We examine the images of hundreds of planetary nebulae (PNe) and find that about one in six PNe might have been shaped by an interacting triple stellar progenitor. For resolved images we classify PNe by one of four categories. (1) PNe that show no need for a tertiary star to account for their morphology. (2) PNe whose structure posses a pronounced departure from axial-symmetry and/or mirror-symmetry. We classify these as `having a triple stellar progenitor’. (3) PNe whose morphology possesses departure from axial-symmetry and/or mirror-symmetry, but not as pronounced as in the previous class, and are classified as `likely shaped by triple stellar system’. (4) PNe with minor departure from axial-symmetry and/or mirror symmetry that could have been as well caused by an eccentric binary system or the inter-stellar medium. These are classified as `maybe shaped by a triple stellar system’. Given a weight eta_t=1, eta_l=0.67, eta_m=0.33 to classes 2, 3 and 4, respectively, we find that about 13 – 21% of PNe have been shaped by triple stellar systems. Although in some evolutionary scenarios not all three stars survive the evolution, we encourage the search for a triple stellar systems at the center of some PNe.
E. Bear and N. Soker
Tue, 28 Jun 16