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Journal of the Korean astronomical society = 천문학회지 21건

  1. [국내논문]   CHEMICAL EVOLUTION IN VeLLOs   피인용횟수: 1

    Lee, Jeong-Eun (Department of Astronomy and Space Science, Sejong University)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 83 - 89 , 2007 , 1225-4614 ,

    초록

    A new type of object called "Very Low Luminosity Objects (VeLLOs)" has been discovered by the Spitzer Space Telescope. VeLLOs might be substellar objects forming by accretion. However, some VeLLOs are associated with strong outflows, indicating the previous existence of massive accretion. The thermal history, which significantly affects the chemistry, between substellar objects with a continuous low accretion rate and objects in a quiescent phase after massive accretion (outburst) must be greatly different. In this study, the chemical evolution has been calculated in an episodic accretion model to show that CO and $N_2H^+$ have a relation different from starless cores or Class 0/I objects. Furthermore, the $CO_2$ ice feature at $15.2{\mu}m$ will be a good tracer of the thermal process in VeLLOs.

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  2. [국내논문]   ALTERNATING DIRECTION IMPLICIT METHOD FOR TWO-DIMENSIONAL FOKKER-PLANCK EQUATION OF DENSE SPHERICAL STELLAR SYSTEMS   피인용횟수: 1

    Shin, Ji-Hye (Kyung Hee University, Dept. of Astronomy & Space Science ) , Kim, Sung-Soo (Kyung Hee University, Dept. of Astronomy & Space Science)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 91 - 97 , 2007 , 1225-4614 ,

    초록

    The Fokker-Planck (FP) model is one of the commonly used methods for studies of the dynamical evolution of dense spherical stellar systems such as globular clusters and galactic nuclei. The FP model is numerically stable in most cases, but we find that it encounters numerical difficulties rather often when the effects of tidal shocks are included in two-dimensional (energy and angular momentum space) version of the FP model or when the initial condition is extreme (e.g., a very large cluster mass and a small cluster radius). To avoid such a problem, we have developed a new integration scheme for a two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI) method given in the Douglas-Rachford split form. We find that our ADI method reduces the computing time by a factor of ${\sim}2$ compared to the fully implicit method, and resolves problems of numerical instability.

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  3. [국내논문]   PREDICTION OF DAILY MAXIMUM X-RAY FLUX USING MULTILINEAR REGRESSION AND AUTOREGRESSIVE TIME-SERIES METHODS  

    Lee, J.Y. (Department of Astronomy and Space Science, Kyung Hee University ) , Moon, Y.J. (Department of Astronomy and Space Science, Kyung Hee University ) , Kim, K.S. (Department of Astronomy and Space Science, Kyung Hee University ) , Park, Y.D. (Korea Astronomy and Space Science Institute ) , Fletcher, A.B. (Korea Astronomy and Space Science Institute)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 99 - 106 , 2007 , 1225-4614 ,

    초록

    Statistical analyses were performed to investigate the relative success and accuracy of daily maximum X-ray flux (MXF) predictions, using both multilinear regression and autoregressive time-series prediction methods. As input data for this work, we used 14 solar activity parameters recorded over the prior 2 year period (1989-1990) during the solar maximum of cycle 22. We applied the multilinear regression method to the following three groups: all 14 variables (G1), the 2 so-called 'cause' variables (sunspot complexity and sunspot group area) showing the highest correlations with MXF (G2), and the 2 'effect' variables (previous day MXF and the number of flares stronger than C4 class) showing the highest correlations with MXF (G3). For the advanced three days forecast, we applied the autoregressive timeseries method to the MXF data (GT). We compared the statistical results of these groups for 1991 data, using several statistical measures obtained from a $2{\times}2$ contingency table for forecasted versus observed events. As a result, we found that the statistical results of G1 and G3 are nearly the same each other and the 'effect' variables (G3) are more reliable predictors than the 'cause' variables. It is also found that while the statistical results of GT are a little worse than those of G1 for relatively weak flares, they are comparable to each other for strong flares. In general, all statistical measures show good predictions from all groups, provided that the flares are weaker than about M5 class; stronger flares rapidly become difficult to predict well, which is probably due to statistical inaccuracies arising from their rarity. Our statistical results of all flares except for the X-class flares were confirmed by Yates' $X^2$ statistical significance tests, at the 99% confidence level. Based on our model testing, we recommend a practical strategy for solar X-ray flare predictions.

