Results of a five-month campaign of optical monitoring the Seyfert 1 galaxy NGC 4593 are presented. High resolution H-alpha and H-Beta spectra and direct images in the Johnson U, B, V, R, and I bands were obtained between January and June 1990. The emission lines and the continuum showed strong variations on time scales of weeks to days. The H

We present lightcurves ofasteroids 31 Euphrosyne, 196 Philomena and 471 Papagena and apply two different amplitude-aspect methods for pole and shape determination.

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We present a detailed analysis on photopolarimetric monitoring on OJ 287 conducted at the Nordic Optical Telescope during January 1991. Large rapid variations were observed in flux, polarization and position angle; the largest being a 40% increase in the flux with a simultaneous 55 degree position angle rotation in five hours. Changes in the

We present polarization profiles observed with the High Altitude Observatory/National Solar Observatory (HAO/NSO) Advanced Stokes Polarimeter (ASP) that demonstrate, in a model-independent way, the presence of strong downflows close to the neutral line of a delta sunspot (a spot with both polarities contained within the same penumbra). The flows

ESTA DISERTACION SE DIVIDE EN DOS PARTES, CLARAMENTE DIFERENCIADAS. UNA PRIMERA PARTE, BIBLIOGRAFICA, COMPRENDE LOS CAPITULOS PRIMERO Y SEGUNDO. LA SEGUNDA PARTE -LOS CAPITULOS TERCERO, CUARTO Y QUINTO -RESUME EL TRABAJO DE INVESTIGACION. TRES APENDICES COMPLEMENTAN LO EXPUESTO EN LA SEGUNDA PARTE DE LA TESIS. EN EL CAPITULO PRIMERO, SE RESUME LO