our knowledge of solar system objects, including extreme elongation and non-gravitational acceleration. Its nature and origins remain a mystery. In this talk, I will first describe the basic observational properties of 'Oumuamua and review various theories proposed to explain these features. I will then present our results, ruling out the most promising proposal that 'Oumuamua was made out of molecular hydrogen ice (solid hydrogen). Finally, I will discuss prospects for the detection of ISOs with LSST and in-depth research through multi-wavelength and tracers.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.49.2-49.2
• /
• 2019

We present results from our long-term observing campaign, using the NASA IRTF at Maunakea, to obtain 2 - 4 ㎛ spectra of 118 red point sources in the line of sight to the Galactic Center (GC). Our sample is largely composed of point sources selected from near- and mid-infrared photometry, but also includes a number of massive young stellar objects. Many of these sources show high foreground extinction as shown by deep 3.4 ㎛ aliphatic hydrocarbon absorption feature, which is a characteristic of the diffuse ISM and comes from the long line of sight through the diffuse medium toward the Central Molecular Zone (CMZ), the central 300 pc region of the GC. The deep 3.1 ㎛ H₂O ice absorption band coming from the local, dense material in the GC CMZ suggests that most sources are likely located in the GC CMZ. A few of these sources show weak CCH₃OH ice absorption at 3.535 ㎛, which can provide a strong constraint on the CCH₃OH ice formation in the unique environment of the CMZ. From the best-fitting models, the optical depths of these features are determined and used to generate a well-rounded view of the ice composition across the GC CMZ and the spectral characteristics of massive YSOs in the GC.

• Journal of Environmental Science International
• /
• v.26 no.7
• /
• pp.827-836
• /
• 2017

Freezing rain is a phenomenon when precipitation falls as a liquid rain drop, but freezes when it comes into contact with surfaces or objects. In this study, we investigated the predictability of freezing rain and its characteristics, which are strongly related with the occurrence of black ice using synoptic scale meteorological observation data. Two different cases occurred at 2012 were analyzed and in the presented cases, freezing rain often occurs in the low-level low pressure with the warm front. The warm front due to the lower cyclone make suitable environment in which snow falling from the upper layer can change into supercooled water. The $0^{\circ}C$ temperature line to generate supercooling water is located at an altitude of 850 hPa in the vertical temperature distribution. And the ground temperature remained below zero, as is commonly known as a condition for black ice formation. It is confirmed that the formation rate of freezing rain is higher when the thickness after 1000-850 hPa is 1290-1310 m and the thickness of 850-700 hPa layer is larger than 1540 m in both cases. It can also be used to predict and estimate the generation of freezing rain by detecting and analyzing bright bands in radar observation.

• The Bulletin of The Korean Astronomical Society
• /
• v.41 no.2
• /
• pp.56.1-56.1
• /
• 2016

A low-mass star-forming region, L1251B, is an excellent example of a small and nearby group of protostellar objects. L1251B has been mapped spectroscopically with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. IRS has provided mid-IR emission lines (e.g., [Fe II], [Ne II], and ro-vibrational H2) and absorption features of CO2 and H2O ice in studying the physical state of the ionized gas and the material residing in the circumstellar environments. We will present the distribution of outflows and ice components in L1251B.

• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.1
• /
• pp.67.4-67.4
• /
• 2019

We present preliminary results of our long-term (2009-2017) observing campaign using the NASA IRTF at Mauna Kea, to obtain $2-5{\mu}m$ spectroscopy of ~200 red point sources in the line of sight to the Galactic center. Point sources in our sample were selected from the mid-infrared images of the Spitzer Space telescope, and include candidate massive young stellar objects, which have previously been identified from our Spitzer/IRS spectroscopy. We show high foreground extinction of these sources from deep $3.1{\mu}m$ H2O ice and aliphatic hydrocarbon absorption features, suggesting that they are likely located in the central 300 pc region of the Galactic center. While many sources reveal photospheric $2.3{\mu}m$ gas CO absorption, few of them clearly indicate $3.54{\mu}m$ CH3OH ice absorption, possibly indicating a large dust column density intrinsic to a massive young stellar object.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1999.12a
• /
• pp.169-180
• /
• 1999

