Chaos in models of the solar neighbourhood

¹ School of Physics & Astronomy, University of Nottingham, Nottingham NG7 2RD, UK e-mail: dalia.chakrabarty$@$nottingham.ac.uk
² Institute for Theoretical Physics, University of Zürich, Winterthurerstrasse 190, Zürich 8057, Switzerland e-mail: sideris@physik.unizh.ch

Received: 21 December 2007
Accepted: 18 April 2008

Abstract

Aims. We quantify the amount of chaos that exists in the local phase space.

Methods. A sample of orbits from four different models of the solar neighbourhood phase space are analysed by a new chaos identification (and quantification) technique. While three of the models we used bear the signature of the perturbation due to both the Galactic bar and the spiral pattern, the last of the models is a bar-only one. We explore the models by comparing the corresponding values of chaos strength that are induced at the various energy levels.

Results. We find that all the viable models that have been demonstrated to successfully reproduce the local phase space structure – models that include the bar as well as the spiral – bear strong chaoticity, though the model that implies the highest degree of chaos is the one in which overlap of the major resonances of the bar and the spiral occurs. The bar-only model is found to display regularity. We advance chaos as primarily responsible for the splitting of the Hyades-Pleiades mode (the larger mode) of the local velocity distribution.