We present preliminary results on the XMM-Newton Survey Science Centre medium sensitivity survey, with 0.5-4.5 keV flux limit 2x 10-14 erg cm-2 s-1. At present, 19 fields have been examined with a total of 239 X-ray sources. Identifications for about 2/3 of these reveal that type 1 AGN dominate, but type 2 AGN, absorption-line galaxies and clusters

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We present a study focusing on the nature of compact groups through the study of their elliptical galaxies. We determine central velocity dispersions (σo) for 18 bright elliptical galaxies located in the core of Hickson compact groups and a control sample of 12 bright bona fide ellipticals located in the field or very loose groups. Several tests

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Analysis of spectral data of two neighboring infrared lines, Fe i 15648.5 Å (g = 3) and Fe i 15652.9 Å (g_eff = 1.53) are carried out for a simple sunspot when it was near the solar disk center (mu = 0.92), to understand the basic structure of sunspot magnetic field. Inversions of Stokes profiles are carried out to derive different atmospheric

In this contribution I present my current work on a new generation of evolutionary synthesis models that compute the multiwavelength energy distribution (from gamma rays to radio) as well as the associated dispersion for young stellar systems. I will also show some statistical effects that may appear in the analysis of surveys, such as bimodal or