모달창 닫기
- 홈으로 이동
1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 33/119
321
- Kwon, Young-Joo
- Journal of the Korean astronomical society = 천문학회지
- 43, n.4
- pp.123-133
- 2010
- 원문 바로보기
In order to study properties of the pulsation in the infrared emission for long period variables, we collect and analyze the infrared observational data at L band for 12 OH/IR. The observation data cover about three decades including recent data from the ISO and Spitzer. We use the Marquardt-Levenberg algorithm to determine the pulsation period and amplitude for each star and compare them with results of previous investigations at infrared and radio bands. We obtain the relationship between the pulsation periods and the amplitudes at L band. Contrary to the results at K band, there is no difference of the trends in the short and long period regions of the period-luminosity relation at L band. This may be due to the molecular absorption effect at K band. The correlations among the L band parameters, IRAS [12-25] colors, and K band parameters may be explained as results of the dust shell parameters affected by the stellar pulsation. The large scatter of the correlation could be due to the existence of a distribution of central stars with various masses and pulsation modes.
322
- Kang, Hye-Sung
- Journal of the Korean astronomical society = 천문학회지
- 43, n.2
- pp.25-39
- 2010
- 원문 바로보기
We perform kinetic simulations of diffusive shock acceleration (DSA) in Type Ia supernova remnants (SNRs) expanding into a uniform interstellar medium (ISM). Bohm-like diffusion due to self-excited <TEX>$Alfv\acute{e}n$</TEX> waves is assumed, and simple models for <TEX>$Alfv\acute{e}nic$</TEX> drift and dissipation are adopted. Phenomenological models for thermal leakage injection are considered as well. We find that the preshock gas temperature is the primary parameter that governs the cosmic ray (CR) acceleration efficiency and energy spectrum, while the CR injection rate is a secondary parameter. For SNRs in the warm ISM of <TEX>$T_0\lesssim10^5K$</TEX>, if the injection fraction is <TEX>$\xi\gtrsim10^{-4}K$</TEX>, the DSA is efficient enough to convert more than 20% of the SN explosion energy into CRs and the accelerated CR spectrum exhibits a concave curvature flattening to <TEX>$E^{-1.6}$</TEX>, which is characteristic of CR modified shocks. Such a flat source spectrum near the knee energy, however, may not be reconciled with the CR spectrum observed at Earth. On the other hand, SNRs in the hot ISM of<TEX>$T_{0}\approx10^{6}K$</TEX> with a small injection fraction, <TEX>$\xi$</TEX><<TEX>$10^{-4}$</TEX>, are inefficient accelerators with less than 10% of the explosion energy getting converted to CRs. Also the shock structure is almost test-particle like and the ensuing CR spectrum can be steeper than <TEX>$E^{-2}$</TEX>. With amplified magnetic field strength of order of <TEX>$30{\mu}G$</TEX> <TEX>$Alfv\acute{e}n$</TEX> waves generated by the streaming instability may drift upstream fast enough to make the modified test-particle power-law as steep as <TEX>$E^{-2.3}$</TEX>, which is more consistent with the observed CR spectrum.
323
- Kyeong, Jae-Mann
- Journal of the Korean astronomical society = 천문학회지
- 43, n.1
- pp.1-8
- 2010
- 원문 바로보기
JHK near-infrared photometry of star clusters in the dwarf irregular/dwarf starburst galaxy NGC 1569 are presented. After adopting several criteria to exclude other sources (foreground stars, background galaxies, etc.), 154 candidates of star clusters are identified in the near-infrared images of NGC 1569, which include very young star clusters. Especially, from analysis based on theoretical background, we found ten very young star clusters near the center of NGC 1569. The total reddening values toward these clusters are estimated to be <TEX>$A_V$</TEX>=1-9 mag from comparison with the theoretical estimates given by the Leitherer et al. (1999)'s star cluster model.
324
- Cheon, So-Ra
- Journal of the Korean astronomical society = 천문학회지
- 43, n.4
- pp.115-121
- 2010
- 원문 바로보기
UBVI CCD photometry is obtained for the Ruprecht 93 (Ru 93)region. We are unable to confirm the existence of an intermediate-age open cluster in Ru 93 from the spatial distribution of blue stars. On the other hand, we find two young star groups in the observed field: the nearer one (Ru 93 group) comprises the field young stars in the Sgr-Car arm at <TEX>$d{\approx}2.1$</TEX> kpc, while the farther one (WR 37 group) is the young stars around WR 37 at <TEX>$d{\approx}4.8$</TEX> kpc. We derive an abnormal extinction law (<TEX>$R_V$</TEX> = 3.5) in the Ruprecht 93 region.
325
- Hanna, Magdy A.
- Journal of the Korean astronomical society = 천문학회지
- 43, n.6
- pp.201-211
- 2010
- 원문 바로보기
We present an analysis of the measurements of mid-eclipse times of V839 Oph, collected from literature sources. Our analysis indicates a period increase of <TEX>$3.2{\times}10^{-7}$</TEX> day/yr. This period increase of V839 Oph can be interpreted in terms of mass transfer of rate <TEX>$1.76{\times}10^{-7}M_{\odot}/yr$</TEX>, from the less to the more massive component. The O - C diagram shows a damping sine wave covering two different complete cycles of 36.73 yr and 19.93 yr with amplitudes approximately equal to 0.0080 and 0.0043 day, respectively. The third cycle has to be expected to cover about 13.5 years with lower amplitude than those of the former two cycles. These unequal duration cycles show a non periodicity which may be explained as resulting from either the presence of a tertiary component to the system or cyclic magnetic activity variations due to star spots. For the later mechanism, the obtained characteristics are consistent when applying Applegate (1992) mechanism.
