Context. Numerical three-dimensional (3D) radiative (magneto-)hydrodynamical [(M)HD] simulations of solar convection are nowadays used to understand the physical properties of the solar photosphere and convective envelope, and, in particular, to determine the Sun's photospheric chemical abundances. To validate this approach, it is important to

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Three new young objects have been found when carrying out a survey of IRAS sources with infrared colors like planetary nebulae, via low resolution spectroscopy. IRAS 14592 - 6311 and IRAS 07173 - 1733 are bright cometary nebulae, showing metal line emission very similar to V1331 Cyg, which is the prototype of a certain number of T-Tauri stars. They

Using a specialized technique sensitive to the presence of expanding ionized gas, we have detected a set of three concentric expanding shells in an H II region in the nearby spiral galaxy M33. After mapping the kinematics in Hα with Fabry-Perot spectroscopy, we used slit spectra to measure the intensities of the [S II] doublet at λλ671.9, 673.1 nm

We present three-dimensional numerical calculations of superbubbles evolving in a two-component interstellar medium composed of small diffuse clouds and a low-density intercloud medium. Cold H I clouds with internal densities n ˜ 10 cm-3 and radii Rcl = 3-5 pc were assumed to be embedded in a warm plane-stratified intercloud medium. The fraction of

Photon-counting techniques have been applied to a study of the movement of the image of an unresolved star at the 50 cm telescope of the Royal Academy of Sciences, at the Roque de los Muchachos Observatory. The temporal autocorrelation function of such movement has been computed, the results are discussed in terms of atmospheric turbulence and in