We present time-resolved optical spectroscopy and photometry of four relatively bright (V˜14.0-15.5) long-period cataclysmic variables (CVs) discovered in the Hamburg Quasar Survey: HS 0139+0559, HS 0229+8016, HS 0506+7725, and HS 0642+5049. Their respective orbital periods, 243.69±0.49 min, 232.550±0.049 min, 212.7±0.2 min, and 225.90±0.23 min are

Dark Matter supposedly dominates the extragalactic Universe, yet no totally dark structure of galactic proportions has ever been convincingly identified. Minchin et al. (2005) suggested that VIRGOHI 21, a 21-cm source found in the Virgo Cluster by Davies et al. (2004), was probably such a dark galaxy because of its broad line-width ( ˜ 200 km s-1)

We have run high resolution N-body models simulating the encounter of a dwarf galaxy with a bright elliptical galaxy. The dwarf absorbs orbital angular momentum and shows counter-rotating features in the external regions of the galaxy. To explain the core-envelope kinematic decoupling observed in some dwarf galaxies in high-density environments

The association of Gamma-Ray Bursts (GRBs) with Supernovae (SNe), or at least of some GRBs with some SN is now confirmed for several events. Of these, the most intense and better followed is the one associated with SN2003dh, namely GRB 030329, detected by HETE-2, a NASA ``explorer'' mission devoted to fast detection and localization of GRBs. Other

We present U and B galaxy number counts from a field that comprises a 0.29 square degrees area of sky, and which covers the Groth-Westphal Strip (Groth et al.,1994). Reached 50% limiting magnitudes are 24.8 magnitudes in U and 25.5 in B in the Vega system, which makes our U number counts to have the biggest area×depth product at the moment. These

The Global Oscillations at Low Frequency: New Generation instrument (GOLF-NG), the successor of GOLF aboard SoHO, is devoted to the study the dynamics of the solar radiative zone thanks to the detection of solar gravity modes and low-frequency acoustic modes. This instrument built under a French-Spanish collaboration, is based on the Doppler