The double degenerate LP 400-22 revisited

• Published in: Astronomy and astrophysics (Berlin) Vol. 507; no. 3; pp. 1613 - 1616
• Main Authors: Vennes, S., Kawka, A., Vaccaro, T. R., Silvestri, N. M.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences 01.12.2009
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; stars: binaries: close; stars: individual: LP 400-22; white dwarfs; White dwarf stars; stars: binaries: close; white dwarfs; Mass function; Metallicity; Close binary stars; Models; stars: individual: LP 400-22; Age
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/200912955

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 $M_\odot$, implying a mass for the companion M2 > 0.41 $M_\odot$. 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 $M_\odot$, and $t_{\mathrm{cool}}$≈1.8 Gyr, and we infer a mass of 0.85–1.0 $M_\odot$ for the progenitor of the white dwarf. We discuss the likely origin of this system.