The double degenerate LP400-22 revisited
Abstract
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= 1.01016 d, somewhat longer than the previously published period, and a mass function f(M2)= 0.180 Msolar implying a mass for the companion M2 > 0.41 Msolar. 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 = 0.19 Msolar and tcool~1.8 Gyr, and we infer a mass of 0.85 - 1.0 Msolar for the progenitor of the white dwarf. We discuss the likely origin of this system.
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