• 천문학회보
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• 제41권2호
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• pp.42.1-42.1
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• 2016

The formation process and the dynamical properties of a large-scale quasi-circular flare ribbon were investigated using the SDO AIA and HMI data along with data from RHESSI and SOT. Within one hour time interval, two subsequent M-class flares were detected from the NOAA 12371 that had a ${\beta}{\gamma}{\delta}$ configuration with one bipolar sunspot group in the east and one unipolar spot in the west embedded in a decayed magnetic field. Earlier M2.0 flare was associated with a coronal loop eruption, and a two-ribbon structure formed within the bipolar sunspot group. On the other hand, the later M2.6 flare was associated with a halo CME, and a quasi-circular ribbon developed encircling the full active region. The observed quasi-circular ribbon was strikingly large in size spanning 650" in north-south and 500" in east-west direction. It showed the well-known sequential brightening in the clockwise direction during the decay phase of the M2.6 flare at the estimated speed of 160.7 km s-1. The quasi-circular ribbon also showed the radial expansion, especially in the southern part. Interestingly, at the time of the later M2.6 flare, the third flare ribbon parallel to the early two-ribbon structure also developed near the unipolar sunspot, then showed a typical separation in pair with the eastern most ribbon of the early two ribbons. The potential field reconstruction based on the PFSS model showed a fan shaped magnetic configuration including fan-like field lines stemming from the unipolar spot and fanning out toward the background decayed field. This large-scale fan-like field overarched full active region, and the footpoints of fan-like field lines were co-spatial with the observed quasi-circular ribbon. From the NLFF magnetic field reconstruction, we confirmed the existence of a twisted flux rope structure in the bipolar spot group before the first M2.0 flare. Hard X-ray emission signatures were detected at the site of twisted flux rope during the pre-flare phase of the M2.0 flare. Based on the analysis of both two-ribbon structure and quasi-circular ribbon, we suggest that a tether-cutting reconnection between sheared arcade overarching the twisted flux rope embedded in a fan-like magnetic field may have triggered the first M2.0 flare, then secondary M2.6 flare was introduced by the fan-spine reconnection because of the interaction between the expanding field and the nearby quasi-null and formed the observed large-scale quasi-circular flare ribbon.

• 천문학회보
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• 제41권2호
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• pp.44.1-44.1
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• 2016

The Sagittarius-Carina spiral arm in the Galaxy contains several massive young open clusters. We present a deep optical photometric study on the massive young open clusters in the Sagittarius-Carina arm, Westerlund 2 and the young open clusters in the ${\eta}$ Carina nebula. Westerlund 2 is a less studied starburst-type cluster in the Galaxy. An abnormal reddening law for the intracluster medium of the young starburst-type cluster Westerlund 2 is determined to be $R_{V,cl}=4.14{\pm}0.08$. The distance modulus is determined from zero-age main-sequence fitting to the reddening-corrected color-magnitude diagrams of the early-type members to be $V_0-M_V=13.9{\pm}0.14mag$. The pre-main sequence (PMS) members of Westerlund 2 are selected by identifying the optical counterparts of X-ray emission sources from the Chandra X-ray observation and mid-infrared emission sources from the Spitzer/IRAC (the Infrared Array Camera) observation. The initial mass function (IMF) shows a slightly flat slope of ${\Gamma}=-1.1{\pm}0.1$ down to $5M_{\odot}$. The age of Westerlund 2 is estimated to be. 1.5 Myr from the main-sequence turn-on luminosity and the age distribution of PMS stars. The ${\eta}$ Carina nebula is the best laboratory for the investigation of the Galactic massive stars and low-mass star formation under the influence of numerous massive stars. We have performed deep wide-field CCD photometry of stars in the ${\eta}$ Carina nebula to determine the reddening law, distance, and the IMF of the clusters in the nebula. We present VRI and $H{\alpha}$ photometry of 130,571 stars from the images obtained with the 4m telescope at Cerro Tololo Inter-American Observatory (CTIO). RV,cl in the η Carina nebula gradually decreases from the southern part (~4.5, around Trumpler 14 and Trumpler 16) to the northern part around Trumpler 15 (~3.5). Distance to the young open clusters in the ${\eta}$ Carina nebula is partly revised based on the zero-age main-sequence fitting to the reddening-corrected color-magnitude diagrams (CMDs) and the (semi-) reddening-independent CMDs. We select the PMS members and candidates by identifying the optical counterparts of X-ray sources from the Chandra Carina Complex Survey and mid-infrared excess emission stars from the Spitzer Vela-Carina survey. From the evolutionary stage of massive stars and PMS stars, we obtain that the northern young open cluster Trumpler 15 is distinctively older than the southern young open clusters, Trumpler 14 (${\leq}2.5 Myr$) and Trumpler 16 (2.5-3.5 Myr). The slopes of the IMF of Trumpler 14, Trumpler 15, and Trumpler 16 are determined to be $-1.2{\pm}0.1$, $-1.5{\pm}0.3$, and $-1.1{\pm}0.1$, respectively. Based on the RV,cl of several young open clusters determined in this work and the previous studies of our group, We suggest that higher RV,cl values are commonly found for very young open clusters with the age of < 4 Myr. We also confirm the correlation between the slope of the IMF and the surface mass density of massive stars.

