[Fe II] bubbles in the young planetary nebula Hubble 12

We have obtained narrowband images of the young planetary nebula Hubble 12 showing [Fe II] line emission in bipolar bubbles near the core. Bright [Fe II] emission is strong evidence for shocks, suggesting the presence of a hi gh-velocity wind emanating from the central star. We compare our data to pr eviously published images of Hubble 12-finding similar structures in hydrog en recombination and free-free emission-and we propose three possible inter pretations of the data: that the bubbles indicate the inner shock of the fa st wind, that the [Fe II] emission is evidence of the outer shock of an epi sodic wind, or that the emission is cooling line radiation from a photodiss ociation region. We argue that the first two interpretations are more likel y, since the [Fe II] emission must be shock excited.