The first sub-70 minute non-interacting WD-BD system: EPIC212235321

TL;DR

This paper reports the discovery of the shortest-period non-interacting white dwarf-brown dwarf binary system, providing insights into common-envelope evolution and the survival of low-mass objects.

Contribution

It presents the first known sub-70 minute non-interacting WD-BD system, with detailed observational data and implications for binary evolution models.

Findings

Shortest-period non-interacting WD-BD system discovered

Spectroscopic evidence of irradiation effects on the brown dwarf

System likely a pre-cataclysmic binary emerging from common-envelope

Abstract

We present the discovery of the shortest-period, non-interacting, white dwarf-brown dwarf post-common-envelope binary known. The K2 light curve shows the system, EPIC 21223532 has a period of 68.2 min and is not eclipsing, but does show a large reflection effect due to the irradiation of the brown dwarf by the white dwarf primary. Spectra show hydrogen, magnesium and calcium emission features from the brown dwarf's irradiated hemisphere, and the mass indicates the spectral type is likely to be L3. Despite having a period substantially lower than the cataclysmic variable period minimum, this system is likely a pre-cataclysmic binary, recently emerged from the common-envelope. These systems are rare, but provide limits on the lowest mass object that can survive common envelope evolution, and information about the evolution of white dwarf progenitors, and post-common envelope evolution.