Mathematics – Logic
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8773h&link_type=abstract
HST Proposal ID #8773
Mathematics
Logic
Hst Proposal Id #8773
Scientific paper
The largest impediment to our understanding of planetary nebulae {PNe} is the lack of reliable distances. Acquired by generalized statistical methods in all but a handful of cases, individual PNe distances are often uncertain by factors of 2 or more. The distance scale of PNe is of great importance since it has direct impact on the total UV radiation in the galaxy and hence, on the state of the interstellar diffuse medium, the chemical evolution of the galaxy, and on the late stages of stellar evolution. Recently, a method known as the Expansion Parallax has begun to yield distances to individual PNe with uncertainties typically near 20-30 involves subtracting two epochs of image data to form a difference map, which is analyzed to extract the angular expansion rate. The PN distance is derived by dividing its Doppler expansion velocity by the nebular angular expansion rate. Only a dozen of the bright, nearest PNe can be studied at the VLA. The sample size is far too sma ll to provide statistical informa t ion on PNe luminosities {needed for tests of cosmological distance scales} or to calibrate other kinds of distance estimation methods. We propose to use the HST/WFPC2 to obtain distances to a sample of PNe using new images acquired during Cycles 7-9 combined, in some cases, with images obtained during previous Cycles. A secondary goal is to study the morphological, kinematical, and ionization structure of nebular microstructures with the highest resolution possible.
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