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

We study the energy flux carried by acoustic waves excited by convective motions at sub-photospheric levels. The analysis of high-resolution spectropolarimetric data taken with IMaX/SUNRISE provides a total energy flux of ~6400-7700 W m-2 at a height of ~250 km in the 5.2-10 mHz range, i.e., at least twice the largest energy flux found in previous

Detection of narrow (δλ < 0.5 Å) absorption features in C IV at λλ1548 and 1550 have been made in the spectra of 4 late B dwarfs within 200 pc of the sun; the Si IV doublet at λλ1393 and 1403 shows up in two of them. The authors argue that it is difficult to account for the strengths, widths, shapes, and C IV/Si IV ratios in terms consistent with a

IPHAS is an ongoing Hα imaging survey of the North Galactic plane. When completed, it is expected to discover several hundred new Galactic planetary nebulae, in addition to a huge number of Hα emitters. We present here the project, the methods used to search for compact and extended ionized nebulae, and some preliminary results about the ~100 new