Research Center for Astronomy


Tuesday 24 May 2022, 12:00


Validation of a wave heated 3D MHD coronal-wind model using Polarized Brightness and EUV observations

Susanna Parenti
Institut d'Astrophysique Spatiale, France


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Featured Picture


Chaoticity in the vicinity of complex unstable periodic orbits in galactic type potentials

We have investigated the evolution of phase space close to complex unstable periodic orbits in two galactic type potentials. They represent characteristic morphological types of disc galaxies, namely barred and normal (non-barred) spiral galaxies. These potentials are known for providing building blocks to support observed features such as the peanut, or X-shaped bulge, in the former case and the spiral arms in the latter. We investigated the possibility that these structures are reinforced, apart by regular orbits, also by orbits in the vicinity of complex unstable periodic orbits. We examine the evolution of the phase space structure in the immediate neighbourhood of the periodic orbits in cases where the stability of a family presents a successive transition from stability to complex instability and then to stability again, as energy increases. We find that we have a gradual reshaping of invariant structures close to the transition points and we trace this evolution in both models. We conclude that for time scales significant for the dynamics of galaxies, there are weakly chaotic orbits associated with complex unstable periodic orbits, which should be considered as structure-supporting, since they reinforce the morphological features we study.

**The shrinking of the volume occupied by regular orbits around the stable x1v1 periodic orbits and the evolution of the tori towards a disky morphology as we approach the critical energy for a S→Δ transition, has been encountered in all studied cases. This is the second case we know that the deformation of a phase space structure close to a periodic orbit as the energy varies, foretells an impending change of stability (the first case has been presented by Patsis and Katsanikas, 2014, for changes in the topology of invariant tori before a S→U transition).

**We underline the role of the phase space environment around a periodic orbit for the determination of the behaviour of the perturbed orbits. In many cases displacements of the initial conditions of a periodic orbit along a certain direction, may bring the initial conditions of the perturbed orbit in zones of influence of other periodic orbits (stable or unstable). The variation of the GALI2 indices may warn us about such cases.

References: P.A. Patsis, T. Manos, L. Chaves-Velasquez, Ch. Skokos, I. Puerari (Physica D - in press- arXiv:2109.09656)


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It is with deep sorrow that we inform you about the passing of our colleague and collaborator in RCAAM projects, Evangelos Chaliasos, last December.

Evangelos was born in Domianous Evritanias, Greece, on the 28th of December, 1947. He received his B.Sc. in Mathematics (1971) and in Physics (1979) from the University of Athens, Greece. He obtained a M.Sc. in Astronomy from the University of Chicago, U.S.A. (1988) and his Ph.D. from the University of Athens. His scientific interest was in relativistic Astrophysics.

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