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통합검색

통합검색

한국천문학회지

1968년 ~ 2019년까지 1,104 건한국천문학회지를 격월간 확인하실 수 있습니다.

  • The Korean Astronomical Society (The Korean Astronomical Society)
  • 계간 (Quarterly)
  • ISSN : 1225-4614 (ISSN : 1225-4614)
  • DB구축현황 : 1,104건 (DB Construction : 1,104 Articles)
안내사항
총 게시글 1,104 페이지 1/111
1
  • Gould, Andrew
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.4
  • pp.121-131
  • 2019
  • 원문 바로보기
I investigate the origin of arc degeneracies in satellite microlens parallax ${\pi}_E$ measurements with only late time data, e.g., t > $t_0+t_E$ as seen from the satellite. I show that these are due to partial overlap of a series of osculating, exactly circular, degeneracies in the ${\pi}_E$ plane, each from a single measurement. In events with somewhat earlier data, these long arcs break up into two arclets, or (with even earlier data) two points, because these earlier measurements give rise to intersecting rather than osculating circles. The two arclets (or points) then constitute one pair of degeneracies in the well-known four-fold degeneracy of space-based microlens parallax. Using this framework of intersecting circles, I show that next-generation microlens satellite experiments could yield good ${\pi}_E$ determinations with only about five measurements per event, i.e., about 30 observations per day to monitor 1500 events per year. This could plausibly be done with a small (hence cheap, in the spirit of Gould & Yee 2012) satellite telescope, e.g., 20 cm.
2
  • Castro Tirado, Miguel Angel
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.4
  • pp.99-108
  • 2019
  • 원문 바로보기
This work addresses the development of the astronomical observatory all through history, from an architectural point of view, as a building in relation to the observing instruments and their functioning as a heterogeneous work center. We focused on 32 observatories (in the period 1259-2007) and carefully analyzed the architectures. Considering the impact of the construction itself or its facilities on the results of the research (thermal or structural stability, poor weather protection, turbulence, etc.), there is little attention paid to theories or studies of the architectural or construction aspects of the observatories. Therefore, this work aims to present a theoretical-critical contribution that, at least, invites the reflection of those involved in the development of astronomical observatories in the future.
3
  • Magara, Tetsuya
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.4
  • pp.89-97
  • 2019
  • 원문 바로보기
We demonstrate the subsurface origin of the observed evolution of the solar active region 10930 (AR10930) associated with merging and breakup of magnetic polarity regions at the solar surface. We performed a magnetohydrodynamic simulation of an emerging magnetic flux tube whose field-line twist is asymmetrically distributed along its axis, which is a key to merging and fragmentation in this active region. While emerging into the surface, the flux tube is subjected to partial splitting of its weakly twisted portion, forming separate polarity regions at the solar surface. As emergence proceeds, these separate polarity regions start to merge and then break up, while in the corona sigmoidal structures form and a solar eruption occurs. We discuss what physical processes could be involved in the characteristic evolution of an active region magnetic field that leads to the formation of a sunspot surrounded by satellite polarity regions.
4
  • Li, Yongchun
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.2
  • pp.49-55
  • 2019
  • 원문 바로보기
The New Vacuum Solar Telescope (NVST) is the largest solar telescope in China. When using CCDs for imaging, equal-thickness fringes caused by thin-film interference can occur. Such fringes reduce the quality of NVST data but cannot be removed using standard flat fielding. In this paper, a correction method based on multi-scale decomposition and adaptive partitioning is proposed. The original image is decomposed into several sub-scales by multi-scale decomposition. The region containing fringes is found and divided by an adaptive partitioning method. The interference fringes are then filtered by a frequency-domain Gaussian filter on every partitioned image. Our analysis shows that this method can effectively remove the interference fringes from a solar image while preserving useful information.
5
  • Singha, Akram Chandrajit
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.1
  • pp.1-9
  • 2019
  • 원문 바로보기
We present the results of the spectral and temporal analysis of eight X-ray point sources in five nearby (distance ${\sim}10^{39}ergs\;s^{-1}$ except for one source (X-8) with $L_X 10^{40}ergs\;s^{-1}$ . Five of these maybe classified as Ultraluminous X-ray sources (ULXs) with powerlaw photon index within the range, ${\Gamma}{\sim}1.63-2.63$ while the inner disk temperature, kT ~ 0.68 - 1.93 keV, when fitted with the disk blackbody model. The black hole masses harboured by the X-ray point sources were estimated using the disk blackbody model to be in the stellar mass range, however, the black hole mass of one source (X-6) lies within the range $68.37M_{\odot}{\leq}M_{BH}{\leq}176.32M_{\odot}$ , which at the upper limit comes under the Intermediate mass black hole range. But if the emission is considered to be beamed by a factor ~ 5, the black hole mass reduces to ${\sim}75M_{\odot}$ . The timing analysis of these sources does not show the presence of any short term variations in the kiloseconds timescales.
6
  • Zhao, Zhen
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.5
  • pp.207-216
  • 2019
  • 원문 바로보기
