The ELM survey. VIII. Ninety-eight double white dwarf binaries
Brown, Warren R.
Andrews, Jeff J.
Heinke, Craig O.
Agüeros, Marcel A.
Kenyon, Scott J.
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Citation (published version)Warren R Brown, Mukremin Kilic, Alekzander Kosakowski, Jeff J Andrews, Craig O Heinke, Marcel A Agüeros, Fernando Camilo, A. Gianninas, J.J. Hermes, Scott J Kenyon. "The ELM Survey. VIII. Ninety-eight Double White Dwarf Binaries." The Astrophysical Journal, Volume 889, Issue 1, pp. 49 - 49. https://doi.org/10.3847/1538-4357/ab63cd
We present the final sample of 98 detached double white dwarf (WD) binaries found in the Extremely Low Mass (ELM) Survey, a spectroscopic survey targeting <0.3 M⊙ He-core WDs completed in the Sloan Digital Sky Survey footprint. Over the course of the survey we observed ancillary low-mass WD candidates like GD 278, which we show is a P = 0.19 day double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too high to be WDs given their Gaia parallaxes. Here, we define a clean sample of ELM WDs that is complete within our target selection and magnitude range 15 < g0 < 20 mag. The measurements are consistent with 100% of ELM WDs being 0.0089 < P < 1.5 day double WD binaries, 35% of which belong to the Galactic halo. We infer that these are mostly He+CO WD binaries given the measurement constraints. The merger rate of the observed He+CO WD binaries exceeds the formation rate of stable mass-transfer AM CVn binaries by a factor of 25, and so the majority of He+CO WD binaries must experience unstable mass transfer and merge. The systems with the shortest periods, such as J0651+2844, are signature LISA verification binaries that can be studied with gravitational waves and light.
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