SIMBAD references

We report our search for optically thick radio cores in 16 narrow-waist bipolar nebulae. Optically thick cores are a characteristic signature of collimated ionized winds. Eleven northern nebulae were observed with the Very Large Array (VLA) at 1.3 and 0.7 cm, and five southern nebulae were observed with the Australia Telescope Compact Array (ATCA) at 6 and 3.6 cm. Two northern objects, 19W32 and M1-91, and three southern objects, He 2-25, He 2-84, and Mz 3, were found to exhibit a compact radio core with a rising spectrum consistent with an ionized jet. Such jets have been seen in M2-9 and may be responsible for shaping bipolar structure in planetary nebulae.