The ELM Survey. VIII. 98 Double White Dwarf Binaries

Understand

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 Msun 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 GD278, which we show is a P=0.19 d double WD binary, as well as candidates that turn out to be field blue straggler/subdwarf A-type stars with luminosities too large 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<g_0<20 mag.
• The measurements are consistent with 100% of ELM WDs being 0.0089 < P < 1.5 d double WD binaries, 35% of which belong to the Galactic halo.