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Iterative schemes based on Gauss-Seidel (G-S) and optimal successive over-relaxation (SOR) iteration are shown to provide a dramatic increase in the speed with which non-LTE radiation transfer (RT) problems can be solved. The convergence rates of these new RT methods are identical to those of upper triangular nonlocal approximate operator splitting

The stellar content and stellar age distribution of the Pegasus Dwarf Irregular Galaxy are discussed in the light of deep CM diagrams for (V - R) and (V - I) color indices, complemented by Hα data. The CM diagrams of Pegasus show two structures-red tail and red tangle-which denote the presence of intermediate-age and old stars in the galaxy. After

Optical spectroscopy of three recently discovered BL Lacs (PG 1246+586, PG 1424+240 and PG 1437+398) in the Palomar-Green optical survey is presented. The three sources have featureless spectra and the continuum is well represented by a power law model with slopes typical of BL Lac objects. The observations together with data at other frequencies

SE HAN REALIZADO OBSERVACIONES ESPECTROSCOPICAS CON RESOLUCION ESPACIAL Y RESOLUCION ESPECTRAL INTERMEDIA PARA UNA MUESTRA DE NEBULOSAS PLANETARIAS (NP) EXTENSAS REPRESENTATIVAS DE DIFERENTES CLASES. SE HAN INCLUIDO NP CON MULTIPLES CAPAS (M 1-46, NGC 2438, NGC 5882 Y NGC 6720), BIPOLARES (K 4-55, M 1-75, NGC 2440 Y NGC 2818) Y DEFICITARIAS EN

We present the results of Thuan & Gunn r CCD imaging observations of the Universidad Complutense de Madrid (UCM) sample of emission-line galaxies (ELGs), selected by the presence of Hα emission in low-resolution objective prism spectra. In this work we characterize photometrically and morphologically a total of 212 objects from the UCM survey. This