2009A&A...507.1613V

We re-examine the properties of the high-velocity and extremely low-mass white dwarf LP 400-22 and its close companion. Based on an extended observation timeline, we determined a binary period of P=1.01016d, somewhat longer than the previously published period, and a mass function f(M₂)=0.180M_☉, implying a mass for the companion M₂>0.41M_☉. We also re-appraised the mass and cooling age of the white dwarf using low-metallicity (Z=0.001) evolutionary models appropriate for an old halo member, M₁=0.19M_☉, and t_cool≃1.8Gyr, and we infer a mass of 0.85-1.0M_☉ for the progenitor of the white dwarf. We discuss the likely origin of this system.