22Ne distillation and the cooling sequence of the old metal-rich open cluster NGC 6791

Vol. 686
5. Galactic structure, stellar clusters and populations

22Ne distillation and the cooling sequence of the old metal-rich open cluster NGC 6791

by Maurizio Salaris, Simon Blouin, Santi Cassisi, Luigi R. Bedin 2024, A&A, 686, A153 alt

There is a significant correlation between the luminosity of white dwarfs (WDs) and their cooling age, rendering WDs invaluable as cosmic timekeepers. However, the accuracy of this temporal gauge hinges upon precise WD models, particularly the processes governing their energy reservoirs. Recent simulations have unveiled a notable phenomenon: the efficient transport of 22Ne within a CO WD toward its core, resulting in the release of gravitational energy and consequent cooling delays spanning several gigayears. This paper presents pioneering calculations that integrate CO crystallization, phase separation, 22Ne diffusion in the liquid phase, and distillation during CO crystallization. The novel model successfully replicates the faint end of the luminosity function observed in WDs within the old, metal-rich open cluster NGC 6791. A forthcoming comparison with the color-magnitude diagram of NGC 6791 observed by the James Webb Space Telescope (JWST) holds promise for validating the models and refining our understanding of neon distillation efficiency.