간행물
천문학회지 KCI 등재 SCOPUS Journal of The Korean Astronomical Society
- 발행기관 한국천문학회
- 자료유형 학술지
- 간기 반년간
- ISSN 1225-4614 (Print)2288-890X (Online)
- 수록기간 1968 ~ 2024
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 440DDC 520
권호리스트/논문검색
제39권 제4호 (2006년 12월) 10건
1.
2006.12
구독 인증기관 무료, 개인회원 유료
A relation between temperature and time has been constructed in the self-consistent model(SCM). This relation is used to calculate the a CMBR temperature. This temperature has been found to be 2.9K. The temperature gradient of microwave background radiation(CMBR) is calculated in the Self Consistent Model. Two relations between Hubble parameter and time derivative of the temperature, have been presented in two different cases. In the first case the temperature is treated as a function of time only, while in the other one, it is assumed to be a function in time and solid angle, beside the assumption that the universe expands adiabatically.
4,000원
2.
2006.12
구독 인증기관 무료, 개인회원 유료
We present JHK-band near-infrared photometry of the star clusters in the dwarf irregular galaxy IC 5152. After excluding possible foreground stars, a number of candidate star clusters are identified in the near-infrared images of IC 5152, which include young populations. Especially, five young star clusters are identified in the(J-H, H-K) two color diagram and the total extinction values toward these clusters are estimated to be Av=2-6 from the comparison with the theoretical values given by the Leitherer et al.(1999)'s theoretical star cluster model.
4,000원
3.
2006.12
구독 인증기관 무료, 개인회원 유료
We have calculated the cosmic ray(CR) acceleration at young remnants from Type Ia supernovae expanding into a uniform interstellar medium(ISM). Adopting quasi-parallel magnetic fields, gasdynamic equations and the diffusion convection equation for the particle distribution function are solved in a comoving spherical grid which expands with the shock. Bohm-type diffusion due to self-excited Alfven waves, drift and dissipation of these waves in the precursor and thermal leakage injection were included. With magnetic fields amplified by the CR streaming instability, the particle energy can reach up to 1016Z eV at young supernova remnants(SNRs) of several thousand years old. The fraction of the explosion energy transferred to the CR component asymptotes to 40-50 % by that time. For a typical SNR in a warm ISM, the accelerated CR energy spectrum should exhibit a concave curvature with the power-law slope flattening from 2 to 1.6 at E ≳ 0.1 TeV.
4,200원
4.
2006.12
구독 인증기관 무료, 개인회원 유료
We conducted an analysis of a selected region from the FCRAO 12CO Outer Galaxy Survey. The selected region is located between galactic longitude 117° and 124° with the velocity of -23 km s-1 < VLSR <-10 km s-1. Molecular clouds in this region show a peculiar velocity field, protruding from the Local Arm population. The selected region is divided into 7 clouds by spatial location. Though we were not able to identify the direct driving source for peculiar velocity of our target region, we find that there are several internal YSOs or star forming activities; there are many associated sources like an outflows, a high-mass protostellar candidate and H2O maser sources. We attribute the driving energy source to older generation of episodic star formation. Masses of main clouds(cloud 1-4) estimated using a conversion factor from 12CO luminosity are larger than 104M⊙. Other components have a small mass as about 103M⊙. Among main clouds, cloud 2 and 4 seem to be marginally gravitational bound systems as their ratio of MCO to MVIR is about 2~3, and the internal velocity dispersion is larger than the centroid velocity dispersion. Total mass estimated using a conversion factor from 12CO luminosity is 7.9 × 104M⊙.
4,000원
5.
2006.12
구독 인증기관 무료, 개인회원 유료
We present JHKS near-infrared CCD photometric study for the Galactic open clusters NGC 1641 and NGC 2394. These clusters have never been studied before, and we provide, for the first time the cluster parameters; reddening, distance, metallicity and age. NGC 1641 is an old open cluster with age 1.6 ± 0.2 Gyr, metallicity [Fe/H]= 0.0 ± 0.2 dex, distance modulus(m-M)0=10.4 ± 0.3 mag(d=1.2 ± 0.2 kpc), and reddening E(B-V)=0.10±0.05 mag. The parameters for the other old open cluster NGC 2394 are estimated to be age=1.1±0.2 Gyr, [Fe/H]=0.0±0.2 dex, (m-M)0=9.1±0.4 mag(d=660±120 pc), and E(B-V)=0.05±0.10 mag. The metallicities and distance values for these two old open clusters are consistent with the relation between the metallicities and the Galactocentric distances of other old open clusters. We find the metallicity gradient of 53 old open clusters including NGC 1641 and NGC 2394 to be Δ[Fe/H]/ΔRgc=-0.067 ± 0.009 dex kpc-1.
4,000원
6.
