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

A survey of interstellar Na I D1 and D2 absorption features in the spectra of 104 early-type stars in the second and third Galactic quadrants reveals the large-scale kinematics of the interstellar gas within the Galactic anticenter hemisphere at distances from the Sun between ~70 and ~250 pc. Employing a technique that uses both the radial

We present ample evidence for the presence of continuing gaseous infall to the Galactic plane, and then show how interaction of this gas with the disc gas yields a warp of the observed amplitude and direction. The mechanism works for galaxies in general, predicting a small proportion of U-shaped warps, as observed.