Although many double white dwarfs ( DWDs ) have been observed , the evolutionary channel by which they are formed from low-mass/long-period red-giant–main-sequence ( RG-MS ) binaries remains uncertain .
The canonical explanations involve some variant of double common-envelope ( CE ) evolution , however it has been found that such a mechanism can not produce the observed distribution .
We present a model for the initial episode of mass transfer ( MT ) in RG-MS binaries , and demonstrate that their evolution into double white dwarfs need not arise through a double-CE process , as long as the initial primary ’ s core mass ( M _ { d,c } ) does not exceed 0.46 M _ { \odot } .
Instead , the first episode of dramatic mass loss may be stable , non-conservative MT .
We find a lower bound on the fraction of transferred mass that must be lost from the system in order to provide for MT , and demonstrate the feasibility of this channel in producing observed low-mass ( with M _ { d,c } < 0.46 M _ { \odot } ) DWD systems .