A photometric study of umbral bright features (umbral dots, clusters of umbral dots, bright grains of light bridges) in sunspots is presented. It is based on white-light images taken with a CCD video camera driven by an automatic image selection system. A direct linear relation between the observed brightness of the features and that of the

We report on intermediate-to-high resolution spectroscopy and standard broadband photometry of late-type visual companions to early-type stars. Our program stars are drawn from the sample of post-T-Tauri candidates studied by Lindroos (1986). Measurement of radial velocities and derivation of the surface abundances of lithium and heavier elements

We analyze the structure of a small sample of galaxies, using a set of CCD images in standard photometric bands presented in a previous paper (Prieto et al. 1991). These and their combinations in the form of color index images, offer high quality information about the structure of the galaxies, allowing us to pick out the major concentrations of

The authors present preliminary results of an infrared monitoring program of selected blazars, conducted at the Carlos Sanches Telescope at Izana Observatory, Teneriffe. Eight blazars have been observed during three observing runs since August 1990. All observed blazars have shown variability.

The paper presents simultaneous monitoring of the BL Lacertae object Markarian 501 obtained in the visible and near infrared using a double photometer system on the 1.5 m Carlos Sanchez Telescope situated in El Observatorio del Teide (Tenerife) and CCD photometry in U and B taken with the 1 m Jacobus Kapteyn Telescope of El Observatorio del Roque

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