More than 1000 coefficients of atmospheric extinction in the U, B and V passbands were obtained as a secondary result of long-term photometric monitoring of stellar objects at Yonsei University Observatory during 1982–1989. The long-term variation of the extinction coefficients of each passband are presented in this paper.

A nearly stationary pulsar wind is shown to be always collimating along the direction of rotation. It follows that the conventional picture of the equatorial pulsar wind can occur only in a highly time-dependent manner, which, if true, may account for the observed time variation within a single pulse. Furthermore, a mechanism, via excitation of magnetosolitons, is proposed for explaining the continuous generation of energetic electrons, which yield the observed radio emission in the Type II supernova remnants. Fully relativistic analyses will be presented to substantiate these claims.

The earlier work on the production of deuterium in the accretion tori around Population III objects has been criticised on the basis of relative production ratios of deuterium, helium-3 and 7Li. It is shown here that the criticism on the basis of helium-3 over-production is unjustified, as no measurement of helium-3 and lithium abundances for the same stars is available. It is predicted that indeed the helium-3 abundance determination will be the best means to verify the original hypothesis.

The anomalously high density of the planet Mercury and the higher-than-solar rock-to-ice ratio in Jupiter’s moons Ganymede and Callisto cannot be explained by the conventional disc models of solar system formation. It is shown here that the unusual chemical signature of these bodies is the outcome of a process of chemical fractionation and orbital focussing which is peculiar to gas ring models of planet and regular satellite formation. Good numerical agreement with the observational data is obtained if the temperature of condensation of the planetary system closely followed the law Tn ≃ 680[R⊕/Rn]0.9 K, where Rn denotes the radial distance from the Sun.

Improved solutions have been obtained for the orbit and equatorial cross-section of Mercury using radar ranging data spanning 22 years. These data have yielded new results on the precession of Mercury’s perihelion and better limits on a possible time variation in the gravitational constant G.

The origin of cylindrically symmetric supernova remnants (SNR) is discussed. The results of numerical simulations of the two best examples of barrel-like SNRs, SN 1006 and G296.5+10.0, are presented.

Thomson scattering in pulsar magnetospheres has previously been studied by several authors. The most distinguishing feature is the fact that the super-strong magnetic field (B ~ 1012 G) greatly affects the Thomson scattering process, resulting in resonances in the scattering cross-section (Canuto et al. 1971; Herold 1979; Chou 1986; Daugherty and Harding 1986). The important consequences of these cyclotron resonances are the increase in the photon mean free path in the scattering regions, and strongly affecting the angular distribution, and polarisation properties of the scattered photons (Chou 1986; Chou et al. 1989).

The effects of including low quality IRAS flux data in colour-colour diagrams is investigated, with a view to identifying Young Stellar Objects from the IRAS database. Colour criteria to perform this task are derived.

Observations of the vector magnetic field imply that there is a net current flowing through the corona, and there is also evidence that this current is directly related to flares. It is argued that if the currents are unneutralised, then this requires a radical rethinking of several widely accepted ideas on solar magnetic fields and their role in solar flares.

We present results of infrared continuum observations of the circumstellar disk surrounding the complex M78-SSV63.

Our recent papers have been devoted to basic studies of diatomic and polyatomic molecules (Singh and Chaturvedi 1989 a,b,c,d; 1990a,b,c). A critical analysis of the 456 available references in literature has been made to select 135 polyatomic molecules, molecular ions and radicals containing from three to thirteen atoms of astrophysical significance. The results have been arranged in a text-cum-tabular form (Singh and Chaturvedi 1989 b,d). The compilation contains various information for each molecule, such as the spectral region, transition levels, and astrophysical objects where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar medium. Galaxy, etc.).

In this paper we present the results of spectroscopic observations for 34 emission-line stars (ELSs) in the Orion belt region, which were detected in an extensive survery. Spectral classification and the intensities of Hα and Hβ emission have revealed that the observed ELSs are probably T-Tauri type stars.

In this paper the relation between the planetary distance law and the resonant structures is shown, in that the resonance relation has been expressed in terms of Roche’s constant (Rawal 1984,1986,1989). This brings forth a coherent, elegant and unified picture of the Solar System and satellite systems.

This paper is the second report since 1984 on the photometric monitoring of long-period eclipsing binary stars at Yonsei University Observatory using a 61-cm reflector.

We have detected a large cold HI cloud consisting of several fragments in the region south of the Chamaeleon I dark cloud. The cold HI cloud is shown to be a future site of star formation.

The atmospheric 14C record, the corresponding WM values derived from a carbon reservoir model, auroral numbers and the Zurich relative annual sunspot numbers all demonstrate a substantial downturn in solar activity for the duration of solar cycles 5 and 6. This reduction is also imbedded in some dendrochronological proxy data sets, which describe an annual index radial growth rate for trees at high-altitude sites. A significant lagged correlation can exist between tree-ring indices and the 11–year solar cycle during periods of high solar activity, a feature which is not evident during quiescent periods.

This paper outlines the plans for a Japanese lunar exploration mission in the mid-1990s.

The cold HI cloud in the region of the M17SW giant molecular cloud comprises three major fragments with a mean size of ~ 30 pc. Their overall distribution is rather similar to that of CO gas, but one of the fragments does not seem to have a molecular counterpart. It is shown that such a cloud is also a future site of star formation.

An instrument is described that can detect clouds at night-time by sensing their infrared emission. The device can readily detect clouds that are difficult to see with the unaided eye on a moon-lit night. It can be used to provide an indication of how photometric the conditions are, to terminate exposures when cloud forms, and to close the dome when conditions become unsuitable for observing. The detector also has applications as an astronomical site-surveying instrument.

An analysis of 1973 RT Andromedae B and V light curves is presented. The results are fitted into a spot evolution sequence found in a previous study which used the same technique on different data. The new values of the system’s physical parameters are in general agreement with the earlier ones.