FUSE Observations of the Loop I/Local Bubble Interaction Region

We used the FUSE (Far Ultraviolet Spectroscopic Explorer) satellite to observe O VI emission along two sightlines towards the edge of the interaction zone (IZ) between the Loop I superbubble and the Local Bubble. One sightline was chosen because material in the interaction zone blocks distant X-ray emission, and should thus do the same for non-local O VI emission. We measured an O VI intensity of Ishadowed = 2750 ± 550 photons cm −2 s sr along this ‘Shadowed’ sightline, and Iunshadowed = 10800 ± 1200 photons cm −2 s sr along the other sightline. Given these results, very little (. 800 photons cm s sr) of the emission arises from the near side of the interaction zone, which likely has an H I column density of about 4×10 cm along the ‘Shadowed’ sightline. The O VI emission arising within Loop I (∼10 photons cm s sr) is probably associated with gas of ne ∼ 0.1 cm −3 and an emitting pathlength of ∼ 1.2 pc, suggesting it arises at interfaces rather than from gas filling Loop I. In contrast, the C III emission is similar along both sightlines, indicating that much of the emission likely arises on the near side of the interaction zone. Subject headings: ISM: general — ISM: bubbles, ISM: supernova remnants, ISM: individual(Loop I), ultraviolet: ISM