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
제42권 제6호 (2009년 12월) 5건
1.
2009.12
구독 인증기관 무료, 개인회원 유료
We present JHK near-infrared photometric study for the old open cluster (OC) Trumpler 5 (Tr 5), based on the 2MASS data. From the color-magnitude diagrams of Tr 5, we have located the position of the red giant clump (RGC) stars, and used the mean magnitude of the RGC stars in K-band to estimate the distance to Tr 5, d = 3:1±0:1 kpc ((m-M)0 = 12:46±0:04). From fitting the theoretical isochrones of Padova group, we have estimated the reddening, metallicity, and age : E(B-V ) = 0:64±0:05, [Fe/H] = -0:4 ± 0:1 dex, and t = 2:8 ± 0:2 Gyr (log t = 9:45 ± 0:04), respectively. These parameters generally agree well with those obtained from the previous studies on Tr 5 and confirms that this cluster is an old OC with metallicity being metal-poorer than solar abundance, located in the anti-Galactic center region.
4,000원
2.
2009.12
구독 인증기관 무료, 개인회원 유료
We present measurements of diffuse interstellar H2 absorption lines in the continuum spectra of 10 early-type stars. The data were observed with the Berkeley Extreme and Far-Ultraviolet Spectrometer (BEFS) of the ORFEUS telescope on board the ORFEUS-SPAS I and II space-shuttle missions in 1993 and 1996, respectively. The spectra extend from the interstellar cutoff at 912 Å to about 1200Åwith a resolution of ~ 3000 and statistical signal-to-noise ratios between 10 and 65. Adopting Doppler broadening velocities from high-resolution optical observations, we obtain the H2 column densities of rotational levels J00 = 0 through 5 for each line of sight. The kinetic temperatures derived from J" = 0 and 1 states show a small variation around the mean value of 80 K, except for the component toward HD 219188, which has a temperature of 211 K. Based on a synthetic interstellar cloud model described in our previous work, we derive the incident UV intensity IUV and the hydrogen density nH of the observed components to be -0.4 ≤ log IUV ≤ 2.2 and 6.3 ≤ nH ≤ 2500 cm-3, respectively.
4,000원
3.
2009.12
구독 인증기관 무료, 개인회원 유료
In order to determine color excess in the uvbyβ color system for high amplitude ± Scuti stars, reddening free [m1], [c1], and β indices data were obtained from the existing literature for 21 stars. Then, the three intrinsic relations of (b- y)0 - [m1], (b- y)0 -[c1], and (b-y)0 - β were investigated. Among these, it was shown that the (b-y)0 -[c1] relation is the most useful. By establishing intrinsic (b-y)0-[c1] relations for six reddening calibration stars, color excesses of other stars were determined.
4,000원
4.
2009.12
구독 인증기관 무료, 개인회원 유료
Observation of standard stars is of crucial importance in stellar photometry. We have studied the standard transformation relations of the UBV RI CCD photometric system at the Maidanak Astronomical Observatory in Uzbekistan. All observations were made with the AZT-22 1.5m telescope, SITe 2k CCD or Fairchild 486 CCD, and standard Bessell UBV RI filters from 2003 August to 2007 September. We observed many standard stars around the celestial equator observed by SAAO astronomers. The atmospheric extinction coefficients, photometric zero points, and time variation of photometric zero points of each night were determined. Secondary extinction coefficients and photometric zero points were very stable, while primary extinction coefficients showed a distinct seasonal variation. We also determined the transformation coefficients for each filter. For B, V , R, and I filters, the transformation to the SAAO standard system could be achieved with a straight line or a combination of two straight lines. However, in the case of the U filter and Fairchild 486 CCD combination, a significant non-linear correction term - related to the size of Balmer jump or the strength of the Balmer lines - of up to 0:08 mags was required. We found that our data matched well the SAAO photometry in V , B - V , V - I, and R - I. But in U - B, the difference in zero point was about 3:6 mmag and the scatter was about 0:02 mag. We attribute the relatively large scatter in U -B to the larger error in U of the SAAO photometry. We confirm the mostly small differences between the SAAO standard UBV RI system and the Landolt standard system. We also attempted to interpret the seasonal variation of the atmospheric extinction coefficients in the context of scattering sources in the earth’s atmosphere.
4,600원
5.
2009.12
구독 인증기관 무료, 개인회원 유료
A method of estimating the lower bound of coronal magnetic field strength in the neighborhood of an ejecting plasmoid is presented. Based on the assumption that the plasma ejecta is within a magnetic island, an analytical expression for the force acting on the ejecta is derived. The method is applied to a limb coronal mass ejection event, and a lower bound of the magnetic field strength just below the CME core is estimated. The method is expected to provide useful information on the strength of reconnecting magnetic field if applied to X-ray plasma ejecta.
4,000원
