The Local Bubble - Origin and evolution

A summary of the lively discussions in working group 2 (WG2) on the origin and evolution of the LB is given below. The debate focussed mainly on the problem of how to pin down the physical properties of the LB. As a first step, we had to critically assess the observational constraints that are put on any model, predominantly from the SXR and EUV data. Next we were discussing models on the origin and evolution of the LB, which are able to explain the observations and which would allow to infer basic LB properties. A simple model, emphasizing the self-consistent dynamical and thermal evolution of a non-equilibrium plasma is presented. We also found, that picturing the LB as an isolated phenomenon is not supported by the data. Instead, the LB environment and its influence on the evolution of the LB have to be taken into consideration. Two different views are presented here. Either the LB and the Loop I superbubble are two physically separate phenomena, which are currently interacting, or star formation epochs in the Scorpius-Centaurus Association interacting with the molecular gas in the Aquila Rift and the interarm region around the Sun may have sculpted the configuration of interstellar matter within 200 parsecs, including the Local Bubble. However, so far observational constraints are insufficient to establish a canonical model of the evolution and the origin of the LB.