An observational study of large-scale star formation processes in spiral galaxies with well-defined arm systems is presented. Combining new data on the current massive star formation (from H-alpha imaging) and on the total gas distribution (both atomic and molecular hydrogen, from H I and CO observations), the star formation efficiencies in- and

We present the results of our observations of stars of type O5 and earlier and show that inclusion of the line blocking between 228 and 912 A solves the problem found by Herrero et al. (1992) in the determination of their stellar parameters. We study the influence of the line blocking and other effects on the mass and helium discrepancies and show

Maralinga is an anomalous CK4 carbonaceous chondrite which contains numerous Ca-, Al-rich inclusions (CAI's) unlike the other members of the CK group. These CAI's are characterized by abundant green hercynitic spinel intergrown with plagioclase and high-Ca clinopyroxene, and a total lack of melilite. Instrumental Neutron Activation Analysis (INAA)

The results of detailed, high-spatial-resolution spectroscopy for a sample of eleven nebulae surrounding Wolf-Rayet stars: S308, NGC 2359, NGC 3199, Anon (MR 26), RCW 78, RCW 104, G 2.4+1.4, M 1-67, L 69.8+1.74, Anon (MR 100), and NGC 6888, are presented. The study of the ionization structure, using diagnostic diagrams, indicates that

ESTE TRABAJO SE ENMARCA EN EL AMBITO DE NUEVOS METODOS TECNICOS APLICADOS A LA ASTRONOMIA, Y POR TANTO CON UNA CONSIDERABLE POTENCIALIDAD. EL NEXO DE UNION SON LAS REDES DE NEURONAS ARTIFICIALES Y CONSISTE BASICAMENTE EN EL ESTUDIO DE SU APLICABILIDAD A TRES PROBLEMATICAS DIFERENTES CON UTILIDAD EN EL CAMPO DE LA ASTRONOMIA: UN METODO PARA

We report how the action of radiation forces on small solid particles in a circumstellar disk could induce a suitable mechanism for orbital migration of protoplanets. Since the ratio of radiation-to-gravitational forces acting on a particle depends on its physical and chemical properties, different particles following the same trajectory move with