• 천문학회지
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• 제38권2호
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• pp.319-324
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• 2005

To date, more than 150 exo-solar planets have been observed by various methods such as spectroscopic, photometric, astrometric, gravitational lensing, pulsar timing methods. However, all these are indirect methods; they do not directly image the planets. Only free-floating planets or their 'ana-log' have been directly detected so far. Thus the next milestone is the direct imaging of any kinds of planetary mass objects orbiting around normal (young) stars, which might have been associated with protoplanetary disks, the sites of planet formation. I will describe some SUBARU efforts to detect self-luminous young giant planets as companions as well as direct imaging of the protoplanetary disks of ${\~}$100 AU size. The results of near-infrared coronagraphic imaging with adaptive optics are briefly presented on AB Aur, HD 142527, T Tau, and DH Tau. Our results demonstrate the importance of high-resolution (${\~}$0.1 arcsec) direct imaging over indirect observations such as modeling based on spectral energy distributions. The SUBARU observations are a prelude to ALMA from the morphological point of view.

• 천문학회보
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• 제40권2호
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• pp.38.1-38.1
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• 2015

Supernova remnants (SNRs) are one of the most energetic astrophysical events and are thought to be the dominant source of Galactic cosmic rays (CRs). A recent report on observations of gamma rays from the vicinity of SNRs have shown strong evidence that Galactic CR protons are accelerated by the shock waves of the SNRs. The actual gamma-ray emission from pion decay should depend on the diffusion of CRs in the interstellar medium. In order to quantitatively analyze the diffusion of high-energy CRs from acceleration sites, we have performed test particle numerical simulations of CR protons using a three-dimensional magnetohydrodynamics (MHD) simulation of an interstellar medium swept-up by a blast wave. We analyse the CRs diffusion at a length scale of order a few pc, and show the Richtmeyer-Meshkov instability can provide enough turbulence downstream of the shock to make the diffusion coefficient close to the Bohm level for energy larger than 30 TeV for a realistic interstellar medium.

• 천문학논총
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• 제13권1호
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• pp.209-223
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• 1998

We have investigated future large telescopes, which should represent the next generation of Korean optical and infrared telescopes. We first studied the history of the development of large telescopes in the USA, European countries, and Japan. Based on these studies, we came up suitable Korean large telescopes, which fit the current status of Korea in terms of financial situation, required technology, sciences, and manpower. We presented the potential impacts of developing large telescopes on the relevant Korean industry and Korean astronomical society. We also discussed a possibility to install large Korean telescopes at foreign sites utilizing highly competitive seeings and twice available observing dates there.

• 천문학논총
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• 제30권2호
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• pp.611-616
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• 2015

The Antarctic high plateau offers exceptional conditions for infrared and terahertz astronomy, as well as for programs requiring long, uninterrupted periods for measurements made with high cadence and photometric precision (i.e. time domain astronomy). In this review we summarise the special conditions of the Antarctic plateau which facilitate these observing regimes. We also outline some high profile science programs in each that could be conducted most effectively from the Antarctic high plateau, involving the first light in the Universe, the life cycle of our Galaxy, and the equation of state for the Universe. Three high plateau sites are under particular consideration for furthering such scientific programs{Dome A, Dome F and Ridge A. We summarise the activity underway at each site, which includes the building of new stations and the construction of facilities for optical, infrared and terahertz astronomy, as well as the plans for their future development.

• 천문학회지
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• 제33권1호
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• pp.47-55
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• 2000

Nonpotential characteristics of magnetic fields in AR 5747 are examined using Mees Solar Observatory magnetograms taken on Oct. 20, 1989 to Oct. 22, 1989. The active region showed such violent flaring activities during the observational span that strong X-ray flares took place including a 2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet 6301.5 and 6302.5. A nonlinear least square method was adopted to derive the magnetic field vectors from the observed Stokes profiles and a multi-step ambiguity solution method was employed to resolve the $180^{\circ}$ ambiguity. From the ambiguity-resolved vector magnetograms, we have derived a set of physical quantities characterizing the field configuration, which are magnetic flux, vertical current density, magnetic shear angle, angular shear, magnetic free energy density, a measure of magnetic field discontinuity MAD and linear force-free coefficient. Our results show that (1) magnetic nonpotentiality is concentrated near the inversion line in the flaring sites, (2) all the physical parameters decreased with time, which may imply that the active region was in a relaxation stage of its evolution, (3) 2-D MAD has similar patterns with other nonpotential parameters, demonstrating that it can be utilized as an useful parameter of flare producing active region, and (4) the linear force-free coefficient could be a evolutionary indicator with a merit as a global nonpotential parameter.

