간행물
천문학논총 KCI 등재 Publications of the Korean Astronomical Society
- 발행기관 한국천문학회
- 자료유형 학술지
- 간기 연3회
- ISSN 1225-1534 (Print)2287-6936 (Online)
- 수록기간 1984 ~ 2024
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
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권호리스트/논문검색
Volume 30 Issue 2 (2015년 9월) 186건
1.
2015.09
구독 인증기관 무료, 개인회원 유료
We overview and discuss the IAU today from the viewpoint of its regions based on historical and statis- tical data, and consider the status and future of astronomy in the Asian-Pacific region. New activities of the IAU, the Office of Astronomy for Development (OAD) and the Office for Astronomy Outreach (OAO) for the future evolution of astronomy are introduced. We also review the recent developments in astron- omy in the Asian-Pacific region, and emphasize the importance of regional cooperation and coordination for the future.
4,000원
2.
2015.09
구독 인증기관 무료, 개인회원 유료
Ground Level Enhancements (GLEs) in cosmic ray intensity observed during the period of 1997-2012 have been studied with energetic solar features and disturbances in solar wind plasma parameters and it is seen that all the GLEs have been found to be associated with coronal mass ejections, hard X-ray solar ares and solar radio bursts. All the GLEs have also been found to be associated with sudden jumps in solar proton ux of energy of ≥ 60 Mev. A positive correlation with correlation coefficient of 0.48 has been found between the maximum percentage intensity (Imax%) of Ground Level Enhancements and the peak value of solar proton ux of energy (≥ 60Mev). All the Ground Level Enhancements have been found to be associated with jumps in solar wind plasma velocity (JSWV) events. A positive correlation with correlation coefficient of 0.43 has been found between the maximum percentage intensity (Imax %) of Ground Level Enhancements and the peak value of solar wind plasma velocity of associated (JSWV) events. All the Ground Level Enhancements have been found to be associated with jumps in solar wind plasma pressure (JSWP) events. A positive correlation with correlation coefficient of 0.67 has been found between the maximum percentage intensity (Imax %) of Ground Level Enhancements and the peak value of solar wind plasma pressure of associated (JSWP) events and of 0.68 between the maximum percentage intensity (Imax %) of Ground Level Enhancements and the magnitude of the jump in solar wind plasma pressure of associated (JSWP) events.
4,000원
3.
2015.09
구독 인증기관 무료, 개인회원 유료
We study MHD wave propagation in a gravitationally stratified isothermal viscous atmosphere of the Sun, permeated by a uniform magentic field. We perform numerical simulations by launching a slow wave on the upper boundary. The driven slow wave propagates down from lowβ- to high-β plasma across the region where the plasma β is unity. It is found that mode conversion takes place at z ≈ -1.8 in the layer β ≈ 1. The amplitudes of horizontal and vertical velocites are smaller than those obtained in the absence of viscosity.
3,000원
4.
2015.09
구독 인증기관·개인회원 무료
In this study, we present geometrical and kinematical analysis of Moreton wave observed in 2012 June 3rd and July 6th, recorded in H-α images of Global Oscillation Network Group (GONG) archive. These large-scale waves exhibit different features compared to each other. The observed wave of June 3rd has angular span of about 70◦ with a diffuse wave front associated to NOAA active region 11496. It was found that the propagating speed of the wave at 17:53 UT is about 93180 km/s. The broadness nature of this Moreton wave can be interpreted as the vertical extension of the wave over the chromosphere. On the other hand, the wave of July 6th associated with X1.1 class are that occurred at 23:01 UT in AR NOAA11515. From the kinematical analysis, the wave propagated with the initial velocity of about 994 ± 70 km/s which is in agreement with the speed of coronal shock derived from type II radio burst, v ~ 1100 km/s. These two identified waves add the inventory of the large-scale waves observed in 24th Solar Cycle.
5.
2015.09
구독 인증기관·개인회원 무료
High resolution, multi-wavelength images from the Dutch Open Telescope were used to study the detailed mechanisms that might be involved in the multiple layer solar atmosphere observed in high cadence multi-wavelength observations. With the exceptional data observed for active region NOAA 10789 on 2005 July 13th, we study the changing pattern of the fibril using multi-wavelength tomography of the Hα line center and blue wing, Ca II H, and the G Band. It is believed that a long fibril that is rooted in the umbra, with longer apparent periodicity, may be due to morphological changes. To determine this, we conduct phase difference and coherency analysis between points along the fibril to understand how the wave propagates.
6.
