1. Kwok, S., Purton, C. R. & Fitzgerald, P. M. On the origin of planetary nebulae. Astrophys. J. 219, L125–L127 (1978).
2. Manchado, A., Villaver, E., Stanghellini, L. & Guerrero, M. in Asymmetrical Planetary Nebulae II. From Origins to Microstructures (eds Kastner, J. H., Stoker, N. & Rappaport, S.) 17–23 (ASP Conf. Ser. 199, Astronomical Society of the Pacific, San Francisco, 2000).
3. Soker, N. & Harpaz, A. Can a single AGB star form an axially symmetric planetary nebula? J. Astron. Soc. Pac. 104, 923–930 (1992).
4. Koester, D., Dreizler, S., Weidemann, V. & Allard, N. F. Search for rotation in white dwarfs. Astron. Astrophys. 338, 612–622 (1998).
5. Balick, B. The evolution of planetary nebulae. I—Structures, ionizations, and morphological sequences. Astron. J. 94, 671–678 (1987).