• 천문학회지
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• 제53권6호
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• pp.125-138
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• 2020

We determine the observing sites for eclipses of large magnitude recorded in ancient Chinese chronicles from 200 BCE to 900 CE, by adopting the difference between terrestrial time and universal time, ΔT, given by Morrison & Stephenson (2004). The records of solar eclipses with large magnitude are divided into four groups in accordance with the historical variations of the capital cities of ancient Chinese dynasties. We determine areas in which all the eclipses in each group, with an eclipse magnitude larger than a certain threshold value, could be observed. We find that these areas coincide with the historical capitals, which agrees with the general idea that the solar eclipses were observed at the capital of each dynasty. This result also verifies the ΔT values during the period from 100 BCE to 400 CE, during which historical records of eclipses are so rare that the ΔT values can only be obtained by interpolating the long-term data. Moreover, we show that the eclipses described by the term Ji in East-Asian history are not all total eclipses; their mean magnitude is 0.96 ± 0.04. We find that complementary expressions, such as dark daytime and appearance of stars during the eclipse, strengthen the possibility that eclipses described by the term Ji were total. We also provide quantitative definitions for expressions such as 'being not complete and like a hook', 'being almost complete', 'visibility of stars during the eclipse', and 'darkness during an eclipse.' The literal meanings of these expressions are in agreement with the recent physical modeling of sky brightness during total eclipses provided by Können & Hinz (2008).

• 천문학회보
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• 제40권1호
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• pp.63.3-64
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• 2015

In our previous work (Kim et al., 2015), we suggested a new classification scheme, which categorizes the SPEs into four groups based on association with flare or CME inferred from onset timings as well as proton acceleration patterns using multienergy observations. In this study, we have tried to find whether there are any typical characteristics of associated events and acceleration sites in each group using 42 SPEs from 1997 to 2012. We find: (i) if the proton acceleration starts from a lower energy, a SPE has a higher chance to be a strong event (>5000pfu) even if the associated flare and CME are not so strong. The only difference between the SPEs associated with flare and CME is the location of the acceleration site. For the former, the sites are very low (~1Rs) and close to the western limb, while the latter has a relatively higher and wider acceleration sites. (ii) When the proton acceleration starts from the higher energy, a SPE tends to be a relatively weak event (<1000pfu), in spite of its associated CME is relatively stronger than previous group. (iii) The SPEs categorized by the simultaneous proton acceleration in whole energy range within 10 minutes, tend to show the weakest proton flux in spite of strong related eruptions. Their acceleration heights are very close to the locations of type II radio bursts. Based on those results, we suggest that the different characteristics of the four groups are mainly due to the different mechanisms governing the acceleration pattern and interval, and different condition such as the acceleration location.

• 천문학회보
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• 제42권1호
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• pp.33.1-33.1
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• 2017

Molecular clouds are the sites of stellar birth, and conditions within the clouds control the mode and tempo of star formation. In particular, turbulence largely determines the density and velocity fields, and can affect the gas kinetic temperature as it decays via shocks. However, despite its central role in star formation and many years of study, the properties of turbulence remain poorly understood. As a part of the TRAO key science program, "Mapping turbulent properties of star-forming molecular clouds down to the sonic scale (PI: Jeong-Eun Lee)", we mapped the northern region of the Orion A molecular cloud and the L1688 region of the ${\rho}$ Ophiuchus molecular cloud in 2 sets of lines (13CO 1-0/C18O 1-0 and HCN 1-0/and HCO+ 1-0) using the Taeduk Radio Astronomy Observatory (TRAO) 14-m telescope. We analyze these maps using a python package 'Turbustat', a toolkit which contains 16 different turbulent statistics. We will present the preliminary results of our TRAO observations and various turbulence statistical analyses.

• 천문학회지
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• 제38권2호
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• pp.291-293
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• 2005

Using 13.7 m telescope of Qinghai station of NAO, PMO at Delin Ha, 43 IRAS sources were mapped with $^{13}CO\;J=1-0\;C^{18}O\;J=1-0$ and CO J=1-0. Each source has one or more cores. The distances of these cores range from 1 pc to several pc, and the masses from $10^2\;M_{\bigodot}$ to $10^5\;M_{\bigodot}$. High velocity outflows were detected. The mass, momentum and energy of these massive cores are larger than those of the low mass ones. With radio, IRAS, MSX data, stellar source distribution were investigated, and sourceless cores that deviate from infrared sources were identified. They are potential high mass star formation sites.

• 천문학논총
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• 제10권1호
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• pp.1-14
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• 1995

We observed impact spots on Jupiter which were formed by the collision with fragments of Shoemaker-Levy 9 comet during the period from 17 July to 13 August, by using the SNU 61cm reflector combined with CCD camera and DBVRI filters. In order to get more clear image of impact spots, the observed data were processed by the unsharp masking method, high-pass filtering method and Richardson-Lucy algorithm after the basic processing through IRAF package. The sizes of impact spots range from 2000km to 1000km, and from this size, the original size of comet fragments before collision with Jupiter is estimated to be less than ${\sim}3km$. From the observed rotating rate of impact spots, the rotational period of Jupiter is determined as $9^h$ $56^m$ $32^s$ at the southern latitude of $47^{\circ}{\sim}49^{\circ}$.