Context. Some models for the topology of the magnetic field in sunspot penumbrae predict regions free of magnetic fields or with only dynamically weak fields in the deep photosphere. Aims: We aim to confirm or refute the existence of weak-field regions in the deepest photospheric layers of the penumbra. Methods: We investigated the magnetic field

We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope Advanced Camera for Surveys. The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the

We present four lines of evidence leading to the conclusion that the HII regions in the discs of normal galaxies,notably the highly luminous regions,are density bounded: (1)The relation of central Hα surface brightness to total luminosity of a region departs from the predictions of uniformly ionization bounded systems (2)The geometry and intensity

We present the detailed chemical abundance patterns of 95 solar analogs, 24 hosting planets and 71 without detected planets, using very high-quality HARPS and UVES spectra. We explore the possibility that the presence of terrestial planets could affect the volatile-to-refratory abundance ratios. We do not see any clear difference between the stars

Over the past 15 years, our knowledge of the interior of the Sun has tremendously progressed by the use of helioseismic measurements. However, to go further in our understanding of the solar core, we need to measure gravity (g) modes. Thanks to the high quality of the Doppler-velocity signal measured by GOLF/SoHO, it has been possible to unveil the

This thesis is divided into two very related parts. In the first part we implement and apply a galaxy cluster detection method, based on multiband observations in visible. For this purpose, we use a new algorithm, the Voronoi Galaxy Cluster Finder, which identifies overdensities over a Poissonian field of objects. By applying this algorithm over