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We present a complete study of the diffuse ionized gas (DIG) in a sample of six spiral galaxies (NGC 157, NGC 3359, NGC 3631, NGC 6764, NGC 6951, NGC 7479) using very high quality Hα images which allow analysis down to very low surface brightness (between 0.3 and 2 pc cm-6). Separation of the diffuse Hα emission from that of the H II regions was

We present a gallery with some of the most interesting microstructures of low-ionization found in planetary nebulae (PNe). A rich zoo of knots, filaments, jets and jet-like systems are introduced, together with their morphological and kinematic properties. We briefly compare the predictions of the theoretical mechanisms for their formation with the

The Hubble Space Telescope NICMOS Camera 2 was used for H-band imaging of 12 BL Lacertae objects taken from the larger sample observed with the WFPC2 in the R band by Urry and coworkers and Scarpa and coworkers. Ten of the 12 BL Lacs are clearly resolved, and the detected host galaxies are large, bright ellipticals with average absolute magnitude =

The effect of scattering processes in the continuum on the formation of spectral lines in a static atmosphere with an arbitrary distribution of the internal energy sources is investigated using Ambartsumian's principle of invariance. Spectral line profiles are calculated to illustrate the effect the assumption of the complete redistribution on

We have observed the planetary nebula NGC 2440 in the transitions [O II] λ3727, He II λ4686, [O III] λλ(4363+5007), H I λλ(4861+6563), He I λ5876, [N II] λ6584, [S II] λλ(6717+6731), and [S III] λ9061, as well as in various continuum filters. As a result, we are able to evaluate the excitation structure of the source and determine the projected