EL OBJETIVO DE ESTA TESIS ES EL ESTUDIO DE LOS DIFERENTES PARAMETROS QUE DEFINEN LAS POBLACIONES ESTELARES DE LAS GALAXIAS. PARA ELLO SE DESARROLLA UN INNOVADOR MODELO DE SINTESIS DE POBLACIONES ACTUALIZADO CON LOS ULTIMOS AVANCES EN LA MATERIA. CON ESTE MODELO SE PREDICEN UN GRAN NUMERO DE OBSERVABLES (COLORES E INDICES) QUE SE COMPARAN CON DATOS

We present the results of the study of visible (UBVRIZ) intra-night microvariability in the blazar OJ 287. Useful observations (at least four integrations in a single band in a single night with a single telescope) were carried out on a total of 26 nights from November 1993 to November 1994. Relative photometry was taken against star 4, 10 and 11

The authors report the first infrared light curve of GS 2000+25. By modelling the brightness variations as ellipsoidal modulations of the secondary star, the authors find the mass of the compact object to lie between 4.8 and 14.4 Msun (90 per cent confidence) for secondary masses ≤0.7 Msun; this result is independent of the mass ratio, q. The upper

A sample of 198 soft X-ray-selected active galactic nuclei (AGN) from the ROSAT International X-ray Optical Survey (RIXOS) is used to investigate the X-ray luminosity function and its evolution. RIXOS, with a flux limit of 3x10^-14 erg s^-1 cm^-2 (0.5 to 2.0 keV), samples a broad range in redshift over 20 deg^2 of sky, and is almost completely

We have studied spectra of the peculiar B[e] star HD 45677. Examination of the Balmer wings enabled us to determine a value of logg=3.9 indicating a possibly luminosity class V. The weak HeI lines together with the SiII 4128 and 4130A doublet indicate a low rotation velocity in the order of 70km/s, which is much lower than the previously claimed

A method for ``time/frequency'' analysis is shortly described, with a discussion of its limitations in time and frequency resolution, and in sensitivity to noise in the signal. This is then applied to observational data. The data used are the luminosity measurements of the IPHIR experiment, and the velocity measurements performed at the