A pilot experiment suitable to test Newton's law of gravity down to the regime of acceleration typical of galaxies has been carried out in Omega Centauri. Stars in the extreme periphery of this globular cluster are used as test particles immersed in such weak gravitational field. The stellar velocity dispersion is found to remain constant at large

We report the results of an HST survey of 17 AGN, selected solely for having a well developed radio jet bright enough to be detectable with HST for a normal radio-to-optical spectral index. It is found that optical jets are much more common then expected, been detected in ˜30% of the cases. The data are then combined with Chandra X-ray and VLA

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We consider the Orion Nebula (M 42) within a project aimed at studying the interaction between massive stars and their surrounding ISM. This is an HII region ionized by θ1 Ori C, one of the four massive stars in the Trapezium Cluster. θ1 Ori C has the earliest spectral type (O7Vp) among them, emitting an ionizing flux several orders of magnitude

It is often stated that there is no point in obtaining mid-infrared data with S/N>20, even in the best of cases, because it is impossible to obtain a calibration to better than 5%, although in many cases 10% or greater is a more accurate reflection of the true quality of calibration. Mid-infrared calibration is difficult because of the lack of

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