Ground penetrating radar(GPR) uses radio waves to detect buried objects in any non-metallic material. Initially it was used to detect structures in ice. GPR has evolved to include the penetration of soils, rocks and man-made structures. GPR uses a sensitive detector to record weak radio waves reflected from objects embedded in the material under investigation. In this study, the GPR is applied to outside plant telecommunication facilities such as cable tunnels, manholes and underground conduits and model experiments to obtain radar characteristics. The thickness and soundness of tunnel lining can be evaluated, and the location of rebars and steel ribs can also be found effectively. The location of underground conduits as well as manholes can be found and the results of GPR give good coincidence with design drawings. In order to investigate the tunnel lining, the GPR mounted vehicle is developed and it is proved that the vehicle can save time and manpower.

• Proceedings of the KSR Conference
• /
• 2006.11b
• /
• pp.414-419
• /
• 2006

The ballast or other objects may be located on the rail road by a lump of ice, repairing operation on the track, or the strong gust due to the high speed running of the train. When a train operated in this condition, it causes serious damages to the wheel, train, and structures near the track, or the secondary ballast flying. To remove these objects safely, a ballast blower is suggested which was attached under the train. Firstly, the numerical analyses are investigated to find out the basic flow characteristics of the ballast blower. Next, the performance of the ballast blower is verified by wind tunnel experiments. Through these studies, it is expected that the ballast blower can be applied practically.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.1
• /
• pp.67.2-67.2
• /
• 2014

Comet nucleus is a solid body consisting of dark dust grains and ice. Cometary volatiles sublimate from subsurface layer by solar heating, leaving behind large dust grains on the surface. Eventually, the appearance could turn into asteroidal rather than cometary. It is, therefore, expected that there would be "dormant comets" in the list of known asteroids. Our research group has undertaken the research on the population of dormant comets. We applied a brand-new asteroidal catalog compiled from data garnered by three infrared astronomical observatories, AKARI, IRAS and WISE. We extracted objects which have comet-like orbits on the basis of their orbital properties (Tisserand parameters with respect to Jupiter, TJ, and aphelion distance, Q). We found that (1) there are a considerable number (>100) of asteroids in comet-like orbits, and (2) 80% of them have low albedo consistent with comets. This result suggest that these low albedo objects could be dormant comets. One unanticipated finding is that 20% of asteroids in comet-like orbit have high albedo similar to S-type asteroids. It is difficult to explain the population of S-type asteroids in comet-like orbits by the classical mechanics theory. We further found that these high-albedo objects are small (D < 2 km) bodies distributed in near-Earth space. We suggest that such high-albedo, small, near-Earth asteroids are susceptible to Yarkovsky effect and injected into comet-like orbits.

• Journal of Korea Multimedia Society
• /
• v.21 no.12
• /
• pp.1493-1503
• /
• 2018

We propose an object recognition system and experiential game contents using Kinect to maximize object recognition rate by utilizing underwater robots. we implement an ice hockey game based on object-aware interactive contents to validate the excellence of the proposed system. The object recognition system, which is a preprocessor module, is composed based on Kinect and OpenCV. Network sockets are utilized for object recognition communications between C/S. The problem of existing research, degradation of object recognition at long distance, is solved by combining the system development method suggested in the study. As a result of the performance evaluation, the underwater robot object recognized all target objects (90.49%) with 80% of accuracy from a 2m distance, revealing 42.46% of F-Measure. From a 2.5m distance, it recognized 82.87% of the target objects with 60.5% of accuracy, showing 34.96% of F-Measure. Finally, it recognized 98.50% of target objects with 59.4% of accuracy from a 3m distance, showing 37.04% of F-measure.