FUSE Observations of the Loop I/Local Bubble Interaction Region

We used the FUSE (Far Ultraviolet Spectroscopic Explorer) satellite to observe OVI emission along two sightlines towards the edge of the interaction zone (IZ) between the Loop I superbubble and the Local Bubble (LB). One sightline was chosen because material in the interaction zone blocks distant X-ray emission, and should thus do the same for non-local OVI emission. We measured an OVI intensity of Ishadowed = 2750+/-550 photons cm^-2 s^-1 sr^-1(LU) along this `Shadowed' sightline, and Iunshadowed = 10800+/-1200 LU along the other sightline. Given these results, very little (less than about 800 LU) of the emission arises from the near side of the interaction zone, which likely has an HI column density of about 4×10<sup>20</sup> per cm<sup>2</sup> along the `Shadowed' sightline. The OVI emission arising within Loop I (about 10⁴ LU) is probably associated with gas of n_e~0.1 per cm³ and an emitting pathlength of about 1.2 pc, suggesting it arises at interfaces rather than from gas filling Loop I. In contrast, the CIII emission is similar along both sightlines, indicating that much of the emission likely arises on the near side of the interaction zone. These results support a model in which the Local Bubble is cooler than the interior of Loop I.