Sub-Arcsecond $\lambda$6 cm Images of PNe and their Expansion Parallax Distances
Session 90 -- Planetary Nebula and Degenerate Stars
Oral presentation, Wednesday, 11, 1995, 10:00am - 11:30am

## [90.02D] Sub-Arcsecond $\lambda$6 cm Images of PNe and their Expansion Parallax Distances

Arsen R. Hajian (Cornell University), Yervant Terzian (Cornell University)

Over the past three years, we have obtained high resolution, high fidelity images of more than 20 PNe at $\lambda$6 cm with the Very Large Array. When these data are combined with a second earlier epoch from the VLA archives, we have been successful in detecting the angular expansion of most nebular shells. Distances can be derived with this method by dividing the Doppler velocity of an appropriate emission line by the angular expansion rate of the nebula. The uncertainties this method poses are generally smaller than errors in more indirect techniques for computing PNe distances. In this paper, we present images of all PNe surveyed, as well as resulting expansion parallax results.