Aims.We made a seismic study of the young massive β Cephei star HD 203664 with the goal of constraining its interior structure.Methods.Our study is based on a time series of 328 new Geneva 7-colour photometric data of the star spread over 496.8 days.Results.The data confirm the frequency of the dominant mode of the star, which we refined to f_1=6

We present a comprehensive treatment of the pixel-lensing theory and apply it to lensing experiments and their results toward M31. Using distribution functions for the distances, velocities, masses, and luminosities of stars, we derive lensing event rates as a function of the event observables. In contrast to the microlensing regime, in the pixel

Aims.We present a detailed dynamical analysis of the rich galaxy cluster A2744, containing a powerful diffuse radio halo.Methods.Our analysis is based on redshift data for 102 galaxies, part of them recovered from unexplored spectra in the ESO archive. We combine galaxy velocity and position information to select the cluster members and determine

TrES-Her0-07621 is a recently discovered detached M Dwarf eclipsing binary system. We present some follow-up observations of this system including new minima times and a refined orbital period. We have also obtained better estimates of the stellar radii and inclination.

OO Ser is a deeply embedded young star which brightened by 5 mag between 1994 and 1995, and gradually faded afterwards. In many respects its eruption resembled the well-known FU Orionis-type (FUor) outbursts. Since very few such events have ever been documented at infrared wavelengths, we monitored OO Ser with the Infrared Space Observatory in the

We propose to perform H I observations of two starburst galaxies that show optical interaction features with surrounding objects and for which we have both broad-band and H-alpha imagery and optical spectroscopy. We will estimate the distribution of the atomic gas throughout the galaxies, looking for morphological features that reveal interaction