We review the structural properties of giant extragalactic HII regions and HII 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 exposed

The penumbra is ideally suited to challenge our understanding of magnetohydrodynamics. The energy transport takes place as magnetoconvection in inclined magnetic fields under the effect of strong radiative cooling at the surface. The relevant processes happen at small spatial scales. In this contribution we describe and elaborate on these small

Spectropolarimetric observations of spicules were carried out with the new optical setup of the Tenerife Infrared Polarimeter (TIP 2) at the VTT, showing the variation of the He I 10830Å multiplet off-limb emission profiles with increasing distance to the solar visible limb. The ratio between the intensities of the blue and the red components of

We present the first results of a 3D numerical modeling of linear MHD wave propagation in a realistic sunspot model. In our simulations, a piston located at the base of the photosphere generates waves with a certain period. The ratio between the acoustic and the Alfven speed, cS /vA, decreases from much larger than one at the photosphere to much

We present new results following up on our deep near-IR imaging of the strong lensing clusters Abell 1835 and AC114, which has allowed us to identify 13 star forming galaxy candidates at z>7 (Richard et al. 2006, A&A in press, [astro-ph/ 0606134]). Our previous optical and near-IR observations (mostly from WFPC2/HST, CFHT, ISAAC/VLT) have now been

The 1.5m solar telescope GREGOR is being constructed at Tenerife, Spain. Its purpose is to observe with high spatial and spectral resolution small-scale dynamic magnetic features on the Sun. The telescope is completely open with retractable dome and actively cooled primary mirror made of silicon carbide to minimize thermal effects on the image