1. Acker, A., Ochsenbein, F., Stenholm, B., Tylenda, R., Marcout, J., Schohn, C., 1992, 1996, Strasbourg-ESO catalogue of Galactic planetary nebulae, ESO
2. Baade, W., 1955, AJ, 60, 151
3. Buzzoni, A., Arnaboldi, M., this book
4. Ciardullo, R., Jacoby, G.H., Ford, H.C., Neill, J.D. 1989, ApJ, 339, 53
5. Ciardullo R., Feldmeier J.J., Jacoby G.H., Kuzio de Naray R., Laychak M., Durrell P.R., 2002, ApJ, 577, 31