We analyze the observed properties of nested and single stellar bar systems in disk galaxies. Our sample consists of 56 Seyfert and 56 non-Seyfert galaxies. We use HST H-band images of the central parts and ground-based images of the outer parts with ellipse fitting to find bars. Our main result is a clear division between the secondary and primary

We are studying the properties of a sample of satellite galaxies around nearby isolated spirals (Zaritsky et al. 1997), with the aim of testing hierarchical models of galaxy formation. Satellite galaxies can give us information on intermediate steps in the merging and aggregation processes which, according to the models, form the larger dynamical

We use isophote analysis performed on near-infrared images of matched samples of Seyfert and non-active galaxies to study the overall bar fractions, and properties of the bars. We conclude that there is a small but significant excess of bars among the host galaxies of Seyferts as compared to non-Seyfert control galaxies. Whereas 59% ± 9% of control

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We have considered the influence of gravitational microlensing on the spectral line profiles generated by a relativistic accretion disc model. We discuss qualitatively the significant perturbations induced in the line profile when the dimensions of the accretion disc are of the order of the Einstein radius associated with the microlens.