The solar core is the region where all the nuclear reactions take place and, therefore, where the energy is generated. Understanding the physics of these internal layers, the theory of solar and stellar structure can be settled into form grounds. However this is the most unknown region of the Sun. Helioseismology, mainly through the gravity modes

Observations of the soft X-ray transient Nova Vela 1993 are presented. These are the first observations, taken during quiescence in 1995 and 1996. An orbital, ellipsoidal modulation is found in the R-band photometry (mean magnitude of 20.6), with an amplitude of 0.23 mags at 6.86 +/- 0.12 h. The H-alpha emission spectra is presumed to arise from

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