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K. Nishikida (U. of Washington), D. N. Burrows (Penn State U.)
We present a study of the geometrical and spectroscopic properties of the Loop I superbubble and its surrounding medium. We have utilized X-ray, IR, 21 cm data, and high-resolution NaI D spectra for selected regions of the Loop I superbubble.
Many X-ray shadows are seen in the soft X-ray band images. Our 21 cm and NaI D observations reveal that the X-ray absorbing clouds are associated with the expanding shells of the LHB and the Loop I superbubble and the region between the two bubbles where they may be interacting. The characteristic radius of the Loop I superbubble is estimated to be about 100 pc.
The X-ray spectra are best fitted with a four-component model consisting of an unabsorbed foreground (LHB) emission, a background power-law emission, and an absorbed two-temperature thermal plasma emission which is located in the interior of Loop I. The temperatures of the plasma inside Loop I vary spatially, and X-ray emission from the Galactic halo and bulge is noticed in some directions.
The energetics and dynamics of the Loop I superbubble are discussed based on the hypothesis that Loop I is powered by stellar winds and supernovae in the Scorpius-Centaurus OB association. The observed geometrical and kinematical properties of Loop I are found to be consistent with theoretical predictions based on the standard wind-blown bubble theory. However, the precise history of events in the Sco-Cen OB association must be known to reconcile the difference in the estimates of kinematic age and nuclear age of Loop I.