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

We present the results of a high resolution (0.27'' px(-1) ) near-infrared H band (1.65 μm) imaging survey of a complete sample of 20 flat spectrum radio quasars (FSRQ) extracted from the 2Jy catalogue of radio sources (Wall & Peacock 1985). The observed objects are intrinsically luminous with median M(B) =3D -25.5. The median redshift of the

Observations of the Local Arm have been carried out in the near-infrared with the 1.5 m ``Carlos Sanchez'' telescope in Tenerife. A model of the disc with adjustable parameters fitted to reproduce the DIRBE-COBE survey, has been subtracted from the observational data in order to obtain a clean map of the Local Arm, uncontaminated by other