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We examine planets orbiting post-common envelope binaries (PCEBs) from theperspective of angular momentum evolution, and conclude that the planets aremore likely to be first generation (FG) planets than second generation (SG)planets. FG planets were born together with the parent stars, while SG planetsform later from a SG proto-planetary disk formed by mass-loss from the evolvedprimary star during its red giant branch (RGB) phase or asymptotic giant branch(AGB) phase. We find that in some systems the SG scenario requires that morethan twenty percent of the SG proto-planetary disk mass ends in planets.Although we cannot rule out SG planet formation in these systems, this fractionof mass that ends in planets is much higher than the value commonly used inplanet formation theories. On the other hand, we find that for each of thesystems we can build a progenitor system composed of a main-sequence binarysystem orbited by the appropriate planets. This can be done if the secondarystar was in a resonance with the inner planet. To account for the progenitorproperties we suggest that in cases where the secondary star has a mass of ~0.1-0.2Msun, it was formed in the same way planets are formed, i.e., from adisk.

First versus second generation planet formation in post common envelope binary (PCEB) planetary systems