The numerical simulation method for variable white dwarfs of Ising & Koester (2001) is extended to variable DB stars (DBVs or V777 Herculis stars). We find the same general behavior of nonlinear effects, with a sinusoidal light-curve at small amplitudes, strongly non-sinusoidal variations at intermediate amplitudes and a change back to smaller and

We present evidence of the coexistence of either an AGN or an ultraluminous X-ray source, together with a young superstellar cluster, in the central 3 pc of NGC 4303. The galaxy contains a low-luminosity AGN and hosts a number of starburst regions in a circumnuclear spiral, as well as in the nucleus itself. A high spatial resolution Chandra image

With the goal of producing a reliable set of model atoms and singly ionized ions for use in building NLTE model atmospheres, we have combined measured energy levels, critically compiled line transition probabilities, and resonance-averaged calculations of photoionization cross sections. A majority of the elements from Li to Ca are considered

A lightcurve of comet 6P/d'Arrest from R-band CCD images taken at La Palma 2.52 m NOT telescope is presented. The lightcurve shows noticeable periodic changes in brightness produced by rotational modulation. The periodogram analysis of the lightcurve shows a peak with a confidence level exceeding 99.9% at 3.336 h. Assuming an elongated nucleus, the

Observations of magnetically sensitive lines in the visible and the infrared yield apparently contradictory values for the intrinsic field strength in the internetwork quiet Sun. It is shown that this discrepancy can be understood if one assumes that the magnetic field is not homogeneous over the resolution element. The difference between visible

We analyze a time sequence of Inter-Network (IN) magnetograms observed at the solar disk center. Speckle reconstruction techniques provide a good spatial resolution (0farcs5 cutoff frequency) yet maintaining a fair sensitivity (some 20 G). Patches with signal above noise cover 60% of the observed area, most of which corresponds to intergranular