• 천문학회보
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• 제41권2호
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• pp.33.1-33.1
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• 2016

We report detection of short-term flux variability in multi-epoch observations and intraday variability in polarized emission at millimeter-wavelength from S5 0716+714 using Korean VLBI Network (KVN) radio telescopes. Over the whole observation epochs, the source shows significant inter-month variations at K- and Q-band with modulation indices of 19% at K-band and 36% at Q-band. In each epoch, the source shows monotonic flux increase in Epoch 1 and 3, and monotonic flux decrease in Epoch 2 and 4. We found an inverted spectrum with mean spectral indices of -0.57 in Epoch 1 and -0.15 in Epoch. On the contrary, we found relatively steep indices of 0.24 and 0.17 in Epoch 2 and Epoch 4, respectively. In the study of intraday variability of polarization, we found significant variations in the degree of linear polarization at 86 GHz, and in polarization angle at 43 and 86 GHz during ~10 h. The spectrum of the source is quite flat with spectral indices of -0.07 to 0.07 at 22-43 GHz and -0.23 to 0.04 at 43-86 GHz. The measured degree of the linear polarization ranges from 2.3% to 3.3 % at 22 GHz, from 0.9% to 2.2 % at 43 GHz and from 0.4 % to 4.0 % at 86 GHz, yielding prominent variations at 86 GHz over 4-5 h. The linear polarization angle is in the range of 4 to $12^{\circ}$ at 22 GHz, -39 to $81^{\circ}$ at 43 GHz, and 66 to 119 at 86 GHz with a maximum rotation of $110^{\circ}$ at 43 GHz over ~4 h. We estimated the Faraday rotation measures (RM) ranging from -9200 to 6300 rad m-2 between 22 and 43 GHz, and from -71000 to 7300 rad m-2 between 43 and 86 GHz, respectively. The frequency dependency of RM was investigated, yielding a mean power-law index, a, of 2.0. This implies that the polarized emission from S5 0716+714 at 22-86 GHz moves through a Faraday screen in or near the jet of the source.

• 천문학회지
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• 제51권3호
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• pp.49-63
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• 2018

We carry out a study of Sub-Millimeter Galaxies (SMGs) in the AKARI NEP-Deep field using the James Clerk Maxwell Telescope (JCMT) SCUBA-2 $850{\mu}m$ source catalog, released as part of the SCUBA-2 Cosmology Legacy Survey (S2CLS) program. The SCUBA-2 $850{\mu}m$ map has a root mean square (rms) noise of $1.2mJy\;beam^{-1}$ and covers an area of $0.60degree^2$. We find four SMGs which have counterparts to Herschel sources with spectroscopic redshifts in the literature. In addition, three dust obscured galaxies (DOGs) detected in Herschel bands are selected as a comparison sample. We derive IR luminosities of SMGs using the CIGALE code, which are similar to those of high redshift SMGs from previous studies. The contribution of AGN to the total IR luminosity in SMGs (2%-11%) is smaller than the lower limit for the one in DOGs (19%-35%), which is consistent with the expectation from the evolutionary scenario of massive galaxies. We search for SMGs in overdense regions as protocluster candidates and investigate four regions, including candidates around three DOGs. Finally, we argue that follow-up spectroscopic observation for the NEP-Deep field will provide crucial information to understand the role of SMGs in the evolution of massive galaxies.

