With ACS-HST images we produced continuum subtracted photometric maps in Hα for the galaxies M51 and NGC 4449. From the Hα luminosity (L), equivalent radius (R) and coordinates of the HII regions with respect to the galaxy centers (over 2000 regions for M51, over 200 regions for NGC 4449), we derived the mean luminosity weighted electron density,

We present a detailed study on the surface composition of 2003 EL61. We use visible and near-infrared spectra of 2003 EL61 obtained for more than three consecutive hours covering more than 80% of the rotational period, in the Telescopio Nazionale Galileo and William Herschel Telescope, sited in the Observatorio del Roque de los Muchachos. First we

Infrared images of the Q0957+561 gravitational lens obtained with the Hubble Space Telescope show two large (~5") lensed images of the zs=1.41 quasar host galaxy. Parts of the host galaxy are doubly imaged, like the quasar, while other parts are quadruply imaged. The distortions of the host galaxy offer the best probe yet of the global structure of

We report on the optical properties of a sample of 30 BL Lac host galaxies in the redshift range 0.03

We have built a hybrid turbulence profiler measuring simultaneously the atmospheric turbulence structure with a Shack- Hartmann wave front sensor and a G-SCIDAR (scintillation sensor). This is the first instrument combining two different techniques to measure simultaneously the turbulence structure. The hybrid profiler has been installed at the