Based on a 5ks Chandra ACIS-I observation of M31 on Nov 11 2009, we report a dramatic brightening of CXOM31 J004321.1+411751, [aka r3-7 (Kong et al. 2002 ApJ 577, 738), source 437 (Pietsch, Freyberg, and Haberl 2005 A&A 434, 483), RX J0043.3+4117 (Supper et al. 2001 A&A 373, 63)]. The spectrum on Nov 11 can be well fit with a power law with photon

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