2001/01/22 by Lars Bildsten, David M. Hall · 7 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Nuclear physics research studies #Scientific Research and Discoveries #astro-ph
paper · pdf · doi:10.1086/319169
To Appear in Ap. J. Letters, 6 pages, 2 figures
arxiv created 2001/01/22 · openalex publication_date 2001/03/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
The nuclear reactions that occur in the stellar progenitors of white dwarfs (WDs) lead to an internal composition of 12 C, 16 O, and a "contaminant" nucleus, 22 Ne. The 22 Ne is produced by helium captures on 14 N left from hydrogen burning via the CNO cycle. By virtue of its two excess neutrons (relative to the predominant A = 2 Z nuclei), a downward force of ≈2 m p g is exerted on 22 Ne in the WD interior. This biases its diffusive equilibrium, forcing 22 Ne to settle toward the center of the WD. We discuss the physics of the gravitational settling when the WD is in the liquid state and the luminosity generated by it. This modifies the cooling of WDs with masses in excess of M ☉ . The current uncertainties in the microphysics even allow for solutions where a 1.2 M ☉ WD remains mostly liquid for a few gigayears because of the internal heating from 22 Ne sedimentation. This highlights the need for an accurate calculation of the interdiffusion coefficient, especially in the quantum liquid regime relevant for high-mass WDs. There is also time in old, liquid WDs (such as those found in cataclysmic variables and possibly in accreting Type Ia progenitors) for partial settling.