  We present results from our ongoing follow-up observations of double white
dwarf binaries detected in the ESO SN Ia Progenitor SurveY
  (SPY). We discuss our observing strategy and data analysis and present the
orbital solutions of five close double white dwarf binaries: HE0320-1917,
HE1511-0448, WD0326-273, WD1013-010 and WD1210+140. Their periods range from
0.44 to 3.22 days. In none of these systems we find any spectral lines
originating from the companion. This rules out main sequence companions and
indicates that the companion white dwarfs are significantly older and cooler
than the bright component. Infrared photometry suggests the presence of a cool,
helium-rich white dwarf companion in the binary
  WD0326-273. We briefly discuss the consequences of our findings for our
understanding of the formation and evolution of double white dwarfs.
