Aims: We present new measurements of the abundances of carbon and oxygen derived from high-excitation C i and O i absorption lines in metal-poor halo stars, with the aim of clarifying the main sources of these two elements in the early stages of the chemical enrichment of the Galaxy. Methods: We target 15 new stars compared to our previous study

We present a few highlights concerning the search for short-period variable stars in four galaxies, namely IC 1613, LGS3, Cetus and Tucana, based on very deep, multi-epoch HST/ACS photometry. These are discussed in the context of the star formation histories obtained from our very deep color-magnitude diagrams. In particular, we show how the

We study the structure and evolution of the magnetic field of the quiet Sun by investigating weak spectro-polarimetric signals. To this end, we observed a quiet region close to the disk center with the German VTT in Tenerife, July 07, 2006. We recorded 38 scans of the same area. Each scan was eight arcsec wide and observed within about 100 seconds

We have developed a robust but user-friendly computer program for the synthesis and inversion of Stokes profiles caused by the joint action of the Hanle and Zeeman effects in some spectral lines of diagnostic interest. The influence of radiative transfer on the emergent spectral line radiation is taken into account through a suitable slab model

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In the present work, we investigate the formation of Stokes profiles and spectro-polarimetric diagnostics in an active region plage near the limb. We use 3-D radiation-MHD simulations with unipolar fields of an average strength of 400 G, which is largely concentrated in flux tubes in which the field reaches typical kilo-Gauss values. We generate