En esta Tesis se analiza la estructura de una mancha solar tipica, redonda, aislada y situada cerca del centro del disco solar, para 25 capas en profundidad óptica. Los datos fueron obtenidos con el "Advanced Stokes Polarimeter", uno de los mejores instrumentos disponibles, y la estratificación de los diferentes parámetros a lo largo de la

We have obtained high-resolution echelle spectroscopy of the recurrent nova T CrB. We find that the surface lithium abundance in T CrB is significantly enhanced compared with the case of field M giants, where it is not detectable. We offer possible explanations for this in terms of either a delay in the onset of convection in the giant star

En la tesis se presenta un método para la inversión de los perfiles de Stokes de lineas espectrales para lasque la aproximación de Equilibrio Termodinámico Local no es adecuada. Este método es aplicado a observaciones espectro-polarimétricas realizadas con vistas al estudio de la dinámica y el magnetismo de la cromosfera sobre laumbra de las

We discuss results on the oxygen abundance in a sample of 23 metal-poor (-3.0≤ [Fe/H] ≤ -0.3) unevolved stars and one giant. High resolutionspectroscopy of OH lines in the near UV allowed us to trace the early evolution of oxygenversus metallicity. Contrary to previous expectations, we find that oxygen abundances derived from these low excitation

IAUC 7219 available at Central Bureau for Astronomical Telegrams.

We report optical observations of the GRB 980329 error box which represent the second earliest detection of the GRB 980329 optical transient. We determine R = 23.7 +/- 0.5 mag on 29.89 March, which is consistent with R = 23.6 +/- 0.2 mag as reported by Palazzi et al. (1998) on 29.99 March. Based on extrapolations of the light curve we claim that