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tokens: Previous studies argued that some fraction of PNe were shaped by brown dwarf or planet companions (e.g. Soker 1996 and De Marco Soker 2011 ). The rest were shaped by stellar companions. Under the assumed low mass-loss rate, AGB stars reach much larger radii, in particular, relative to their maximum radius on the RGB. This leaves a relatively large range of initial planetary orbital separations for planets to be engulfed during the upper AGB phase of their parent stars. The much larger radius of the AGB stars not only increases the chance for planetary interaction, but also implies that the envelope is more vulnerable to the influence of the planet towards higher final mass-loss rate. A higher mass-loss rate also implies a faster post-AGB evolution. Both effects make the formation of a PN much more likely. Our assumed low mass-loss rate, therefore, supports the notion that a fraction of elliptical PNe were shaped by sub-stellar companions. The planetary nebula luminosity function (PNLF). Observations show that the brightest PNe in [O iii ] λ5007, i.e. the bright-end cutoff of the PNLF, does not depend on the age or metallicity of the stellar population (e.g. Ciardullo 2010 ). Namely, old stellar populations for which stars of initial mass of M 1, ZAMS ≃ 1–1.2 M ⊙ are forming PNe have their brightest [O iii ] λ5007 PNe as young stellar populations have. This is still a puzzle as the post-AGB stellar luminosity to ionize the nebula should be at least ≈5000 L ⊙ . Our results hint to a possible solution to this puzzle. As evident from the last column of Table 2 , in the case of a reduced mass-loss rate the post-AGB stellar luminosity of stars with initial masses of M 1, ZAMS ≳ 1.05 M ⊙ is L pAGB ≳ 5000 L ⊙ . This, together with the interaction with a low-mass companion on the upper AGB will have the necessary ingredient for a bright PN, a dense nebula of mass ≳ 0.2 M ⊙ and a bright central ionizing star. The full solution to the puzzle might include another component. Miller Bertolami ( 2016 ) finds in a new set of simulations that the post-AGB luminosity values are higher than the values obtained in older simulations. He does not fully address the topic of the PNLF in old stellar populations, whereas we here present preliminary results on the matter. Mendez ( 2017 ) does show a fit to the PNLF of NGC 4697 based on the Miller Bertolami ( 2016 ) tracks, yet notes that it is not a full solution to the PNLF puzzle. It is conceivable that the new simulations of Miller Bertolami ( 2016 ) together with our assumed low mass-loss rate with a late engulfment of a planet (or a brown dwarf or a low-mass star), account for the brightest PNe in old stellar populations. We point out another difference in the two works, where in contrast to Miller Bertolami ( 2016 ), we focus on binary-shaped PNe (non spherical). The initial-final mass relation. There is an observed relation between the initial mass of stars and the mass of their descendant WDs (e.g. Kalirai