• 천문학회보
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• 제36권2호
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• pp.113.2-113.2
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• 2011

We observed a low-mass pre-main sequence star, HBC722 (also known as $LkH{\alpha}$ 188 G4), with Camera for QUasars in EArly uNiverse (CQUEAN) attached to 2.1 Otto Struve telescope at McDonald Observatory, USA. HBC722 is a new FU orionis-type object in the direction of NGC7000/IC5070, which produced large amplitude optical outbursts (${\delta}V$=4.7 mag over one year) for a few months and reached the peak in 2010 September. We carried out the photometric observation in SDSS r,i, and z band in 2011 April, July and August to monitor the long term decrease of its brightness. We also made continuous observation in r-band for half night in July, and whole two nights in August to investigate short term variability which could be related to the rotation of the central star or the inner circumstellar disk. In this poster, we present a preliminary result of the photometric observation for HBC722.

• 천문학회보
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• 제36권2호
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• pp.125.2-125.2
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• 2011

We are developing medium resolution cross-dispersed silicon grisms in the near IR region ($1.45{\sim}5.2{\mu}m$). The grisms will be installed in MIMIR, a multifunction instrument at the Lowel Observatory, USA. The two devices are designed to cover H and K band and L and M band simultaneously. Our goal is to make grism with R=3000 at 1.2 arcsec slit. The Silicon has high refractive index (n=3.4 at $1.5{\mu}m$) which enhances the resolving power by up to 5 times when compared to conventional material such as BK-7 (n=1.5 at 1.5 ${\mu}m$). The bonded grisms will be installed in a filter wheel for the uses switch from spectroscopic mode to imaging mode easily. Our device is compact and light weighted while it provides a decent resolving power. We produce monolithic grisms using e-beam lithography at the NASA JPL and chemically etching the grooves on the silicon prisms. Moreover, the main-disperser and cross-disperser will be contacted together by direct Si-Si bonding technique and eventually turn into one piece. The bonded pair offers more stability in terms of the layout of the spectrum and removes the Fresnel loss at the intersection of two grisms. We report on the proper wafer bonding steps through this research, and inspected the bonding quality thermally, optically and mechanically.

• 천문학회지
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• 제49권5호
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• pp.175-192
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• 2016

CCD photometric observations of the globular cluster (GC), M53 (NGC 5024), are performed using the 1.8 m telescope at the Bohyunsan Optical Astronomy Observatory in Korea on the same nights (2002 April and 2003 May) as the observations of the GC M92 (NGC 6341) reported by Cho and Lee using the same instrumental setup. The data for M53 is reduced using the same method as used for M92 by Cho and Lee, including preprocessing, point-spread function fitting photometry, and standardization etc. Therefore, M53 and M92 are on the same photometric system defined by Landolt, and the photometry of M53 and M92 is tied together as closely as possible. After complete photometric reduction, the V versus B − V , V versus V − I, and V versus B − I color-magnitude diagrams (CMDs) of M53 are produced to derive the relative ages of M53 and M92 and derive the various characteristics of its CMDs in future analysis. From the present analysis, the relative ages of M53 and M92 are derived using the Δ(B − V ) method reported by VandenBerg et al. The relative age of M53 is found to be 1.6 ± 0.85 Gyr younger than that of M92 if the absolute age of M92 is taken to be 14 Gyr. This relative age difference between M53 and M92 causes slight differences in the horizontal-branch morphology of these two GCs.

• 천문학회지
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• 제50권4호
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• pp.125-129
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• 2017

We investigate the solar cycle variation of microwave and extreme ultraviolet (EUV) intensity in latitude to compare microwave polar brightening (MPB) with the EUV polar coronal hole (CH). For this study, we used the full-sun images observed in 17 GHz of the Nobeyama Radioheliograph from 1992 July to 2016 November and in two EUV channels of the Atmospheric Imaging Assembly (AIA) $193{\AA}$ and $171{\AA}$ on the Solar Dynamics Observatory (SDO) from 2011 January to 2016 November. As a result, we found that the polar intensity in EUV is anti-correlated with the polar intensity in microwave. Since the depression of EUV intensity in the pole is mostly owing to the CH appearance and continuation there, the anti-correlation in the intensity implies the intimate association between the polar CH and the MPB. Considering the report of Gopalswamy et al. (1999) that the enhanced microwave brightness in the CH is seen above the enhanced photospheric magnetic field, we suggest that the pole area during the solar minimum has a stronger magnetic field than the quiet sun level and such a strong field in the pole results in the formation of the polar CH. The emission mechanism of the MPB and the physical link with the polar CH are not still fully understood. It is necessary to investigate the MPB using high resolution microwave imaging data, which can be obtained by the high performance large-array radio observatories such as the ALMA project.

• 천문학논총
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• 제29권3호
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• pp.53-58
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• 2014

We improved the antenna efficiency of the Taeduk Radio Astronomy Observatory (TRAO) 13.7-m radio telescope by adjusting the antenna panels based on digital photogrammetric measurements. First of all, we measured the surface accuracy of the main reflector of this antenna at three elevation angles of $35^{\circ}$, $45^{\circ}$, and $60^{\circ}$. We performed a total of four sets of the photogrammetric measurements and panel adjustments. When adjusting the panels, we positioned the antenna to the zenith and applied the measured data sets at the elevation of $45^{\circ}$. We found that the antenna surface accuracy has been improved by a factor of ~ 3 times after the final adjustment in comparison with the value before the adjustments. And we also found that the antenna surface accuracy tended to be slightly better at the elevation angles of $35^{\circ}$ and $60^{\circ}$ than that at the elevation angle of $45^{\circ}$. After the final panel adjustment, the aperture and beam efficiencies of the telescope have has been improved from 35% to 44%, and from 41% to 51%, respectively.

