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- 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 113/123
1121
- Park, Yong-Sun
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.1
- pp.15-31
- 1986
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We have analyzed Gray's observed mean line bisectors of FS, G0, G2, and G5 normal dwarf stars and interpreted them by computing theoretical line bisectors based on a two stream model. A set of perturbed models has been derived, and their detailed structures on temperature fluctuations and velocity fields are presented as a function of depth, which account for the observed bisectors. From the present study, it is found that the degree of stellar convective overshootings and temperature fluctuations in the upper atmospheres increases towards earlier spectral types. The convection cell size inferred from these models is found to increase also with the advancing earlier type. We demonstrated the usefulness of line bisector analysis as a diagnostic probe for stellar convection.
1122
- Yoo, Chin-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.1
- pp.33-49
- 1986
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Radial distribution of internal density has been determined for thirteen subclouds in the three giant molecular cloud complexes accompanying Mon OB1, Mon OB2 and CMa OB1 associations, We modeled their radial density structures with the density distribution of isothermal gas spheres. Most of the subclouds, nine out of the thirteen, are well described by isothermal spheres of single component; while the rest four require an additional component. Total mass and potential energy of each subcloud are also derived from the radial density structure; thermal energy and internal velocity dispersion required for sustaining the density structure are deduced from the isothermal gas model. Our derived masses of the clouds are comparable to the values determined by Blitz (1978) under LTE assumption. This agreement suggests that the correction factor for non-LTE effect on mass-estimate is not far from unity. The ratio of the gravitational potential energy to the kinetic energy of thermal motion is as large as 250; hence the thermal motion alone cannot support these clouds against the gravity. Being supported by turbulence motion with velocities of six to seven times the thermal velocity, the clouds of one-component type seem to be in equilibrium with the gravity; while the clouds of two-component type are likely to be in the stage of gravitational collapse.
1123
- Chang, Kyong-Ae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.63-68
- 1986
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In this paper we deal with the orientation and the deformation of the circular light bundle passing in a static bounded gravitational field. The properties of caustic of the gravitational lens are discussed.
1124
- Park, Chang-Bum
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.91-107
- 1986
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Making use of our extended version of <TEX>$\ddot{O}pik's$</TEX> convection theory, we have calculated magnetic cycle periods of the sun and late type stars by using Parker's dynamo theory, where we have included the non-linear effect. We presented a relationship between the computed cycle period and spectral type to analyze observed magnetic activities of the late type stars and long-term luminosity variations. It is found that (1) the stellar magentic-cycle period increases towards the later spectral type, (2) the rapid rotation facilitates the activity-related luminosity variation of stars later than about K5, (3) differential rotation plays a critical role in determining the magnetic activity-cycle period, and (4) the non-local effect should be taken into account in order to understand the observed long-term luminosity variations.
1125
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.2
- pp.51-62
- 1986
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The Wielen dip over the ragne of 6 < <TEX>$M_{\upsilon}$</TEX> < 9 in the luminosity function (LF) for the solar neighborhood stars could be explained by the combination of two different IMFs which yields the age of 13 billion years of the solar neighborhood. This smaller age than the Galactic age, 15 billion years indicates the slow collapse model of the Galaxy, solving the G-dwarf problem. Two different IMFs suggest two different mechanisms for star formation in the solar neighborhood.
1126
- Chang, Kyong-Ae
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.1
- pp.11-14
- 1986
- 원문 바로보기
It is shown in this paper that the astigmatic property of single gravitational lens in static bounded gravitational field can be retained, if n-gravitating body as a whole acts simultaneously as gravitational lens.
1127
- Park, Nam-Kyu
- 天文學會誌 = The journal of the Korean Astronomical Society
- 19, n.1
- pp.1-9
- 1986
- 원문 바로보기
We present a method for deriving most optimal filter system by which the accuracy of derived physical quantities can be maximized. Using Kurucz(1978)'s model atmospheres, an optimal four filter system for F and G dwarfs is suggested, for which mean wavelengths are located at <TEX>$3400{\AA}$</TEX>, <TEX>$3850{\AA}$</TEX>, <TEX>$4190{\AA}$</TEX>, and <TEX>$4600{\AA}$</TEX> with half-bandwidth of <TEX>$200{\AA}$</TEX>. It is found that 35, 38 and 42 filters of the DDO system and the <TEX>$Str{\ddot{o}}mgren$</TEX> u and <TEX>$\nu$</TEX> filters are close to those of the most optimal system.
1128
- Jung, Jae-Hoon
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.1
- pp.1-13
- 1985
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We present the data of photoelectric photometric observations of BW Vul carried out for four nights during the period of <TEX>$1982{\sim}1984$</TEX>. The light curves with asymmetric shape show a stillstand on the ascending branch at phase of <TEX>${\phi}{\approx}0.85$</TEX> just before the maximum light, and also the ampitude and shape of light curves are changed from night to night. Using all the published data, a new ephemeris of maximum time is derived, in which the period of light variation is <TEX>$P=0^d.20102977$</TEX> and its increasing rate is 2.2 see/century.
1129
- Lee, See-Woo
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.41-69
- 1985
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For the well observed 16 globular clusters with known metal abundance (Z), the helium abundances (Y) and ages are determined by various methods, and the relations between Y, Z and age are examined. The luminosity <TEX>$L_{RR}$</TEX> of RR Lyrae stars is known to be dependent of evolutionary models and pulsation theory in the sense that the pulsation theory and horizontal branch (HB) models yield the anticorrelation between <TEX>$L_{RR}$</TEX> and Z whereas main sequence (MS) and red giant branch (RGB) models yield the direct correlation between them. Similarly the anticorrelation between Y and Z is obtained from the HB models and pulsation theory whereas the direct correlation between them is obtained when the RGB model is applied. The current evolutionary models yield the anticorrelation between Z and age of clusters whenever the direct correlation between Y and Z holds. However when the anticorrelation between Y and Z is applied for age determination, the similar age of clusters is obtained as shown by Sandage (1982b). The ages, which are determined by the fitting of C-M diagrams to isochrones in the (<TEX>$M_v$</TEX>, B-V)-plane, suggest the two different chemical enrichment processes, which could be accounted for by the disk-halo model for the chemical evolution of the Galaxy (Lee and Ann 1981). Also it is known that the R-method is very useful for Y-determination and the derived Y's show the increasing rate of <TEX>$\frac{{\Delta}Y}{{\Delta}Z}{\simeq}0.5$</TEX> which is comparable to the observed value of <TEX>$\frac{{\Delta}Y}{{\Delta}Z}{\simeq}0.3$</TEX> from HII regions and planetary nebulae by Peimbert and Torres-Peimbert (1976). In this case, the age-metallicity relation of globular clusters could be explained by the disk-halo model.
1130
- Minn, Young-Key
- 天文學會誌 = The journal of the Korean Astronomical Society
- 18, n.2
- pp.100-110
- 1985
- 원문 바로보기
The HI features associated with HII regions and radio sources in the galactic-plane are searched in the Maryland-Green Bank Galactic 21-cm Line Survey. Among the twenty-eight such objects, twenty-five show HI depression features, two no feature, and an emission feature with excess HI brightness temperature. Most of these feature are surrounded by strong HI emissions. The depth of the HI depression is proportional to the radio continuum brightness temperature. The angular dimensions of the HI feature and radio source are comparable. The small HI depressions shown at the positions of HII region located in the outer solar circle are considered to be HI self-absorption features of very cold HI gas.