Binary white dwarfs in the halo of the Milky WayPim van Oirschot, Gijs Nelemans, Silvia Toonen, Onno Pols, Anthony G. A. Brown, Amina Helmi and Simon Portegies ZwartA&A, 569 (2014) A42DOI: https://doi.org/10.1051/0004-6361/201424195