Period variations in BZ Eridani?

Recent claims that strong period variations are indicated in the O–C diagram of the eclipsing binary BZ Eri are shown to be based on a gross overestimation of the accuracy of photographic and visual times of minima. There is no evidence for any period change within the last fifty years.     

Stability of particulate discs

Collisionally-induced amplification of density fluctuations can also produce non-axisymmetric local condensations in particulate discs if the optical thickness is between definite values. Gravitational instability occurs above this interval. The theory of both phenomena is derived from collisional equations. The conventional criterion for gravitational instability in a gaseous medium cannot be used for particulate discs, in which the equilibrium depends on the collisional energy loss. These instabilities can produce an unbounded growth in density or a gravitational coagulation of particles, but the typical consequence is the formation of highly elongated clouds which are denser than the background matter and have a relatively long lifetime before decay. The third type of instability, the thermal one, appears at low values of velocity dispersion. It only affects the random motion of particles without producing condensations.     

Buchbesprechung

Ohne Zusammenfassung     

Synchrotron radiation and galactic field configurations

Models of the galactic magnetic field are discussed with respect to their influence on calculated contour maps as well as longitudinal distributions of the synchrotron brightness temperature. A comparison is made with Landecker-Wielebinski (1970) data.     

Feeding Monsters – A Study of Active Galaxies

We present new interferometric observations of the molecular gas distribution and kinematics in the nuclei of different active galaxies at high angular resolution and high sensitivity carried out with the IRAM Plateau de Bure interferometer (PdBI). The observations cover galaxies in a redshift range of 0.03–1.4. We have so far observed five different active galaxies: NGC3718, NGC1068, HE1029–1831, 3C48 and Q0957+561. The first two objects belong to the NUGA (NUclei of GAlaxies) project – an international collaboration mainly between Spain, France and Germany – containing about 30 Seyfert and LINER galaxies. Both are at the same distance of 14Mpc and show a warped gas and dust disk. The new mosaic map of NGC3718 corrected for short-spacing effects with IRAM 30 m observations well demonstrates the existence of the warped gas disk with several secondary maxima in the projected gas distribution caused by orbit crowding effects. Based on these new data we have improved recent simulations of the warped disk in NGC3718. HE1029–1831 and 3C48 are nearby QSOs. HE1029–1831 is taken out of the Cologne nearby QSO sample. The maps of the integrated CO(1–0) and CO(2–1) emission clearly show that the molecular gas is mostly related to the central bulge with a non-negligible fraction distributed along the bar known from optical observations. Our new CO data of 3C48 unveil new information about the kinematics of its molecular gas complementing and improving further studies based on previous infrared observations and detailed multi-particle simulations. Finally, new measurements of the CO(1–0) line in Q0957+561 – a highly-red-shifted, gravitationally lensed quasar – will be presented as a link to earlier evolutionary stages of active galaxies and their hosts.     

East-west asymmetry of Saturn's rings

The energy distribution curves of eleven Ap stars, three Am stars, four normal A stars and one F0 V magnetic star have been obtained between 478 nm and 680 nm. For four of the Ap stars, two Am stars and all the four normal A stars, the effective temperatures are believed to have been estimated for the first time. For the rest, these estimates are expected to be an improvement over previously available values.It is concluded that the Ap and Am stars are not much different from the normal A stars in so far as their temperatures are concerned.     

Radio observations of the radio galaxy 3C 390.3 at 0.6 GHz

Observations of the radio galaxy 3C 390.3 made with the 3-km WSRT at 0.6 GHz are presented. This is an edge-brightened double source with strong bridges connecting the hot spots to the core. Complex linear polarization structure has been detected. The south component is double, the north component, triple. This 3-km observation at 0.6 GHz has been compared with the 1.5-km WSRT observation at 1.4 GHz and some important physical parameters of the sources have been evaluated.     

Interaction of the Large Magellanic Cloud with the halo population and the companions of the Galaxy

Numerical simulations have been performed in order to study the gravitational interaction between the outlying population of the Galaxy and the Large Magellanic Cloud (LMC). The following effects have been noted: (1) halo objects are partially removed from the orbital distance of the LMC such that a local minimum is created in the radial density profile; (2) a large number of halo objects go into escape orbits. This possibility makes the determination of the mass of the Galaxy by virial theorem arguments unreliable; (3) the orbit of the LMC decays faster than what one would expect on the basis of the classical dynamical friction calculation. The excess friction derives from three-body effects, which are not accounted for in the classical dynamical friction. Finally, the fates of globular clusters and dwarf galaxies near the Galaxy and the LMC are discussed.