As part of our Guaranteed Time Observer program on the Chandra X-Ray Observatory, we have an M31 observing program which has two major objectives. First to monitor the galaxy on a monthly basis to detect transient sources and follow their evolution. Second to obtain a deep image of the central region of M31 in order to measure the luminosity

One of the intents of the ground-based gamma-ray astronomy is to obtain a sky survey in the TeV energy region, and nowadays this target can be reached with giant arrays of telescopes, which however need many pointings due to their small field of view. A different approach is on the basis of GAW, acronym for Gamma Air Watch, an array of three

We contribute to the subject of the physical interpretation of exact solutions by characterizing them through a systematic study in terms of unambiguous physical concepts coming from systems in linearized gravity. We use the physical meaning of the leading order behavior of the Weyl spinor components $Psi_0^0$, $Psi_1^0$ and $Psi_2^0$ and of the

The calculation of solar absolute fluxes in the near-UV is revisited, discussing in some detail recent updates in theoretical calculations of bound free opacity from metals. Modest changes in the abundances of elements such as Mg and iron-peak elements have a significant impact on atmospheric structure, and therefore self-consistent calculations

We present the abundances of volatile and refractory elements in the atmospheres of 95 solar analogs, 24 planet hosts and 71 "single" stars, to investigate its possible connection with terrestial planets, using very high-quality HARPS and UVES spectra. The whole sample of stars with and without planets show almost the same mean abundance pattern

Theoretical studies suggest that C/O and Mg/Si are the most important elemental ratios in determining the mineralogy of terrestrial planets. The C/O ratio controls the distribution of Si among carbide and oxide species, while Mg/Si gives information about the silicate mineralogy. We present a detailed and uniform study of C, O, Mg, and Si