We confirm recent results about the differences in temperature and magnetic field strength between the umbra of large and small sunspots. Five Stokes I- and V-spectra from the darkest cores of three different umbrae have been analyzed with the inversion code of the radiative transfer equation by Ruiz Cobo & del Toro Iniesta (1992). The run with

Following our recent report of a strong Li lambda 6708 resonance line in the secondary of the black hole candidate V404 Cyg, we present here its detection in the quiescent spectrum of the neutron star binary Cen X-4. We obtain, via a spectral synthesis Local Thermodynamic Equilibrium (LTE) analysis, a surface lithium abundance in the K-type

We have analyzed long-slit spectroscopic data for a sample of 12 tidally disturbed elliptical galaxies. The spectra were obtained with the Kitt Peak National Observatory (KPNO) 4 m RC spectrograph. Rotation curves and velocity dispersion profiles have been measured at a variety of position angles in these galaxies and have been used to analyze the

EN LA PRIMERA PARTE DE LA TESIS SE ESTUDIA LA DINAMICA DE NEBULOSAS DE ANILLO INTERPRETADAS COMO UN PRODUCTO RESULTANTE DEL MATERIAL ESTELAR EYECTADO. SE DISCUTEN NUEVOS MODELOS HIDRODINAMICOS QUE PUEDEN EXPLICAR LA MAYORIA DE LAS CARACTERISTICAS QUE APARECEN EN LAS OBSERVACIONES DE LAS NEBULOSAS DE ANILLO. CON VISTAS A UNA PRIMERA APROXIMACION DE

We present intermediate dispersion (0.7-2.2 A/pixel) optical spectroscopic observations aimed at applying the 'lithium test' to a sample of 10 brown dwarf candidates located in the general field, two in young open clusters, and two in close binaries. We find evidence for strong Li depletion in all of them, and thus infer lower mass limits of 0.065

ESTA MEMORIA PRESENTA UN TRABAJO DE 4 AÑOS DE CONTRIBUCION, CON EXITO, A LA INTRODUCCION DE LOS CCDS, COMO DETECTORES FOTOMETRICOS PRECISOS, EN EL MUNDO DE LA ASTROSISMOLOGIA. SE EXPONEN Y DISCUTEN LOS DIFERENTES METODOS DE REDUCCION DE DATOS OBTENIDOS CON FOTOMETRIA DIFERENCIAL RAPIDA, COMPARANDO VARIOS PROGRAMAS DE REDUCCION Y PROPONIENDO ALGUNOS