Context: The dependence of amplitude on the pulsation period differs from other Cepheid-related relationships. Aims: We attempt to revise the period-amplitude (P-A) relationship of Galactic Cepheids based on multi-colour photometric and radial velocity data. Reliable P-A graphs for Galactic Cepheids constructed for the U, B, V, R_C, and IC

Comet 67P, the target of Rosetta mission, was observed in the visible and near-IR spectral regions during its perihelion approach. The observations were performed in four epochs, at heliocentric distances varying from about 3 to 1.4 AU, i. e. in the same range of the Rosetta mission. The aims of the observations were the study of the dust coma and

Context: To obtain a significant Zeeman signature in the polarised spectra of a magnetic star, we usually “add” the contributions of numerous spectral lines; the ultimate goal is to recover the spectropolarimetric prints of the magnetic field in these line additions. Aims: Here we want to clarify the meaning of these techniques of line addition; in

Context: We present observations of the GRB 080319B afterglow at optical, mm, and radio frequencies between a few hours and 67 days after the burst. Aims: We attempt to understand the nature of this extraordinarily bright explosion based on the observed properties and its comparison with afterglow models. Methods: Our observations and other

Context: Substructures - dark lanes and tails - of umbral dots (UDs) were predicted by numerical simulations of magnetoconvection and have been detected later in some observations. Aims: To provide constraints for realistic theoretical models of sunspot umbrae, we describe the observed properties and evolutionary characteristics of UDs (including

Future large and extremely large ground-based telescopes will demand stable geological settings.Remote sensing could be an unvaluable tool to analyse the impact of geological activity at selected astronomical sites, namely the observatories of El Teide (Tenerife, Canary Islands), Roque de los Muchachos (La Palma, Canary Islands), Mauna Kea (Hawaii)