Photometry of a large field around the young globular cluster Palomar 12 has revealed the main sequence of a low surface brightness stellar system. This main sequence is indicative of a stellar population that varies significantly in metallicity and/or age but in the mean is more metal-poor than Pal 12. Under different assumptions for the

In a recent Letter, we showed the remarkable result that the atomic alignment of the levels P1/2 and S1/2 of the D1 line of Na I is practically destroyed in the presence of magnetic fields sensibly larger than 10 G, irrespective of the field direction. In this paper, we analytically demonstrate that this property is a consequence of the decoupling

We have designed, constructed, and put into operation a large-area CCD camera that covers a large fraction of the image plane of the 1 m Schmidt telescope at Llano del Hato in Venezuela. The camera consists of 16 CCD devices arranged in a 4×4 mosaic covering 2.3d×3.5d of sky. The CCDs are 2048×2048 LORAL devices with 15 μm pixels. The camera is

We use long-slit spectroscopy along the major axis of a sample of 23 nearby disk galaxies to study the kinematic properties of the ionized-gas component in their inner regions. For each galaxy, we derive the position-velocity diagram of the ionized gas from its emission lines. We discuss the variety of shapes observed in such position-velocity

We present NLTE abundances of CNO for a sample of four O9 stars in the Galaxy, together with new determinations of their stellar parameters, T_eff, log g, epsilon (He) and microturbulence. These new analyses take into account the effect of line-blocking in the spectral synthesis with our classical NLTE, plane-parallel and hydrostatic model

We are developing a project aimed at studying the physical properties, origin and evolution of low-ionization structures in planetary nebulae. Within this project we have identified a number of pairs of highly collimated low-ionization jet-like features (Gonçalves et al. 2001). In spite of being very similar to real jets, they have the intriguing