Planet formation in post-common-envelope binaries

TL;DR

This paper investigates the origins of planets in post-common-envelope binaries, proposing that they likely form after the CE phase from ejected material, challenging the idea they formed beforehand.

Contribution

It introduces a second-generation formation scenario for planets in PCEBs, supported by analysis of observed planetary properties and evolution models.

Findings

Pure first-generation formation is inconsistent with data.

Second-generation formation from ejected material explains observed planetary masses.

Hybrid scenarios involving pre-CE formation and accretion are plausible.

Abstract

To understand the evolution of planetary systems, it is important to investigate planets in highly evolved stellar systems, and to explore the implications of their observed properties with respect to potential formation scenarios. Observations suggest the presence of giant planets in post-common-envelope binaries (PCEBs). A particularly well-studied system with planetary masses of 1.7 M_J and 7.0 M_J is NN Ser. We show here that a pure first-generation scenario where the planets form before the common envelope (CE) phase and the orbits evolve due to the changes in the gravitational potential is inconsistent with the current data. We propose a second-generation scenario where the planets are formed from the material that is ejected during the CE, which may naturally explain the observed planetary masses. In addition, hybrid scenarios where the planets form before the CE and evolve due to the accretion of the ejected gas appear as a realistic possibility.