Physics
Scientific paper
Jul 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002hst..prop.9366h&link_type=abstract
HST Proposal ID #9366
Physics
Hst Proposal Id #9366
Scientific paper
H_2 emission provides an excellent probe of the physical conditions in planetary nebulae {PNs} and also in proto- planetary nebulae {PPNs}, objects in transition between the asymptotic giant branch {AGB} and PN phases. It is thought that the shaping of the PN occurs when a fast wind interacts with the remnant of the AGB progenitor during the PPN phase. The study of shock-excited H_2 in PPNs will allow us to study this process. We request HST/NICMOS H_2 and complementary K and H broad-band images of 13 PPNs with a range of spectral types of the central star. We presently have very high- resolution { 100, 000} H_2 spectra for 7 of these, which we will use with the high-resolution images to study the velocity structure of the fast wind. We will also explore the relationship between the presence of H_2 and a bipolar shape for the nebula, as has been found in PNs. However, the role of the equatorial torus is expected to be different in these two cases, and in the PPNs it is expected to collimate the wind rather than shield the molecules. Thus the H_2 in the PPNs is expected at the ends of the lobes rather than in the torus. Radiatively-excited H_2 emission appears to be common in PPNs with central stars of B spectral types; this appears to be a transitional stage in the evolution of the H_2 in the nebula which these images will help us to better understand.
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