A photoionization analysis of Hubble Space Telescope UV and ground-based optical spectrophotometry is given for eight more planetary nebulae (PNs) in the Large Magellanic Cloud (LMC). This allows the central stars to be placed accurately on the H-R diagram and permits the determination of the He, C, N, O, Ne, S, and Ar abundances. In some cases

This paper presents the second part of an extensive study of the properties of the H II region population in a sample of spiral galaxies with active nucleus. This study comprises some 2000 H II regions, distributed in 27 out of the 55 galaxies in the original sample, observed in narrow-band H alpha CCD imaging. About 70% of these H II regions are

This paper presents the distribution of ionized gas in the disk and circumnuclear region of a sample of 55 galaxies with active nuclei, Seyfert galaxies of type 1 and 2, and low-ionization nuclear emission line regions (LINERs). We use CCD narrow-band H alpha + [N II] images to map the distribution of H II regions and the morphology of the

ROSAT Position Sensitive Proportional Counter (PSPC) observations of the double-lobed radio source 3C 390.3 show resolved X-ray emission spatially located at the position of the northern radio hotspot. Possible origins for this X-ray emission are discussed. It is found that neither thermal emission nor inverse Compton emission could account for the

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Numerical simulations of the interstellar medium under the action of a density wave provide an accurate method for determining the positions of the main resonances in grand-design spiral galaxies. Barred spiral galaxies are among the best candidates for a single and well defined wave mode, because bars are standing waves which may share the same