2015.09
구독 인증기관 무료, 개인회원 유료
The brightness of Io's magnetic footprint, an indicator of electromagnetic interaction at the satellite, appears to be strongly connected to the satellite's distance from the plasma equator. As a result, the brightest footprints were detected when Io is near the interception location between the satellite's or- bital plane and the plasma equator. However, volcanic activities on Io show strong correlation with the equatorward shift of Jupiter's main auroral oval, consequently causing the disappearance of Io's footprint. The same conclusion was suggested via the observation of Jupiter's hectometric radio emission, called HOM, which closely corresponds to Jupiter's auroral activity. The plasma environment near the Jovian satellites was found to vary significantly at different observational epochs. The electron density increased by approximately a factor of three from the Voyager epoch (1979) to the Galileo epoch (1995), while the electron density was found to be significantly higher (~ 5 times) in the Cassini epoch (2001). In this current study, the magnetic footprints were clearly brighter ten years ago (from peak brightness in 1998 2001) than the footprints detected in 2007. For volcanic activities on Io in 2007, there are two clear activities in February and late May. The magnetic footprint appeared to be dimmer in March 2007, expected to be the result of volcano activities in Feb 2007. However, the magnetic footprint brightness in June appeared to be slightly brighter than the footprints observed in May. The reason could be the time delay between the brightening of the sodium nebula on approximately May 31st and, a while later, the enhancement of ux tube content peaking on approximately June 5th. On the other hand, Io's magnetic footprints were observed during June 1st - 10th when they may not yet have been affected by the increase in mass out ow due to the increase of plasma density.
3,000원
7.
2015.09
구독 인증기관 무료, 개인회원 유료
The surfaces of most atmosphereless solar system objects are referred to as regolith, layers of loosely connected fragmentary debris, produced by meteorite impacts. Measurements of light scattered from such surfaces provides information about the composition and structure of the surface. A suitable way to characterize the scattering properties is to consider how the intensity and polarization of scattered light depends on the particle size, composition, porosity, roughness, wavelength of incident light and the geometry of observation. In the present work, the effect of porosity on bidirectional re ectance as a function of phase angle is studied for alumina powder with grain size of 0.3 μm and olivine powder with grain size of 49 μm at 543.5 nm. The optical constants of the alumina sample for each porosity were calculated with Maxwell Garnett e ective medium theory. On using each of the optical constants of alumina sample in Mie theory with the Hapke model the variation of bidirectional re ectance is obtained as a function of phase angle with porosity as a parameter. Experimental re ectance data are in good agreement the model. For the olivine sample the effect of porosity is studied using Hapke (2008).
3,000원
8.
2015.09
구독 인증기관 무료, 개인회원 유료
In our previous work, we investigated the orbital dynamics of Asteroid 1934 CT (or 1989 AC or 4179 Toutatis) from epoch 2012-Jul-24 (JDE2456132.5) using the Mercury program package. Asteroid 4179 Toutatis has an Earth and Mars crossing orbit with semimajor axis a = 2.5292 AU and eccentricity e = 0.6294, and therefore the perihelion distance is q = 0.9373 AU and the aphelion distance is Q = 4.1211 AU. After more than 300,000 years, asteroid 4179 Toutatis will escape from the Solar System, but during this time, it will have close-encounters with other planets from Venus to Uranus. As a continuation of this project, we investigated its energy changes in each close encounter. We also determine the energy of this asteroid when it escapes from the Solar System. The result is that during its orbital evolution, the energy of this asteroid changes and gives us negative, zero and positive values.
3,000원
9.
2015.09
구독 인증기관 무료, 개인회원 유료
A growing body of evidence has been supporting the existence of so-called "dark molecular gas" (DMG), which is invisible in the most common tracer of molecular gas, i.e., CO rotational emission. DMG is be- lieved to be the main gas component of the intermediate extinction region from Av~0.05-2, roughly corresponding to the self-shielding threshold of H2 and 13CO. To quantify DMG relative to HI and CO, we are pursuing three observational techniques; HI self-absorption, OH absorption, and THz C+ emission. In this paper, we focus on preliminary results from a CO and OH absorption survey of DMG candidates. Our analysis shows that the OH excitation temperature is close to that of the Galactic continuum back- ground and that OH is a good DMG tracer co-existing with molecular hydrogen in regions without CO. Through systematic "absorption mapping" by the Square Kilometer Array (SKA) and ALMA, we will have unprecedented, comprehensive knowledge of the ISM components including DMG in terms of their temperature and density, which will impact our understanding of galaxy evolution and star formation profoundly.
3,000원
10.
