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
제24권 제2호 (1991년 12월) 6건
1.
1991.12
구독 인증기관 무료, 개인회원 유료
An attempt has been made to examine the characteristics of acoustic and MHD waves generated in stellar convection zones( 4000 K ≤ T e f f ≤ 7000 K , 3 ≤ log g ≤ 4.5 ). With the use of wave generation theories formulated for acoustic waves by Stein (1967), for MHD body waves by Musielak and Rosner (1987, 1988) and for MHD tube waves by Musielak et al.(l989a, 1989b), the energy fluxes are calculated and their dependence on effective temperature, surface gravity and megnetic field strength are analyzed by optimization techniques. In computing magneto-convection models, the effect of magnetic fields on the efficiency of convection has been taking into account by extrapolating it from Yun's sunspot models(1968; 1970). Our study shows that acoustic wave fluxes are dominant in F and G stars, while the MHD waves dominant in K and M stars, and that the MHD wave fluxes vary as T 4 e f f ∼ T 7 e f f in contrast to the acoustic fluxes, as T 10 e f f . The gravity dependence, on the other hand, is found to be relatively weak; the acoustic wave fluxes ∝ g − 0.5 , the longitudinal tube wave fluxes ∝ g 0.3 and the transverse tube wave fluxes ∝ g 0.3 . In the case of the MHD body waves their gravity dependence is found to be nearly negligible. Finally we assesed the computed energy fluxes by comparing them with the observed fluxes F o b of CIV( λ 1549 ) lines and soft X-rays for selected main sequence stars. When we scaled the corrected wave fluxes down to F o b , it is found that these slopes are almost in line with each other.
5,700원
2.
1991.12
구독 인증기관 무료, 개인회원 유료
Using the photographic imagery of the SO galaxy NGC 5102, the equivalent luminosity profile and the fractional integrated luminosity curve have been derived. Several photometric parameters of the galaxy, such as a total magnitude ( B T ), equivalent radius ( r ∗ e ), effective surface brightness ( μ ∗ e ), and concentration indices ( C 21 , C 32 ) were derived from the luminosity profiles. According to the decomposition method from the nonlinear least squares fitting, photometric parameters of the bulge ( μ e , r e ) and the exponential disk ( μ ( 0 ) , α − 1 ), and the bulge to total luminosity ratio (B/T) were obtained. The derived central disk surface brightness ( μ ( 0 ) = 22.06 ± 0.18 m a g / □ " ) and the evaluated B/T ratio (= 0.52) of the NGC 5102 are close to the mean values ( μ ( 0 ) = 21.65 ± 0.3 m a g / □ " , B/T=0.63) of the SO galaxies. Analysis showed that a lens-like hump is embedded in the equivalent luminosity profile of the NGC 5102.
4,000원
3.
1991.12
구독 인증기관 무료, 개인회원 유료
We have derived the luminosity function for subdwarfs on the basis of the proper motion data in LHS Catalogue, utilizing the reduced proper motion diagram for the selection of sub dwarfs and the hybrid method combining the mean absolute magnitude method and V/ V m method to estimate the distance and density of subdwarfs. The luminosity function found here is almost flat, showing a very slow increase up to M V = 9 or M B = 10 , and the overall halo density is larger than those derived by Schmidt (1975), Chiu (1980), Reid (1984), Lee (1985), and Dawson (1986), but smaller than that by Eggen (1983). Comparison with 1/100 of disk stellar luminosity function implies that no conclusive dip in the halo luminosity function is found.
4,200원
4.
1991.12
구독 인증기관 무료, 개인회원 유료
Disk stellar luminosity function has been derived with stars in the Lowell Proper Motion Survey which contains about 9000 stars with μ ≥ 0 " .27 of arc/yr, $8\;<\;m_{pg}\;<\;17$ and with bright stars in the Smithsonian Astrophysical Observatory (SAO) Star Catalogue, Luminosity function has been obtained with stars within 20 pc by Luyten's mean absolute magnitudes method using Reduced Proper Motion Diagram to select disk stars. Magnitudes and colors, in the SAO Star Catalogue as well as in the Lowell Proper Motion Survey have been transformed to the UBV system from the published UBV data. It has been found that stars which have higher proper motion than the original limit of the proper motion survey are missed, when the relation between the absolute magnitude and reduced proper motion is applied to sample stars without considering the dispersion in magnitude. Correction factors for missing stars have been estimated according to their limits of proper motion which are dependent on the absolute magnitude. Resulting luminosity function shows Wielen's dip at M B ∼ 10 , and systematic enhancement of stars on the average of about Δ log Φ ( M B ) ∼ 0.2 compared with Luyten's luminosity function.
