PHL 5038: a spatially resolved white dwarf brown dwarf binary

¹ Department of Physics & Astronomy, University of Leicester, Leicester, LE1 7RH, UK e-mail: prs15@star.le.ac.uk
² Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
³ Anglo-Australian Observatory, PO Box 296, Epping, Sydney, NSW 1710, Australia

Accepted: 19 March 2009

Abstract

A near-infrared excess is detected at the white dwarf PHL 5038 in UKIDSS photometry, consistent with the presence of a cool, substellar companion. We have obtained H- and K-grism spectra and images of PHL 5038 using NIRI on Gemini North. The target is spatially and spectrally resolved into two components: an 8000 K DA white dwarf, and a likely L8 brown dwarf companion, separated by . 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 55 AU, so it becomes only the second known wide WD+dL binary to be found after GD 165AB. This object could potentially be used as a benchmark for testing substellar evolutionary models at intermediate to older ages.