1. Acker, A., Marcout, J., Ochsenbein, F., Stenholm, B. & Tylenda, R. 1992, Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Garching: ESO)
2. Barnard, E. E. 1927, A Photographic Atlas of Selected Regions of the Milky Way (Washington, DC: Carnegie Institution)
3. The airglow spectrum, 3100-10,000 A
4. Calabretta, M. & Greisen, E. W. 2000, in ASP Conf. Ser. 216, Astronomical Data Analysis Software and Systems IX, ed. N. Manset, C. Veillet, & D. R. Crabtree (San Francisco: ASP), 571