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

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.