Mid Infrared Observations of Van Maanen 2: No Substellar Companion
  The results of a comprehensive infrared imaging search for the putative 0.06 solar mass astrometric companion to the 4.4 pc white dwarf van Mannen 2 are reported. Adaptive optics images acquired at 3.8 microns reveal a diffraction limited core of 0.09" and no direct evidence of a secondary. Models predict that at 5 Gyr, a 50 jupiter mass brown dwarf would be only 1 magnitude fainter than van Maanen 2 at this wavelength and the astrometric analysis suggested a separation of 0.2". In the case of a chance alignment along the line of sight, a 0.4 mag excess should be measured. An independent photometric observation at the same wavelength reveals no excess. In addition, there exist published ISO observations of van Maanen 2 at 6.8 and 15.0 microns which are consistent with photospheric flux of a 6750 K white dwarf. If recent brown dwarf models are correct, there is no substellar companion with T > 500 K. 
J. Farihi, E.E. Becklin, B.A. Macintosh