We review the structural properties of giant extragalactic H II regions and H II galaxies based on two-dimensional hydrodynamic calculations and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus

We present a general analytical procedure for computing the number density of voids with radius above a given value within the context of gravitational formation of the large-scale structure of the Universe out of Gaussian initial conditions. To this end, we develop an accurate (under generally satisfied conditions) extension of the unconditional

Recently, the HESS array has reported the detection of γ-ray emission above a few hundred GeV from eight new sources located close to the Galactic plane. The source HESS J1834-087 is spatially coincident with the supernova remnant G23.3-0.3 (W41). Here we present MAGIC observations of this source, resulting in the detection of a differential γ-ray

We report the discovery of a possible nova in M31 on a R band CCD image at JD 2453877.5 (2006, May 22.1 UT) with 18.7 mag (accuracy 0.1 mag). The image was obtained with the Wendelstein telescope (0.8 m, 1k x 1k CCD camera with 24mu sq. pixels). The position obtained for the nova candidate is RA(2000) = 00h 43m 11.81s, Dec(2000) = +41° 13' 44.7"

Aims.Properties of multiplicity, such as the multiplicity frequency, the distribution of mass ratios and periods, provide important informations on the formation processes at work. Studying these properties in different environments and at different ages allows us to constrain the models of formation and to understand the influence of the

Aims.We study the buoyant rise of magnetic flux tubes in a stratified layer over a range of Reynolds numbers (25 ⪉ Re ⪉ 2600) by means of numerical simulations. Special emphasis is placed on studying the fragmentation of the rising tube, its trailing wake and the formation of a vortex street in the high-Reynolds number regime. Furthermore, we