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1968년 ~ 2025년까지 1,227 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 34/123
331
- Kim, Ju-Han
- Journal of the Korean astronomical society = 천문학회지
- 44, n.6
- pp.217-234
- 2011
- 원문 바로보기
We present two large cosmological N-body simulations, called Horizon Run 2 (HR2) and Horizon Run 3 (HR3), made using <TEX>$6000^3$</TEX> = 216 billions and <TEX>$7210^3$</TEX> = 374 billion particles, spanning a volume of <TEX>$(7.200\;h^{-1}Gpc)^3$</TEX> and <TEX>$(10.815\;h^{-1}Gpc)^3$</TEX>, respectively. These simulations improve on our previous Horizon Run 1 (HR1) up to a factor of 4.4 in volume, and range from 2600 to over 8800 times the volume of the Millennium Run. In addition, they achieve a considerably finer mass resolution, down to <TEX>$1.25{\times}10^{11}h^{-1}M_{\odot}$</TEX>, allowing to resolve galaxy-size halos with mean particle separations of <TEX>$1.2h^{-1}$</TEX>Mpc and <TEX>$1.5h^{-1}$</TEX>Mpc, respectively. We have measured the power spectrum, correlation function, mass function and basic halo properties with percent level accuracy, and verified that they correctly reproduce the CDM theoretical expectations, in excellent agreement with linear perturbation theory. Our unprecedentedly large-volume N-body simulations can be used for a variety of studies in cosmology and astrophysics, ranging from large-scale structure topology, baryon acoustic oscillations, dark energy and the characterization of the expansion history of the Universe, till galaxy formation science - in connection with the new SDSS-III. To this end, we made a total of 35 all-sky mock surveys along the past light cone out to z = 0.7 (8 from the HR2 and 27 from the HR3), to simulate the BOSS geometry. The simulations and mock surveys are already publicly available at http://astro.kias.re.kr/Horizon-Run23/.
332
- Deng, Lin-Hua
- Journal of the Korean astronomical society = 천문학회지
- 44, n.6
- pp.209-215
- 2011
- 원문 바로보기
In this paper, the long-term hemispheric variation of the polar faculae is investigated. It is found that, (1) both the N-S asymmetry and N-S asynchrony of the polar faculae exhibit a long-term persistence, which suggests that they should not be regarded as a stochastic phenomenon; (2) both the N-S asynchrony and N-S asymmetry of the polar faculae are functions of the latitude, implying that the N-S asynchrony of the polar faculae is related to the N-S asymmetry of the polar faculae; (3) from a long-term view, the dominant hemisphere of the polar faculae seems to have close connection with the phase-leading hemisphere of the polar faculae.
333
- Le, Huynh Anh Nguyena
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.125-134
- 2011
- 원문 바로보기
We present medium resolution (R = 5000 - 6000) spectra in the near-infrared band, 1.4 - 1.8 <TEX>${\mu}m$</TEX>, for template stars in G, K, and M types observed by the echelle spectrometer, IRCS, at the SUBARU 8.2 m telescope. The identification of lines is based on the spectra of Arcturus (K2 III) in the literature. We measured the equivalent of widths and compared our results to those of Meyer et al. (1998). We conclude that our spectral resolution (R = 6000) data can investigate more accurately the properties of lines in stellar spectra. The library of the template stellar spectra in ASCII format are available for download on the World Wide Web.
334
- Andronov, Ivan L.
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.89-96
- 2011
- 원문 바로보기
We present results of two-color VR photometry of the intermediate polar RXS J1803. The data were aquired using the Korean 1-m telescope located at Mt. Lemmon, USA. Different 'high' and 'low' luminosity states, similar to other intermediate polars, were discovered. No statistically significant variability of the color index with varying luminosity was detected. The orbital variability was found to be not statistically significant. Spin maxima timings were determined, as well as the photometric ephemeris for the time interval of our observations. The spin period variations, caused by interaction of the accretion structure with the rotating magnetic white dwarf, were also detected. These variations are of complicated character, and their study requires further observations. We determine the color transformation coefficients for our photometric systems, and improve on the secondary photometric standards.
335
- Kim, Jae-Yeong
- Journal of the Korean astronomical society = 천문학회지
- 44, n.4
- pp.135-142
- 2011
- 원문 바로보기
A <TEX>$200'{\times}200'$</TEX> region around 30 Doradus in the Large Magellanic Cloud (LMC) is observed and analyzed in the near-infrared. We obtain polarimetry data in the J, H, and Ks bands using the SIRIUS polarimeter SIRPOL at the Infrared Survey Facility 1.4 m telescope. We measure the Stokes parameters of 2562 point-like sources to derive the degree of polarization and the polarization position angles. We discuss the statistics of the groups classified by color-magnitude diagram and proper motions of the sources, in order to separate the Galactic foreground sources from those present in the LMC. We notice that groups classified by the proper motion data show a tendency towards different polarimetric properties.
