The Puzzling White Dwarf Cooling Sequence in NGC6791: A Simple Solution
  In this paper we demonstrate that the puzzling bright peak in the luminosity function of the white dwarf (WD) cooling sequence of NGC6791 can be naturally accounted for if ~34% of the observed WDs are WD+WD binary systems. 
L. R. Bedin (1), M. Salaris (2), G. Piotto (3), S. Cassisi (4), A. P.   Milone (3), J. Anderson (1), I. R. King (5) ((1) STS...