5,200원
5.
1991.12
구독 인증기관 무료, 개인회원 유료
We have compared the column densities of H 2 C O , 13 C O , C 18 O , 12 C O , CS, and H C O + to the visual extinctions derived from star counts in eight dark clouds, L1317, B1, L1551, L1535, L1544, L134, L134N, and B335. We examined the degree of correlation between molecules and extinctions. The contours of 13 C O , H 2 C O , and CS distributions show an excellent coincidence with those of the visual extinction. Even though the plots of molecule brightness temperature or column density as a function of the visual extinction show a considerable scatter, a good correlation is found between the two quantities. The turnover of the ratios of 13 C O and H 2 C O column densities to the visual extinction at high extinctions observed in several clouds is not apparent in this work. The ratios seem to maintain constant values within the range of A V we studied. The slopes of the relations between the molecule column density and extinction, and the threshold values of extinction for detection of molecules are comparable to the other works. The cause of the slope difference is discussed. We derived, for the first time, the relations of CS and H C O + column densities and the visual extinction. The ratio of CS column density to extinction is at least two orders of magnitude lower than the mean value for 13 C O , but the threshold for detection of CS is comparable to that of 13 C O . The ratio of the H C O + column density to extinction is one to two orders of magnitude lower than the mean ratio for H 2 C O .
6,300원
6.
1991.12
구독 인증기관 무료, 개인회원 유료
We have observed dense core around young stellar objects, DR21, S140, Orion-KL, and L1551 using four millimeter-wave transitions of H C 3 N J =4-3, J=5-4, J=10-9, and J=12-11. The spatial distribution of H C 3 N emission closely resembles the morphology of the previous CS observations that trace high density gas. These observations reveal the existence of H C 3 N dense cores around central IR source, elliptical in shape and almost perpendicular to the CO bipolar outflow axis. Small differences can be explained by that H C 3 N molecular line is more optically thin and is seen to be more detailed structure in the neighborhood of central IR sources. In S140 and Orion-KL, massive( ∼ 10 M ⊙ ), slowly rotating dense cores lie near at the central IR sources of bipolar outflows. The velocity channel maps of DR21 show that the bipolar outflow gas may have a correlation with the dense core of DR21. We analyzed intensities of the four lines to derive physical conditions in dense core from two methods, LTE and LVG. The column density of H C 3 N , N ( H C 3 N ) , between LTE and LVG calculations agree well with each other. The abundances of H C 3 N in each observing source have been estimated using the average values of n ( H 2 ) and N ( H C 3 N ) and assuming the size of dense core. The fractional H C 3 N abundances in massive dense cores of DR21, S140, and Orion-KL have a range of ( 2 − 7 ) × 10 − 10 , while that of low mass dense core, L1551, has one order of magnitude greater value of 2 × 10 − 9 . This should be considered good agreement with the result by Morris et al.(1976). It may be considered that dense cores of DR21, S140, and Orion-KL may have almost same stage of chemical evolution, and their abundances have a small values relative to that of L1551. The column density N ( H C 3 N ) decreases with increasing distance from the densest part of the cloud, the central infrared source, and have the relation of N ( H C 3 N ) ∝ R α , where a has a range of 0.65 to 0.89. The values of n ( H 2 ) are not varied with increasing distance from the dense core, and have almost same values. Therefore, it is considered that the dense cores in these regions probably consist of dense clumps in diffuse molecular gas medium, and n ( H 2 ) of each clump is ∼ 10 5 c m − 3 . Levels in the T e x increases with n ( H 2 ) . It is considered that the H C 3 N dense cores are not completely thermalized. We examine the relationships between the luminosity of central infrared sources versus mass of the dense cores, and the luminosity of central infrared sources versus molecular hydrogen column density. Luminosities of the central IR sources show good correlation with mass and hydrogen column density of the dense core. Same has been found from CS observations. However, mass and size derived from H C 3 N observations are one order of magnitude smaller than those from CS. It can be interpreted that we see more central part of the cloud cores in N C 3 N lines than CS lines.
11,300원
