The accelerated Lambda iteration method is used to obtain better theoretical profiles of He II in hot stars by considering more levels and Stark broadening in the statistical equilibrium equations. It is found that an appropriate He II model atom must consist of 14 non-LTE levels and that Stark broadening must be included for all lines with upper

In the pipeline processing of Chandra data, a uniform random blur, currently defaulted to +/- 0.5 pixels, is added to the sky coordinate of ACIS data. Its primary objective is to remove artificial components which may be introduced by the aspect solution in this undersampled data and hence improve the PSF. However, one can also point out that the 0

We discuss, in terms of particle acceleration, the results from optical VLT observations of hot spots associated with radio galaxies. On the basis of observational and theoretical grounds, the following is shown. (i) Relatively low radio-radio power hot spots are the optimum candidates for being detected at optical waves. This is supported by an

Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (

Infrared photometry is reported from 1.25 to 10 micrometers for 10 Seyfert 1.8 and 1.9 galaxies identified by Osterbrock and his collaborators and drawn originally from the Markarian lists. The three objects whose infrared colors are the most nonstellar in nature are objects whose ultraviolet or optical spectra preclude heavy reddening of either

Dwarf galaxies are the most common galaxies in the Universe. They are systems believed to consist of matter in a near-primordial state, from which giant galaxies probably form. As such, they are important probes for studying matter in its near-primordial state. In an effort to study the main physical and chemical properties of dwarfs, the present