It is now well established that there is a diffuse ionized medium which extends far beyond the discs of spirals. The mechanism responsible for the ionization is still an issue of debate, and the method of measuring the total luminosity, independently of the observational set-up, has to be defined. Here we analyse the case of the Magellanic

Long slit spectrophotometry of 13 bipolar planetary nebulae has been used to study their physical and chemical properties. In each nebula, one to seven different spatial regions have been considered in order to search for possible abundance variations through the nebulae. We obtained the following main results: - within the errors, the He, O, and N

There are two principal problems in explaining, in terms of the emission from OB stars, the ionisation of the gas which emits the diffuse H-alpha in spiral galaxies. One is the long pathlengths which the ionising photons need to traverse to reach their objectives, the other is whether sufficient photons can escape from within the HII regions which

Different estimates of the vertical gradient of magnetic field inclination in penumbrae disagree by 2 orders of magnitude. This disagreement may be resolved if measuring with typical angular resolutions implies averaging hundreds of independent fibrils whose residual variation, upon spatial averaging, gives rise to the observed large-scale

The authors have used HST/WFPC2 to observe the optical jet of the two extragalactic radio sources PKS 0521-365 (z = 0.055) and 3C 371 (z = 0.050). For PKS 0521-365, the optical and radio images are similar, with the general shape and the total length of the jet almost identical in the two bands. Radio and optical emission from the jet of 3C 371

We report on the results of optical follow-up observations of the counterpart of the gamma-ray burst GRB 970508, starting 7 hr after the event. Multicolor U-, B-, V-, Rc-, and Ic-band observations were obtained during the first three consecutive nights. The counterpart was monitored regularly in Rc until ~4 months after the burst. The light curve