A spectroscopic analysis of the DAB white dwarf PG 1115 + 166 is presented .
The observed hydrogen and helium line profiles are shown to be incompatible with model spectra calculated under the assumption of homogeneous or stratified chemical compositions .
In contrast , an excellent fit to the optical spectrum of PG 1115 + 166 can be achieved if the object is interpreted as an unresolved double degenerate composed of a hydrogen-line DA star and a helium-line DB star .
The atmospheric parameters obtained from the best fit are T _ { eff } = 22 , 090 K and \log g = 8.12 for the DA star , T _ { eff } = 16 , 210 K and \log g = 8.19 for the DB star .
This binary interpretation is consistent with the results recently reported by Burleigh et al .
that PG 1115 + 166 also exhibits radial velocity variations .
The implications of this discovery with respect to the DAB spectral class are discussed .