The substellar companion in the eclipsing white dwarf binary SDSS J141126.20+200911.1

TL;DR

This paper reports the discovery and characterization of the first known eclipsing white dwarf/brown dwarf binary, providing detailed measurements of the companion's mass, radius, and spectral type, and discussing irradiation effects.

Contribution

It presents the first confirmed eclipsing white dwarf/brown dwarf binary and provides detailed measurements and analysis of the companion’s properties and system age.

Findings

Confirmed substellar companion in an eclipsing binary

Measured companion mass and radius consistent with models

Detected infrared excess suggesting irradiation effects

Abstract

We present high time resolution SDSS-$g'$ and SDSS-$z'$ light curves of the primary eclipse in SDSS J141126.20+200911.1, together with time-resolved X-Shooter spectroscopy and near-infrared $JHK_{s}$ photometry. Our observations confirm the substellar nature of the companion, making SDSS J141126.20+200911.1 the first eclipsing white dwarf/brown dwarf binary known. We measure a (white dwarf model dependent) mass and radius for the brown dwarf companion of $M_{2} = 0.050 \pm 0.002$ $M_{\odot}$ and $R_{2} = 0.072 \pm 0.004$ $M_{\odot}$, respectively. The lack of a robust detection of the companion light in the $z'$-band eclipse constrains the spectral type of the companion to be later than L5. Comparing the NIR photometry to the expected white dwarf flux reveals a clear $K_s$-band excess, suggesting a spectral type in the range L7-T1. The radius measurement is consistent with the predictions of evolutionary models, and suggests a system age in excess of three Gyr. The low companion mass is inconsistent with the inferred spectral type of L7-T1, instead predicting a spectral type nearer T5. This indicates that irradiation of the companion in SDSS J1411 could be causing a significant temperature increase, at least on one hemisphere.