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  4. [국내논문]   THE ORIGINAL ENVIRONMENT OF THE SOLAR SYSTEM INFERRED FROM THE OXYGEN ISOTOPE ANOMALIES  

    Lee, Jeong-Eun (Department of Astronomy and Space Science, Sejong University ) , Bergin, Edwin A. (Department of Astronomy, The University of Michigan ) , Lyons, James R. (Institute of Geophysics and Planetary Physics, Department of Earth and Space Sciences, University of California)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 107 - 111 , 2007 , 1225-4614 ,

    초록

    The original environment of the solar system can be inferred by studying the oxygen isotope ratios in the Sun as well as in primitive meteorites and comets. The oxygen isotopic fractionation measured in primitive meteorites is mass-independent, which can be explained by the isotopic-selective photodissociation of CO. The isotopic-selective photodissociation model in a collapsing cloud by Lee et al. (2007) imply the birth of the Sun in a stellar cluster with an enhanced radiation field, which is consistent with the inferred presence of $^{60}Fe$ .

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  5. [국내논문]   POLARIZATION OF FIR EMISSION FROM T TAURI DISKS  

    Cho, Jung-Yeon (Dept. of Astronomy & Space Science, Chungnam National Univ. ) , Lazarian, A. (Astronomy Dept., Univ. of Wisconsin)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 113 - 118 , 2007 , 1225-4614 ,

    초록

    Recently far infra-red (FIR) polarization of the $850{\mu}m$ continuum emission from T Tauri disks has been detected. The observed degree of polarization is around 3 %. Since thermal emission from dust grains dominates the spectral energy distribution at the FIR regime, dust grains might be the cause of the polarization. We explore alignment of dust grains by radiative torque in T Tauri disks and provide predictions for polarized emission for disks viewed at different wavelengths and viewing angles. In the presence of magnetic field, these aligned grains produce polarized emission in infrared wavelengths. When we take a Mathis-Rumpl-Nordsieck-type distribution with maximum grain size of $500-1000{\mu}m$ , the degree of polarization is around 2-3 % level at wavelengths larger than ${\sim}100{\mu}m$ . Our study indicates that multifrequency infrared polarimetric studies of protostellar disks can provide good insights into the details of their magnetic structure.

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  6. [국내논문]   DENSITY AND VELOCITY PROFILES IN COLLAPSING CLOUD L694-2  

    Seo, Y.M. (Department of Physics and Astronomy, SeouI National University ) , Hong, S.S. (Department of Physics and Astronomy, SeouI National University ) , Lee, S.H. (Department of Physics and Astronomy, SeouI National University ) , Park, Y.S. (Department of Physics and Astronomy, SeouI National University ) , Kim, Jong-Soo (Korea Astronomy and Space Science Institute)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 119 - 122 , 2007 , 1225-4614 ,

    초록

    From the HCN observations of dense molecular cloud L694-2, Lee et al.(2007) determined internal distributions of density and velocity for the cloud. The density profile collaborates roughly with the Bonnor- Ebert gas sphere, but the velocity field departs significantly from the result of numerical simulations that are started from the BE sphere. Taking L694-2 as an example of collapsing clouds, we have performed a series of collapse simulations and determined initial configurations for the cloud in such a way that the resulting density and velocity profiles both match with the empirically deduced ones. Among many trial configurations the cloud which is initially uniform in density and bound by an expanding envelop depicts most closely the empirically obtained profiles of both density and velocity.

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  7. [국내논문]   WATER MASERS FROM THE PROTOSTELLAR DISK AND OUTFLOW IN THE NGC 1333 IRAS 4 REGION  

    Park, Geum-Sook (International Center for Astrophysics, Korea Astronomy and Space Science Institute ) , Choi, Min-Ho (International Center for Astrophysics, Korea Astronomy and Space Science Institute)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 123 - 125 , 2007 , 1225-4614 ,

    초록

    NGC 1333 is a nearby star forming region, and IRAS 4A and IRAS 4BI are low-mass Class 0 protostars. IRAS 4A is a protobinary system. The NGC 1333 IRAS 4 region was observed in the 22 GHz water maser with a high resolution (0.08") using the Very Large Array. Two groups of masers were detected: one near A2 and the other near BI. Most of the masers associated with A2 are located very close (

