The double degenerate LP400-22 revisited

TL;DR

This paper re-examines the properties of the high-velocity, low-mass white dwarf LP 400-22 and its companion, refining its orbital parameters, mass estimates, and evolutionary history based on extended observations and models.

Contribution

It provides updated orbital, mass, and age estimates for LP 400-22 using extended data and low-metallicity models, offering new insights into its origin.

Findings

Binary period determined as 1.01016 days.

White dwarf mass estimated at 0.19 M_solar.

Cooling age approximately 1.8 billion years.

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(M_2)= 0.180 M_solar implying a mass for the companion M_2 > 0.41 M_solar. 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, M_1 = 0.19 M_solar and t_cool~1.8 Gyr, and we infer a mass of 0.85 - 1.0 M_solar for the progenitor of the white dwarf. We discuss the likely origin of this system.