• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.121.2-121.2
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• 2014

2013년 설립된 부산일과학고등학교 천문대는 교육 및 연구목적으로 12인치 굴절망원경, 16인치 반사망원경 및 다수의 소형망원경들이 설치되어 있다. 우리는 본격적인 관측, 연구를 수행하기에 앞서 망원경의 다양한 성능을 검증하여 향후 연구 활동에 기초자료로 사용하고자 한다. 본 연구에서는 망원경에 4K CCD 및 DSLR을 장착하여 얻은 관측 영상으로부터 망원경의 추적 특성, 지향정밀도, 광학적 특성을 고찰하고, Landolt (1992)의 표준성을 이용한 BV측광을 수행하여 표준계변환의 특성을 조사하였다. 또한 산개성단의 BV관측을 통해 한계등급을 측정하였다. 이 연구결과로부터 향후 부산일과학고등학교 천문대에서 수행할 수 있는 적합한 관측 연구의 방향을 제시한다.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.96.1-96.1
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• 2014

The rotation of asteroids can help reveal not only the fundamental characteristics of asteroids but also the origin and evolution of our Solar System. From the photometric observations for NEA 162173 (1999 JU3) and Maria family asteroids using 0.5 m- to 2 m- class telescopes at 10 observatories in the northern hemisphere, I obtained a total of 260 lightcurves for 97 asteroids and derived synodic rotational periods for 51 objects, including newly obtained periods of 34 asteroids. For the sake of efficiency, I developed an observation scheduler, SMART (Scheduler for Measuring Asteroid RoTation) and a photometric analysis software subsystem, ASAP (Asteroid Spin Analysis Package). Based on the lightcurve analysis of NEA 162173 (1999 JU3) and Maria family asteroids, 1) I present the rotational and observational characteristics of 1999 JU3 and provided the Hayabusa-2 Science team with the information on pole orientations, 2) I investigated correlations among rotational periods, amplitudes of lightcurves, and sizes, and conclude that the rotational properties of old-type family asteroids have been changed considerably by the YORP effect. 3) Finally, I found the Yarkovsky footprints on the Maria asteroid family and estimated that approximately 37 to 75 Maria family asteroids larger than 1 km have entered the near-Earth space every 100 Myr. This study should reveal the collisional history and transport route of the members from the resonance region to the near Earth space, for the first time.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.60.1-60.1
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• 2014

In the center of an Active Galactic Nuclei(AGN) is a supermassive black hole which accretes matter from its surroundings. The radio-loud AGN launch two relativistic jets perpendicular to the accretion disk which terminates into radio lobes located up to megaparsec away. Blazars form a small subset of radio-loud AGNs with one of two relativistic jets pointing toward the observer's line of sight. Many blazars often show flares at different frequencies. And these flares at different frequencies are known that they often correlate with each other. In 2013 December, there was a gamma-ray flare in 3C 279, one of the brightest blazars, Dec 2013. So we want to reveal that whether this flare correlates with radio flare or not, and where the flare originate. With polarization observation at radio frequencies, we can study the physical properties of the magnetic field in the innermost regions of the relativistic jets. Therefore, we have conducted polarization monitoring of this source from Dec. 2013 to Jun. 2014 with KVN(Korea VLBI Network) radio telescopes at 22, 43 and 86GHz. Here we present the initial results of the monitoring of 3C 279. We prospect that we can reveal the origin of this gamma-ray flare by comparing with our radio data.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.83.3-84
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• 2017

On 2016 April $13^{th}$ the Jovian satellite Ganymede occulted a $7^{th}$ magnitude star. The predicted occultation track (occultation shadow) crossed the Northern Pacific Ocean, Japan, and South Korea. Hence, it was a very favorable event due to the star brightness in order to be accessible for small-aperture telescopes as well. While no other similar event is expected for the next 10 years, only two occultation events are reported in the literature in the past, from Earth in 1972 and from Voyager, in large disagreement in respect to the atmospheric detection. However, evidence of an exosphere around Ganymede was inferred through H Lyman alpha emission detected by Galileo UVS, through HST/GHRS detection of far-UV atomic O airglow emissions, signature of dissociated molecular oxygen. We organized a short-notice international coordinated occultation monitoring network with the aim to search for a signature of Ganymede's exosphere in the occultation light-curve by using facilities on Mauna Kea (NASA-IRTF) and Sobaeksan Optical Astronomy Observatory (SOAO) in South Korea.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.57.2-57.2
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• 2017

KVN is a millimeter VLBI array composed of three 21m-diameter radio telescopes at Seoul, Ulsan and Jeju island in Korea. KVN has unique simultaneous multi-frequency receiving systems, which enable us to correct phase fluctuation of troposphere by transferring phase solution of low frequency data to higher frequency data. Although KVN can achieve very high performance up to 130 GHz through multi-frequency technique, imaging capability is highly limited because of lack of the number of baselines. In order to enhance imaging capability and maximizing multi-frequency capability, we plan to extend KVN baselines from 3 to 10 (or more) by constructing new KVN stations. This talk introduce expected performances, science cases, required budgets and periods of the Extended-KVN.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.77.1-77.1
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• 2017

