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2. Acker, A., Ochsenbein, F., Stenholm, B., Tylenda, R., Marcout, J. & Schohn, C. 1992, Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Garching: ESO)
3. Asymmetrical planetary nebulae and central star masses
4. Asida, S. M. & Tuchman, Y. 1995a, in Asymmetrical Planetary Nebulae, ed. A. Harpaz & N. Soker (Ann. Israel Phys. Soc., 11) (Bristol: IOP), 108