From an observational point of view, magnetic field leaves its imprint, via Zeeman effect, on spectral line splitting and the induced wavelength dependence of the polarization state of the observed photons. The characteristics of the most recent polarimetric analyzers are described, together with their limitations. Next, inversion techniques are

En esta memoria de tesis llevamos a cabo la exposición de los resultados más interesantes obtenidos durante los últimos cuatro años de investigación sobre los procesos de formación estelar y la cinemática del gas ionizado en un grupo de galaxias Wolf-Rayet. Nuestro estudio se ha basado en la obtención de imágenes en la línea de emisión de Ha y en

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During the years 1996 through 1998 the MDI and GOLF experiments on the SOHO mission have provided unique and nearly uninterrupted sequences of helioseismic observations. This paper describes the analysis carried out on power spectra from 759 days of calibrated velocity signals provided by these two experiments. The time series investigated in this

The advent of large 8-10m telescopes heralds a new age in stellar astronomy. It is now possible to carry out detailed spectroscopic observations at high resolution of the brightest stars of galaxies in the Local Group, and it is envisaged that intermediate resolution observations will be extended to stars in the nearest galaxy clusters such as

Stars with masses greater than about ten solar masses are thought to end their lives either in a supernova or in a direct gravitational collapse process, either of which could have a black hole as a remnant. But there is as yet no direct observational evidence to support either gravitational collapse in general or the formation of black hole