SIMBAD references

We present near-IR narrowband continuum-subtracted images in the H₂ 2.122 µm, and Brγ 2.166 µm emission lines for a sample of 15 bipolar planetary nebulae (PNe). H₂ emission was definitely detected for most of the objects in this sample (13 of 15). The very high H₂ detection rate supports the idea that bipolar PNe have important reservoirs of molecular material and offer suitable physical conditions for the excitation of H₂. The strength of the H₂ emission and the H₂/Brγ flux ratio are found to correlate with the morphology of the bipolar PNe observed. Bipolar PNe with broad and bright rings exhibit stronger H₂ emission than bipolar PNe with narrow twists. High-quality (subarcsec) [N II] and Hα optical images have been used to compare the distribution of the ionized and molecular material. The H₂ emission lies just outside the optical [N II] emission zone.