Frankowski & Soker 2009, стр. 654–8 Frankowski, Adam; Soker, Noam (новембар 2009), „Very late thermal pulses influenced by accretion in planetary nebulae”, New Astronomy, 14 (8): 654—8, Bibcode:2009NewA...14..654F, doi:10.1016/j.newast.2009.03.006, „A planetary nebula (PN) is an expanding ionized circumstellar cloud that was ejected during the asymptotic giant branch (AGB) phase of the stellar progenitor.”
Frankowski & Soker 2009, стр. 654–8 Frankowski, Adam; Soker, Noam (новембар 2009), „Very late thermal pulses influenced by accretion in planetary nebulae”, New Astronomy, 14 (8): 654—8, Bibcode:2009NewA...14..654F, doi:10.1016/j.newast.2009.03.006, „A planetary nebula (PN) is an expanding ionized circumstellar cloud that was ejected during the asymptotic giant branch (AGB) phase of the stellar progenitor.”
