Molecular clumping in planetary nebulae

Cometary knots are clumps of molecular gas and dust in ionized regions in planetary nebulae (PNe), whose origins remain unknown. One hypothesis suggests that these clumps originate from dense regions in circumstellar shells of AGB stars that produce maser emissions. In the circumstellar shells of oxygen (O)-rich AGB stars, masers emissions due to SiO, H₂O, and OH have been observed. To make the connection between clumps in PNe and those from which AGB star maser emissions emanate, we need to learn more about clumping observed in PNe. In general, clumps in PNe are classified as knots or filaments but these categories could be simply a manifestation of the orientation of either the clumps or the PNe themselves. We investigate the classification of clumps along with the gross physical parameters of their host PNe, in an effort to investigate the effect of orientation on how we view clumpy structures in Planetary Nebulae.