The double degenerate LP 400-22 revisited

摘要

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