* Astronomy

Title: NLTT5306: The shortest Period Detached White Dwarf + Brown Dwarf Binary
Authors: P. R. Steele, R. P. Saglia, M. R. Burleigh, T. R. Marsh, B. T. Gänsicke, K. Lawrie, M. Cappetta, J. Girven, R. Napiwotzki

We have spectroscopically confirmed a brown dwarf mass companion to the hydrogen atmosphere white dwarf NLTT5306. The white dwarf's atmospheric parameters were measured using Sloan Digital Sky Survey and X-Shooter spectroscopy as T_eff=7756±35K and log(g)=7.68±0.08, giving a mass for the primary of M_WD=0.44±0.04 solar masses, at a distance of 71±4 pc with a cooling age of 710±50 Myr. The existence of the brown dwarf secondary was confirmed through the near-infrared arm of the X-Shooter data and a spectral type of dL4-dL7 was estimated using standard spectral indices. Combined radial velocity measurements from the Sloan Digital Sky Survey, X-Shooter and the Hobby-Eberly Telescope's High Resolution Spectrograph of the white dwarf gives a minimum mass of 56±3 Jupiter masses for the secondary, confirming the substellar nature. The period of the binary was measured as 101.88±0.02 mins using both the radial velocity data and i'-band variability detected with the INT. This variability indicates 'day' side heating of the brown dwarf companion. We also observe H{\alpha} emission in our higher resolution data in phase with the white dwarf radial velocity, indicating this system is in a low level of accretion, most likely via a stellar wind. This system represents the shortest period white dwarf + brown dwarf binary and the secondary has survived a stage of common envelope evolution, much like its longer period counterpart, WD0137-349. Both systems likely represent bona-fide progenitors of cataclysmic variables with a low mass white dwarf and a brown dwarf donor.

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