The primordial abundance of 4He, YP, is one of the hottest themes in present-day astronomy, mostly due to its cosmological relevance. The disagreement between different determinations has been currently reduced to the 1-2% level, but these differences are still large enough to have deep implications for Big-Bang nucleosynthesis. It is therefore

Based on observations of HII regions and on the new computations of the recombination coefficients of the HeI lines by Porter el al. we obtain a primordial helium abundance by mass of Y_P = 0.2446 ± 0.0029. We consider thirteen sources of error for the Y_P determination; some of them are mainly due to systematic effects, while the rest are mainly

We present near-infrared imaging obtained with ESO VLT/ISAAC of a sample of 16 low luminosity radio-quiet quasars (RQQs) at the epoch around the peak of the quasar activity (2 z 3), aimed at investigating their host galaxies. For 11 quasars, we are able to detect the host galaxies and derive their properties, while for the other 5 quasars, upper

We present high-quality, wide spectral coverage long-slit optical spectra for 12 powerful radio sources at low and intermediate redshifts (z 0.7) that show evidence for a substantial ultraviolet (UV) excess. These data were taken using the William Herschel Telescope and the ESO Very Large Telescope with the aim of determining the detailed

The photometric and kinematic properties of Sb NGC 1292 suggest it hosts a pseudobulge. The properties of the stellar population of such a pseudobulge are consistent with a slow buildup within a scenario of secular evolution.

An analysis of about 27 h of fast photometry of the cool ZZ Ceti white dwarf PG2303+243 reveals (1) the presence of many modes (as many as 22), some of them of low enough amplitude to have escaped previous detection, and (2) a short time scale (less than 10 d) drastic variation in amplitude. A preliminary identification of the modes observed in