Numerical simulations of rising magnetic flux tubes in the solar convection zone have contributed significantly to our understanding of the basic properties of sunspot groups. They have provided an important clue to the operation of the solar dynamo by predicting strong (super-equipartition) magnetic fields near the bottom of the convection zone

H alpha and adjacent continuum images are presented for a sample of nearby groups of galaxies extracted from the Atlas of Compact Groups of Galaxies. Also, more detailed H alpha maps of the most remarkable galaxies are shown in this paper. A short description of the H alpha emission for each of the galaxies with accordant redshift is presented

Isophotal analyses developed in recent years (CCD images and numerical mapping techniques) have revealed that triaxial structures are frequently present in bulges of spirals and in elliptical galaxies. In the first case, these non-axisymmetric oval structures have been proposed as the corresponding sources of the energy necessary to maintain the

We describe a method of determining the system parameters in non-eclipsing interacting binaries. We find that the extent to which an observer sees the shape of the Roche lobe of the secondary star governs the amount of distortion of the absorption-line profiles. The width and degree of asymmetry of the phase-resolved absorption-line profiles show a

We have performed photometric optical observations of a sample of 17 core-dominated radio-loud quasars (CRLQs) and 17 radio-quiet quasars (RQQs). The aims were to confirm the existence of microvariations in strictly radio-quiet objects and to compare the properties of the variations in both types of quasars. Great care was taken to avoid selection

IAUC 6933 available at Central Bureau for Astronomical Telegrams.