PHL 5038: A spatially resolved white dwarf + brown dwarf binary

TL;DR

This paper reports the discovery and characterization of a wide binary system consisting of a white dwarf and a brown dwarf, providing a valuable benchmark for substellar evolution models.

Contribution

First spatially and spectrally resolved white dwarf + brown dwarf binary, with detailed spectral classification and orbital parameters.

Findings

White dwarf is 8000K DA type

Brown dwarf is likely L8 spectral type

Projected orbital separation is 55 AU

Abstract

A near-infrared excess is detected at the white dwarf PHL5038 in UKIDSS photometry, consistent with the presence of a cool, substellar companion. We have obtained H- and K-grism spectra and images of PHL5038 using NIRI on Gemini North. The target is spatially and spectrally resolved into two components; an 8000K DA white dwarf, and a likely L8 brown dwarf companion, separated by 0.94". The spectral type of the secondary was determined using standard spectral indices for late L and T dwarfs. The projected orbital separation of the binary is 55AU, and so it becomes only the second known wide WD+dL binary to be found after GD165AB. This object could potentially be used as a benchmark for testing substellar evolutionary models at intermediate to older ages.