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

About 500 asymptotic giant branch (AGB) stars have been resolved and photometrically measured in the Local Group (LG) dwarf irregular galaxy NGC 6822. They draw an AGB well shaped, densely populated, and extending to very red colors. It is the first time that this kind of AGB has been clearly detected. Using recent stellar evolutionary models and

We present UBV Johnson CCD photometry of two young clusters of the Large Magellanic Cloud (LMC), namely NGC 1850 and NGC 1858, which are located at the NW part of the Bar. We determine their reddening, age and slope of the initial mass function (IMF). The age of NGC 1858 is 8 x 106 yr, while that for the majority of stars in NGC 1850 is 70 x 106 yr

We present Johnson CCD photometry in the B and V passbands for the stellar content of two intermediate age star clusters of the Large Magellanic Cloud (LMC), NGC 2134 and NGC 2249. In total 1613 stars are measured in NGC 2134 and 850 in NGC 2249. With the aid of two grids of stellar models calculated with convective overshoot (both from the core