Gravitational Settling of22Ne in Liquid White Dwarf Interiors: Cooling and Seismological Effects

We assess the impact of the trace element ^{22}Ne on the cooling andseismology of a liquid C/O white dwarf (WD). Due to this elements' neutronexcess, it sinks towards the interior as the liquid WD cools. The subsequentgravitational energy released slows the cooling of the WD by 0.25--1.6 Gyrs bythe time it has completely crystallized, depending on the WD mass and theadopted sedimentation rate. The effects will make massive WDs or those in metalrich clusters (such as NGC 6791) appear younger than their true age. Ourdiffusion calculations show that the ^{22}Ne mass fraction in the crystallizedcore actually increases outwards. The stability of this configuration has notyet been determined. In the liquid state, the settled ^{22}Ne enhances theinternal buoyancy of the interior and changes the periods of the high radialorder g-modes by approximately 1%. Though a small adjustment, this level ofchange far exceeds the accuracy of the period measurements. A full assessmentand comparison of mode frequencies for specific WDs should help constrain thestill uncertain ^{22}Ne diffusion coefficient for the liquid interior.Comment: 26 pages (11 text pages with 15 figures); to appear in The Astrophysical Journa