Hot Gas in Planetary Nebulae

Diffuse X-ray emission has been detected in a small number of planetary nebulae (PNe), indicating the existence of shocked fast stellar winds and providing support for the interacting-stellar-winds formation scenario of PNe. However, the observed X-ray luminosities are much lower than expected, similar to the situation seen in bubbles or superbubbles blown by massive stars. Ad hoc assumptions have been made to reconcile the discrepancy between observations and theoretical expectations. We have initiated FUSE programs to observe OVI absorption and emission from PNe, and our preliminary results indicate that OVI emission provides an effective diagnostic for hot gas in PN interiors.