1. A. Acker, F. Ochsenbein, B. Stenholm, et al., The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Publ. ESO, 1992).
2. L. H. Aller, Physics of Thermal Gaseous Nebulae (Reidel, Dordrecht, 1984).
3. V. P. Arkhipova, Perem. Zvezdy 22, 631 (1988).
4. V. P. Arkhipova, G. V. Zaitseva, R. I. Noskova, et al., Astron. Tsirk. No. 1250, 1 (1983).
5. V. P. Arkhipova, V. F. Esipov, N. P. Ikonnikova, et al., Pis’ma Astron. Zh. 35, 592 (2009).