• 한국지구과학회지
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• 제31권3호
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• pp.267-275
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• 2010

본 연구의 목적은 9학년 학생의 공간능력 차이에 따른 지구자전 개념을 알아보는 것이다. 광역시 소재 9학년 학생 83명중 천체의 공간운동 개념 평가(김기정, 1997)에서 개념 획득 정도가 비슷하면서 공간능력에 차이가 있는 남학생 2명과 여학생 2명을 각각 표집하여 질적 분석의 대상으로 삼았다. 연구 결과, 공간능력이 높은 학생일수록 개념이 올바르고 개념들을 입체적 공간으로 재구성하여 이해하였다. 공간능력이 낮을수록 개념이 불완전하고 단편적인 개념들을 암기하고 있었다. 성별에 따라서는 공간능력이 높은 남학생은 개념들을 간단 명료하게 표현하였고, 낮은 학생은 자전에 대한 방향을 일주운동과 연관시켜 해석하지 못했다. 반면에 여학생은 공간능력이 높을 때 개념들을 구체적으로 표현하였으며, 낮을수록 개념들을 입체적으로 표현하지 못하였다. 따라서 공간능력이 높은 학생은 문제 상황을 제시하여 스스로 해결할 수 있도록 하고, 낮은 학생은 현상들을 직접 관찰하여 쉽게 이해 할 수 있도록 학습 자료를 개발하여야겠다. 여학생은 공간을 입체적으로 조작해 볼 수 있도록 하고 남학생은 사물을 여러 관점으로 생각해 볼 수 있도록 교수 전략 및 학습 자료 등을 개발 한다면 천문단원의 공간능력이 향상되고, 개념 획득이 잘 될 수 있을 것이라 기대한다.

• 한국지구과학회지
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• 제29권1호
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• pp.98-115
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• 2008

조선(朝鮮)시대 관상감(觀象監) 천문(天文), 지리(地理), 역수(曆數), 점산(占算), 측후(測候)등의 업무를 관장했던 왕립기관이었다. 그 왕립기관은 학문에 따라 천문학(天文學), 지리학(地理學), 그리고 명과학(命課學) 세 개의 부서로 이루어져 있었으며, 그 중 천문학 부서는 오늘날 지구과학의 학문 분야들과도 일맥상통하는 업무들을 수행했었다. 본 논문에서는 천문학 부서를 중심으로 관상감의 직제와 시험제도에 대한 연구를 수행하였다. 관상감은 조선시대 왕립기관들 중의 하나였기 때문에 직제, 기능, 그리고 과거시험(科擧試驗)에 관한 규정들은 그 시대에 발간된 법전들에 법으로 명시되어있다. 따라서 조선시대의 법전들, 관서지들, 그리고 실록(實錄)의 기록들에 대한 연구로부터, 먼저 우리는 관상감은 인원수의 규모면에서 기존에 알려져 있던 것 보다 더 큰 규모임을 알았다. 왜냐하면 관상감 인원의 추정에 대한 선행 연구들에 있어서는 서리(胥吏), 관노비, 장인(匠人)등과 같은 하급계층들은 무시되었기 때문이다. 또한 우리는 관상감 관원이 되기 위한 과거시험에 사용된 천문학 교재에 대한 연구도 수행하였다. 내용에 있어서의 부족함에도 불구하고, 이러한 시도는 과거시험에 사용된 천문학 교재들에 대한 체계적인 첫 번째 연구이다. 마지막으로, 관상감을 포함한 당시 예전(禮典)에 속했던 기관들의 과거시험에 적용되었던 몇 가지 시험 규정들에 대해서도 간략히 살펴보았다.

• 대한소아치과학회지
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• 제31권3호
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• pp.372-380
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• 2004

쇄골두개 이형성증은 골격과 치아 이상을 동반하는 선천성 질환으로서 다수의 조직과 장기에 직접적인 영향을 주는 중배엽성 기능장애이다. 쇄골두개 이형성증에서 일반적인 골격 결함은 두개 봉합과 천문의 지연 폐쇄, wormian bone, clavicle aplasia가 나타날 수 있다. 또한 장골, 지골, 척추, 골반 등의 전체 골격 뿐 아니라 근육, 중앙 신경계 등에 영향을 줄 수 있다. 구강내 특징으로 유치의 만기잔존, 다수의 과잉치, 미맹출된 영구치, 낭 형성 등이 나타난다. 그러나 쇄골두개 이형성증 환아의 경우 정신적 및 신체적으로 특별한 이상을 나타내지 않아 스스로 질환을 인식하지 못하는 경우가 많으며 이의 결과유치 탈락 후 영구치의 미맹출로 인하여 저작 및 심리적인 문제가 초래되는 경우가 많다. 따라서 쇄골두개 이형성증은 조기진단이 필요하며, 적절한 시기에 과잉치 제거 및 영구치 맹출을 유도하는 치료를 시행하여 저작기능의 회복 뿐 아니라 환자의 안모도 개선시킬 수 있어야 한다.