We present the preliminary results from our intensive monitoring campaign for measuring continuum and line variability of a low-mass Seyfert galaxy, NGC 4395, which host a smallest known AGN black hole in the reverberation mapping studies. We performed consecutive photometric observations during 5 nights in April 2017. Various telescopes in the world, including BOAO 1.8-m, NYSC 1-m, MDM 2.4-m, 1.3-m, etc, were dedicated for this campaign. Preliminary results show that the tentative time lag can be determined, which is approximately order of 1-2 hours.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.10 s.181
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• pp.2502-2512
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• 2000

Truss structures are widely used in many space structures, such as large antenna systems, space stations, precision segmented telescopes because they are light in weight and amenable in assembly or deployment. But, due to the low damping capacity, they remain excited for a long time once disturbed. These structural vibrations can reduce life of the structures and cause unstable dynamic characteristics. In this research, vibration suppression experiment has carried out with a three-dimensional 15-member truss structure using two piezoelectric actuators. Piezoelectric actuators which consist of stacks of thin piezoelectric material disks are directly inserted to the truss structure collocated with the strain sensors. Each actuator is controlled digitally in decentralized manner, based on local integral and proportional feedback. The optimal positions of the actuators are determined by the modal damping ratio and the control force. Numerical simulation has carried out to determine optimal position of each actuator.

• Journal of The Korean Astronomical Society
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• v.49 no.4
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• pp.157-162
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• 2016

High resolution reconstruction technology is developed to help enhance the spatial resolution of observational images for ground-based solar telescopes, such as speckle masking. Near real-time reconstruction performance is achieved on a high performance cluster using the Message Passing Interface (MPI). However, much time is spent in reconstructing solar subimages in such a speckle reconstruction. We design and implement a novel parallel method for speckle masking reconstruction of solar subimage on a shared memory machine using the OpenMP. Real tests are performed to verify the correctness of our codes. We present the details of several parallel reconstruction steps. The parallel implementation between various modules shows a great speed increase as compared to single thread serial implementation, and a speedup of about 2.5 is achieved in one subimage reconstruction. The timing result for reconstructing one subimage with 256×256 pixels shows a clear advantage with greater number of threads. This novel parallel method can be valuable in real-time reconstruction of solar images, especially after porting to a high performance cluster.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.33.2-33.2
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• 2010

Galaxy clusters are known to be very bright in X-ray and contain a large number of X-ray point sources within the X-ray emission. However, due to the fluctuations of the X-ray emission, it is very difficult to detect faint X-ray sources and to extract accurately the photometric properties of the X-ray point sources in galaxy clusters. In addition, the most X-ray telescopes show spatially varying point spread function (PSF) and suffer from severe vignetting. The Chandra Archival Survey of Galaxy Clusters project is a wide-area ($\sim40deg^2$) survey of serendipitous Chandra X-ray sources in galaxy cluster fields, containing ~58,000 X-ray point sources in ~800 Chandra ACIS observations of ~600 galaxy clusters. This project aim to investigate the density environmental effects on the physical properties of the X-ray point sources, comparing physical properties of the X-ray point sources in galaxy clusters to those in typical fields. To utilize the sensitivity and detection probability of the X-ray point sources in galaxy clusters, we perform extensive Monte-Carlo simulations. In this poster, we compare the detection probability of the X-ray point sources in galaxy clusters to that of typical fields, and discuss quantitatively the difference between them.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.54-54
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• 2010

Interplanetary space is filled with dust particles originating mainly from comets and asteroids. Such interplanetary dust particles lose their angular momentum by olar radiation pressure, causing the dust grains to slowly spiral inward Poynting-Robertson effect). As dust particles move into the Sun under the influence of Poynting-Robertson drag force, they may encounter regions of resonance just outside planetary orbits, and be trapped by their gravities, forming the density enhancements in the dust cloud (circumsolar resonance ring). The circumsolar resonance ring near the Earth orbit was detected in the zodiacal cloud through observations of infrared space telescopes. So far, there is no observational evidence other than Earth because of the detection difficulty from Earth bounded orbit. A Venus Climate Orbiter, AKATSUKI, will provide a unique opportunity to study the Venusian resonance ring. It equips a near-infrared camera for the observations of the zodiacal light during the cruising phase. Here we consider whether Venus gravity produces the circumsolar resonance ring around the orbit. We thus perform the dynamical simulation of micron-sized dust particles released outside the Earth orbit. We consider solar radiation pressure, solar gravity, and planetary perturbations. It is found that about 40 % of the dust particles passing through the Venus orbit are trapped by the gravity. Based on the simulation, we estimate the brightness of the Venusian resonance ring from AKATSUKI's locations.