2006.12
구독 인증기관 무료, 개인회원 유료
In order to determine the precise effective temperature and surface gravity of warm stars, all synthetic spectral lines in the wavelength range of 4000-5700Å with T=6000-7750 K, and log g=3.5, 4.0, and 4.5 for [M/H]=0.0, Vrot=10 km s-1, and Vtubl=2 km s-1 were calculated using the SYNSPEC package(Hubeny, et al., 1995) and the Kurucz(1995) model. Then, the depth-ratios for all line pairs were investigated and we selected two and six depth-ratios appropriate for the surface gravity and temperature indicators, respectively. We plotted six grids with X- and Y-axes for the depth-ratios of surface gravity and temperature, respectively, for the simultaneous estimation of these two atmospheric parameters. This method was applied to the spectum of δ Scu for the determination of its temperature and surface gravity simultaneously.
3,000원
7.
2006.12
구독 인증기관 무료, 개인회원 유료
A period study of the semi-detached eclipsing binary system W Delphini based on the extensive series of minimum timings covering more than a century(109 years) indicates a cyclic(O-C) variation of the system. This variation can be explained as due either to (1) stellar magnetic activity cycles of the cool subgiant G5 secondary component of the binary with a subsurface magnetic field equals to 3 kG, or (2) a long-term orbital period increases with a rate of 1.68 × 10-8 day/cycle caused by a mass transfer rate of 4.9 × 10-8M⊙yr-1 from the less to more massive component modulated by a light time effect due to a hypothetical third body with period of 53.4±1.06 years. The former explanation is more recommended than the later one since the obtained third body mass value(M3=1.58 M⊙) is quite large but it can not manifest itself observationally and also it cannot be a white dwarf. In the contrary, from the magnetic activity point of view, the obtained characteristics are in good consistent when applying Applegate(1992) mechanism. However, further precise photometric and CCD observations for minima timings with brightness determinations are needed to confirm the present solution.
4,000원
8.
2006.12
구독 인증기관 무료, 개인회원 유료
We have made a comprehensive statistical study on the coronal mass ejections(CMEs) associated with helmet streamers. A total number of 3810 CMEs observed by SOHO/LASCO coronagraph from 1996 to 2000 have been visually inspected. By comparing their LASCO images and running difference images, we picked out streamer-associated CMEs, which are classified into two sub-groups: Class-A events whose morphological shape seen in the LASCO running difference image is quite similar to that of the pre-existing streamer, and Class-B events whose ejections occurred in a part of the streamer. The former type of CME may be caused by the destabilization of the helmet streamer and the latter type of CME may be related to the eruption of a filament underlying the helmet streamer or narrow CMEs such as streamer puffs. We have examined the distributions of CME speed and acceleration for both classes as well as the correlation between their speed and acceleration. The major results from these investigations are as follows. First, about a quarter of all CMEs are streamer-associated CMEs. Second, their mean speed is 413 km s-1 for Class-A events and 371 km s-1 for Class-B events. And the fraction of the streamer-associated CMEs decreases with speed. Third, the speed-acceleration diagrams show that there are no correlations between two quantities for both classes and the accelerations are nearly symmetric with respect to zero acceleration line. Fourth, their mean angular width are about 60°, which is similar to that of normal CMEs. Fifth, the fraction of streamer-associated CMEs during the solar minimum is a little larger than that during the solar maximum. Our results show that the kinematic characteristics of streamer-associated CMEs, especially Class-A events, are quite similar to those of quiescent filament-associated CMEs.
4,000원
9.
2006.12
구독 인증기관 무료, 개인회원 유료
In this paper, initial value problem for dynamical astronomy will be established using parabolic cylindrical coordinates. Computation algorithm is developed for the initial value problem of gravity perturbed trajectories. Applications of the algorithm for the problem of final state predication are illustrated by numerical examples of seven test orbits of different eccentricities. The numerical results are extremely accurate and efficient in predicating final state for gravity perturbed trajectories which is of extreme importance for scientific researches as well as for military purposes. Moreover, an additional efficiency of the algorithm is that, for each of the test orbits, the step size used for solving the differential equations of motion is larger than 70% of the step size used for obtaining its reference final state solution.
3,000원
10.
2006.12
구독 인증기관 무료, 개인회원 유료
Long slit spectrometers are widely used in optical and infrared bands in astronomy. Absolute flux calibration for extended sources, however, is not straightforward, because a portion of the radiation energy from a flux calibration star is blocked by the narrow slit width. Assuming that the point spread function(PSF) of the star is circularly symmetric, we develop a robust method to extrapolate the detected stellar flux to the unobscured flux using the measured PSF along the slit-length direction. We apply this method to our long slit data and prove that the uncertainty of the absolute flux calibration is less than a few percents.
4,000원
