M31 has been monitored by the HRC and ACIS detectors aboard Chandra from 1999 to 2002. We report here a summary of properties of X-ray sources in M31 with a focus on an ongoing Chandra/HST program to monitor X-ray transients in M31. By comparing individual X-ray images, more than 100 sources were found to be variable (half the total number observed

We present a second paper of a complete characterization of stars whose low-depth transits were discovered by the OGLE-III campaign to select the most promising candidates for spectroscopic confirmation. This paper follows a similar analysis to one previously performed in Gallardo et al. (2005, A&A, 431, 707). We present new optical and near-IR

The GAW project aims to test the feasibility of a new generation of Imaging Atmospheric Cherenkov Telescopes that join high flux sensitivity with Large Field of View capability. It consists of an array of 3 imaging Cherenkov telescopes each equipped with a Fresnel refractive lens of about 3.6 m2 geometrical area and an array of multi-anode

Carrying out detailed analyses on massive blue stars further than the Milky Way is a demanding task, however it is feasible and the best way to comprehend the stellar evolution in environments with different metallicity. We present the first quantitative study performed on a massive blue star sample belonging to NGC~55, about 1.9 Mpc away. The

Atmospheric extinction data covering a long period are analysed. We present infrared atmospheric extinction in the J, H and K bands obtained at the Teide Observatory from 1989 to 1997. We find high-quality statistical values, similar to those of other good sites, such as Mauna Kea. We devote special attention to the study of the dependence of the

Context. Open clusters are ideal test particles for studying the chemical evolution of the Galactic disc. However, the number and accuracy of existing high-resolution abundance determinations, not only of [Fe/H], but also of other key elements, remains largely insufficient. Aims: We attempt to increase the number of Galactic open clusters that have