Context. During the past 100 years, helium emission lines have never been observed in RR Lyrae stars, especially in RRab-type ones where strong shock waves are nevertheless present in their atmosphere. Only recently have the observation of He I emission lines in 10 RRab stars and the detection of very weak He II emission in 3 of them been reported

In a recent published study we have analysed the evolution of the bar pattern speed with redshift using morphological measurements of a sample of low-inclination ringed galaxies from the SDSS and the COSMOS survey. In this paper we summarise the results obtained in that work. The sample covers a redshift range 0

An optically and geometrically thick torus obscures the central engine of active galactic nuclei (AGN) from some lines of sight. From a magnetohydrodynamical framework, the torus can be considered to be a particular region of clouds surrounding the central engine where the clouds are dusty and optically thick. In this framework, the magnetic field

Magnetic field plays a crucial role to understand most phenomena happening in the solar atmosphere. Sunspots, flares, prominences, coronal mass ejections are well known examples of its interaction with the solar plasma. To study the properties of this interaction, one needs to analyze the imprint it leaves in the radiation through the polarization

We investigate the suitability of GTC/OSIRIS Tunable Filters (TFs) for obtaining emission-line maps of extended objects. We developed a technique to reconstruct an emission-line image from a set of images taken at consecutive central wavelengths. We demonstrate the feasibility of the reconstruction method by generating a flux calibrated Hα image of

We have used the tuneable filter system of OSIRIS to observe the [SII] doublet lines at λλ617.7 and 673.1 nm in emission across the full face of NGC 6946, and estimated the in situ electron densities for 387 HII regions, so far. The values decline steadily from over 350 cm^-3 at 1/3 R_{25} to around 175 cm^-3 at 2/3 R_{25}.