Using CCD observations in the narrow band filters in Hα , Hβ , [O Ii], [O Iii], [S Ii] and [S Iii] lines we have compiled a catalogue of 338 H Ii regions for the inner parts of NGC 5457 and 158 for NGC 4395. The extinction, equivalent widths, distributions, excitations, ionization hardness, ionization parameters and metallicities for these regions

Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a

Numerical simulations of galaxy formation predict direct gas accretion from the cosmic web to be the main mode of disk galaxy formation. However, observational evidence of the process are so far scarce and indirect. This write up should be regarded as a progress report listing several of our works which, in the long term, aim at finding evidence

Comet Hale-Bopp has shown an extremely elevated level of dust activity during its apparition. We examine the dust activity of the comet, particularly the dust jets which were observed so frequently between discovery and perihelion + 5 months. Other results from observations carried out during the observing campaign have shown that the dust emission

Spitzer/infrared spectrograph (IRS) spectra from 5 to 37 μm for a complete sample of 31 R Coronae Borealis stars (RCBs) are presented. These spectra are combined with optical and near-infrared photometry of each RCB at maximum light to compile a spectral energy distribution (SED). The SEDs are fitted with blackbody flux distributions and estimates

Observations carried out with a 8-13 micron grating-spectrometer of Mrk 231 and NGC 4151 are reported. The Mrk 231 data can be fitted to various thermal dust emission models or a single power law, with dust extinction. In all the model fits, except for that of graphite and silicon carbide grain emission, a component of silicate absorption of