We have monitored the photometric, spectroscopic and polarimetric variations of the classical T Tauri star (CTTS) AA Tau over a period of a month. The light curve consists of more than 260 measurements in each of the B and V-bands over a continuous time period of 30 days and more than 180 measurements in the R and I-bands. This provides

{A high-resolution, high signal-to-noise HIRES-Keck spectrum of APM 08279+5255 reveals a feature in the HI Lyalpha profile of the z_abs=3.514 absorber at the expected position of the corresponding DI Lyalpha line. The absorber shows a relatively simple velocity structure, with a major component detected in several metallic lines including CII, CIV

Time series of high-resolution white-light images of solar pores are analyzed. Granular motions in the vicinity of pores are driven by mesogranular flows: Motions toward the pore dominate in the 2 arcsec zone around the pore boundary, while at larger distances the granules move away from the pore. Triggered by these motions, small granules and

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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