ESTA TESIS DOCTORAL CONTIENE LOS RESULTADOS DE UN PROGRAMA DE INVESTIGACION EN EL QUE SE HAN DETERMINADO EMPIRICAMENTE LAS RELACIONES TEMPERATURA EFECTIVA-COLOR-METALICIDAD PARA ESTRELLAS DE SECUENCIA PRINCIPAL CON TIPOS ESPECTRALES COMPRENDIDOS EN EL RANGO F0-K5. PARA LLEVAR A CABO ESTA CALIBRACION HA SIDO NECESARIO DESARROLLAR UNA SERIE DE

EL OBJETO DE ESTA MEMORIA ES EL ESTUDIO DE LA RELACION ENTRE LOS PROCESOS DE FORMACION ESTELAR Y LA ACTIVIDAD EN EL NUCLEO DE LAS GALAXIAS. CON ESTE FIN SE ESTUDIA, EN PRIMER LUGAR, LA FORMACION ESTELAR EN LAS GALAXIAS ANALIZANDO ESTADISTICAMENTE MAS DE 500 REGIONES HII EN 55 GALAXIAS. A PARTIR DE ESTOS DATOS SE DETERMINAN FUNCIONES DE LUMINOSIDAD

We present I-band photometry of the soft X-ray transient (SXT) J0422+32 taken during a low-brightness state over two weeks in 1993 October. The object had a mean V magnitude of 19.9, approximately 2mag above its subsequent, presumably quiescent, level of V~22.4. These data revealed a periodicity at 16.18h (significance level>99 per cent), but we

Bolometric fluxes for 118 dwarfs and subdwarfs with 4000K less than Teff less than 7000K and +0.5 less than (Fe/H) less than -3.5 are derived by integrating UBVRIJHK photometry. For these stars (typical of the galactic and globular cluster main sequences) at least 80% of the energy emitted is measured by those bands. A grid of theoretical model

We have investigated in detail the uncertainties in deriving beryllium abundances for metal-poor stars from the BeII resonance doublet at λ 3131A. These uncertainties are related to the quality of the observations, the physical data used, and the adopted stellar parameters. We have taken into account the NLTE effects on the lines formation for the

By describing the dynamical evolution of a test charged particle in the presence of an electromagnetic field and a succession of infinitesimal Lorentz boosts and rotations it is possible to obtain the Lorentz force of electrodynamics. A consequence of this heuristic derivation at the classical level is that, given the existence of electric and