Recent focus on the importance of cold, unshocked gas accretion in galaxy formation - not explicitly included in semi-analytic studies - motivates the following detailed comparison between two inherently different modelling techniques: direct hydrodynamical simulation and semi-analytic modelling. By analysing the physical assumptions built into the

The highest resolution images ever taken in the visible were obtained by combining Lucky Imaging and low order adaptive optics. This paper describes a new instrument to be deployed on the WHT 4.2m and GTC 10.4 m telescopes on La Palma, with particular emphasis on the optical design and the expected system performance. A new design of low order

Context. Ground-based imaging and imaging spectropolarimetric data are often subjected to post-facto reconstruction techniques to improve the spatial resolution. Aims: We test the effects of reconstruction techniques on two-dimensional data to determine the best approach to improve our data. Methods: We obtained an 1-h time-series of

In July, the transient neutron star low-mass X-ray binary Aql X-1 was detected in outburst at X-ray, UV, optical and near-infrared wavelengths (ATel #2742, #2744, #2748). On 1st September the X-rays re-brightened (ATel #2850). Here we report on our ongoing optical monitoring campaign (ATel #1218, #1970, #2288) with the Faulkes Telescopes North and

One of the problems found in the design of the electronics for astronomical instruments is the difficulty to find precise digitizers (16 bits) at high speed. In fact, most of the chips which claim to have 16-bit actually have a lower ENOB (Effective Number Of Bits), normally around 14, when considering their noise effects. In this paper, a

Context: The physical interpretation of scattering line polarization offers a novel diagnostic window for exploring the thermal and magnetic structure of the quiet regions of the solar atmosphere. Aims: We evaluate the impact of isotropic collisions with neutral hydrogen atoms on the scattering polarization signals of the 13 lines of multiplet 42