O'Dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; Burkert, A. (2002). “Knots in Nearby Planetary Nebulae”. The Astronomical Journal123 (6): 3329–3347. Bibcode: 2002AJ....123.3329O. doi:10.1086/340726.
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O'dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; Burkert, A.; Balick; Hajian; Henney; Burkert (2003). “Knots in Planetary Nebulae”. Winds, Bubbles, and Explosions: a conference to honor John Dyson, Pátzcuaro, Michoacán, México, September 9-13, 2002 (Eds. S. J. Arthur & W. J. Henney) Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias) (http://www.astroscu.unam.mx/~rmaa/)15: 29–33. Bibcode: 2003RMxAC..15...29O.
O'Dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; Burkert, A. (2002). “Knots in Nearby Planetary Nebulae”. The Astronomical Journal123 (6): 3329–3347. Bibcode: 2002AJ....123.3329O. doi:10.1086/340726.
O'dell, C. R.; Balick, B.; Hajian, A. R.; Henney, W. J.; Burkert, A.; Balick; Hajian; Henney; Burkert (2003). “Knots in Planetary Nebulae”. Winds, Bubbles, and Explosions: a conference to honor John Dyson, Pátzcuaro, Michoacán, México, September 9-13, 2002 (Eds. S. J. Arthur & W. J. Henney) Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias) (http://www.astroscu.unam.mx/~rmaa/)15: 29–33. Bibcode: 2003RMxAC..15...29O.