We have used the Chandra X-ray Observatory to observe the following six black hole X-ray transients in quiescence: GRO J0422+32 (orbital period Porb=5.1 hr), A0620--00 (Porb=7.8 hr), GS2000+25 (Porb=8.3 hr), 4U1543--47 (Porb=27.0 hr), GRO J1655--40 (Porb=62.9 hr), GS2023+338 (Porb=155 hr). Previous to these Chandra observations there was only a

Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the

We present the detailed spectral analysis of a sample of M33 B-type supergiant stars, aimed at the determination of their fundamental parameters and chemical composition. The analysis is based on a grid of non-LTE metal line-blanketed model atmospheres including the effects of stellar winds and spherical extension computed with the code FASTWIND

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