Aims: Our science goals are to characterise the optical properties of Y dwarfs and to study their consistency with theoretical models. Methods: A sample of five Y dwarfs was observed with three optical and near-infrared instruments at the 10.4m Gran Telescopio Canarias. Deep near-infrared (J- or H-band) and multicolour optical images (z-, i-, r-, G

Previous studies have found that red giants (RGs) in close binary systems undergoing spin-orbit resonance exhibit an enhanced level of magnetic activity with respect to single RGs rotating at the same rate, from measurements of photometric variability, S ph ', and the chromospheric emission S-index, S Ca II. Here, we consider a sample of 4465 RGs

Aims: The goal of this work is to scrutinise the surface brightness fluctuation (SBF) calculation methodology. We analysed the SBF derivation procedure, measured the accuracy of the fitted SBF under controlled conditions, retrieved the uncertainty associated with the variability of a system that is inherently stochastic, and studied the SBF