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

As a parallel result from a project aimed at determining accurate distances to more than 30 Planetary Nebulae using the extinction-distance method, we report here the serendipitous discovery of a giant halo around NGC 7027. We obtained the spectra of more than 50 field stars around each PN with the LDSS2 multi-slit spectrograph in the 4.2m

Context. Determining empirical atmospheric models for the solar chromosphere is difficult since it requires the observation and analysis of spectral lines that are affected by non-local thermodynamic equilibrium (NLTE) effects. This task is especially difficult in sunspot umbrae because of lower continuum intensity values in these regions with