In this paper we study how the normal fast modes of a coronal loop are modified by the addition of density structure along the loop axis. Using isobaric and thermal equilibria with different heating functions, a density profile for a loop is derived, and then its oscillatory modes are studied with techniques similar to those in our previous works

We report on ESO Very Large Telescope optical spectroscopy of 42 BL Lacertae objects of unknown redshift. Nuclear emission lines were observed in 12 objects, while for another six we detected absorption features due to the host galaxy. The new high signal-to-noise ratio spectra therefore allow us to measure the redshift of 18 sources. Five of the

OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the optical Day One instrument for the 10.4m Spanish telescope GTC (Gran Telescopio Canarias). The instrument spectral range covers from 365 up to 1000 nm. One of the most important elements of OSIRIS is its two commercial ICOS ET100 wide field Fabry-Perot tunable

EMIR, currently entering into its fabrication and AIV phase, will be one of the first common user instruments for the GTC, the 10 meter telescope under construction by GRANTECAN at the Roque de los Muchachos Observatory (Canary Islands, Spain). EMIR is being built by a Consortium of Spanish and French institutes led by the Instituto de Astrofisica

Large segmented mirrors require efficient co-phasing techniques in order to avoid the image degradation due to segments misalignment. For this purpose in the last few years new co-phasing techniques have been developed in collaboration with several European institutes. The Active Phasing Experiment (APE) will be a technical instrument aimed at

The Configurable Slit Unit (CSU) for EMIR shall enable the possibility to generate a multi-slit configuration, a long slit, or an imaging aperture at the entrance focal plane of the GTC-EMIR instrument. The CSU is therefore a cryogenic reconfigurable slit mechanism. It contains 100 sliding bars which can be positioned within the 307x307mm wide