[en] Here the author briefly reviews the dynamics of sinking satellites and the effect of companions on elliptical galaxies. The author then discusses recent work on interacting disk systems, and finally focuses on a favorite interacting pair, NGC 5194/5195

[en] It is pointed out that the outer parts of galaxies often exhibit distinct surface brightness enhancements. The development of rings and shells around galaxies has been ascribed to mechanisms in which the interaction of a galaxy with its neighbors plays a key role. According to some concepts, the big events, such as those leading to the formation of ring galaxies, are interspersed with an entire set of smaller ones. In particular, small galaxies in a group are inclined to fall into their bigger neighbors without affecting the latter very much. After the event, the big galaxy is provided with certain features, taking into account ellipticals with shells, and S0s with polar rings. A review is conducted of the properties of these types of galaxies, insofar as their outskirts have identifiable shells or rings. Attention is given to ring galaxies, outer rings around spirals and S0s, polar ring galaxies, and shells around elliptical galaxies. 157 references

[en] The mass distribution in spiral galaxies is investigated by means of numerical simulations, summarizing the results reported by Athanassoula et al. (1986). Details of the modeling technique employed are given, including bulge-disk decomposition; computation of bulge and disk rotation curves (assuming constant mass/light ratios for each); and determination (for spherical symmetry) of the total halo mass out to the optical radius, the concentration indices, the halo-density power law, the core radius, the central density, and the velocity dispersion. Also discussed are the procedures for incorporating galactic gas and checking the spiral structure extent. It is found that structural constraints limit disk mass/light ratios to a range of 0.3 dex, and that the most likely models are maximum-disk models with m = 1 disturbances inhibited. 19 references

[en] In this paper, the author concentrates on some theoretical questions concerning rings and lenses in disk galaxies, in particular to their formation. First, he discusses the model of Schwartz according to which inner and outer rings are connected to Lindblad resonances and other resonances. Next, he proposes a new scenario for the formation of lenses. According to it, lenses - like bars - are due to instabilities of galactic disks. The difference in eccentricity between the two components is due to the different amounts of random motions initially present in the disk, i.e. the different initial distribution functions. (Auth.)

[en] Simple numerical simulations are used to study the effects of baryonic infall on the halo mass distribution in disk galaxies. Three populations are used: stars and gas, which are closely coupled through star formation, mass loss, cooling and heating, and a halo population which interacts only gravitationally. For several values of the star-gas coupling parameters and initial halo configurations we find final configurations with flat rotation curves. Some of them are maximum disk solutions with asymmetries suppressed (no m = 1 solutions), and some of them have such strong halos that bisymmetric disturbances are suppressed (no m = 2 solutions)

[en] The flow of gas in and around bars is calculated using a second order flux splitting code. For appropriate bar models shocks form aling the leading edges of the bar, at positions where dust lanes are observed in barred galaxies. The excistence of an inner Lindblad resonance is a necessary, though not sufficient, condition for this. The curvature of the shock loci depends on th axial ratio of the bar. (author). 12 refs.; 7 figs

No abstract available

[en] Several independent lines of evidence suggest that the isophotes or isodensities of bars in barred galaxies are not really elliptical in shape but more rectangular. The effect this might have on the orbits in two different types of bar potentials is studied, and it is found that in both cases the percentage of stochastic orbits is much larger when the shapes are more rectangularlike or, equivalently, when the m = 4 components are more important. This can be understood with the help of the Chirikov criterion, which can predict the limit for the onset of global stochasticity. 9 refs

[en] The authors have set out to apply the method of Fourier analysis of the observed distribution of spiral tracers (HII regions) to a sufficiently large number of galaxies to permit a statistical treatment. The long-term program is outlined and the first testing results are reported. (Auth.)

[en] We briefly discuss mass models of spiral galaxies involving decomposition into disk and halo components using rotation curves and radial luminosity profiles. Suitable models are obtained by assuming constant mass-to-light ratio in the disk (and bulge, if present), and constraining the value of this ratio by spiral structure theory