It is assumed that the two-fold disc-wide symmetry of spirals is caused by density waves, but also the potential of a bar component may have a significant influence on structural properties. The strength of the bar component appears to be anti-correlated with the degree of symmetry of star-forming regions in the spiral arms (Rozas et al., 1998). We

El trabajo se ha centrado en el estudio de los procesos que acompañan a la emergencia de mancaas en la superficie del sol. Para ello se ha utilizado el método de seguimiento de trazas y el espectroscópico. El primero de ellos permite determinar los movimientos transversales de las estructuras, mientras que el seguno permite medir los movimientos a

We present the results of two studies of the inner Galaxy : on the one hand, a maximum likelihood fitting method using the Besançon model of Galaxy to constrain the density laws of the outer bulge and the holed disc; on the other hand, the comparison of Besançon simulations with infrared data on fields near longitude 20 27 degrees to verify the

Evolutionary synthesis models have been used to study the physical properties of unresolved populations in a wide range of scenarios. Unfortunately, their self-consistency is difficult to test and there are some theoretical open questions without an answer: (1) The change of the homology relations assumed in the computation of isochrones due to the

We present a Monte Carlo model to compute cometary dust tail brightnesses. The model, anologous in many ways to that developed by Fulle (1989, Astron. Astrophys. 217, 283), computes the keplerian orbit of each grain released from the nucleus surface in the Sun gravity field reduced by the radiation pressure. It can be used to derive the time

The quantification of the solar magnetic field is a crucial step in modern solar physics to understand the dynamics, activity and variability of our star. Presently, a reliable inference of these fields is only possible by means of a computer-intensive process that has so far limited scientists to the analysis of observations from small regions of