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Paper: Simulations of White Dwarf Mergers
Volume: 469, 18th European White Dwarf Workshop (EUROWD12)
Page: 137
Authors: Staff, J.; Menon, A.; Herwig, F.; Clayton, G. C.; Even, W. P.; Fryer, C. L.; Motl, P.; Tohline, J. E.; Geballe, T.; Pignatari, M.
Abstract: R Coronae Borealis (RCB) stars may be the result of the merger of a CO and a He WD. We have performed six 3 dimensional hydrodynamic simulations of the merger of two WDs, keeping a total mass of 0.9 solar masses and varying the mass ratio (q) between 0.5 and 1. The simulations show that for high q, the two cores merge leading to a combined core consisting of material from both the former accretor and donor. For lower q, the donor star gets tidally disrupted and most of the donor material ends up outside the accretor core, with a hot interaction layer forming between them. A lower q leads to higher temperatures. We locate conditions that are suitable for nucleosynthesis to take place, especially looking for conditions favorable for creating 18O, since the 16O to 18O ratio in RCB stars is observed to be unusually low, of order unity. Using conditions found in the hydrodynamic simulations as input to our post-processing nucleosynthesis code, we find that oxygen ratios down to 4 can be reached, but only after a hundred years, assuming the conditions will remain constant for that long. The main problem preventing the oxygen ratio to drop lower is that much 16O is dredged up from the accretor in the merger process, thereby necessitating production of large amount of 18O in order to achieve ratios of order unity.
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