Toda teoría que pretenda explicar la formación de las galaxias y su evolución posterior debe dar cuenta de la influencia del entorno sobre sus propiedades observacionales. Los cúmulos de galaxias, dadas las peculiares características que presentan --una alta densidad de materia bariónica en forma de galaxias y un medio intracumular caliente

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Using the near-infrared spectral stellar library of Cenarro et al., the behaviour of the MgI line at 8807 Å and nearby TiO bands is analyzed in terms of the effective temperature, surface gravity and metallicity of the library stars. New spectroscopic indices for both spectral features - namely MgI and sTiO - are defined, and their sensitivities to

Aims: We study the vector magnetic field of a filament observed over a compact active region neutral line. Methods: Spectropolarimetric data acquired with TIP-II (VTT, Tenerife, Spain) of the 10 830 Å spectral region provide full Stokes vectors that were analyzed using three different methods: magnetograph analysis, Milne-Eddington inversions, and

Context: The young active G-dwarf star V889 Herculis (HD 171488) shows pronounced spots in Doppler images as well as large variations in photometry and radial velocity (RV) measurements. However, the lifetime and evolution of its active regions are not well known. Aims: We study the existence and stability of active regions on the star's surface