Abstract
We present results from a search through existing Far Ultraviolet Spectroscopic Explorer (FUSE) and HST data for neutron capture species in planetary nebulae (PNe), which can be enriched by slow neutron capture (the s-process) in the progenitor stars. Measurements of such enrichments shed light on the s-process in AGB stars and the heavy element enrichment of the interstellar medium. We derive Ge (Z=32) abundances relative to S or Fe from observations of Ge III lambda 1088.46 for five PNe; four of these exhibit Ge abundances elevated by a factor of >3-10 above solar, depending on assumptions about depletion into dust. In contrast, we find an approximately solar abundance for Ge in IC 4776, and also in the ISM towards Abell 36 as derived from Ge II lambda 1237.06. Another neutron-capture element, Ga (Z = 31), is probably detected in SwSt 1 via Ga III lambda 1495.05, with a strength indicating a greatly enhanced Ga abundance. The strongest evidence for enrichment of Ge is seen for PNe with H-deficient, C-rich Wolf-Rayet central stars. While the evolutionary path producing a [WR] central star is not well understood at present, these objects are likely to have experienced extensive mixing and dredge-up of nuclear-processed material.
