Physics
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6792r&link_type=abstract
HST Proposal ID #6792
Physics
Hst Proposal Id #6792 Interstellar Medium
Scientific paper
Recent work has shown that nebular abundances derived from recombination lines are up to a factor of five larger than those obtained from the traditional optical/UV collisionally excited lines. These can be brought into agreement at the higher value if large unexplained temperature fluctuations {t^2} exist. We have been granted observing time on ISO to do IR spectroscopy of two planetary nebulae {PNs} to address this problem. The ISO line data and cospatial optical/UV spectra {including high dispersion IUE}, will permit the measurement of the average N_e, T_e, and t^2 for several ionic species not possible previously. This provides information on how t^2 depends on level of ionization or excitation of the gas. Here we propose to complement the above macroscopic knowledge by observing the same PNs with several WFPC2 narrow filters in order to understand the origin of physical conditions on the microscopic scale { 0.1''}. With the significantly improved resolution afforded by HST, there will be new knowledge of the morphology, stellar wind - gas interactions, and N_e structure. More realistic photoionization and dynamical models should result. Our goals are to understand the conditions within the nebulae and the physical origin of the inferred T_e variations, and to find a prescription for determining reliable nebular abundances - fundamental to understanding the chemical evolution of the Galaxy.
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