Discovery of Enhanced Germanium Abundances in Planetary Nebulae with the Far Ultraviolet Spectroscopic Explorer

Abstract

We report the discovery of Ge III λ1088.46 in the planetary nebulae (PNe) SwSt 1, BD +30°3639, NGC 3132, and IC 4593, observed with the Far Ultraviolet Spectroscopic Explorer. This is the first astronomical detection of this line and the first measurement of Ge (Z=32) in PNe. We estimate Ge abundances using S and Fe as reference elements, for a range of assumptions about gas-phase depletions. The results indicate that Ge, which is synthesized in the initial steps of the s-process and therefore can be self-enriched in PNe, is enhanced by factors of >=3-10. The strongest evidence for enrichment is seen for PNe with Wolf-Rayet central stars, which are likely to contain heavily processed material. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which is operated for NASA by Johns Hopkins University under NASA contract NAS5-3298.