We present the results of an investigation of the dredge-up and mixing during the merger of two white dwarfs with different chemical compositions by conducting hydrodynamic simulations of binary mergers for three representative mass ratios .
In all the simulations , the total mass of the two white dwarfs is \lesssim 1.0 ~ { } { M _ { \odot } } .
Mergers involving a CO and a He white dwarf have been suggested as a possible formation channel for R Coronae Borealis type stars , and we are interested in testing if such mergers lead to conditions and outcomes in agreement with observations .
Even if the conditions during the merger and subsequent nucleosynthesis favor the production of ^ { 18 } { \mathrm { O } } , the merger must avoid dredging up large amounts of ^ { 16 } { \mathrm { O } } , or else it will be difficult to produce sufficient ^ { 18 } { \mathrm { O } } to explain the oxygen ratio observed to be of order unity .
We performed a total of 9 simulations using two different grid-based hydrodynamics codes using fixed and adaptive meshes , and one smooth particle hydrodynamics ( SPH ) code .
We find that in most of the simulations , > 10 ^ { -2 } ~ { } { M _ { \odot } } of ^ { 16 } { \mathrm { O } } is indeed dredged up during the merger .
However , in SPH simulations where the accretor is a hybrid He/CO white dwarf with a \sim 0.1 ~ { } { M _ { \odot } } layer of helium on top , we find that no ^ { 16 } { \mathrm { O } } is being dredged up , while in the q = 0.8 simulation < 10 ^ { -4 } ~ { } { M _ { \odot } } of ^ { 16 } { \mathrm { O } } has been brought up , making a WD binary consisting of a hybrid CO/He WD and a companion He WD an excellent candidate for the progenitor of RCB stars .