Evidence for Deuterium Astration in the Planetary Nebula Sh 2-216?

We present FUSE observations of the line of sight to WD 0439+466 (LS V +46 21), the central star of the old planetary nebula Sh 2-216. The FUSE data show absorption by many interstellar and stellar lines, in particular D I, H2 (J = 0-9), HD J = 0-1, and CO. Many other stellar and ISM lines are detected in the STIS E140M HST spectra of this sight line, which we use to determine N(H I). We derive, for the neutral gas, D/H = 0.76 × 10-5, O/H = 0.89 × 10-4, and N/H = 3.24 × 10-5. We argue that most of the gas along this sight line is associated with the planetary nebula. The low D/H ratio is likely the result of this gas being processed through the star (astrated) but not mixed with the ISM. This would be the first time that the D/H ratio has been measured in predominantly astrated gas. The O/H and N/H ratios derived here are lower than typical values measured in other planetary nebulae likely due to unaccounted for ionization corrections.