Aims:To conduct an intensive study of the rich, X-ray luminous galaxy cluster Abell 773 at z = 0.22 containing a diffuse radio halo to determine its dynamical status. Methods: Our analysis is based on new spectroscopic data obtained at the TNG telescope for 107 galaxies, 37 spectra recovered from the CFHT archive and new photometric data obtained

GREGOR is a new open solar telescope with an aperture of 1.5 m. It replaces the former 45-cm Gregory Coudé telescope on the Canary island Tenerife. The optical concept is that of a double Gregory system. The main and the elliptical mirrors are made from a silicon-carbide material with high thermal conductivity. This is important to keep the mirrors

We discuss the emission of gravitational radiation produced in encounters of dark matter galactic halos. To this aim we perform a number of numerical simulations of typical galaxy mergers, computing the associated gravitational radiation waveforms as well as the energy released in the processes. Our simulations yield dimensionless gravitational

Bimodality is a common feature of globular cluster (GC) color distributions in galaxies. Although it is well known that the GC system of the Milky Way is bimodal in metallicity, this has yet to be directly demonstrated for an elliptical galaxy. We use Lick index measurements from the literature to derive metallicities for 47 GCs in the giant Virgo

We present observations of the full Stokes vector in a flaring region, taken in the chromospheric He I 10830 Å multiplet. The data were recorded with the new Tenerife Infrared Polarimeter (TIP 2) at the German Vacuum Tower Telescope (VTT) during May 2005. The He profiles during the flare are extraordinary, showing extremely broad Stokes I

Aims:We study two dimensional Fabry-Perot interferometric observations of the nearby face-on late-type spiral galaxy, NGC 628, in order to analyse the ionized gas component of the interstellar medium. Covering the galaxy out to a radius larger than 12 kpc, and with a spatial sampling of 1.6'', we aim to investigate the large-scale dynamics as well