PLANETARY-NEBULAE EXPANSION DISTANCES

We present two epochs of lambda6 cm VLA maps of the planetary nebulae NGC 7027 and BD + 30-3639 with subarsecond angular resolution. By taking advantage of the high dynamic range possible with the VLA as well as the almost 6 yr time baseline between the two epochs, we have constructed difference maps that show the signature characteristic of the radial expansion of the ionization front surrounding the nebulae. We have combined these results with the Doppler expansion velocities to estimate the distance to both objects. Our results indicate that D(NGC 7027) = 703 +/- 95 pc and D(BD + 30) = 2680 +/- 810 pc.