Studies of black holes are at a threshold. There is compelling evidence for the existence of both stellar-mass and supermassive black holes, and research is now focused on determining their properties and environmental effects. Most importantly, we are starting to realize the long-held promise of black holes as the ultimate laboratories for

Aims: The amplitude and scaleheight of the Galactic gas disc density are not axisymmetric against expectations in a self-gravity axisymmetric disc. However, this lopsidedness can be explained in terms of intergalactic accretion flows, which produce non-axisymmetric pressure on the disc. This mechanism could be also responsible for the formation of

We have defined a new Hβ absorption index definition, Hβo, which has been optimized as an age indicator for old and intermediate age stellar populations. Rather than using stellar spectra, we employed for this purpose a library of stellar population spectral energy distributions of different ages and metallicities at moderately high resolution. Hβo

Jupiter was imaged during the Science Demonstration of the MCAO Demonstrator (MAD) at the European Southern Observatory's Very Large Telescope. Io and Europa were used as natural guide stars on either side of Jupiter, separated from each other by about 1.6 arcmin from 23:41 to 01:32 UT (2008 Aug 16/17). The corrected angular resolution was 0.090

Context: Nearby young clusters are privileged places to study the star formation history. Over the last decade, the σ-Orionis cluster has been a prime location for the study of young very low mass stars, substellar and isolated planetary mass objects and the determination of the initial mass function. Aims: To extend previous studies of this

Aims: We investigate the origin of a flux increase found during a transit of TrES-1, observed with the HST (Hubble Space Telescope). This feature in the HST light curve cannot be attributed to noise and is supposedly a dark area on the stellar surface of the host star eclipsed by TrES-1 during its transit. We investigate the likelihood of two