• 천문학회지
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• 제41권2호
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• pp.39-47
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• 2008

Spectral line profiles of filaments/prominences to be observed by the Fast Imaging Solar Spectrograph (FISS) are studied. The main spectral lines of interests are $H{\alpha}$, Ca II 8542, and Ca II K. FISS has a high spectral resolving power of $2{\times}10^5$, and supports simultaneous dual-band recording. This instrument will be installed at the 1.6m New Solar Telescope (NST) of Big Bear Solar Observatory, which has a high spatial resolution of 0.065" at 500nm. Adopting the cloud model of radiative transfer and using the model parameters inferred from pre-existing observations, we have simulated a set of spectral profiles of the lines that are emitted by a filament on the disk or a prominence at the limb. Taking into account the parameters of the instrument, we have estimated the photon count to be recorded by the CCD cameras, the signal-to-noise ratios, and so on. We have also found that FISS is suitable for the study of multi-velocity threads in filaments if the spectral profiles of Ca II lines are recorded together with $H{\alpha}$ lines.

• 천문학회보
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• 제38권1호
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• pp.52.1-52.1
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• 2013

We present preliminary results of the photometric variability analysis in SDSS r, i and z bands for a newly confirmed FU Orionis-type object, HBC 722. We observed HBC 722 from 2011 April to 2012 November, with Camera for Quasars in Early uNiverse (CQUEAN) attached to the 2.1m Otto Struve telescope at McDonald Observatory, USA. The rapid cadence monitoring observations (minute timescale) were conducted in chosen photometric nights during observation campaigns to get adequate number of samples for short term period analysis. As this object is in active state, temperature at the inner disk/stellar surface can be characterized by the colors between r, i and z bands. Also, It is theorized that a sudden cataclysmic accretion associated with FU Orionis-type outburst can give rise to detectable "hot spots" on the central star and rotational asymmetries in the disk instability region. Thus the periodic variabilities of three bands would trace the stellar rotation or Keplerian rotation at the instability region of the inner accretion disk. Additionally, the range of instabilities could be estimated on the assumption of a temperature distribution for the HBC 722 disk. This analysis can provide a clue for understanding enhanced disk accretion of Class II young stellar object.

• 천문학논총
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• 제28권1호
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• pp.7-13
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• 2013

We present a multi-dimensional reduction method of the surveyed cube database obtained using a single- dish radio telescope in Taeduk Radio Astronomy Observatory (TRAO). The multibeam receiver system installed at the 14 m telescope in TRAO was not optimized at the initial stage, though it became more stabilized in the following season. We conducted a Galactic Plane survey using the multibeam receiver system. We show that the noise level of the first part of the survey was higher than expected, and a special reduction process seemed to be definitely required. Along with a brief review of classical methods, a multi-dimensional method of reduction is introduced; It is found that the 'background' task within IRAF (Image Reduction and Analysis Facility) can be applied to all three directions of the cube database. Various statistics of reduction results is tested using several IRAF tasks. The rms value of raw survey data is 0.241 K, and after primitive baseline subtraction and elimination of bad channel sections, the rms value turned out to be 0.210 K. After the one-dimensional reduction using 'background' task, the rms value is estimated to be 0.176 K. The average rms of the final reduced image is 0.137 K. Thus, the image quality is found to be improved about 43% using the new reduction method.

• 천문학회보
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• 제38권1호
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• pp.63.2-63.2
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• 2013

We have investigated the EUV coronal jets observed by Solar Dynamic Observatory (SDO) / Atmospheric Imaging Assembly (AIA). From the Heliophysics Events Knowledgebase (HEK), we consider all recorded 40 EUV jets in $171{\AA}$ from May 2010 to July 2011 and use 19 jets whose location can be clearly identified, excluding limb events because of the ambiguity of their positions. According to the positions of their roots, these coronal jets are classified into two types: bright point jet (BPJ, 9 jets) and active region boundary jet (ABJ, 10 jets). BPJs are located at the top of bright points and ABJs at the boundaries of active regions. There are significant differences in speed and size between two types. Here the speed and size of a jet are assumed to be its maximum values in the case that the jet has several ejections. The average speed and size of 9 BPJs are about 110 km/s and 69,000km, respectively. The average speed and size of 10 ABJs are about 660 km/s and 194,000 km, respectively. The speed distribution of ABJs has two peaks at about 270 km/s and 1700 km/s. It is very interesting to note that three ABJs have very high speeds larger than 1600 km/s and they are all composed of a group of recurrent jets with low and high speed at the same location. In addition, we are investigating these events in other wavelengths and compare their characteristics.

• 천문학논총
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• 제32권3호
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• pp.381-405
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• 2017

We give a detailed description of the installation and operation of a double-station meteor detection system which formed part of a research & education project between Korea Astronomy Space Science Institute (KASI) and Daejeon Science Highschool. A similar system is currently not existing in South Korea. A total of six light-sensitive CCD cameras were installed with three cameras at SOAO and three cameras at BOAO observatory. A double-station observation of a meteor event enables the determination of the three-dimensional heliocentric orbit in space. This project was initiated in response to the Jinju fireball event in March 2014. The cameras were installed in October/November 2014. The two stations are identical in hardware as well as software. Each station employes sensitive "Watec-902H2" cameras in combination with relatively fast f/1.2 lenses. Various fields of views were used for measuring differences in detection rates of meteor events. We employed the SonotaCo UFO software suite for meteor detection and their subsequent analysis. The system setup as well as installation/operation experience is described and first results are presented. We also give a brief overview of historic as well as recent meteor (fall) detections in South Korea. For more information please consult http://meteor.kasi.re.kr.