Narrow - Band Imaging of Bipolar Planetary Nebulae

We present near-IR narrow-band continuum-subtracted images in the H2 2:122 m, and Br 2:166 m emission lines for a sample of 15 bipolar planetary nebulae. H2 emission was definitely detected for most of the objects in this sample (13 out of 15). The very high H2 detection rate supports the idea that bipolar planetary nebulae 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/Br flux ratio are found to correlate with the morphology of the bipolar nebulae observed. Bipolar PNe with broad and bright rings exhibit stronger H2 emission than bipolar PNe with narrow twists. High-quality (sub-arcsec) [N II] and H 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. Subject headings: infrared: interstellar medium: lines and bands – interstellar medium: molecules – planetary nebulae: general