Physics
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992hst..prop.3880d&link_type=abstract
HST Proposal ID #3880
Physics
Hst Proposal Id #3880
Scientific paper
We propose to use GHRS observations of planetary nebula central stars to detect and study massive envelopes of residual neutral material around the ionized gas. Discovery of these envelopes has major implications for understanding the process that transforms a star from a red giant into a white dwarf. Previous radio and infrared work has shown that a signifi- cant fraction of planetaries (20 - 33%) contain 0.1-1 solar masses of molecules. Neutral atomic material, although harder to detect from the ground, may be even more common and contain substantial mass. This con- clusion is supported by the results of a pilot study by the proposers in the optical Na I lines. Observations of UV resonance lines of abundant species offer the most sensitive means for detecting neutral material, and will provide unique information on the physical and velocity structure of the nebular envelopes. The far-UV also offers the oppor- tunity to detect small amounts of vibrationally-excited H2. The GHRS is the only instrument that can provide sensitive measurements of these faint stars with high enough spectral resolving power to separate the nebular from interstellar absorption lines and to optimize detection of weak lines needed to determine accurate column densities. These obser- vations will also provide serendipitous information about the central stars and the ISM along new lines of sight through the galactic halo.
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