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arXiv · 2010.00036

Neon Cluster Formation and Phase Separation During White Dwarf Cooling

M. E. Caplan·C. J. Horowitz·A. Cumming
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Abstract

Recent observations of Galactic white dwarfs (WDs) with Gaia suggest there is a population of massive crystallizing WDs exhibiting anomalous cooling -- the Q branch. While single-particle $^{22}$Ne sedimentation has long been considered a possible heat source, recent work suggests that $^{22}$Ne must separate into clusters, enhancing diffusion, in order for sedimentation to provide heating on the observed timescale. We show definitively that $^{22}$Ne cannot separate to form clusters in C/O WDs using molecular dynamics simulations, and we further present a general C/O/Ne phase diagram showing that strong $^{22}$Ne enrichment is not achievable for $^{22}$Ne abundance $\lesssim 30\%$. We conclude that the anomalous heating cannot be due to $^{22}$Ne cluster sedimentation and that Q branch WDs may have an unusual composition, possibly rich with heavier elements.

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M. E. Caplan, C. J. Horowitz, A. Cumming. 2020-09-30. Neon Cluster Formation and Phase Separation During White Dwarf Cooling. https://doi.org/10.3847/2041-8213%2Fabbda0

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