The ignition of nuclear burning in merging white dwarfs is investigated for various combinations of component stars composed of He, C + O, and O + Ne + Mg. It is assumed that a rapidly accreting white dwarf mimics the massive component of a merging double-white-dwarf binary system. By computing steady models the location of nuclear ignition is obtained as a function of the accretion rate and the mass of accreting stars. For C + O dwarf pairs, accretion at a rate higher than about 2.7 x 10 to the -6th solar mass/yr leads to the off-center carbon ignition. The white dwarf mass (WDM) at the off-center ignition is smaller for higher accretion rate. For the highest accretion rate, the Eddington accretion limit, WDM = 1.07 solar mass when carbon ignites off-center. For WDM smaller than this value, no carbon ignition occurs. The off-center Ne ignition in an O + Ne + Mg white dwarf does not occur even in a model with the Eddington accretion rate. Helium ignition in He-accreting C + O white dwarfs is also considered.
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Kawai et al. (1987) studied this question.