The Detection of Dust around NN Ser

TL;DR

This paper reports the ALMA detection of a dust disc around NN Ser, supporting theories of second-generation planet formation from common-envelope material in post-common-envelope binary systems.

Contribution

First detection of a dust disc around NN Ser, providing evidence for circumbinary discs formed from common-envelope material, and supporting second-generation planet formation theories.

Findings

Detected 1.3 mm flux likely from a dust disc of ~0.8 Earth masses.

Simulations suggest the dust originated from common-envelope material.

Supports the existence of circumbinary discs predicted by theory.

Abstract

Eclipse timing variations observed from the post common-envelope binary (PCEB) NN Ser offer strong evidence in favour of circumbinary planets existing around PCEBs. If real, these planets may be accompanied by a disc of dust. We here present the ALMA detection of flux at 1.3 mm from NN Ser, which is likely due to thermal emission from a dust disc of mass $\sim0.8\pm0.2\,M_{\oplus}$. We performed simulations of the history of NN Ser to determine possible origins of this dust, and conclude that the most likely origin is, in fact, common-envelope material which was not expelled from the system and instead formed a circumbinary disc. These discs have been predicted by theory but previously remained undetected. While the presence of this dust does not prove the existence of planets around NN Ser, it adds credibility to the possibility of planets forming from common-envelope material in a 'second-generation' scenario.