Aims.We present a study of the neutron star X-Ray Transient Cen X-4. Our aim is to look for any evidence of irradiation of the companion with a detailed analysis of its radial velocity curve, relative contribution of the donor star and Doppler tomography of the main emission lines. Methods: .To improve our study all our data are compared with a set

One of the classical tests of the early dynamical evolution of the Milky Way is the prediction of the monolithic collapse model (e.g., Eggen, Lynden-Bell, & Sandage 1962) of a decline in the mean stellar abundance of the halo population as one proceeds to stars at greater distances, or equivalently, with higher local space velocities in the solar

The optical afterglow spectrum of GRB 050401 (at z=2.8992+/-0.0004) shows the presence of a damped Lyα absorber (DLA), with logNHI=22.6+/-0.3. This is the highest column density ever observed in a DLA and is about 5 times larger than the strongest DLA detected so far in any QSO spectrum. From the optical spectrum, we also find a very large Zn

A new method of calculating microlensing magnification patterns is proposed that is based on the properties of the backward gravitational lens mapping of a lattice of polygonal cells defined at the image plane. To a first-order approximation, the local linearity of the transformation allows us to compute the contribution of each image-plane cell to

Aims.We investigate the effects of varying the magnetic field strength and the twist of a flux tube as it rises through the solar interior and emerges into the atmosphere. Methods: .Using a 3D numerical MHD code, we consider a simple stratified model, comprising of one solar interior layer and three overlying atmospheric layers. We set a horizontal

Optical novae have recently been identified as the major class of supersoft X-ray sources in M 31 based on ROSAT and early XMM-Newton and Chandra observations. This paper reports on a search for X-ray counterparts of optical novae in M 31 based on archival Chandra HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region