The missing mass conundrum of post-common-envelope planetary nebulae

TL;DR

This study investigates the mass of post-common-envelope planetary nebulae, finding they are less massive than regular PNe, which challenges existing theories about their formation and evolution.

Contribution

The paper provides the first mass comparison between post-CE and regular PNe, questioning the current understanding of post-CE nebulae formation.

Findings

Post-CE PNe have lower masses than regular PNe.

Results challenge the common envelope ejection hypothesis.

Findings suggest alternative formation mechanisms may be needed.

Abstract

Most planetary nebulae (PNe) show beautiful, axisymmetric morphologies despite their progenitor stars being essentially spherical. Angular momentum provided by a close binary companion is widely invoked as the main agent that would help eject an axisymmetric nebula, after a brief phase of engulfment of the secondary within the envelope of the Asymptotic Giant Branch (AGB) star, known as a common envelope (CE). The evolution of the AGB would be thus interrupted abruptly, its (still quite) massive envelope fully ejected to form the PN, which should be more massive than a PN coming from the same star were it single. We test this hypothesis by deriving the ionised+molecular masses of a pilot sample of post-CE PNe and comparing them to a regular PNe sample. We find the mass of post-CE PNe to be actually lower, on average, than their regular counterparts, raising some doubts on our understanding of these intriguing objects.