SIMBAD references

We revisit Chandra observations of planetary nebulae NGC 7027 and BD +30°3639 in order to address the question of abundance anomalies in the X-ray-emitting gas. Enhanced abundances relative to solar of magnesium (Mg) for NGC 7027 and neon (Ne) for BD +30°3639 are required to fit their X-ray spectra, whereas observations at optical and infrared wavelengths show depleted Mg and Ne in these systems. We attribute the enhancement of Mg in NGC 7027 in the X-ray, relative to the optical, to the depletion of Mg onto dust grains within the optical nebula. For BD +30°3639, we speculate that the highly enhanced Ne comes from a white dwarf companion, which accreted a fraction of the wind blown by the asymptotic giant branch progenitor and went through a novalike outburst that enriched the X-ray-emitting gas with Ne.