2015.09
구독 인증기관 무료, 개인회원 유료
Tie Liu, Yuefang Wu, Diego Mardones, Kee-Tae Kim, Karl M. Menten, Ken Tatematsu, Maria Cunningham, Mika Juvela, Qizhou Zhang, Paul F Goldsmith, Sheng-Yuan Liu, Hua-Wei Zhang, Fanyi Meng, Di Li, Nadia Lo, Xin Guan, Jinghua Yuan, Arnaud Belloche, Christian Henkel, Friedrich Wyrowski, Guido Garay, Isabelle Ristorcelli, Jeong-Eun Lee, Ke Wang, Leonardo Bronfman, L. Viktor Toth, Scott Schnee, Shengli Qin, Shaila Akhter
The physical and chemical properties of prestellar cores, especially massive ones, are still far from being well understood due to the lack of a large sample. The low dust temperature (< 14 K) of Planck cold clumps makes them promising candidates for prestellar objects or for sources at the very initial stages of protostellar collapse. We have been conducting a series of observations toward Planck cold clumps (PCCs) with ground-based radio telescopes. In general, when compared with other star forming samples (e.g. infrared dark clouds), PCCs are more quiescent, suggesting that most of them may be in the earliest phase of star formation. However, some PCCs are associated with protostars and molecular out ows, indicating that not all PCCs are in a prestellar phase. We have identi ed hundreds of starless dense clumps from a mapping survey with the Purple Mountain Observatory (PMO) 13.7-m telescope. Follow-up observations suggest that these dense clumps are ideal targets to search for prestellar objects.
3,000원
11.
2015.09
구독 인증기관 무료, 개인회원 유료
We present observational results characterizing molecular out ows from very low-mass objects in ρ Ophiuchi and Taurus. Our results provide us with important implications that clarify the formation process of very low-mass objects.
3,000원
12.
2015.09
구독 인증기관·개인회원 무료
We present results of our R-band polarimetry of a bright-rimmed cloud, IC1396A (with BRC 36), associated with the H II region S131 and the cometary globule LDN 1616 to study their magnetic field geometry. The distances of these clouds have been reported to be ~ 750 pc and ~ 450 pc, respectively in the literature. The young open cluster Trumpler 37 in the vicinity of IC1396A and the high mass stars in the Orion belt near L1616 are found to be responsible for the structure of these clouds. We made polarimetry of foreground stars inferred from their distances measured by the Hipparcos satellite to subtract the foreground contribution to the observed polarization results. We discuss the optical polarimetric results and compare our findings with MHD simulations towards BRCs and CGs.
13.
2015.09
구독 인증기관 무료, 개인회원 유료
Observed spectra of stars around the Sun have indicated that the Sun is located in a gas cavity, extending to 100pc. This gas cavity is called the "Local Bubble". The density of the interstellar medium (ISM) in the local bubble is about one tenth that of the average for the ISM in the Milky Way. Furthermore, some structures such as gas planes and strings in the local bubble are probably the result of supernovae. These, due to their low temperatures, can not be observed in the visible and infrared. The only way to do so is to measure the spectra of nearby stars so that the light of stars passing through the local bubble is absorbed by existing gas and the resulting spectral lines from absorption can be measured. In this study, we use binary stars to trace the local bubble structures through lines such as the Na I Doublet. First, we determined the observed spectral lines of stars by HARPS and FEROS echelle spectrographs. Then, we made synthetic spectra with the ATLAS9 code. Finally, the difference between the observational and synthetic spectra confirms the existence of the Na I Doublet in the local ISM.
3,000원
14.
2015.09
구독 인증기관 무료, 개인회원 유료
How high-mass stars form is currently unclear. Calculations suggest that the radiation pressure of a forming star can halt spherical infall, preventing further growth when it reaches 10 M⊙. Two major theoretical models on the further growth of stellar mass have been proposed. One model suggests the merging of less massive stellar objects, and the other is through accretion, but with the help of a disk. In ow motions are key evidence for how forming stars gain further mass to build up massive stars. Recent developments in technology have boosted the search for in ow motion. A number of high-mass collapse candidates were obtained with single dish observations, and mostly showed blue pro les. Infalling signatures seem to be more common in regions which have developed radiation pressure than in younger cores, which is the opposite of the theoretical prediction and is also very different from observations of low mass star formation. Interferometer studies so far confirm this tendency with more obvious blue profiles or inverse P Cygni profiles. Results seem to favor the accretion model. However, the evolution of the infall motion in massive star forming cores needs to be further explored. Direct evidence for monolithic or competitive collapse processes is still lacking. ALMA will enable us to probe more detail of the gravitional processes.
4,000원
15.
2015.09
구독 인증기관 무료, 개인회원 유료
Massive stars are some of the most in uential objects in the Universe, shaping the evolution of galaxies, creating chemical elements and hence shaping the evolution of the Universe. However, the processes by which they form and how they shape their environment during their birth processes are not well understood. We use NH3 data from "The H2O Southern Galactic Plane Survey" (HOPS) survey to de ne the positions of dense cores/clumps of gas in the southern Galactic plane that are likely to form stars. Then, using data from "The Millimetre Astronomy Legacy Team 90 GHz" (MALT90) survey, we search for the presence of infall and out ow associated with these cores. We subsequently use the "3D Molecular Line Radiative Transfer Code" (MOLLIE) to constrain properties of the infall and outflow, such as velocity and mass flow. The aim of the project is to determine how common infall and outflow are in star forming cores, and therefore to provide valuable constraints on the timescales and physical process involved in massive star formation. Preliminary results are presented here.
