Brown Dwarf Companions to White Dwarfs

TL;DR

This paper reports new observations and a survey indicating that brown dwarf companions to white dwarfs are rare, with an estimated occurrence rate of 0.3% to 1.3%, and discusses the effects of irradiation on such systems.

Contribution

It presents new observational data on specific white dwarf systems and a near-infrared survey estimating the frequency of brown dwarf companions to white dwarfs.

Findings

Irradiation effects observed on the secondary in WD0137-349.

Identification of 8-10 potential brown dwarf companions in the survey.

Estimated brown dwarf companion fraction to white dwarfs is between 0.3% and 1.3%.

Abstract

Brown dwarf companions to white dwarfs are rare, but recent infra-red surveys are slowly reveal- ing examples. We present new observations of the post-common envelope binary WD0137-349, which reveals the effects of irradiation on the ~ 0.05M* secondary, and new observations of GD 1400 which show that it too is a close, post-comon envelope system. We also present the lat- est results in a near-infrared photometric search for unresolved ultracool companions and to white dwarfs with UKIDSS. Twenty five DA white dwarfs were identified as having photometric excesses indicative of a low mass companion, with 8-10 of these having a predicted mass in the range asso- ciated with brown dwarfs. The results of this survey show that the unresolved (< 2") brown dwarf companion fraction to DA white dwarfs is 0.3 \leq fWD+BD \leq 1.3%.