Physics
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992hst..prop.3603b&link_type=abstract
HST Proposal ID #3603
Physics
Hst Proposal Id #3603 Interstellar Medium
Scientific paper
We propose to undertake a "snapshot" survey of protoplanetary nebulae (PPNe) based on a list of approx. 100 candidate targets. Theoretical models of the formation of planetary nebulae have indicated that observable changes can take place on timescales as short as decades, i.e., the lifetime of HST. Such predictions have since been confirmed by observations. So it is now known that the evolution of many PPNe can be studied if snapshots of them are taken in the near future and again five or ten years later. The evolution which will be detected by the proposed (and future) snapshots results from various processes depending on the phase in which the target is currently viewed -- old asymptotic giant branch stars, OH/IR stars, or more advanced PPNe. Even before a future generation of snapshots is acquired, important information in the short term will result from these snapshots. The deconvolved images obtained from this initial program will immediately distinguish among differing models of planetary nebula formation. For example, some PPNe will show evidence of ionization fronts or shocks. While many phases of stellar evolution do not lend themselves to this sort of scrutiny, PPNe present observable changes on a short enough timescale that it is highly desirable to take snapshots of as many of them as possible and establish a baseline from which the evolution of these objects can be analyzed. Furthermore, evolutionary changes which are detected in individual PPNe will enable distances to be determined for these objects.
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