• 대한소아치과학회지
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• 제36권3호
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• pp.456-463
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• 2009

쇄골두개 이형성증(Cleidocranial Dysplasia)은 안면, 두개골, 쇄골의 비정상적인 성장을 보이는 증후군으로 상염색체 우성으로 유전되거나 유전적 요인 없이 돌연변이에 의해 야기된다. 쇄골두개 이형성증의 일반적 소견은 두개 봉합과 천문의 지연 폐쇄, 편측이나 양측성으로 쇄골의 형성 장애, 상대적으로 커진 이마에 의해 상악골이 함몰된 것처럼 보이는 안면 형태가 특징적이다. 구강내 소견으로는 유치의 만기 잔존, 그로 인한 영구치의 맹출 지연을 보이며 방사선 사진 상에서 매복된 다수의 과잉치가 존재한다. 쇄골두개 이형성증은 정신적 및 신체적으로 특별한 이상을 나타내지 않아 진단이 늦어지는 경우가 많아 영구치의 미맹출로 인하여 저작 및 심리적인 문제가 초래되는 경우가 많다. 따라서 조기 진단을 통해 적절한 시기에 유치 발치 및 과잉치 제거 후 교정적 처치로 영구치의 맹출을 유도하여 저작 기능의 회복뿐 아니라 환자의 안모도 개선시켜야 한다. 본 증례는 영구치 맹출 장애와 전치부 반대교합을 주소로 내원하여 쇄골두개 이형성증으로 진단받은 환아들의 구강내 증상과 치아 맹출 유도법을 통하여 치아를 맹출시킬 수 있었기에 보고하는 바이다.

• 천문학회지
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• 제29권spc1호
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• pp.429-432
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• 1996

An x-ray astronomy experiment consisting of three collimated proportional counters and an X-ray Sky Monitor (XSM) was flown aboard the Indian Satellite IRS-P3 launched on March 21, 1996 from SHAR range in India. The Satellite is in a circular orbit of 830 km altitude with an orbital inclination of $98^{\circ}$ and has three axis stabilized pointing capability. Each pointed-mode Proportional Counter (PPC) is a multilayer, multianode unit filled with P-10 gas ($90\%$ Ar + $10\%\;CH_4$) at 800 torr and having an aluminized mylar window of 25 micron thickness. The three PPCs are identical and have a field of view of $2^{\circ}{\times}2^{\circ}$ defined by silver coated aluminium honeycomb collimators. The total effective area of the three PPCs is about 1200 $cm^2$. The PPCs are sensitive in 2-20 keV band. The XSM consists of a pin-hole of 1 $cm^2$ area placed 16 cm above the anode plane of a 32 cm$\times$32 cm position sensitive proportional counter sensitive in 3-8 keV interval. The position of the x-ray events is determined by charge division technique using nichrome wires as anodes. The principal objective of this experiment is to carry out timing studies of x-ray pulsars, x-ray binaries and other rapidly varying x-ray sources. The XSM will be used to detect transient x-ray sources and monitor intensity of bright x-ray binaries. Observations of black-hole binary Cyg X-1 and few other binary sources were carried out in early May and July-August 1996 period. Details of the x-ray detector characteristics are presented and preliminary results from the observations are discussed.

• 천문학회지
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• 제49권1호
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• pp.25-35
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• 2016

Multiple color selection techniques are successful in identifying quasars from wide-field broadband imaging survey data. Among the quasars that have been discovered so far, however, there is a redshift gap at 5 ≲ z ≲ 5.7 due to the limitations of filter sets in previous studies. In this work, we present a new selection technique of high redshift quasars using a sequence of medium-band filters: nine filters with central wavelengths from 625 to 1025 nm and bandwidths of 50 nm. Photometry with these medium-bands traces the spectral energy distribution (SED) of a source, similar to spectroscopy with resolution R ~ 15. By conducting medium-band observations of high redshift quasars at 4.7 ≤ z ≤ 6.0 and brown dwarfs (the main contaminants in high redshift quasar selection) using the SED camera for QUasars in EArly uNiverse (SQUEAN) on the 2.1-m telescope at the McDonald Observatory, we show that these medium-band filters are superior to multi-color broad-band color section in separating high redshift quasars from brown dwarfs. In addition, we show that redshifts of high redshift quasars can be determined to an accuracy of Δz/(1 + z) = 0.002 - 0.026. The selection technique can be extended to z ~ 7, suggesting that the medium-band observation can be powerful in identifying quasars even at the re-ionization epoch.