PKS 0537-441, a bright gamma -ray emitting blazar, was observed at radio, optical, UV and X-ray frequencies during various EGRET pointings, often quasi-simultaneously. In 1995 the object was found in an intense emission state at all wavelengths. BeppoSAX observations made in 1998, non-simultaneously with exposures at other frequencies, allow us to

We have discovered three certain (SAX J1324.5-6313, 2S 1711-339 and SAX J1828.5-1037) and two likely (SAX J1818.7+1424 and SAX J2224.9+5421) new thermonuclear X-ray burst sources with the BeppoSAX Wide Field Cameras, and observed a second burst ever from a sixth one (2S 0918-549). Four of them (excluding 2S 1711-339 and 2S 0918-549) are newly

Esta tesis forma parte de un proyecto a largo plazo cuyo objetivo es estudiar la evolución de los parámetros estructurales de las galaxias en función de su desplazamiento al rojo y en relación a la densidad local que las rodea. La meta principal de esta tesis ha sido desarrollar un software de análisis morfológico capaz de extraer información

10199 Chariklo is the largest Centaur so far known. To investigate its surface composition and possible surface variations, spectroscopic observations have been carried out at the largest available telescopes. We obtained near-infrared spectra at ESO-VLT (Cerro Paranal, Chile) and TNG (La Palma, Spain) on April 2001 and March 2002, respectively

From a comparison of the different parameters of warped galaxies in the radio, and especially in the visible, we find that: a) No large galaxy (large mass or radius) has been found to have high amplitude in the warp, and there is no correlation of size/mass with the degree of asymmetry of the warp. b) The disc density and the ratio of dark to

We present optical photometry and spectroscopy of the X-ray transient XTE J1859+226, obtained during outburst and its subsequent decay to quiescence. Both the X-ray and optical properties are very similar to those of well-studied black hole soft X-ray transients. We have detected three mini-outbursts, when XTE J1859+226 was approaching quiescence