On the stability of particular solutions of the singly averaged Hill problem

We consider the particular solutions of the evolutionary system of equations in elements that correspond to planar and spatial circular orbits of the singly averaged Hill problem. We analyze the stability of planar and spatial circular orbits to inclination and eccentricity, respectively. We construct the instability regions of both particular solutions in the plane of parameters of the problem.     

Prospects for astrometry with the Hubble Space Telescope

The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by the National Aeronautics and Space Administration. This telescope will be placed into earth orbit by the space shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of ±0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package (ADRS). The variety of astrometric problems to be investigated with HST is discussed.     

Friedmann cosmology with a cosmological constant in the modified Brans-Dicke theory

Homogenous isotropic cosmologies in the presence of a cosmological constant A are studied in the modified Brans-Dicke theory. A class of exact solutions are obtained in Dicke's revised units for empty space as well as for the models filled with dust or radiation. Behaviour of these models near the singularity are discussed.     

A comparison of theoretical Sv emission line strengths with extreme ultraviolet observations of a sunspot

Electron impact excitation rates for transitions in the S v ion, calculated with theR-matrix code, are used to derive the electron temperature sensitive emission line ratiosR ₁ =I(854.8 Å)/I(786.9 Å),R ₂ =I(852.2 Å)/I(786.9 Å),R ₃ =I(849.2 Å)/I(786.9 Å), andR ₄ =I(1199.1 Å)/I(786.9 Å), which are found to be significantly different from previous estimates. A comparison of the present results with observational data for a sunspot obtained with the Harvard S-055 spectrometer on boardSkylab reveals generally good agreement between theory and experiment, except in the case ofR ₁, which is probably due to blending in the 854.8 Å feature. The possible effects of Lyman continuum absorption on the observed line ratios is briefly discussed.     

The dust coma of periodic comet Churyumov-Gerasimenko (1982 VIII)

The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ～2 × 10⁵ g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ～0.04 at 1.25 μm and ～0.05 at 2.2 μm.     

On spatial characteristics of five-minute oscillations in the sunspot umbra

Using a differential method we have carried out observations of oscillations in six sunspots. Spectral lines Fe i 5434 Å and Fe i 5576 Å were used. Horizontal waves are not observed in the sunspot umbra photosphere. Results obtained indicate that, at least, the sunspot umbra oscillates as a single whole.     

Asymmetry of 56Ni ejecta and polarization in the type-IIP supernova 2004dj

I study the question of whether the asymmetry of ⁵⁶Ni ejecta that results in the asymmetry of the Hα emission line at the nebular epoch of the type-IIP supernova SN 2004dj can account for the recently detected polarization of the supernova radiation. I have developed a model of the Hα profile and luminosity with nonthermal ionization and excitation in a spherically symmetric envelope for an asymmetric bipolar ⁵⁶Ni distribution. I have calculated the polarized radiation transfer against the background of the recovered electron density distribution. The observed polarization is shown to be reproduced at the nebular epoch around day 140 for the same parameters of the envelope, and the ⁵⁶Ni distribution for which the evolution of the Hα luminosity and profile is explained. Yet the model polarization decreases with time more slowly than is observed. The origin of the additional component responsible for the early polarization on day 107 is discussed.     

Central regions of the early-type galaxies in the NGC 3169 group

We have investigated the central regions of the galaxies in the NGC 3169/NGC 3166/NGC 3156 group with the multipupil fiber spectrograph of the 6-m telescope; the first (central) galaxy in the group is a spiral (Sa) one and the other two galaxies are lenticular ones. The group is known to have an extended HI cloud with a size of more than 100 kpc that is associated in its position, orientation, and rotation with the central galaxy NGC 3169. The mean age of the stellar populations in the centers of all three galaxies has been found to be approximately the same, ～1 Gyr. Since the galaxies are early-type ones and since NGC 3166 and NGC 3156 show no global star formation, we are dealing here with a synchronous star formation burst in the centers of all three galaxies.