(Hα+[NII])/[OIII] ratio images have been used to search for low-ionization small-scale structures in a sample of 258 planetary nebulae. Radially symmetrical knots or jet-like structures, which are enhanced in the ratio images compared to the neighbouring regions of the nebulae, have been identified in 23 objects. Some of these features are barely

The propagation of a shock wave into a medium is expected to heat the material beyond the shock, producing noticeable effects in intensity line ratios such as [O iii]/Hα. To investigate the occurrence of shocks in planetary nebulae (PNe), we have used all narrow-band [O iii] and Hα images of PNe available in the HST archive to build their [O iii]

The origin of the unification model for active galactic nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ˜30-40 per

We perform a search for gravitational wave bursts using data from the second science run of the LIGO detectors, using a method based on a wavelet time-frequency decomposition. This search is sensitive to bursts of duration much less than a second and with frequency content in the 100-1100 Hz range. It features significant improvements in the

Aims: We study the massive stars in OB associations and their surrounding interstellar medium environment, using a population synthesis code. Methods: We developed a new population synthesis code for groups of massive stars, where we model the emission of different forms of energy and matter from the stars of the association. In particular, the

PG 1351+64 is a bright radio quiet quasar (z = 0.088, mV ≅ 14). IUE observations obtained within few months in 1982 - 1983 showed variations in the 1200 - 2000 Å band up to a factor of 2. Since then the object has been monitored regularly. The observations of 1984 - 1986, including also archival data, have more than doubled the number of available