The Planets around the Post-Common Envelope Binary NN Serpentis

TL;DR

This paper reports the detection of two circumbinary planets around NN Serpentis using eclipse timing variations, discussing their possible formation scenarios and implications for planetary evolution in post-common-envelope systems.

Contribution

First detection of circumbinary planets around a post-common-envelope binary using eclipse timing variations, exploring their formation and evolutionary history.

Findings

Detected two circumbinary planets via eclipse timing variations.

Proposed possible formation scenarios: orbital migration or second-generation formation.

Highlighted the complexity of planetary formation in evolved binary systems.

Abstract

We have detected 2 circumbinary planets around the close binary system NN Serpentis using the orbital time delay effect measured via the sharp eclipses of the white dwarf primary. The present pre-cataclysmic binary was formed when the original - 2 M primary expanded into a red giant, causing the secondary star to drop from its original orbit at a separation of about 1.4 A.U. down to its current separation at 0.0043 A.U. A quasi-adiabatic evolution of the circumbinary planets' orbits during the common-envelope phase would have placed them in unstable configurations, suggesting that they may have suffered significant orbital drag effects and were originally in much larger orbits. Alternatively, they may have been created as 2nd-generation planets during the last million years from the substantial amount of material lost during the creation of the binary, making them the youngest planets known. Either solution shows how little we actually understand about planetary formation.