336
- Kang, Hye-Sung
- Journal of the Korean astronomical society = 천문학회지
- 44, n.2
- pp.49-58
- 2011
- 원문 바로보기
We calculate the energy spectra of cosmic ray (CR) protons and electrons at a plane shock with quasi-parallel magnetic fields, using time-dependent, diffusive shock acceleration (DSA) simulations, including energy losses via synchrotron emission and Inverse Compton (IC) scattering. A thermal leakage injection model and a Bohm type diffusion coefficient are adopted. The electron spectrum at the shock becomes steady after the DSA energy gains balance the synchrotron/IC losses, and it cuts off at the equilibrium momentum <TEX>$p_{eq}$</TEX>. In the postshock region the cutoff momentum of the electron spectrum decreases with the distance from the shock due to the energy losses and the thickness of the spatial distribution of electrons scales as <TEX>$p^{-1}$</TEX>. Thus the slope of the downstream integrated spectrum steepens by one power of p for <TEX>$p_{br}$</TEX> < p < <TEX>$p_{eq}$</TEX>, where the break momentum decreases with the shock age as <TEX>$p_{br}\;{\infty}\;t^{-1}$</TEX>. In a CR modified shock, both the proton and electron spectrum exhibit a concave curvature and deviate from the canonical test-particle power-law, and the upstream integrated electron spectrum could dominate over the downstream integrated spectrum near the cutoff momentum. Thus the spectral shape near the cutoff of X-ray synchrotron emission could reveal a signature of nonlinear DSA.
337
- Ann, Hong-Bae
- Journal of the Korean astronomical society = 천문학회지
- 44, n.1
- pp.23-32
- 2011
- 원문 바로보기
We present a deep CCD imaging in B and V bands which allows us to analyze the vertical structure of NGC 4631. We derive the scale heights of the thin and thick disks at a variety of positions along the major axis of the disk. The scale heights of the thin disk are nearly constant while those of the thick disk tend to increase with increasing galactocentric distance. The mean scale heights of the thin disk derived from B and V images are similar to each other (~ 450 pc). Instead, those of the thick disk show a strong east-west asymmetry which is caused by the diffuse stellar emission that is most prominent in the north west regions above the disk plane. The ratio of scale heights (<TEX>$z_{thick}/z_{thin}$</TEX>) is about 2.5 in the east side of the disk. However, this ratio is greater than 4 for the thick disk above the disk plane in the west side of the galaxy.
338
HALF-TURN ROTATION OF A POLARITY INVERSION LINE AND ASSOCIATED QUADRUPOLAR-LIKE STRUCTURE IN THE SUN
- Magara, Tetsuya
- Journal of the Korean astronomical society = 천문학회지
- 44, n.5
- pp.143-150
- 2011
- 원문 바로보기
This paper reports a characteristic motion of a polarity inversion line (PIL) formed at the solar surface, which is newly found by performing a three-dimensional magnetohydrodynamic simulation of flux emergence in the Sun. A magnetic flux tube composed of twisted field lines is assumed to emerge below the surface, forming a bipolar region with a PIL at the surface. A key finding is the successive half-turn rotation of the PIL, leading to the formation of a quadrupolar-like region at the surface and a magnetic configuration in the corona; this configuration is reminiscent of, but essentially different from the so-called inverse-polarity configuration of a filament magnetic field. We discuss a physical mechanism for producing the half-turn rotation of a PIL, which gives new insights into the magnetic structure formed via flux emergence. This presents a reasonable explanation of the configuration of a filament magnetic field suggested by observations.
339
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 44, n.1
- pp.33-38
- 2011
- 원문 바로보기
We study near-infrared properties of the old open cluster King 11, based on the 2MASS photometric data. We determine the location of the red giant clump(RGC) in the (K, J - K) colo-magnitude diagram and derive the distance modulus of King 11 to be <TEX>$(m-M)_0$</TEX> = <TEX>$12.50{\pm}0.10$</TEX> using the mean K magnitude of RGC. From the red giant branch slope - [Fe/H] relation we obtain the metallicity of this cluster, [Fe/H]=<TEX>$-0.17{\pm}0.07$</TEX>. The age and interstellar reddening of this cluster are estimated to be log t = <TEX>$9.48{\pm}0.05$</TEX>, E(B-V)=<TEX>$0.90{\pm}0.03$</TEX>, by applying Padova isochrone fits to the data.
340
- Hanna, Magdy A.
- Journal of the Korean astronomical society = 천문학회지
- 44, n.3
- pp.97-108
- 2011
- 원문 바로보기
The photometric light curves of the W-type W UMa eclipsing contact binary system BB Pegasi have been found to be extremely asymmetric over all the observed 63 years in all wavelengths UBVR. The light curves have been characterized by occultation primary minima. Hence, the morphology of these light curves has been studied in view of these different asymmetric degrees. The system shows a distinct O'Connell effect, as well as depth variation. A 22.96 years of stellar dark spots cycle has been determined for the system. Almost the same cycle (22.78 yr) has been found for the depth variation of MinI and MinII. We also present an analysis of mid-eclipse time measurements of BB Peg. The analysis indicates a period decrement of <TEX>$5.62{\times}10^{-8}$</TEX> day/yr, which can be interpreted in terms of mass transfer at a rate of <TEX>$-4.38{\times}10^{-8}M_{\odot}$</TEX>/yr, from the more to the less massive component. The O - C diagram shows a damping sine wave covering two different cycles of 17.0 yr and 12.87 yr with amplitudes equal to 0.0071 and 0.0013 day, respectively. These unequal durations show a non-periodicity which may be explained as a result of magnetic activity cycling variations due to star spots. The obtained characteristics are consistent with similar chromospherically active stars, when applying the Applegate's (1992) mechanism.