326
- Yi, Su-Kyoung K.
- Journal of the Korean astronomical society = 천문학회지
- 43, n.4
- pp.135-139
- 2010
- 원문 바로보기
We present the result of our investigation on the impact of the low Solar abundance of Asplund and collaborators (2004) on the derived ages for the oldest star clusters based on isochrone fittings. We have constructed new stellar models and corresponding isochrones using this new solar mixture with a proper Solar calibration. We have found that the use of the Asplund et al. (2004) metallicity causes the typical ages for old globular clusters in the Milky Way to be increased roughly by 10%. Although this may appear small, it has a significant impact on the interpretation for the formation epoch of Milky Way globular clusters. The Asplund et al. (2004) abundance may not necessarily threaten the current concordance cosmology but would suggest that Milky Way globular clusters formed before the reionization epoch and before the main galaxy body starts to build up. This is in contrast to the current understanding on the galaxy formation.
327
- Isayev, Alexander A.
- Journal of the Korean astronomical society = 천문학회지
- 43, n.5
- pp.161-168
- 2010
- 원문 바로보기
Magnetars are neutron stars possessing a magnetic field of about <TEX>$10^{14}-10^{15}$</TEX> G at the surface. Thermodynamic properties of neutron star matter, approximated by pure neutron matter, are considered at finite temperature in strong magnetic fields up to <TEX>$10^{18}$</TEX> G which could be relevant for the inner regions of magnetars. In the model with the Skyrme effective interaction, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter corresponds to the case when the majority of neutron spins are oriented opposite to the direction of the magnetic field (i.e. negative spin polarization). Moreover, starting from some threshold density, the self-consistent equations have also two other branches of solutions, corresponding to positive spin polarization. The influence of finite temperatures on spin polarization remains moderate in the Skyrme model up to temperatures relevant for protoneutron stars. In particular, the scenario with the metastable state characterized by positive spin polarization, considered at zero temperature in Phys. Rev. C 80, 065801 (2009), is preserved at finite temperatures as well. It is shown that, above certain density, the entropy for various branches of spin polarization in neutron matter with the Skyrme interaction in a strong magnetic field shows the unusual behavior, being larger than that of the nonpolarized state. By providing the corresponding low-temperature analysis, we prove that this unexpected behavior should be related to the dependence of the entropy of a spin polarized state on the effective masses of neutrons with spin up and spin down, and to a certain constraint on them which is violated in the respective density range.
328
- Shanmugarju, A.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.55-60
- 2009
- 원문 바로보기
The properties of SOHO/LASCO CMEs are subjected to projection effects. Their dependence on the source position is important to be studied. Our main aim is to study the dependence of CME properties on helio-longitude and latitude using the CMEs associated with type IIs observed by Wind/WAVES spacecraft (Deca-hecta metric type IIs - DH type IIs). These CMEs were identified as a separate population of geo-effective CMEs. We considered the CMEs associated with the Wind/WAVE type IIs observed during the period January 1997 - December 2005. The source locations of these CMEs were identified using their associated GOES X-ray flares and listed online. Using their locations and the cataloged properties of CMEs, we carried out a study on the dependence of CME properties on source location. We studied the above for three groups of CMEs: (i) all CMEs, (ii) halo and non-halo CMEs, and (iii) limb and non-limb CMEs. Major results from this study can be summarized as follows. (i) There is a clear dependence of speed on both the longitude and latitude; while there is an increasing trend with respect to longitude, it is opposite in the case of latitude. Our investigations show that the longitudinal dependence is caused by the projection effect and the latitudinal effect by the solar cycle effect. (ii) In the case of width, the disc centered events are observed with more width than those occurred at higher longitudes, and this result seems to be the same for latitude. (iii) The dependency of speed is confirmed on the angular distance between the sun-center and source location determined using both the longitude and latitude. (iv) There is no dependency found in the case of acceleration. (v) Among all the three groups of CMEs, the speeds of halo CMEs show more dependency on longitude. The speed of non-halo and non-limb CMEs show more dependency on latitude. The above results may be taken into account in correcting the projection effects of geo-effective CMEs.
329
- Hasan, M. Khayrul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.5
- pp.107-123
- 2009
- 원문 바로보기
We investigate the wave properties for isothermal plasma state around to the de Sitter black hole's horizon using 3+1 split of spacetime. The corresponding Fourier analyzed perturbed perfect GRMHD equations are used to obtain the complex dispersion relations. We obtain the real values of the wave number k, from these relations, which are used to evaluate the quantities like phase and group velocities etc. These have been analyzed graphically in the neighborhood of the horizon.
330
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.155-159
- 2009
- 원문 바로보기
In order to determine color excess in the <TEX>$uvby\beta$</TEX> color system for high amplitude <TEX>$\delta$</TEX> Scuti stars, reddening free <TEX>$[m_1]$</TEX>, <TEX>$[c_1]$</TEX>, and <TEX>$\beta$</TEX> indices data were obtained from the existing literature for 21 stars. Then, the three intrinsic relations of <TEX>$(b-y)_0$</TEX> - <TEX>$[m_1]$</TEX>, <TEX>$(b-y)_0$</TEX> - <TEX>$[c_1]$</TEX>, and <TEX>$(b-y)_0$</TEX> - <TEX>$\beta$</TEX> were investigated. Among these, it was shown that the <TEX>$(b-y)_0$</TEX>-<TEX>$[c_1]$</TEX> relation is the most useful. By establishing intrinsic <TEX>$(b-y)_0$</TEX>-<TEX>$[c_1]$</TEX> relations for six reddening calibration stars, color excesses of other stars were determined.