3,000원
16.
2015.09
구독 인증기관 무료, 개인회원 유료
The 22 m diameter Mopra telescope in Australia is being used to undertake an improved survey of the CO J = 1-0 line at 3mm along the 4th quadrant of the Galaxy, achieving an order of magnitude better spatial and spectral resolution (i.e. 0.6 and 0.1 km/s) than the Dame et al. (2001) survey that is publically available for the Southern Galactic plane. Furthermore, the Mopra CO survey includes the four principal isotopologues of the CO molecule (i.e. 12CO, 13CO, C18O and C17O). The survey makes use of an 8 GHz-wide spectrometer and a fast mode of on-the- y mapping developed for the Mopra telescope, where the cycle time has been reduced to just 1=4 of a second. 38 square degrees of the Galaxy, from l = 306-344°, b = ±0:5° have currently been surveyed, together with additional 9 sq. deg. regions around the Carina complex and the Central Molecular Zone. We present new results from the survey (see also Burton et al., 2013, 2014). The Mopra CO data are being made publically available as they are published; for the latest release see the project website at www.phys.unsw.edu.au/mopraco.
3,000원
17.
2015.09
구독 인증기관·개인회원 무료
In this project, all available databases of molecular and gas-dust clouds in the Galaxy were cross- identified by taking into account available properties, including position, angular dimensions, velocity, density, temperature and mass. An initial list of about 7000 entries was condensed into a cross-identified all-sky catalogue containing molecular and gas-dust clouds. Some relationships were studied between the main physical features of clouds. Finally, we prepared a complex observing program and address future work for filling in the gaps.
18.
2015.09
구독 인증기관 무료, 개인회원 유료
We present [Fe ii] ⋋ 1.257 μm spectra toward the interacting binary UY Aur with 0:0014 angular resolution, obtained with the Near infrared Integral Field Spectrograph (NIFS) combined with the adaptive optics system Altair of the GEMINI observatory. In the [Fe ii] emission, UY Aur A (primary) is brighter than UY Aur B (secondary). The blueshifted and redshifted emission between the primary and secondary show a complicated structure. The radial velocities of the [Fe ii] emission features are similar for UY Aur A and B: ~ —100 km s-1 and ~ +130 km s-1 for the blueshifted and redshifted components, respectively. Considering the morphologies of the [Fe ii] emissions and bipolar out ow context, we concluded that UY Aur A drives fast and widely opening out ows with an opening angle of ~90° while UY Aur B has micro collimated jets.
3,000원
19.
2015.09
구독 인증기관·개인회원 무료
Recent high-resolution, high-sensitivity observations of protostellar jets have shown many to possess an underlying `wiggle' structure. HH 211 is one such example where recent sub-mm observations revealed a clear re ection-symmetric wiggle. An explanation for this is that the HH211 jet source is moving as part of a protobinary system. Here we test this assumption by simulating HH211 through 3D hydrodynamic simulations using the pluto code with a molecular chemistry and cooling module, and initial conditions based on an analytical model derived from SMA observations. Molecular chemistry allows us to accurately plot synthetic molecular emission maps and position-velocity diagrams for direct comparison to observa- tions, enabling us to test the observational assumptions and put constraints on the physical parameters of HH211. Our preliminary results show that the re ection-symmetric wiggle can be recreated through the assumption of a jet source being part of a binary system.
20.
2015.09
구독 인증기관 무료, 개인회원 유료
RADIO ASTROMETRIC OBSERVATIONS AND THE GALACTIC CONSTANT AS THE BASIS OF A GALACTIC KINEMATICS STUDY
We made phase-referencing Very Long Baseline Interferometry (VLBI) observations of Galactic 22 GHz H2O maser sources with VLBI Exploration of Radio Astrometry (VERA). We measured the parallax dis- tances of G48.61+0.02, G48.99-0.30, G49.19-0.34, ON1, IRAS 20056+3350, IRAS 20143+3634, ON2N, and IRAS 20126+4104, which are located near the tangent point and the Solar circle. The angular ve- locity of the Galactic rotation at the LSR (i.e. the ratio of the Galactic constants) is derived using the measured parallax distances and proper motions of these sources. The derived value of Ω0 = 28:8 1:7 km s-1 kpc-1 is consistent with recent values obtained using VLBI astrometry but 10% larger than the International Astronomical Union (IAU) recommended value of 25.9 km s-1 kpc-1 = (220 km s-1) / (8.5 kpc).
3,000원
