This paper presents semiempirical models of various solar magnetic structures, extending from the photosphere to the chromosphere. The models have been derived from non-LTE inversions of high-resolution spectropolarimetric observations of four Ca II and Fe I lines. The observed targets are dark and bright components of a sunspot umbra; dark and

Aims:In this paper we investigate the dependence of umbral core brightness, as well as the mean umbral and penumbral brightness on the phase of the solar cycle and on the size of the sunspot. Methods: Albregtsen & Maltby (1978, Nature, 274, 41) reported an increase in umbral core brightness from the early to the late phase of solar cycle from the

En esta tesis hemos realizado un estudio detallado de poblaciones estelares de galaxias elíptica en cúmulos de distinta masa. Nuestros resultados sugieren que las escalas de tiempo de formación de las estrellas en este tipo de galaxias dependen del entorno en el que se encuentran: las estrellas de galaxias de cúmulos masivos se forman más

Aims:We detected tertiary components of close binaries from spectroscopy and light curve modelling, investigated the light-travel time effect and the possibility of magnetic activity cycles, measured mass ratios for unstudied systems, and derived absolute parameters. Methods: We carried out new photometric and spectroscopic observations of five

The abundances of iron and oxygen are homogeneously determined in a sample of 523 nearby (d 5500 K and [Fe/H] -0.3, we find no obvious indication of a sudden decrease (i.e., a "knee") in the [O/Fe] vs. [Fe/H] pattern of thick-disk stars that would connect the thick and thin disk trends at a high metallicity. We conclude that Type Ia supernovae (SN

We report the discovery of a periodic modulation in the optical lightcurve of the candidate ultracompact X-ray binary 4U1822-000. Using time-resolved optical photometry taken with the William Herschel Telescope we find evidence for a sinusoidal modulation with a semi-amplitude of 8 per cent and a period of 191min, which is most likely close to the