In this paper we introduce a software package, the Very long baseline interferometry Network SIMulator (VNSIM), which provides an integrated platform assisting radio astronomers to design Very Long Baseline Interferometry (VLBI) experiments and evaluate the network performance, with a user-friendly interface. Though VNSIM is primarily motivated by the East Asia VLBI Network, it can also be used for other VLBI networks and generic interferometers. The software package not only integrates the functionality of plotting (u, v) coverage, scheduling the observation, and displaying the dirty and CLEAN images, but also adds new features including sensitivity calculations for a given VLBI network. VNSIM provides flexible interactions on both command line and graphical user interface and offers friendly support for log reports and database management. Multi-processing acceleration is also supported, enabling users to handle large survey data. To facilitate future developments and updates, all simulation functions are encapsulated in separate Python modules, allowing independent invoking and testing. In order to verify the performance of VNSIM, we performed simulations and compared the results with other simulation tools, showing good agreement.
7
  • Minh, Young Chol
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.3
  • pp.83-88
  • 2019
  • 원문 바로보기
Using ALMA observations of the $^{13}CN$ and DCN lines in the massive star-forming region G33.92+0.11A, we investigate the CN/HCN abundance ratio, which serves as a tracer of photodissociation chemistry, over the whole observed region. Even considering the uncertainties in calculating the abundance ratio, we find high ratios ( ${\gg}1$ ) in large parts of the source, especially in the outer regions of star-forming clumps A1, A2, and A5. Regions with high CN/HCN ratios coincide with the inflows of accreted gas suggested by Liu et al. (2015). We conclude that we found strong evidence for interaction between the dense gas clumps and the accreted ambient gas which may have sequentially triggered the star formation in these clumps.
8
  • Zhao, Guang-Yao
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.1
  • pp.23-30
  • 2019
  • 원문 바로보기
The KVN(Korean VLBI Network)-style simultaneous multi-frequency receiving mode is demonstrated to be promising for mm-VLBI observations. Recently, other Very long baseline interferometry (VLBI) facilities all over the globe start to implement compatible optics systems. Simultaneous dual/multi-frequency VLBI observations at mm wavelengths with international baselines are thus possible. In this paper, we present the results from the first successful simultaneous 22/43 GHz dual-frequency observation with KaVA(KVN and VERA array), including images and astrometric results. Our analysis shows that the newly implemented simultaneous receiving system has brought a significant extension of the coherence time of the 43 GHz visibility phases along the international baselines. The astrometric results obtained with KaVA are consistent with those obtained with the independent analysis of the KVN data. Our results thus confirm the good performance of the simultaneous receiving systems for the nonKVN stations. Future simultaneous observations with more global stations bring even higher sensitivity and micro-arcsecond level astrometric measurements of the targets.
9
  • Yeom, Bum-Suk
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.3
  • pp.57-69
  • 2019
  • 원문 바로보기
We present an analysis of the chemical abundances and kinematics of six low-mass dwarf stars, previously claimed to be candidate hypervelocity stars (HVSs). We obtained moderate-resolution (R ~ 6000) spectra of these stars to estimate the abundances of several chemical elements (Mg, Si, Ca, Ti, Cr, Fe, and Ni), and derived their space velocities and orbital parameters using proper motions from the Gaia Data Release 2. All six stars are shown to be bound to the Milky Way, and in fact are not even considered high-velocity stars with respect to the Galactic rest frame. Nevertheless, we attempt to characterize their parent Galactic stellar components by simultaneously comparing their element abundance patterns and orbital parameters with those expected from various Galactic stellar components. We find that two of our program stars are typical disk stars. For four stars, even though their kinematic probabilistic membership assignment suggests membership in the Galactic disk, based on their distinct orbital properties and chemical characteristics, we cannot rule out exotic origins as follows. Two stars may be runaway stars from the Galactic disk. One star has possibly been accreted from a disrupted dwarf galaxy or dynamically heated from a birthplace in the Galactic bulge. The last object may be either a runaway disk star or has been dynamically heated. Spectroscopic follow-up observations with higher resolution for these curious objects will provide a better understanding of their origin.
10
  • Lim, Daye
  • Journal of the Korean astronomical society = 천문학회지
  • 52, n.4
  • pp.133-144
  • 2019
  • 원문 바로보기
We develop forecast models of daily probabilities of major flares (M- and X-class) based on empirical relationships between photospheric magnetic parameters and daily flaring rates from May 2010 to April 2018. In this study, we consider ten magnetic parameters characterizing size, distribution, and non-potentiality of vector magnetic fields from Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) and Geostationary Operational Environmental Satellites (GOES) X-ray flare data. The magnetic parameters are classified into three types: the total unsigned parameters, the total signed parameters, and the mean parameters. We divide the data into two sets chronologically: 70% for training and 30% for testing. The empirical relationships between the parameters and flaring rates are used to predict flare occurrence probabilities for a given magnetic parameter value. Major results of this study are as follows. First, major flare occurrence rates are well correlated with ten parameters having correlation coefficients above 0.85. Second, logarithmic values of flaring rates are well approximated by linear equations. Third, using total unsigned and signed parameters achieved better performance for predicting flares than the mean parameters in terms of verification measures of probabilistic and converted binary forecasts. We conclude that the total quantity of non-potentiality of magnetic fields is crucial for flare forecasting among the magnetic parameters considered in this study. When this model is applied for operational use, it can be used using the data of 21:00 TAI with a slight underestimation of 2-6.3%.