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 } _ { -0.2 } \times 10 ^ { 6 } 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 .