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  8. [국내논문]   WATER VAPOR MASERS: A SIGNPOST FOR LOW MASS STAR FORMATION  

    Migenes, V. (University of Gunajuato, Department of Astronomy ) , Trinidad, M.A. (University of Gunajuato, Department of Astronomy ) , Valdettaro, R. (INAF - Osservatorio Astrofisico di Arcetri, Largo E. ) , Brand, J. (INAF - Istituto di Radioastronomia ) , Palla, F. (INAF - Osservatorio Astrofisico di Arcetri, Largo E.)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 127 - 129 , 2007 , 1225-4614 ,

    초록

    It is well known that water vapor maser emission at 22.2 GHz is associated with the earliest stages of both low- and high-mass star formation and it can be considered a reliable diagnostic of their evolutionary state. Bright Rimmed Clouds (BRCs) are clouds that have been compressed by an external ionization-shock front which focuses the neutral gas into compact globules. The boundary layer between the neutral gas and the gas ionized by the incident photons is often called "bright rim" but the clumps are sometimes classified also as speck globules or cometary globules depending on their appearance. Small globules with bright rims have been considered to be potential sites of star formation and have been studied in several individual regions. We present results from high resolution VLA observations searching for new candidates of recent star formation in bright-rimmed clouds/globules associated with IRAS point sources.

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  9. [국내논문]   THE STUDY OF SCATTERING IN THE ISM WITH HIGH RESOLUTION OBSERVATIONS OF OH MASERS  

    Migenes, Victor (University of Guanajuato, Department of Astronomy ) , Slysh, V.I. (Astro Space Center, Lebedev Physical Institute, Profsoyuznaya str. ) , Velasco, A.E.Ruis (University of Guanajuato, Department of Astronomy ) , Villalpando, S. (University of Guanajuato, Department of Astronomy)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 131 - 132 , 2007 , 1225-4614 ,

    초록

    The research of OH maser emission sources with high angular resolution is complicated by the effects of interstellar scattering: more over, most of the OH maser sources are located in the galactic plane where the scattering is largest. However, the data available from pulsar studies on the spatial distribution of the amount of scattering indicate that there is a strong non-uniformity in the distribution of the amount of scattering material. There are directions in the galactic plane where the scattering is an order of magnitude higher than the average, as well as directions where the scattering is much lower. The latter provide an opportunity to investigate OH masers with the full angular resolution offered by very long baseline interferometry instruments, like the VLBA, and measure their true angular size, shape and brightness temperature. We have observed approximately 100 OH maser sources, distributed all over the northern hemisphere, with the VLBA in order to study the scattering properties of the interstellar medium.

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  10. [국내논문]   THE 13CO OUTER GALAXY SURVEY OF TRAO USING MULTIBEAM ARRAY RECEIVER SYSTEM  

    Lee, Young-Ung (Korea Astronomy and Space Science Institute ) , Kim, B.G. (Korea Astronomy and Space Science Institute ) , Jung, J.H. (Korea Astronomy and Space Science Institute ) , Kim, H.G. (Korea Astronomy and Space Science Institute ) , Yim, I.S. (Korea Astronomy and Space Science Institute ) , Kim, K.D. (Korea Astronomy and Space Science Institute ) , Kang, H.W. (Korea Astronomy and Space Science Institute ) , Choi, J.H. (Korea Astronomy and Space Science Institute)
    Journal of the Korean astronomical society = 천문학회지 v.40 no.4 ,pp. 133 - 135 , 2007 , 1225-4614 ,

    초록

    A survey project of TRAO with the fifteen beam array receiver system is presented. A multibeam array receiver system has been purchased from FCRAO, and is being installed on TRAO 14m telescope. The target region of the survey is from ${\iota}=120^{\circ}{\sim}137^{\circ},\;b=-1^{\circ}{\sim}+ 1^{\circ}$ , and velocity resolution would be 1 km/sec after smoothing from the original resolution of $0.64km\;s^{-1}$ in the transition of J = 1-0 of $^{13}CO$ . The survey region is a part of the $^{12}CO$ Outer Galaxy Survey(OGS), and would be an extension of the Bell Laboratories $^{13}CO$ Galactic Plane Survey. By combining with the existing $^{12}CO$ database of the Outer Galaxy Survey, we will derive physical properties of identified molecular clouds and will conduct and statistical analysis of the Outer Galalxy molecular clouds. Reduction process and analysis methods will be introduced.

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