SIMBAD references

We have obtained X-ray observations of the bipolar planetary nebulae (PNe) NGC 2346 and NGC 7026 with XMM-Newton. These observations detected diffuse X-ray emission from NGC 7026 but not from NGC 2346. The X-ray emission from NGC 7026 appears to be confined within the bipolar lobes of the PN and has spectral properties suggesting a thermal plasma emitting at a temperature of 1.1^+0.5_–0.2x10⁶ K. The X-ray spectrum of NGC 7026 is modeled using nebular and stellar abundances to assess whether a significant amount of nebular material has been mixed into the shocked wind, but the results of this comparison are not conclusive owing to the small number of counts detected. Observations of bipolar PNe indicate that diffuse X-ray emission is much less likely detected in open-lobed nebulae than closed-lobed nebulae, possibly because open-lobed nebulae do not have strong fast winds or are unable to retain hot gas.