H2 Spectroscopy of Protoplanetary Nebulae

Observations of planetary and protoplanetary nebulae in the spectral line of molecular hydrogen at 2.1218 μm are providing new insights into the processes of formation and evolution of post-AGB stars. In this paper, we present three significant results from the study of H2 toward planetary and protoplanetary nebulae. First, the presence of H2 emission is sufficient to determine that the source is bipolar; second, the formation of bipolar structure in protoplanetary nebulae precedes the event(s) that produces H2 emission; and third, along the polar axes of PPNe, the velocity of molecular gas H2 emission decreases with distance from the central star.