Observations of Planetary Nebulae
Abstract
The scientific objective of the proposed observing program is to use the IUE for obtaining ultraviolet spectrograms of planetary nebulae in order to study their physical conditions, excitation processes, degree of excitation, stages of ionization, structure, and chemical abundances. Spectrograms in both the short and the long wavelength ranges are required in order to cover the entire spectral range between 1150A and 3200A.. Exposure times ranging from ~10 minutes to ~2 hours are required for the low resolution spectrograms. These exposures will be used primarily to establish which emission lines are present, to determine the relative intensities of the lines and their absolute intensities, and to evaluate the feasibility of exposing at high resolution in order to resolve the astrophysically significant doublets. Typical exposure times of 1 to 4 hours are estimated to be required for the high resolution spectrograms in those cases where they are warranted. Certain emission line ratios yield electron densities, others yield excitation conditions, others contribute to the determination of electron temperatures, and still others yield information about the interstellar excitation in the ultraviolet which is needed for the proper interpretation of the other data. The strength of the broad absorption feature near 2200A also yields information about interstellar extinction when it is observable in the ultraviolet continuum of the central stars, as has been demonstrated by observations of the central stars of planetary nebulae with the ANS.
- Publication:
-
IUE Proposal
- Pub Date:
- 1979
- Bibcode:
- 1979iue..prop..174B