We obtained at the Coude Echelle Spectrometer (CES) attached to the 1.4m CAT telescope of the European Southern Observatory ,high resolution (R=1O0000),high signal to noise (S/N=30-20O) spectra of the Ca II H and k,H alpha and Ca II infrared triplet lines on a sample of southern late-type dwarfs also observed with lUE for the Mg II h and k lines

B-magnitudes have been compiled from the literature for 3C 345, covering a period from 1965 to 1980, 905 values in all. Since the last major study of the light-curve of this object (Barbieri et al., 1977), new and also revised data have been presented, which extend the light-curve and improve the temporal resolution. A compilation of the

A model of the galactic stellar distribution has been developed and the surface stellar densities in the near infrared are compared with observations along the galactic plane between l = 0° and l = 10°. The model, based on data taken from the literature, is in reasonable agreement with the observational results. However, the mass distribution

An effort is made to determine the differential rotation of the sun on the basis of the complete sample (1874-1976) of the Greenwich Photoheliographic Results. In order to improve the representation of differential rotation, a modified fit formula whose constant lies at 15 deg latitude (where sunspots nearly always occur) is introduced. Rotation is

EN LA PRESENTE TESIS SE ABORDA UNO DE LOS TEMAS DE MAS INTERES Y ACTUALIDAD DE LA FISICA SOLAR Y EN GENERAL DE LA ESTRUCTURA Y EVOLUCION ESTELAR. LA TECNICA DE OBSERVACION EL GRAN NUMERO DE ELLAS Y SU RIGUROSO ANALISIS HAN PERMITIDO LA DETECCION DE LOS MODOS GRAVITATORIOS DEL ESPECTRO DE OSCILACIONES SOLARES. SU IMPORTANCIA ES EXTRAORDINARIA POR