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arXiv · 2211.05938

The Merger Fraction of Ultramassive White Dwarfs

Mukremin Kilic·Adam G. Moss·Alekzander Kosakowski·P. Bergeron·Annamarie A. Conly·Warren R. Brown·Silvia Toonen·Kurtis A. Williams·P. Dufour
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Abstract

We search for merger products among the 25 most massive white dwarfs in the Montreal White Dwarf Database 100 pc sample through follow-up spectroscopy and high-cadence photometry. We find an unusually high fraction, 40%, of magnetic white dwarfs among this population. In addition, we identify four outliers in transverse velocity and detect rapid rotation in five objects. Our results show that $56^{+9}_{-10}$\% of the $M\approx1.3~M_{\odot}$ ultramassive white dwarfs form through mergers. This fraction is significantly higher than expected from the default binary population synthesis calculations using the $\alpha$-prescription (with $\alpha \lambda = 2$), and provides further support for efficient orbital shrinkage, such as with low values of the common envelope efficiency.

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Mukremin Kilic, Adam G. Moss, Alekzander Kosakowski, P. Bergeron, Annamarie A. Conly, Warren R. Brown, Silvia Toonen, Kurtis A. Williams, P. Dufour. 2022-11-11. The Merger Fraction of Ultramassive White Dwarfs. https://doi.org/10.1093/mnras%2Fstac3182

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